History of Mars observation
Encyclopedia
The history of Mars observation dates back to the era of the ancient Egyptian astronomers
. Detailed records regarding the position of the planet Mars
were made by Babylonian astronomers who developed arithmetic techniques to predict the future position of the planet. The ancient Greek philosophers
and Hellenistic astronomers developed a detailed geocentric model
to explain the planet's motions. Indian and Islamic astronomers estimated the size of Mars and its distance from Earth. In the 16th century, Nicholas Copernicus proposed a heliocentric model
for the Solar System
with the planets following circular orbits about the Sun
. This was revised by Johannes Kepler
, yielding an elliptic orbit
for Mars that more accurately fitted the observational data.
The first telescopic
observation of Mars was by Galileo Galilei
in 1610. Within a century, astronomers discovered distinct albedo
features on the planet, including the dark patch Syrtis Major Planum and polar ice cap
s. They also determined the planet's rotation period
and axial tilt
. Some even speculated about the possibility of life on Mars. These observations of Mars were primarily made when the planet reached opposition to the Sun, at which point Mars made its closest approach to the Earth during an orbit.
Better telescopes introduced early in the 19th century allowed permanent Martian albedo
features to be mapped in some detail. The first crude map of Mars was published in 1840, followed by more detailed maps from 1877 onward. After astronomers seemingly detected the spectroscopic signature of water in the Martian atmosphere, the idea of life on Mars became popularized among the public. Percival Lowell
believed he could see an artificial network of canals on Mars. These observations later proved to be an optical illusion
, and the atmosphere was found to be too thin and dry to support an Earth-like environment
.
Yellow clouds on Mars have been observed since the 1870s, which Eugène M. Antoniadi suggested these were windblown sand or dust. During the 1920s, the range of Martian surface temperature was measured and the planet was shown to have extreme desert conditions. In 1947, Gerard Kuiper
showed that the thin Martian atmosphere contained extensive carbon dioxide
. The first standard nomenclature for Mars albedo
features was adopted in 1960 by the International Astronomical Union
. Since the 1960s, multiple robotic spacecraft
have been sent to explore Mars from orbit and the surface. The planet has remained under observation by ground and space-based instruments across a broad range of the electromagnetic spectrum
. The discovery of meteorite
s on Earth that originated on Mars
has allowed laboratory examination of the chemical conditions on the planet.
The existence of Mars as a wandering object in the night sky was recorded by ancient Egyptian astronomers
and by 1534 BCE they were familiar with the retrograde motion of the planet, where it appears to move in the opposite direction across the sky from its normal progression. Mars was portrayed on the ceiling of the tomb of Seti I
and on the Ramesseum
ceiling, though it was missing from the Senenmut
star map. In the latter case, the planet may have been in conjunction with the Sun.
By the period of the Neo-Babylonian Empire
, the Babylonian astronomers were making systematic observations of the positions and behavior of the planets. For Mars, they knew, for example, that the planet made 37 synodic periods, or 42 circuits of the zodiac, every 79 years. They also invented arithmetic methods for making minor corrections to the predicted positions of the planets. This Babylonian planetary theory was primarily derived from timing measurements, rather than the less accurately known position of the planet in the night sky.
Chinese records about the appearances and motions of Mars appear from before the founding of the Zhou Dynasty
(1045 BCE), and by the Chin Dynasty (221 BCE) astronomers maintained close records of planetary conjunctions, including those of Mars. In 375 CE, an occultation
of Mars by Venus
was noted. The period and motion of the planet's orbit was known in some detail during the Tang Dynasty
(618 CE).
The early astronomy of ancient Greece
was influenced by knowledge transmitted from the Mesopotamia
n culture. Thus the Babylonians associated Mars with Nergal
, their god of war and pestilence, while the Greeks connected the planet with their god of war Ares
. During this period, the motions of the planets were of little interest to the Greeks, and Hesiod
's Works and Days
(c. 650 BCE) makes no mention of the planets.
The Greeks used the word planēton to refer to the seven celestial bodies that moved with respect to the background stars and they held a geocentric view that these bodies moved about the Earth
. The Greek philosopher Plato
provided the oldest known statement regarding the Greek astronomical tradition for the order of these objects in his work, The Republic (X.616E–617B). His list, in order of the most distant to the nearest object, was as follows: Saturn
, Jupiter
, Mars, Mercury
, Venus, the Sun
and the Moon
. In his dialogue Timaeus
, Plato proposed that the rotation of these objects across the skies depended on their distance, with the furthest object moving the slowest.
Aristotle
, a student of Plato, observed an occultation
of Mars by the Moon in 365 BCE. From this he concluded that Mars must lie further from the Earth than the Moon. He also noted that other such occultations of stars and planets had been observed by the Egyptians and Babylonians. Aristotle used this observational evidence to support the Greek sequencing of the planets. Aristotle's work De Caelo presented a model of the universe in which the Sun, Moon and planets all circle about the Earth at a fixed distance. A more sophisticated version of the geocentric model was developed by the Greek astronomer Hipparchus
when he presented a model in which Mars moved along a circular track that in turn orbited about the Earth—termed the deferent and epicycle
.
In Roman Egypt during the 2nd century CE, Claudius Ptolemaeus (Ptolemy) attempted to address the problem of the orbital motion of Mars. Observations of Mars had shown that the planet appeared to move 40% faster on one side of its orbit than the other, in conflict with the Aristotelian model of uniform motion. Ptolemy modified the model of planetary motion by adding a point offset
from the center of the planet's circular orbit about which the planet moves with a uniform rate of rotation
. Ptolemy's model and his collective work on astronomy was presented in the multi-volume collection Almagest
, which became the authoritative treatise on Western astronomy for the next fourteen centuries.
In the 5th century CE, the Indian astronomical text Surya Siddhanta
estimated the angular size of Mars as 2 arc-minutes
(1/30 of a degree) and its distance to Earth as 10,433,000 km (1,296,600 yojana
, where one yojana is equivalent to eight km in the Surya Siddhanta). From this the diameter of Mars is deduced to be 6,070 km (754.4 yojana), which has an error within 11% of the currently accepted value of 6,788 km. However, this estimate was based upon an inaccurate guess of the planet's angular diameter as 2.0 arc-minutes. The result may have been influenced by the measurements of Ptolemy, who found a value of 1.57 arc-minutes. This is close to the resolution of the human eye and is significantly larger than the value later obtained by telescope.
In 1543, Nicolaus Copernicus
published a heliocentric model in his work De revolutionibus orbium coelestium
. This approach placed the Earth in a orbit around the Sun between the circular orbits of Venus and Mars. His model successfully explained why the planets Mars, Jupiter and Saturn were on the opposite side of the sky from the Sun whenever they were in the middle of their retrograde motions. Copernicus was able to sort the planets into their correct heliocentric order based solely on the period of their orbits about the Sun. His theory gradually gained acceptance with European astronomers, particularly after the publication of the Prutenic Tables
by the German astronomer Erasmus Reinhold
in 1551, which were computed using the Copernican model.
On October 13, 1590, the German astronomer Michael Maestlin
observed the only recorded occultation
of Mars by Venus. One of his students, Johannes Kepler
, quickly became an adherent to the Copernican system. After the completion of his education, Kepler became an assistant to the Danish nobleman and astronomer, Tycho Brahe
. With access granted to Tycho's detailed observations of Mars, Kepler was set to work mathematically assembling a replacement to the Prutenic Tables. After repeatedly failing to fit the motion of Mars into a circular orbit as required under Copernicanism, he succeeded in matching Tycho's observations by assuming the orbit was an ellipse
, with the Sun located at one of the foci
. His model became the basis for Kepler's laws of planetary motion
, which were published in his multi-volume work Epitome astronomia Copernicanae (Epitome of Copernican Astronomy) between 1615 and 1621.
was the first person known to use a telescope
to make astronomical observations. His records indicate that he began observing Mars through a telescope in September 1610, with the goal of seeing if the planet exhibited phases
of partial darkness similar to Venus
or the Moon
. Although uncertain of his success, by December he did note that Mars had shrunk in angular size. Polish astronomer Johannes Hevelius
succeeded in observing a phase of Mars in 1645.
In 1644, the Italian Jesuit Daniello Bartoli
reported seeing two darker patches on Mars. During the oppositions of 1651, 1653 and 1655, when the planet made its closest approaches to the Earth, the Italian astronomer Giovanni Battista Riccioli
and his student Francesco Maria Grimaldi
noted patches of differing reflectivity
on Mars. The first person to draw a map of Mars that displayed any terrain features was the Dutch astronomer Christiaan Huygens. On November 28, 1659 he made an illustration of Mars that showed the distinct dark region now known as Syrtis Major Planum, and possibly also one of the polar ice cap
s. The same year, he also succeeded in measuring the rotation period of the planet, giving it as approximately 24 hours. He made a rough estimate of the diameter of Mars, guessing that it is about 60% of the size of the Earth, which compares well with the modern value of 53%.
Perhaps the first definitive mention of Mars's southern polar ice cap was by the Italian astronomer Giovanni Domenico Cassini
, in 1666. That same year, he used observations of the surface markings on Mars to determine a rotation period of 24h 40m. This differs from the correct value by less than three minutes. In 1672, Christiaan Huygens noticed a fuzzy white cap at the north pole.
After Cassini became the first director of the Paris Observatory
in 1671, he tackled the problem of the physical scale of the Solar System. For this purpose, the position of Mars
was measured against the background stars from different points on the Earth—the diurnal parallax. During this year, the planet was near the point along its orbit when it was nearest to the Sun (a perihelical opposition), thereby also making a particularly close approach to the Earth. Cassini and Jean Picard
determined the position of Mars in Paris
, while French astronomer Jean Richer
made the measurements in Cayenne
, South America
. Although these observations were hampered by the quality of the instruments, Cassini's result came within 10% of the correct value. The English astronomer John Flamsteed
made comparable measurement attempts and had similar results.
In 1704, French-Italian astronomer Jacques Philippe Maraldi made a systematic study of the southern cap and noticed that it underwent variation as the planet rotated. This indicated that the cap was not centered on the pole. He also observed that the cap varied in size over time.
The German-English astronomer William Herschel
began making observations of the planet Mars in 1777; particularly of the planet's polar caps. In 1781, he noted that the south cap appeared "extremely large", which he ascribed to that pole being in darkness for the past twelve months. By 1784, the southern cap appeared much smaller, thereby suggesting that the caps vary with the planet's seasons and thus were made of ice. In 1781, he estimated the rotation period of Mars as 24h 39m 21.67s and measured the axial tilt
of the planet's poles to the orbital plane as roughly 28.5°. He noted that Mars had a "considerable but moderate atmosphere, so that its inhabitants probably enjoy a situation in many respects similar to ours".
Between 1796 and 1809, the French astronomer Honoré Flaugergues
noticed some obscurations of Mars, suggesting "ochre-colored veils" covered the surface. This may be the earliest report of yellow clouds or storms on Mars.
of the German optician Joseph von Fraunhofer
that essentially eliminated coma
—an optical effect that can distort the outer edge of the image. By 1812, Fraunhofer had succeeded in creating an achromatic objective lens 190 mm (7.5 in) in diameter. The size of this primary lens is the main factor in determining the light gathering ability and resolution of a telescope.
During the opposition of Mars in 1830, the German astronomers Johann Heinrich Mädler and Wilhelm Beer used a 95 mm (3.7 in) Fraunhofer refracting telescope
to launch an extensive study of the planet. They chose a feature located 8° south of the equator
as their point of reference. (This was later named the Sinus Meridiani
, and it would become the zero meridian
of Mars.) During their observations, they established that most of Mars’ surface features were permanent, and more precisely determined the planet's rotation period. In 1840, Mädler combined ten years of observations and drew the first map of Mars. Rather than giving names to the various markings, Beer and Mädler simply designated them with letters; Meridian Bay (Sinus Meridiani) was thus feature "a".
Working at the Vatican Observatory
during the opposition of Mars in 1858, Italian astronomer Angelo Secchi noticed a large blue triangular feature, which he named the "Blue Scorpion". This same seasonal cloud-like formation was seen by English astronomer J. Norman Lockyer in 1862, and it has been viewed subsequently by other observers. During the 1862 opposition, Dutch astronomer Frederik Kaiser
produced drawings of Mars. By comparing his illustrations with those of Huygens and the English natural philosopher Robert Hooke
, he was able to further refine the rotation period of Mars. His value of 24h 37m 22.6s is accurate to within a tenth of a second.
Father Secchi produced some of the first color illustrations of Mars in 1863. He used the names of famous explorers for the distinct features. In 1869, he observed two dark linear features on the surface that he referred to as canali, which is Italian for 'channels' or 'grooves'. In 1867, English astronomer Richard A. Proctor created a more detailed map of Mars based on the 1864 drawings of English astronomer William R. Dawes. Proctor named the various lighter or darker
features after astronomers, past and present, who had contributed to the observations of Mars. During the same decade, comparable maps and nomenclature were produced by the French astronomer Camille Flammarion
and the English astronomer Nathan Green
.
At the University of Leipzig
in 1862–64, German astronomer Johann K. F. Zöllner
used a photometer
he had developed to measure the reflectivity of the Moon, planets and bright stars. For Mars, he derived an albedo
of 0.27. Between 1877 and 93, German astronomers Gustav Müller
and Paul Kempf observed Mars using Zöllner's photometer. They found a small phase coefficient—the variation in reflectivity with angle—indicating that the surface of Mars is relatively smooth and without large irregularities.
In 1867, French astronomer Pierre Janssen and British astronomer William Huggins
used spectroscopes to examine the atmosphere of Mars. Both compared the optical spectrum of Mars to that of the Moon
. As the spectrum of the latter did not display absorption lines of water, they believed they had detected the presence of water vapor in the atmosphere of Mars. This result was confirmed by German astronomer Herman C. Vogel
in 1872 and English astronomer Edward W. Maunder in 1875, but would later come into question.
A particularly favorable perihelic opposition occurred in 1877. The English astronomer David Gill
used this opportunity to measure the diurnal parallax of Mars from Ascension Island
. With these measurements, he was able to more accurately determine the distance from the Earth to the Sun, based upon the relative size of the orbits of Mars and the Earth. He also noted that the edge of the disk of Mars appeared fuzzy because of the atmosphere, which limited the precision he could obtain for the planet's position.
In August 1877, the American astronomer Asaph Hall
discovered the two moons of Mars using a 660 mm (26 in) telescope at the U.S. Naval Observatory. The names of the two satellites, Phobos
and Deimos
, were chosen by Hall based upon a suggestion by Henry Madan
, a science instructor at Eton College
in England.
used a 22 cm (8.7 in) telescope to help produce the first detailed map of Mars. These maps notably contained features he called canali, which were later shown to be an optical illusion
. These canali were supposedly long straight lines on the surface of Mars to which he gave names of famous rivers on Earth. His term canali was popularly mistranslated in English as canals. In 1886, the English astronomer William F. Denning observed that these linear features were irregular in nature and showed concentrations and interruptions. By 1895, English astronomer Edward Maunder became convinced that the linear features were merely the summation of many smaller details.
In his 1892 work La planète Mars et ses conditions d'habitabilité, Camille Flammarion wrote about how these channels resembled man-made canals, which an intelligent race could use to redistribute water across a dying Martian world. He advocated for the existence of such inhabitants, and suggested they may be more advanced than humans.
Influenced by the observations of Schiaparelli, the orientalist Percival Lowell founded an observatory
with 30 and 45 cm (11.8 and 17.7 in) telescopes. The observatory was used for the exploration of Mars during the last good opportunity in 1894 and the following less favorable oppositions. He published several books on Mars and life on the planet, which had a great influence on the public. The canali were also found by other astronomers, such as Henri Joseph Perrotin and Louis Thollon with a 38 cm (15 in) refractor at the Nice Observatory
, one of the largest telescopes of that time.
Beginning in 1901, efforts were made to photograph the canal features of Mars by A. E. Douglass. These efforts appeared to succeed when Carl O. Lampland published photographs of the canals in 1905. Although these results were widely accepted, they became contested by Greek astronomer Eugène M. Antoniadi, English naturalist Alfred Russel Wallace
and others as imagined features. As bigger telescopes were used, fewer long, straight canali were observed. During an observation in 1909 by Flammarion with a 84 cm (33.1 in) telescope, irregular patterns were observed, but no canali were seen.
found that the spectrum of Mars was identical to the spectrum of the Moon, throwing doubt on the burgeoning theory that the atmosphere of Mars is similar to that of the Earth. Previous detections of water in the atmosphere of Mars were explained by unfavorable conditions, and Campbell determined that the water signature came entirely from the Earth's atmosphere. Although he agreed that the ice caps did indicate there was some water in the atmosphere, he did not believe the caps were sufficiently large to allow the water vapor to be detected. At the time, Campbell's results were considered controversial and were criticized by some members of the astronomical community, but they were later confirmed by American astronomer Walter S. Adams in 1925.
Baltic German
astronomer Hermann Struve
used the observed changes in the orbits of the martian moons to determine the gravitational influence of the planet's oblate shape. In 1895, he used this data to estimate that the equatorial diameter was 1/190 larger than the polar diameter. In 1911, he refined the value to 1/192. This result was confirmed by American meteorologist Edgar W. Woolard in 1944.
Surface obscuration caused by yellow clouds had been noted in the 1870s when they were observed by Schiaparelli. Further evidence for such clouds was observed during the oppositions of 1892 and 1907. In 1909, Antoniadi noted that the presence of yellow clouds was associated with the obscuration of albedo features. He discovered that Mars appeared more yellow during oppositions when the planet was closest to the Sun and was receiving more energy. He suggested windblown sand or dust as the cause of the clouds.
Using a vacuum thermocouple
attached to the 2.54 m (100 in) Hooker Telescope at Mount Wilson Observatory
, in 1924 the American astronomers Seth Barnes Nicholson
and Edison Pettit
were able to measure the thermal energy being radiated by the surface of Mars. They determined that the temperature ranged from -68 C at the pole up to 7 °C (45 °F) at the mid-point of the disk (corresponding to the equator
). Beginning in the same year, radiated energy measurements of Mars were made by American physicist William Coblentz
and American astronomer Carl Otto Lampland
. The results showed that the night time temperature on Mars dropped to -85 C, indicating an "enormous diurnal fluctuation" in temperatures. The temperature of Martian clouds was measured as -30 C.
In 1926, by measuring spectral lines that were red shift
ed by the orbital motions of Mars and Earth, American astronomer Walter Sydney Adams
was able to directly measure the amount of oxygen and water vapor in the atmosphere of Mars. He determined that "extreme desert conditions" were prevalent on Mars. In 1934, Adams and American astronomer Theodore Dunham, Jr. found that the amount of oxygen in the atmosphere of Mars was less than one percent of the amount over a comparable area on Earth.
During the 1920s, French astronomer Bernard Lyot
used a polarimeter
to study the surface properties of the Moon and planets. In 1929, he noted that the polarized light emitted from the martian surface is very similar to that radiated from the Moon, although he speculated that some of his observations could be explained by frost and possibly vegetation. Based on the amount of sunlight scattered by the Martian atmosphere, he set an upper limit of 1/15 the thickness of the Earth's atmosphere. This restricted the surface pressure to no greater than 2.4 kPa (24 mbar).
Using infrared
spectrometry, in 1947 the Dutch-American astronomer Gerard Kuiper
detected carbon dioxide
in the Martian atmosphere. He was able to estimate that the amount of carbon dioxide over a given area of the surface is double that on the Earth. However, because he over-estimated the surface pressure on Mars, Kuiper concluded erroneously that the ice caps could not be composed of frozen carbon dioxide. In 1948, American meteorologist Seymour L. Hess determined that the formation of the thin Martian clouds would only require 4 mm (0.15748031496063 in) of precipitatable water and a vapor pressure
of 0.1 kPa (1 mbar).
Based upon observations of the near Earth
asteroid
Eros
from 1926 to 1945, German-American astronomer Eugene K. Rabe was able to estimate the mass of Mars from the planet's gravitational perturbations
of the asteroid.
The first standard nomenclature for Martian albedo features was introduced by the International Astronomical Union
(IAU) when in 1960 they adopted 128 names from the 1929 map of Antoniadi named La Planète Mars. The Working Group for Planetary System Nomenclature (WGPSN) was established by the IAU in 1973 to standardize the naming scheme for Mars and other bodies.
was formed in 1969 as a consortium to continually monitor planetary changes. This worldwide group focused on observing dust storms on Mars. The resulting images allow martian seasonal patterns to be studied globally, and they showed that most Martian dust storms occur when the planet is closest to the Sun.
Since the 1960s, robotic spacecraft
have been sent to explore Mars
from orbit and the surface
in extensive detail. In addition, remote sensing of Mars from Earth by ground-based and orbiting telescopes has continued across much of the electromagnetic spectrum
. These include infrared
observations to determine the composition of the surface, ultraviolet
and submillimeter observation of the atmospheric composition, and radio
measurements of wind velocities.
The Hubble Space Telescope
(HST) has been used to perform systematic studies of Mars and has taken the highest resolution images of Mars ever captured from Earth. This telescope can produce useful images of the planet when it is at an angular distance
of at least 50° from the Sun. The HST can take images of a hemisphere
, which yields views of entire weather systems. Earth-based telescopes equipped with charge-coupled device
s can also produce useful images of Mars, allowing for regular monitoring of the planet's weather during oppositions.
X-ray
emission from Mars was first observed by astronomers in 2001 using the Chandra X-ray Observatory
, and in 2003 it was shown to have two components. The first component is caused by X-rays from the Sun scattering off the upper Martian atmosphere, while the second comes from interactions between ion
s that result in an exchange of charges. The emission from the latter source has been observed out to eight times the radius of Mars by the XMM-Newton
orbiting observatory.
In 1983, the analysis of the Shergottite
, Nakhlite
and Chassigny (SNC) group of meteorites showed that they may have originated on Mars
. The Allan Hills 84001 meteorite, discovered in Antarctica in 1984, is believed to have originated on Mars but it has an entirely different composition than the SNC group. In 1996, it was announced that this meteorite might contain evidence for microscopic fossil
s of Martian bacteria
. However, this finding remains controversial. Chemical analysis of the Martian meteorites found on Earth suggests that the ambient near-surface temperature of Mars has most likely been below the freezing point of water (0 C°) for much of the last four billion years.
Egyptian astronomy
Egyptian astronomy begins in prehistoric times, in the Predynastic Period. In the 5th millennium BCE, the stone circles at Nabta Playa may have made use of astronomical alignments...
. Detailed records regarding the position of the planet Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
were made by Babylonian astronomers who developed arithmetic techniques to predict the future position of the planet. The ancient Greek philosophers
Greek philosophy
Ancient Greek philosophy arose in the 6th century BCE and continued through the Hellenistic period, at which point Ancient Greece was incorporated in the Roman Empire...
and Hellenistic astronomers developed a detailed geocentric model
Geocentric model
In astronomy, the geocentric model , is the superseded theory that the Earth is the center of the universe, and that all other objects orbit around it. This geocentric model served as the predominant cosmological system in many ancient civilizations such as ancient Greece...
to explain the planet's motions. Indian and Islamic astronomers estimated the size of Mars and its distance from Earth. In the 16th century, Nicholas Copernicus proposed a heliocentric model
Heliocentrism
Heliocentrism, or heliocentricism, is the astronomical model in which the Earth and planets revolve around a stationary Sun at the center of the universe. The word comes from the Greek . Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center...
for the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
with the planets following circular orbits about the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. This was revised by Johannes Kepler
Johannes Kepler
Johannes Kepler was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican...
, yielding an elliptic orbit
Elliptic orbit
In astrodynamics or celestial mechanics an elliptic orbit is a Kepler orbit with the eccentricity less than 1; this includes the special case of a circular orbit, with eccentricity equal to zero. In a stricter sense, it is a Kepler orbit with the eccentricity greater than 0 and less than 1 . In a...
for Mars that more accurately fitted the observational data.
The first telescopic
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
observation of Mars was by Galileo Galilei
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
in 1610. Within a century, astronomers discovered distinct albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
features on the planet, including the dark patch Syrtis Major Planum and polar ice cap
Polar ice cap
A polar ice cap is a high latitude region of a planet or natural satellite that is covered in ice. There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor any geological requirement for it to be over land; only that it must be a body of...
s. They also determined the planet's rotation period
Rotation period
The rotation period of an astronomical object is the time it takes to complete one revolution around its axis of rotation relative to the background stars...
and axial tilt
Axial tilt
In astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...
. Some even speculated about the possibility of life on Mars. These observations of Mars were primarily made when the planet reached opposition to the Sun, at which point Mars made its closest approach to the Earth during an orbit.
Better telescopes introduced early in the 19th century allowed permanent Martian albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
features to be mapped in some detail. The first crude map of Mars was published in 1840, followed by more detailed maps from 1877 onward. After astronomers seemingly detected the spectroscopic signature of water in the Martian atmosphere, the idea of life on Mars became popularized among the public. Percival Lowell
Percival Lowell
Percival Lawrence Lowell was a businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars, founded the Lowell Observatory in Flagstaff, Arizona, and formed the beginning of the effort that led to the discovery of Pluto 14 years after his death...
believed he could see an artificial network of canals on Mars. These observations later proved to be an optical illusion
Optical illusion
An optical illusion is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source...
, and the atmosphere was found to be too thin and dry to support an Earth-like environment
Planetary habitability
Planetary habitability is the measure of a planet's or a natural satellite's potential to sustain life. Life may develop directly on a planet or satellite or be transferred to it from another body, a theoretical process known as panspermia...
.
Yellow clouds on Mars have been observed since the 1870s, which Eugène M. Antoniadi suggested these were windblown sand or dust. During the 1920s, the range of Martian surface temperature was measured and the planet was shown to have extreme desert conditions. In 1947, Gerard Kuiper
Gerard Kuiper
Gerard Peter Kuiper , Netherlands – December 24, 1973, Mexico City) was a Dutch-American astronomer after whom the Kuiper belt was named.-Early life:...
showed that the thin Martian atmosphere contained extensive carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. The first standard nomenclature for Mars albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
features was adopted in 1960 by the International Astronomical Union
International Astronomical Union
The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...
. Since the 1960s, multiple robotic spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
have been sent to explore Mars from orbit and the surface. The planet has remained under observation by ground and space-based instruments across a broad range of the electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
. The discovery of meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
s on Earth that originated on Mars
Mars meteorite
A martian meteorite is a rock that formed on the planet Mars, was ejected from Mars by the impact of an asteroid or comet, and landed on the Earth. Of over 53000 meteorites that have been found on Earth, 99 are martian...
has allowed laboratory examination of the chemical conditions on the planet.
Earliest records
Egyptian astronomy
Egyptian astronomy begins in prehistoric times, in the Predynastic Period. In the 5th millennium BCE, the stone circles at Nabta Playa may have made use of astronomical alignments...
and by 1534 BCE they were familiar with the retrograde motion of the planet, where it appears to move in the opposite direction across the sky from its normal progression. Mars was portrayed on the ceiling of the tomb of Seti I
Seti I
Menmaatre Seti I was a Pharaoh of Ancient Egypt , the son of Ramesses I and Queen Sitre, and the father of Ramesses II...
and on the Ramesseum
Ramesseum
The Ramesseum is the memorial temple of Pharaoh Ramesses II . It is located in the Theban necropolis in Upper Egypt, across the River Nile from the modern city of Luxor...
ceiling, though it was missing from the Senenmut
Senenmut
Senenmut was an 18th dynasty ancient Egyptian architect and government official. His name translates literally as "mother's brother."- Family :...
star map. In the latter case, the planet may have been in conjunction with the Sun.
By the period of the Neo-Babylonian Empire
Neo-Babylonian Empire
The Neo-Babylonian Empire or Second Babylonian Empire was a period of Mesopotamian history which began in 626 BC and ended in 539 BC. During the preceding three centuries, Babylonia had been ruled by their fellow Akkadian speakers and northern neighbours, Assyria. Throughout that time Babylonia...
, the Babylonian astronomers were making systematic observations of the positions and behavior of the planets. For Mars, they knew, for example, that the planet made 37 synodic periods, or 42 circuits of the zodiac, every 79 years. They also invented arithmetic methods for making minor corrections to the predicted positions of the planets. This Babylonian planetary theory was primarily derived from timing measurements, rather than the less accurately known position of the planet in the night sky.
Chinese records about the appearances and motions of Mars appear from before the founding of the Zhou Dynasty
Zhou Dynasty
The Zhou Dynasty was a Chinese dynasty that followed the Shang Dynasty and preceded the Qin Dynasty. Although the Zhou Dynasty lasted longer than any other dynasty in Chinese history, the actual political and military control of China by the Ji family lasted only until 771 BC, a period known as...
(1045 BCE), and by the Chin Dynasty (221 BCE) astronomers maintained close records of planetary conjunctions, including those of Mars. In 375 CE, an occultation
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
of Mars by Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
was noted. The period and motion of the planet's orbit was known in some detail during the Tang Dynasty
Tang Dynasty
The Tang Dynasty was an imperial dynasty of China preceded by the Sui Dynasty and followed by the Five Dynasties and Ten Kingdoms Period. It was founded by the Li family, who seized power during the decline and collapse of the Sui Empire...
(618 CE).
The early astronomy of ancient Greece
Greek astronomy
Greek astronomy is astronomy written in the Greek language in classical antiquity. Greek astronomy is understood to include the ancient Greek, Hellenistic, Greco-Roman, and Late Antiquity eras. It is not limited geographically to Greece or to ethnic Greeks, as the Greek language had become the...
was influenced by knowledge transmitted from the Mesopotamia
Mesopotamia
Mesopotamia is a toponym for the area of the Tigris–Euphrates river system, largely corresponding to modern-day Iraq, northeastern Syria, southeastern Turkey and southwestern Iran.Widely considered to be the cradle of civilization, Bronze Age Mesopotamia included Sumer and the...
n culture. Thus the Babylonians associated Mars with Nergal
Nergal
The name Nergal, Nirgal, or Nirgali refers to a deity in Babylon with the main seat of his cult at Cuthah represented by the mound of Tell-Ibrahim. Nergal is mentioned in the Hebrew bible as the deity of the city of Cuth : "And the men of Babylon made Succoth-benoth, and the men of Cuth made Nergal"...
, their god of war and pestilence, while the Greeks connected the planet with their god of war Ares
Ares
Ares is the Greek god of war. He is one of the Twelve Olympians, and the son of Zeus and Hera. In Greek literature, he often represents the physical or violent aspect of war, in contrast to the armored Athena, whose functions as a goddess of intelligence include military strategy and...
. During this period, the motions of the planets were of little interest to the Greeks, and Hesiod
Hesiod
Hesiod was a Greek oral poet generally thought by scholars to have been active between 750 and 650 BC, around the same time as Homer. His is the first European poetry in which the poet regards himself as a topic, an individual with a distinctive role to play. Ancient authors credited him and...
's Works and Days
Works and Days
Works and Days is a didactic poem of some 800 verses written by the ancient Greek poet Hesiod around 700 BC. At its center, the Works and Days is a farmer's almanac in which Hesiod instructs his brother Perses in the agricultural arts...
(c. 650 BCE) makes no mention of the planets.
Orbital models
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. The Greek philosopher Plato
Plato
Plato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...
provided the oldest known statement regarding the Greek astronomical tradition for the order of these objects in his work, The Republic (X.616E–617B). His list, in order of the most distant to the nearest object, was as follows: Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
, Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
, Mars, Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
, Venus, the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
and the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. In his dialogue Timaeus
Timaeus (dialogue)
Timaeus is one of Plato's dialogues, mostly in the form of a long monologue given by the title character, written circa 360 BC. The work puts forward speculation on the nature of the physical world and human beings. It is followed by the dialogue Critias.Speakers of the dialogue are Socrates,...
, Plato proposed that the rotation of these objects across the skies depended on their distance, with the furthest object moving the slowest.
Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...
, a student of Plato, observed an occultation
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
of Mars by the Moon in 365 BCE. From this he concluded that Mars must lie further from the Earth than the Moon. He also noted that other such occultations of stars and planets had been observed by the Egyptians and Babylonians. Aristotle used this observational evidence to support the Greek sequencing of the planets. Aristotle's work De Caelo presented a model of the universe in which the Sun, Moon and planets all circle about the Earth at a fixed distance. A more sophisticated version of the geocentric model was developed by the Greek astronomer Hipparchus
Hipparchus
Hipparchus, the common Latinization of the Greek Hipparkhos, can mean:* Hipparchus, the ancient Greek astronomer** Hipparchic cycle, an astronomical cycle he created** Hipparchus , a lunar crater named in his honour...
when he presented a model in which Mars moved along a circular track that in turn orbited about the Earth—termed the deferent and epicycle
Deferent and epicycle
In the Ptolemaic system of astronomy, the epicycle was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets...
.
In Roman Egypt during the 2nd century CE, Claudius Ptolemaeus (Ptolemy) attempted to address the problem of the orbital motion of Mars. Observations of Mars had shown that the planet appeared to move 40% faster on one side of its orbit than the other, in conflict with the Aristotelian model of uniform motion. Ptolemy modified the model of planetary motion by adding a point offset
Equant
Equant is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of heavenly bodies....
from the center of the planet's circular orbit about which the planet moves with a uniform rate of rotation
Angular velocity
In physics, the angular velocity is a vector quantity which specifies the angular speed of an object and the axis about which the object is rotating. The SI unit of angular velocity is radians per second, although it may be measured in other units such as degrees per second, revolutions per...
. Ptolemy's model and his collective work on astronomy was presented in the multi-volume collection Almagest
Almagest
The Almagest is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths. Written in Greek by Claudius Ptolemy, a Roman era scholar of Egypt,...
, which became the authoritative treatise on Western astronomy for the next fourteen centuries.
In the 5th century CE, the Indian astronomical text Surya Siddhanta
Surya Siddhanta
The Surya Siddhanta is one of the earliest siddhanta in archeo-astronomy of the Hindus by an unknown author. It describes the archeo-astronomy theories, principles and methods of the ancient Hindus. This siddhanta is supposed to be the knowledge that the Sun god gave to an Asura called Maya. Asuras...
estimated the angular size of Mars as 2 arc-minutes
Minute of arc
A minute of arc, arcminute, or minute of angle , is a unit of angular measurement equal to one sixtieth of one degree. In turn, a second of arc or arcsecond is one sixtieth of one minute of arc....
(1/30 of a degree) and its distance to Earth as 10,433,000 km (1,296,600 yojana
Yojana
A Yojana is a Vedic measure of distance used in ancient India. The exact measurement is disputed amongst scholars with distances being given between 6 to 15 kilometers ....
, where one yojana is equivalent to eight km in the Surya Siddhanta). From this the diameter of Mars is deduced to be 6,070 km (754.4 yojana), which has an error within 11% of the currently accepted value of 6,788 km. However, this estimate was based upon an inaccurate guess of the planet's angular diameter as 2.0 arc-minutes. The result may have been influenced by the measurements of Ptolemy, who found a value of 1.57 arc-minutes. This is close to the resolution of the human eye and is significantly larger than the value later obtained by telescope.
In 1543, Nicolaus Copernicus
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....
published a heliocentric model in his work De revolutionibus orbium coelestium
De revolutionibus orbium coelestium
De revolutionibus orbium coelestium is the seminal work on the heliocentric theory of the Renaissance astronomer Nicolaus Copernicus...
. This approach placed the Earth in a orbit around the Sun between the circular orbits of Venus and Mars. His model successfully explained why the planets Mars, Jupiter and Saturn were on the opposite side of the sky from the Sun whenever they were in the middle of their retrograde motions. Copernicus was able to sort the planets into their correct heliocentric order based solely on the period of their orbits about the Sun. His theory gradually gained acceptance with European astronomers, particularly after the publication of the Prutenic Tables
Prutenic Tables
The Prutenic Tables , were an ephemeris by the astronomer Erasmus Reinhold published in 1551. They are sometimes called the Prussian Tables after Albert I, Duke of Prussia, who supported Reinhold and financed the printing...
by the German astronomer Erasmus Reinhold
Erasmus Reinhold
Erasmus Reinhold was a German astronomer and mathematician, considered to be the most influential astronomical pedagogue of his generation. He was born and died in Saalfeld, Saxony....
in 1551, which were computed using the Copernican model.
On October 13, 1590, the German astronomer Michael Maestlin
Michael Maestlin
Michael Maestlin was a German astronomer and mathematician, known for being the mentor of Johannes Kepler.-Career:...
observed the only recorded occultation
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
of Mars by Venus. One of his students, Johannes Kepler
Johannes Kepler
Johannes Kepler was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican...
, quickly became an adherent to the Copernican system. After the completion of his education, Kepler became an assistant to the Danish nobleman and astronomer, Tycho Brahe
Tycho Brahe
Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...
. With access granted to Tycho's detailed observations of Mars, Kepler was set to work mathematically assembling a replacement to the Prutenic Tables. After repeatedly failing to fit the motion of Mars into a circular orbit as required under Copernicanism, he succeeded in matching Tycho's observations by assuming the orbit was an ellipse
Ellipse
In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...
, with the Sun located at one of the foci
Focus (geometry)
In geometry, the foci are a pair of special points with reference to which any of a variety of curves is constructed. For example, foci can be used in defining conic sections, the four types of which are the circle, ellipse, parabola, and hyperbola...
. His model became the basis for Kepler's laws of planetary motion
Kepler's laws of planetary motion
In astronomy, Kepler's laws give a description of the motion of planets around the Sun.Kepler's laws are:#The orbit of every planet is an ellipse with the Sun at one of the two foci....
, which were published in his multi-volume work Epitome astronomia Copernicanae (Epitome of Copernican Astronomy) between 1615 and 1621.
Early telescope observations
The Italian scientist Galileo GalileiGalileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
was the first person known to use a telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
to make astronomical observations. His records indicate that he began observing Mars through a telescope in September 1610, with the goal of seeing if the planet exhibited phases
Planetary phase
Planetary phase is the term used to describe the appearance of the illuminated section of a planet. Like lunar phases, the planetary phase depends on the relative position of the sun, the planet and the observer....
of partial darkness similar to Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
or the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. Although uncertain of his success, by December he did note that Mars had shrunk in angular size. Polish astronomer Johannes Hevelius
Johannes Hevelius
Johannes Hevelius Some sources refer to Hevelius as Polish:Some sources refer to Hevelius as German:*Encyplopedia Britannica * of the Royal Society was a councilor and mayor of Danzig , Pomeranian Voivodeship, in the Polish-Lithuanian Commonwealth...
succeeded in observing a phase of Mars in 1645.
In 1644, the Italian Jesuit Daniello Bartoli
Daniello Bartoli
thumb|right| Daniello Bartoli "Obiit Romae, die 13 Januarii, anno 1685, aet. 77"Daniello Bartoli was an Italian Jesuit writer and historiographer, celebrated by Francesco de Sanctis as the "Dante of Italian prose".-Ferrara:He was born in Ferrara. His father, Tiburzio was a chemist associated with...
reported seeing two darker patches on Mars. During the oppositions of 1651, 1653 and 1655, when the planet made its closest approaches to the Earth, the Italian astronomer Giovanni Battista Riccioli
Giovanni Battista Riccioli
Giovanni Battista Riccioli was an Italian astronomer and a Catholic priest in the Jesuit order...
and his student Francesco Maria Grimaldi
Francesco Maria Grimaldi
Francesco Maria Grimaldi was an Italian Jesuit priest, mathematician and physicist who taught at the Jesuit college in Bologna....
noted patches of differing reflectivity
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
on Mars. The first person to draw a map of Mars that displayed any terrain features was the Dutch astronomer Christiaan Huygens. On November 28, 1659 he made an illustration of Mars that showed the distinct dark region now known as Syrtis Major Planum, and possibly also one of the polar ice cap
Ice cap
An ice cap is an ice mass that covers less than 50 000 km² of land area . Masses of ice covering more than 50 000 km² are termed an ice sheet....
s. The same year, he also succeeded in measuring the rotation period of the planet, giving it as approximately 24 hours. He made a rough estimate of the diameter of Mars, guessing that it is about 60% of the size of the Earth, which compares well with the modern value of 53%.
Perhaps the first definitive mention of Mars's southern polar ice cap was by the Italian astronomer Giovanni Domenico Cassini
Giovanni Domenico Cassini
This article is about the Italian-born astronomer. For his French-born great-grandson, see Jean-Dominique Cassini.Giovanni Domenico Cassini was an Italian/French mathematician, astronomer, engineer, and astrologer...
, in 1666. That same year, he used observations of the surface markings on Mars to determine a rotation period of 24h 40m. This differs from the correct value by less than three minutes. In 1672, Christiaan Huygens noticed a fuzzy white cap at the north pole.
After Cassini became the first director of the Paris Observatory
Paris Observatory
The Paris Observatory is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world...
in 1671, he tackled the problem of the physical scale of the Solar System. For this purpose, the position of Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
was measured against the background stars from different points on the Earth—the diurnal parallax. During this year, the planet was near the point along its orbit when it was nearest to the Sun (a perihelical opposition), thereby also making a particularly close approach to the Earth. Cassini and Jean Picard
Jean Picard
Jean-Felix Picard was a French astronomer and priest born in La Flèche, where he studied at the Jesuit Collège Royal Henry-Le-Grand. He was the first person to measure the size of the Earth to a reasonable degree of accuracy in a survey conducted in 1669–70, for which he is honored with a...
determined the position of Mars in Paris
Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...
, while French astronomer Jean Richer
Jean Richer
Jean Richer was a French astronomer and assistant of Giovanni Domenico Cassini.Between 1671 and 1673 he traveled to Cayenne at the request of the French Academy of Sciences to observe Mars during its perigee...
made the measurements in Cayenne
Cayenne
Cayenne is the capital of French Guiana, an overseas region and department of France located in South America. The city stands on a former island at the mouth of the Cayenne River on the Atlantic coast. The city's motto is "Ferit Aurum Industria" which means "Work brings wealth"...
, South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
. Although these observations were hampered by the quality of the instruments, Cassini's result came within 10% of the correct value. The English astronomer John Flamsteed
John Flamsteed
Sir John Flamsteed FRS was an English astronomer and the first Astronomer Royal. He catalogued over 3000 stars.- Life :Flamsteed was born in Denby, Derbyshire, England, the only son of Stephen Flamsteed...
made comparable measurement attempts and had similar results.
In 1704, French-Italian astronomer Jacques Philippe Maraldi made a systematic study of the southern cap and noticed that it underwent variation as the planet rotated. This indicated that the cap was not centered on the pole. He also observed that the cap varied in size over time.
The German-English astronomer William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...
began making observations of the planet Mars in 1777; particularly of the planet's polar caps. In 1781, he noted that the south cap appeared "extremely large", which he ascribed to that pole being in darkness for the past twelve months. By 1784, the southern cap appeared much smaller, thereby suggesting that the caps vary with the planet's seasons and thus were made of ice. In 1781, he estimated the rotation period of Mars as 24h 39m 21.67s and measured the axial tilt
Axial tilt
In astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...
of the planet's poles to the orbital plane as roughly 28.5°. He noted that Mars had a "considerable but moderate atmosphere, so that its inhabitants probably enjoy a situation in many respects similar to ours".
Between 1796 and 1809, the French astronomer Honoré Flaugergues
Honoré Flaugergues
Honoré Flaugergues was a French astronomer.....
noticed some obscurations of Mars, suggesting "ochre-colored veils" covered the surface. This may be the earliest report of yellow clouds or storms on Mars.
Geographical period
At the start of the 19th century, improvements in the size and quality of telescope optics proved a significant advance in observation capability. Most notable among these enhancements was the two-component achromatic lensAchromatic lens
An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration. Achromatic lenses are corrected to bring two wavelengths into focus in the same plane....
of the German optician Joseph von Fraunhofer
Joseph von Fraunhofer
Joseph von Fraunhofer was a German optician. He is known for the discovery of the dark absorption lines known as Fraunhofer lines in the Sun's spectrum, and for making excellent optical glass and achromatic telescope objectives.-Biography:Fraunhofer was born in Straubing, Bavaria...
that essentially eliminated coma
Coma (optics)
In optics , the coma in an optical system refers to aberration inherent to certain optical designs or due to imperfection in the lens or other components which results in off-axis point sources such as stars appearing distorted, appearing to have a tail like a comet...
—an optical effect that can distort the outer edge of the image. By 1812, Fraunhofer had succeeded in creating an achromatic objective lens 190 mm (7.5 in) in diameter. The size of this primary lens is the main factor in determining the light gathering ability and resolution of a telescope.
During the opposition of Mars in 1830, the German astronomers Johann Heinrich Mädler and Wilhelm Beer used a 95 mm (3.7 in) Fraunhofer refracting telescope
Refracting telescope
A refracting or refractor telescope is a type of optical telescope that uses a lens as its objective to form an image . The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used for long focus camera lenses...
to launch an extensive study of the planet. They chose a feature located 8° south of the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
as their point of reference. (This was later named the Sinus Meridiani
Sinus Meridiani
Sinus Meridiani is a feature name for an albedo feature on Mars stretching east-west just south of that planet's equator. It was named by the French astronomer Camille Flammarion in the late 1870s.-Observational History:...
, and it would become the zero meridian
Meridian (astronomy)
This article is about the astronomical concept. For other uses of the word, see Meridian.In the sky, a meridian is an imaginary great circle on the celestial sphere. It passes through the north point on the horizon, through the celestial pole, up to the zenith, through the south point on the...
of Mars.) During their observations, they established that most of Mars’ surface features were permanent, and more precisely determined the planet's rotation period. In 1840, Mädler combined ten years of observations and drew the first map of Mars. Rather than giving names to the various markings, Beer and Mädler simply designated them with letters; Meridian Bay (Sinus Meridiani) was thus feature "a".
Working at the Vatican Observatory
Vatican Observatory
The Vatican Observatory is an astronomical research and educational institution supported by the Holy See. Originally based in Rome, it now has headquarters and laboratory at the summer residence of the Pope in Castel Gandolfo, Italy, and an observatory at the Mount Graham International...
during the opposition of Mars in 1858, Italian astronomer Angelo Secchi noticed a large blue triangular feature, which he named the "Blue Scorpion". This same seasonal cloud-like formation was seen by English astronomer J. Norman Lockyer in 1862, and it has been viewed subsequently by other observers. During the 1862 opposition, Dutch astronomer Frederik Kaiser
Frederik Kaiser
Frederik Kaiser was a Dutch astronomer.He was director of the Leiden Observatory from 1838 until his death....
produced drawings of Mars. By comparing his illustrations with those of Huygens and the English natural philosopher Robert Hooke
Robert Hooke
Robert Hooke FRS was an English natural philosopher, architect and polymath.His adult life comprised three distinct periods: as a scientific inquirer lacking money; achieving great wealth and standing through his reputation for hard work and scrupulous honesty following the great fire of 1666, but...
, he was able to further refine the rotation period of Mars. His value of 24h 37m 22.6s is accurate to within a tenth of a second.
Father Secchi produced some of the first color illustrations of Mars in 1863. He used the names of famous explorers for the distinct features. In 1869, he observed two dark linear features on the surface that he referred to as canali, which is Italian for 'channels' or 'grooves'. In 1867, English astronomer Richard A. Proctor created a more detailed map of Mars based on the 1864 drawings of English astronomer William R. Dawes. Proctor named the various lighter or darker
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
features after astronomers, past and present, who had contributed to the observations of Mars. During the same decade, comparable maps and nomenclature were produced by the French astronomer Camille Flammarion
Camille Flammarion
Nicolas Camille Flammarion was a French astronomer and author. He was a prolific author of more than fifty titles, including popular science works about astronomy, several notable early science fiction novels, and several works about Spiritism and related topics. He also published the magazine...
and the English astronomer Nathan Green
Nathan Green
Nathan Andrew Green is an Australian professional golfer.Green was born in Newcastle, New South Wales. He turned professional in 1998. During his early career, he played mostly on the PGA Tour of Australasia, and the Canadian Tour during the Australian winter...
.
At the University of Leipzig
University of Leipzig
The University of Leipzig , located in Leipzig in the Free State of Saxony, Germany, is one of the oldest universities in the world and the second-oldest university in Germany...
in 1862–64, German astronomer Johann K. F. Zöllner
Johann Karl Friedrich Zöllner
Johann Karl Friedrich Zöllner was a German astrophysicist who studied optical illusions. He invented the Zöllner illusion where lines that are parallel appear diagonal. The lunar Zöllner crater is named in his honor...
used a photometer
Photometer
In its widest sense, a photometer is an instrument for measuring light intensity or optical properties of solutions or surfaces. Photometers are used to measure:*Illuminance*Irradiance*Light absorption*Scattering of light*Reflection of light*Fluorescence...
he had developed to measure the reflectivity of the Moon, planets and bright stars. For Mars, he derived an albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
of 0.27. Between 1877 and 93, German astronomers Gustav Müller
Gustav Müller
Karl Hermann Gustav Müller was a German astronomer.He was born in Schweidnitz, Silesia to a merchant father; his father died...
and Paul Kempf observed Mars using Zöllner's photometer. They found a small phase coefficient—the variation in reflectivity with angle—indicating that the surface of Mars is relatively smooth and without large irregularities.
In 1867, French astronomer Pierre Janssen and British astronomer William Huggins
William Huggins
Sir William Huggins, OM, KCB, FRS was an English amateur astronomer best known for his pioneering work in astronomical spectroscopy.-Biography:...
used spectroscopes to examine the atmosphere of Mars. Both compared the optical spectrum of Mars to that of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. As the spectrum of the latter did not display absorption lines of water, they believed they had detected the presence of water vapor in the atmosphere of Mars. This result was confirmed by German astronomer Herman C. Vogel
Hermann Carl Vogel
Hermann Carl Vogel was a German astronomer. He was born in Leipzig, Kingdom of Saxony.Vogel pioneered the use of the spectroscope in astronomy...
in 1872 and English astronomer Edward W. Maunder in 1875, but would later come into question.
A particularly favorable perihelic opposition occurred in 1877. The English astronomer David Gill
David Gill (astronomer)
Sir David Gill FRS was a Scottish astronomer who is known for measuring astronomical distances, for astrophotography, and for geodesy. He spent much of his career in South Africa.- Life and work :...
used this opportunity to measure the diurnal parallax of Mars from Ascension Island
Ascension Island
Ascension Island is an isolated volcanic island in the equatorial waters of the South Atlantic Ocean, around from the coast of Africa and from the coast of South America, which is roughly midway between the horn of South America and Africa...
. With these measurements, he was able to more accurately determine the distance from the Earth to the Sun, based upon the relative size of the orbits of Mars and the Earth. He also noted that the edge of the disk of Mars appeared fuzzy because of the atmosphere, which limited the precision he could obtain for the planet's position.
In August 1877, the American astronomer Asaph Hall
Asaph Hall
Asaph Hall III was an American astronomer who is most famous for having discovered the moons of Mars in 1877...
discovered the two moons of Mars using a 660 mm (26 in) telescope at the U.S. Naval Observatory. The names of the two satellites, Phobos
Phobos (moon)
Phobos is the larger and closer of the two natural satellites of Mars. Both moons were discovered in 1877. With a mean radius of , Phobos is 7.24 times as massive as Deimos...
and Deimos
Deimos (moon)
Deimos is the smaller and outer of Mars's two moons . It is named after Deimos, a figure representing dread in Greek Mythology. Its systematic designation is '.-Discovery:Deimos was discovered by Asaph Hall, Sr...
, were chosen by Hall based upon a suggestion by Henry Madan
Henry George Madan
Henry George Madan wasan English chemist, teacher and academic.He was born in Cam Vicarage, Gloucestershire, England, the...
, a science instructor at Eton College
Eton College
Eton College, often referred to simply as Eton, is a British independent school for boys aged 13 to 18. It was founded in 1440 by King Henry VI as "The King's College of Our Lady of Eton besides Wyndsor"....
in England.
Martian canals
During the 1877 opposition, Italian astronomer Giovanni SchiaparelliGiovanni Schiaparelli
Giovanni Virginio Schiaparelli was an Italian astronomer and science historian. He studied at the University of Turin and Berlin Observatory. In 1859-1860 he worked in Pulkovo Observatory and then worked for over forty years at Brera Observatory...
used a 22 cm (8.7 in) telescope to help produce the first detailed map of Mars. These maps notably contained features he called canali, which were later shown to be an optical illusion
Optical illusion
An optical illusion is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source...
. These canali were supposedly long straight lines on the surface of Mars to which he gave names of famous rivers on Earth. His term canali was popularly mistranslated in English as canals. In 1886, the English astronomer William F. Denning observed that these linear features were irregular in nature and showed concentrations and interruptions. By 1895, English astronomer Edward Maunder became convinced that the linear features were merely the summation of many smaller details.
In his 1892 work La planète Mars et ses conditions d'habitabilité, Camille Flammarion wrote about how these channels resembled man-made canals, which an intelligent race could use to redistribute water across a dying Martian world. He advocated for the existence of such inhabitants, and suggested they may be more advanced than humans.
Influenced by the observations of Schiaparelli, the orientalist Percival Lowell founded an observatory
Lowell Observatory
Lowell Observatory is an astronomical observatory in Flagstaff, Arizona. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark in 1965....
with 30 and 45 cm (11.8 and 17.7 in) telescopes. The observatory was used for the exploration of Mars during the last good opportunity in 1894 and the following less favorable oppositions. He published several books on Mars and life on the planet, which had a great influence on the public. The canali were also found by other astronomers, such as Henri Joseph Perrotin and Louis Thollon with a 38 cm (15 in) refractor at the Nice Observatory
Nice Observatory
The Observatoire de Nice is an astronomical observatory located in Nice, France on the summit of Mont Gros. The observatory was initiated in 1879 by the banker Raphaël Bischoffsheim...
, one of the largest telescopes of that time.
Beginning in 1901, efforts were made to photograph the canal features of Mars by A. E. Douglass. These efforts appeared to succeed when Carl O. Lampland published photographs of the canals in 1905. Although these results were widely accepted, they became contested by Greek astronomer Eugène M. Antoniadi, English naturalist Alfred Russel Wallace
Alfred Russel Wallace
Alfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...
and others as imagined features. As bigger telescopes were used, fewer long, straight canali were observed. During an observation in 1909 by Flammarion with a 84 cm (33.1 in) telescope, irregular patterns were observed, but no canali were seen.
Refining planetary parameters
In 1894, American astronomer William W. CampbellWilliam Wallace Campbell
William Wallace Campbell was an American astronomer, and director of Lick Observatory from 1900 to 1930. He specialized in spectroscopy.-Biography:...
found that the spectrum of Mars was identical to the spectrum of the Moon, throwing doubt on the burgeoning theory that the atmosphere of Mars is similar to that of the Earth. Previous detections of water in the atmosphere of Mars were explained by unfavorable conditions, and Campbell determined that the water signature came entirely from the Earth's atmosphere. Although he agreed that the ice caps did indicate there was some water in the atmosphere, he did not believe the caps were sufficiently large to allow the water vapor to be detected. At the time, Campbell's results were considered controversial and were criticized by some members of the astronomical community, but they were later confirmed by American astronomer Walter S. Adams in 1925.
Baltic German
Baltic German
The Baltic Germans were mostly ethnically German inhabitants of the eastern shore of the Baltic Sea, which today form the countries of Estonia and Latvia. The Baltic German population never made up more than 10% of the total. They formed the social, commercial, political and cultural élite in...
astronomer Hermann Struve
Hermann Struve
Karl Hermann Struve was a Russian astronomer. In Russian, his name is sometimes given as German Ottovich Struve or German Ottonovich Struve ....
used the observed changes in the orbits of the martian moons to determine the gravitational influence of the planet's oblate shape. In 1895, he used this data to estimate that the equatorial diameter was 1/190 larger than the polar diameter. In 1911, he refined the value to 1/192. This result was confirmed by American meteorologist Edgar W. Woolard in 1944.
Surface obscuration caused by yellow clouds had been noted in the 1870s when they were observed by Schiaparelli. Further evidence for such clouds was observed during the oppositions of 1892 and 1907. In 1909, Antoniadi noted that the presence of yellow clouds was associated with the obscuration of albedo features. He discovered that Mars appeared more yellow during oppositions when the planet was closest to the Sun and was receiving more energy. He suggested windblown sand or dust as the cause of the clouds.
Using a vacuum thermocouple
Thermocouple
A thermocouple is a device consisting of two different conductors that produce a voltage proportional to a temperature difference between either end of the pair of conductors. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a...
attached to the 2.54 m (100 in) Hooker Telescope at Mount Wilson Observatory
Mount Wilson Observatory
The Mount Wilson Observatory is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 5,715 foot peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles...
, in 1924 the American astronomers Seth Barnes Nicholson
Seth Barnes Nicholson
Seth Barnes Nicholson was an American astronomer.Nicholson was born in Springfield, Illinois and was raised in rural Illinois...
and Edison Pettit
Edison Pettit
Edison Pettit was an American astronomer.He was born in Peru, Nebraska. He taught astronomy at Washburn College in Topeka, Kansas from 1914 to 1918. He married Hannah Steele, who was an assistant at Yerkes Observatory, and received his Ph.D...
were able to measure the thermal energy being radiated by the surface of Mars. They determined that the temperature ranged from -68 C at the pole up to 7 °C (45 °F) at the mid-point of the disk (corresponding to the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
). Beginning in the same year, radiated energy measurements of Mars were made by American physicist William Coblentz
William Coblentz
William Weber Coblentz was an American physicist notable for his contributions to infrared radiometry and spectroscopy.-Early life, education, and employment:...
and American astronomer Carl Otto Lampland
Carl Otto Lampland
Carl Otto Lampland was an American astronomer.Carl Otto Lampland was born near Hayfield in Dodge County, Minnesota. He was born into a family of ten children...
. The results showed that the night time temperature on Mars dropped to -85 C, indicating an "enormous diurnal fluctuation" in temperatures. The temperature of Martian clouds was measured as -30 C.
In 1926, by measuring spectral lines that were red shift
Red shift
-Science:* Redshift, the increase of wavelength of detected electromagnetic radiation with respect to the original wavelength of the emission* Red shift, an informal term for a bathochromic shift...
ed by the orbital motions of Mars and Earth, American astronomer Walter Sydney Adams
Walter Sydney Adams
Walter Sydney Adams was an American astronomer.-Life and work:He was born in Antioch, Syria to missionary parents, and was brought to the U.S. in 1885 He graduated from Dartmouth College in 1898, then continued his education in Germany...
was able to directly measure the amount of oxygen and water vapor in the atmosphere of Mars. He determined that "extreme desert conditions" were prevalent on Mars. In 1934, Adams and American astronomer Theodore Dunham, Jr. found that the amount of oxygen in the atmosphere of Mars was less than one percent of the amount over a comparable area on Earth.
During the 1920s, French astronomer Bernard Lyot
Bernard Lyot
Bernard Ferdinand Lyot was a French astronomer.His interest in astronomy started in 1914. He soon acquired a telescope and soon upgraded to a . From graduation in 1918 until 1929, he worked as a demonstrator at the Ecole Polytechnique...
used a polarimeter
Polarimeter
A polarimeter is a scientific instrument used to measure the angle of rotation caused by passing polarized light through an optically active substance....
to study the surface properties of the Moon and planets. In 1929, he noted that the polarized light emitted from the martian surface is very similar to that radiated from the Moon, although he speculated that some of his observations could be explained by frost and possibly vegetation. Based on the amount of sunlight scattered by the Martian atmosphere, he set an upper limit of 1/15 the thickness of the Earth's atmosphere. This restricted the surface pressure to no greater than 2.4 kPa (24 mbar).
Using infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
spectrometry, in 1947 the Dutch-American astronomer Gerard Kuiper
Gerard Kuiper
Gerard Peter Kuiper , Netherlands – December 24, 1973, Mexico City) was a Dutch-American astronomer after whom the Kuiper belt was named.-Early life:...
detected carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
in the Martian atmosphere. He was able to estimate that the amount of carbon dioxide over a given area of the surface is double that on the Earth. However, because he over-estimated the surface pressure on Mars, Kuiper concluded erroneously that the ice caps could not be composed of frozen carbon dioxide. In 1948, American meteorologist Seymour L. Hess determined that the formation of the thin Martian clouds would only require 4 mm (0.15748031496063 in) of precipitatable water and a vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
of 0.1 kPa (1 mbar).
Based upon observations of the near Earth
Near-Earth object
A near-Earth object is a Solar System object whose orbit brings it into close proximity with the Earth. All NEOs have a perihelion distance less than 1.3 AU. They include a few thousand near-Earth asteroids , near-Earth comets, a number of solar-orbiting spacecraft, and meteoroids large enough to...
asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
Eros
Eros
Eros , in Greek mythology, was the Greek god of love. His Roman counterpart was Cupid . Some myths make him a primordial god, while in other myths, he is the son of Aphrodite....
from 1926 to 1945, German-American astronomer Eugene K. Rabe was able to estimate the mass of Mars from the planet's gravitational perturbations
Perturbation (astronomy)
Perturbation is a term used in astronomy in connection with descriptions of the complex motion of a massive body which is subject to appreciable gravitational effects from more than one other massive body....
of the asteroid.
The first standard nomenclature for Martian albedo features was introduced by the International Astronomical Union
International Astronomical Union
The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...
(IAU) when in 1960 they adopted 128 names from the 1929 map of Antoniadi named La Planète Mars. The Working Group for Planetary System Nomenclature (WGPSN) was established by the IAU in 1973 to standardize the naming scheme for Mars and other bodies.
Remote sensing
The International Planetary Patrol ProgramInternational Planetary Patrol Program
The NASA International Planetary Patrol Program consists of a network of astronomical observatories to collect uninterrupted images and observations of the large-scale atmospheric and surface features of the planets...
was formed in 1969 as a consortium to continually monitor planetary changes. This worldwide group focused on observing dust storms on Mars. The resulting images allow martian seasonal patterns to be studied globally, and they showed that most Martian dust storms occur when the planet is closest to the Sun.
Since the 1960s, robotic spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
have been sent to explore Mars
Exploration of Mars
The exploration of Mars has been an important part of the space exploration programs of the Soviet Union, the United States, Europe, and Japan. Dozens of robotic spacecraft, including orbiters, landers, and rovers, have been launched toward Mars since the 1960s...
from orbit and the surface
Mars landing
A Mars landing is a landing of a spacecraft on the surface of Mars. Of multiple attempted Mars landings by robotic, unmanned spacecraft, six were successful. There have also been studies for a possible manned mission to Mars, including a landing, but none have been attempted.-Mars probe program:In...
in extensive detail. In addition, remote sensing of Mars from Earth by ground-based and orbiting telescopes has continued across much of the electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
. These include infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
observations to determine the composition of the surface, ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
and submillimeter observation of the atmospheric composition, and radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
measurements of wind velocities.
The Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
(HST) has been used to perform systematic studies of Mars and has taken the highest resolution images of Mars ever captured from Earth. This telescope can produce useful images of the planet when it is at an angular distance
Angular distance
In mathematics and all natural sciences , the angular distance between two point objects, as observed from a location different from either of these objects, is the size of the angle between the two directions originating from...
of at least 50° from the Sun. The HST can take images of a hemisphere
Sphere
A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...
, which yields views of entire weather systems. Earth-based telescopes equipped with charge-coupled device
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
s can also produce useful images of Mars, allowing for regular monitoring of the planet's weather during oppositions.
X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
emission from Mars was first observed by astronomers in 2001 using the Chandra X-ray Observatory
Chandra X-ray Observatory
The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.Chandra...
, and in 2003 it was shown to have two components. The first component is caused by X-rays from the Sun scattering off the upper Martian atmosphere, while the second comes from interactions between ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s that result in an exchange of charges. The emission from the latter source has been observed out to eight times the radius of Mars by the XMM-Newton
XMM-Newton
The XMM-Newton is an orbiting X-ray observatory launched by ESA in December 1999 on a Ariane 5 rocket...
orbiting observatory.
In 1983, the analysis of the Shergottite
Shergotty meteorite
The Shergotty meteorite is the first example of the shergottite Mars meteorite family. It was a Martian meteorite which fell to Earth at Shergotty , in the Gaya district, Bihar, India on 25 August 1865, and was retrieved by witnesses almost immediately...
, Nakhlite
Nakhla meteorite
Nakhla is a famous martian meteorite fallen in Egypt in 1911.-History:It fell to Earth on June 28, 1911, at approximately 09:00, in the Nakhla region of Abu Hommos, Alexandria, Egypt...
and Chassigny (SNC) group of meteorites showed that they may have originated on Mars
Mars meteorite
A martian meteorite is a rock that formed on the planet Mars, was ejected from Mars by the impact of an asteroid or comet, and landed on the Earth. Of over 53000 meteorites that have been found on Earth, 99 are martian...
. The Allan Hills 84001 meteorite, discovered in Antarctica in 1984, is believed to have originated on Mars but it has an entirely different composition than the SNC group. In 1996, it was announced that this meteorite might contain evidence for microscopic fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s of Martian bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
. However, this finding remains controversial. Chemical analysis of the Martian meteorites found on Earth suggests that the ambient near-surface temperature of Mars has most likely been below the freezing point of water (0 C°) for much of the last four billion years.
See also
- Classical albedo features on MarsClassical albedo features on MarsThe classical albedo features of Mars are the light and dark features that can be seen on the planet Mars through an Earth-based telescope. Before the age of space probes, several astronomers created maps of Mars on which they gave names to the features they could see. The most popular system of...
- Exploration of MarsExploration of MarsThe exploration of Mars has been an important part of the space exploration programs of the Soviet Union, the United States, Europe, and Japan. Dozens of robotic spacecraft, including orbiters, landers, and rovers, have been launched toward Mars since the 1960s...
- Mars in historyMars in historyThe planet Mars is named after the Roman god of war Mars. In Babylonian astronomy, the planet was named after Nergal, their deity of fire, war, and destruction, most likely due to the planet's reddish appearance. Whether the Greeks equated Nergal with their god of war, Ares, or whether both...