XO-1b
Encyclopedia
XO-1b is an extrasolar planet
approximately 600 light-year
s away in the constellation
of Corona Borealis
. The planet was discovered orbiting the yellow dwarf
star
now designated XO-1
in 2006.
s discovered a Jupiter
-sized planet, later named XO-1b, orbiting a Sun
-like star. The team, led by Peter McCullough
of the Space Telescope Science Institute
in Baltimore
, had four amateur astronomers hailing from North America
and Europe
.
McCullough and his team employed a relatively inexpensive telescope called an XO Telescope
, made from commercial equipment, to search for extrasolar planets. This telescope consists of two 200-millimeter telephoto camera lenses
, and resembles binoculars
in shape. It stands on the summit of the Haleakalā
volcano in Hawaii
.
From September 2003 to September 2005, the XO Telescope
detected tens of thousands of bright stars. In that time, McCullough's team of amateur astronomers studied a few dozen stars they had previously identified as promising candidates for extrasolar planets. The star XO-1
, in particular, was marked as a promising candidate in June 2005. The amateur astronomers observed it from June to July 2005, eventually confirming that a planet-sized object was eclipsing it. McCullough's team then turned to the McDonald Observatory
in Texas
for information on the object's mass and to confirm it was a planet.
McCullough's team found the planet by detecting slight reductions in the star's intensity
as the planet moved into transit of the star. The light from the star reduces by approximately two percent when XO-1b is in transit. Their observation revealed that XO-1b is in a tight, four-day orbit around its parent star.
While astronomers have detected more than 180 extrasolar planets, XO-1b is only the tenth planet discovered using the transit method. It is only the second planet found using telephoto lenses. The first, TrES-1
, in the constellation Lyra
, was reported in 2004. The transit method allows astronomers to determine a planet's mass
and size
. Astronomers use this information to deduce the planet's characteristics, such as density
.
and the Hobby-Eberly Telescope
at the University of Texas's McDonald Observatory
to measure slight perturbations induced by the planet on its parent star. The radial velocity method allowed the team to calculate a precise mass of the planet, which is slightly less than Jupiter
's. This planet is much larger than its mass would suggest. McCullough has said, "Of the planets that pass in front of their stars, XO-1b is the most similar to Jupiter yet known, and the star XO-1 is the most similar to the Sun, but XO-1b is much, much closer to its star than Jupiter is to the Sun."
The technique used by the team to find XO-1b is an innovative method in that it uses a relatively inexpensive telescope to hunt for extrasolar planets. It, however, is limited primarily to planets orbiting close to their parent stars, and only finds planets large enough to cause a measurable depression in starlight.
and Spitzer Space Telescope
s. Hubble can precisely measure the star's distance and the planet's size, while Spitzer can photograph infrared radiation from the planet. By timing the disappearance of the planet behind the star, Spitzer can also measure the eccentricity
of the planet's orbit
—how much its orbital shape deviates from a circle. A high eccentricity implies a highly elliptical orbit, which would mean that the varying gravitational force from its parent star must heat the planet, expanding its atmosphere
and perhaps explaining why the object's diameter exceeds the expectation from its calculated mass.
in a close-orbit around its star, this planet falls into the category of hot Jupiter
s. Like other known transiting hot Jupiters such as HD 209458 b
and TrES-1
, the low density of XO-1b indicates that this planet is a gas giant
composed mainly of hydrogen
and helium
.
)
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
approximately 600 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Corona Borealis
Corona Borealis
Corona Borealis is a small constellation in the northern sky. Its name is Latin for "northern crown", a name inspired by its shape; its main stars form a semicircular arc. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy and remains one of the 88 modern...
. The planet was discovered orbiting the yellow dwarf
Yellow dwarf
A G-type main-sequence star , often called a yellow dwarf, is a main-sequence star of spectral type G and luminosity class V. Such a star has about 0.8 to 1.2 solar masses and surface temperature of between 5,300 and 6,000 K., Tables VII, VIII...
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
now designated XO-1
XO-1
XO-1 is a magnitude 11 yellow dwarf star located approximately 600 light-years away in the constellation Corona Borealis. XO-1 has a mass and radius similar to the Sun...
in 2006.
Discovery
In 2006, an international team of professional and amateur astronomerAmateur astronomy
Amateur astronomy, also called backyard astronomy and stargazing, is a hobby whose participants enjoy watching the night sky , and the plethora of objects found in it, mainly with portable telescopes and binoculars...
s discovered a 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,...
-sized planet, later named XO-1b, orbiting a 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...
-like star. The team, led by Peter McCullough
Peter McCullough
Peter R. McCullough is an American astronomer, founder of the XO Project and discoverer of extrasolar transiting planets, such as XO-1b. Soon after the U.S. declassification of the laser beacon adaptive optics technique in 1991, he identified dusty disks around new born stars, later referred to as...
of the Space Telescope Science Institute
Space Telescope Science Institute
The Space Telescope Science Institute is the science operations center for the Hubble Space Telescope and for the James Webb Space Telescope...
in Baltimore
Baltimore
Baltimore is the largest independent city in the United States and the largest city and cultural center of the US state of Maryland. The city is located in central Maryland along the tidal portion of the Patapsco River, an arm of the Chesapeake Bay. Baltimore is sometimes referred to as Baltimore...
, had four amateur astronomers hailing from North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
.
McCullough and his team employed a relatively inexpensive telescope called an XO Telescope
XO Telescope
The XO Telescope is a telescope located on the 3,054 m summit of Haleakala on Maui, Hawaii, formed by a pair of 200 mm telephoto lenses. It is used to detect extrasolar planets using the transit method. It is similar to the TrES survey telescope...
, made from commercial equipment, to search for extrasolar planets. This telescope consists of two 200-millimeter telephoto camera lenses
Telephoto lens
In photography and cinematography, a telephoto lens is a specific type of a long-focus lens in which the physical length of the lens is shorter than the focal length. This is achieved by incorporating a special lens group known as a telephoto group that extends the light path to create a long-focus...
, and resembles binoculars
Binoculars
Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
in shape. It stands on the summit of the Haleakalā
Haleakala
Haleakalā , or the East Maui Volcano, is a massive shield volcano that forms more than 75% of the Hawaiian Island of Maui. The western 25% of the island is formed by the West Maui Mountains.- History :...
volcano in Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
.
From September 2003 to September 2005, the XO Telescope
XO Telescope
The XO Telescope is a telescope located on the 3,054 m summit of Haleakala on Maui, Hawaii, formed by a pair of 200 mm telephoto lenses. It is used to detect extrasolar planets using the transit method. It is similar to the TrES survey telescope...
detected tens of thousands of bright stars. In that time, McCullough's team of amateur astronomers studied a few dozen stars they had previously identified as promising candidates for extrasolar planets. The star XO-1
XO-1
XO-1 is a magnitude 11 yellow dwarf star located approximately 600 light-years away in the constellation Corona Borealis. XO-1 has a mass and radius similar to the Sun...
, in particular, was marked as a promising candidate in June 2005. The amateur astronomers observed it from June to July 2005, eventually confirming that a planet-sized object was eclipsing it. McCullough's team then turned to the McDonald Observatory
McDonald Observatory
The McDonald Observatory is an astronomical observatory located near the unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Fowlkes and Mount Locke in the Davis Mountains of West Texas...
in Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
for information on the object's mass and to confirm it was a planet.
Transit
Radiance
Radiance and spectral radiance are radiometric measures that describe the amount of radiation such as light or radiant heat that passes through or is emitted from a particular area, and falls within a given solid angle in a specified direction. They are used to characterize both emission from...
as the planet moved into transit of the star. The light from the star reduces by approximately two percent when XO-1b is in transit. Their observation revealed that XO-1b is in a tight, four-day orbit around its parent star.
While astronomers have detected more than 180 extrasolar planets, XO-1b is only the tenth planet discovered using the transit method. It is only the second planet found using telephoto lenses. The first, TrES-1
TrES-1
TrES-1b is an extrasolar planet approximately 512 light-years away in the constellation of Lyra . The planet's mass and radius indicate that it is a Jovian planet with a similar bulk composition to Jupiter...
, in the constellation Lyra
Lyra
Lyra is a small constellation. It is one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations recognized by the International Astronomical Union. Its principal star, Vega — a corner of the Summer Triangle — is one of the brightest...
, was reported in 2004. The transit method allows astronomers to determine a planet's mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
and size
Radius
In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
. Astronomers use this information to deduce the planet's characteristics, such as density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
.
Radial velocity
The team confirmed the planet's existence by using the Harlan J. Smith TelescopeHarlan J. Smith Telescope
The Harlan J. Smith Telescope is a 2.7m telescope located at the McDonald Observatory, in Texas, in the United States. This telescope is one of several research telescopes that are part of the University of Texas at Austin observatory perched atop Mount Locke in the Davis Mountains of west Texas...
and the Hobby-Eberly Telescope
Hobby-Eberly Telescope
The Hobby-Eberly Telescope is a 9.2-meter aperture telescope located at the McDonald Observatory. It combines a number of features that differentiate it from most telescope designs, resulting in greatly lowered construction costs...
at the University of Texas's McDonald Observatory
McDonald Observatory
The McDonald Observatory is an astronomical observatory located near the unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Fowlkes and Mount Locke in the Davis Mountains of West Texas...
to measure slight perturbations induced by the planet on its parent star. The radial velocity method allowed the team to calculate a precise mass of the planet, which is slightly less than 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,...
's. This planet is much larger than its mass would suggest. McCullough has said, "Of the planets that pass in front of their stars, XO-1b is the most similar to Jupiter yet known, and the star XO-1 is the most similar to the Sun, but XO-1b is much, much closer to its star than Jupiter is to the Sun."
The technique used by the team to find XO-1b is an innovative method in that it uses a relatively inexpensive telescope to hunt for extrasolar planets. It, however, is limited primarily to planets orbiting close to their parent stars, and only finds planets large enough to cause a measurable depression in starlight.
Space telescopes
McCullough believes the newly found planet is a perfect candidate for study by the HubbleHubble 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...
and Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
s. Hubble can precisely measure the star's distance and the planet's size, while Spitzer can photograph infrared radiation from the planet. By timing the disappearance of the planet behind the star, Spitzer can also measure the eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
of the planet's orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
—how much its orbital shape deviates from a circle. A high eccentricity implies a highly elliptical orbit, which would mean that the varying gravitational force from its parent star must heat the planet, expanding its atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
and perhaps explaining why the object's diameter exceeds the expectation from its calculated mass.
Physical characteristics
As a planet with a mass comparable to that of JupiterJupiter
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,...
in a close-orbit around its star, this planet falls into the category of hot Jupiter
Hot Jupiter
Hot Jupiters are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter...
s. Like other known transiting hot Jupiters such as HD 209458 b
HD 209458 b
HD 209458 b is an extrasolar planet that orbits the Solar analog star HD 209458 in the constellation Pegasus, some 150 light-years from Earth's solar system, with evidence of water vapor....
and TrES-1
TrES-1
TrES-1b is an extrasolar planet approximately 512 light-years away in the constellation of Lyra . The planet's mass and radius indicate that it is a Jovian planet with a similar bulk composition to Jupiter...
, the low density of XO-1b indicates that this planet is a gas giant
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
composed mainly of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
.
External links
(Amateur's observation using Differential PhotometryPhotometry (astronomy)
Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical object's electromagnetic radiation...
)