3200 Phaethon
Encyclopedia
3200 Phaethon is an asteroid
with an unusual orbit that brings it closer to the Sun
than any other named asteroid (though there are several unnamed asteroids, including three numbered ones, with smaller perihelia, e.g. ). For this reason, it was named after the Greek myth
of Phaëton
, son of the sun god Helios
. It is 5.10 km in mean
diameter
.
and John K. Davies discovered it in images from October 11, 1983 while searching Infrared Astronomical Satellite (IRAS) data for moving objects. It was announced on October 14 in IAUC 3878 along with optical confirmation by Charles T. Kowal
, who reported it to be asteroidal in appearance. Its provisional designation was 1983 TB.
(because its semi-major axis
is greater than that of the Earth
's and its perihelion is less than 1.017 astronomical unit
s. It is also suspected to be a member of the Pallas family
of asteroids.
One of Phaethon's most remarkable distinctions is that it approaches the Sun
closer than any other named asteroid: its perihelion is only 0.140 AU
— less than half of Mercury
's perihelion distance. It is a Mercury-, Venus-, Earth-, and Mars-crosser. The surface temperature at perihelion could reach ~1025 K, or 1400 F.
than an asteroid. However, it has never been observed to exhibit a coma
, gas jet, or dust tail, typical features of comets. Despite this, shortly after its discovery, Fred Whipple observed that the "orbital elements of 1983 TB shown on IAUC 3879 are virtually coincident with the mean orbital elements of 19 Geminid meteors photographed with the super-Schmidt meteor cameras". In other words, Phaethon is the long-sought parent body of the Geminids
meteor shower
of mid-December.
Phaethon's composition fits the notion of its cometary origin; it is classified as a B-type asteroid
because it is composed of dark material. Since Phaethon, several other objects showing mixed cometary and asteroidal features have been discovered, such as 133P/Elst-Pizarro
.
of Earth on December 10, 2007. It will draw nearer in 2017, 2050, 2060, and closer still on December 14, 2093, passing within 0.0198 AU
(3.0 Gm).
When Phaethon came to perihelion in July 2009, it was brighter than expected. As Phaethon approached perihelion in June 2009, the STEREO
-A spacecraft detected an unexpected brightening, by a factor of two.
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...
with an unusual orbit that brings it closer to 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...
than any other named asteroid (though there are several unnamed asteroids, including three numbered ones, with smaller perihelia, e.g. ). For this reason, it was named after the Greek myth
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
of Phaëton
Phaëton
In Greek mythology, Phaëton or Phaethon was the son of Helios and the Oceanid Clymene. Alternate, less common genealogies make him a son of Clymenus by Merope, of Helios and Rhode or of Helios and Prote....
, son of the sun god Helios
Helios
Helios was the personification of the Sun in Greek mythology. Homer often calls him simply Titan or Hyperion, while Hesiod and the Homeric Hymn separate him as a son of the Titans Hyperion and Theia or Euryphaessa and brother of the goddesses Selene, the moon, and Eos, the dawn...
. It is 5.10 km in mean
Geometric mean
The geometric mean, in mathematics, is a type of mean or average, which indicates the central tendency or typical value of a set of numbers. It is similar to the arithmetic mean, except that the numbers are multiplied and then the nth root of the resulting product is taken.For instance, the...
diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
.
Discovery
Phaethon was the first asteroid to be discovered using images from a spacecraft. Simon F. GreenSimon F. Green
Dr. Simon F. Green is an astronomer. He is a Senior Lecturer in Planetary and Space Science at the Open University. He specializes in the study of asteroids and trans-Neptunian objects, and for a long time worked with the IRAS satellite to detect fast moving objects. In 1983, along with John K....
and John K. Davies discovered it in images from October 11, 1983 while searching Infrared Astronomical Satellite (IRAS) data for moving objects. It was announced on October 14 in IAUC 3878 along with optical confirmation by Charles T. Kowal
Charles T. Kowal
Charles Thomas Kowal was an American astronomer.He discovered two moons of Jupiter: Leda in 1974 and Themisto in 1975, although the latter was lost and not rediscovered until 2000....
, who reported it to be asteroidal in appearance. Its provisional designation was 1983 TB.
Orbit
It is categorized as an Apollo asteroidApollo asteroid
The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, the first asteroid of this group to be discovered by Karl Wilhelm Reinmuth...
(because its semi-major axis
Semi-major axis
The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape...
is greater than that of the Earth
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...
's and its perihelion is less than 1.017 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s. It is also suspected to be a member of the Pallas family
Pallas family
The Pallas or Palladian family of asteroids is a grouping of B-type asteroids at very high inclinations in the intermediate asteroid belt . It was first noted by Kiyotsugu Hirayama in 1928....
of asteroids.
One of Phaethon's most remarkable distinctions is that it approaches 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...
closer than any other named asteroid: its perihelion is only 0.140 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
— less than half of 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...
's perihelion distance. It is a Mercury-, Venus-, Earth-, and Mars-crosser. The surface temperature at perihelion could reach ~1025 K, or 1400 F.
Physical characteristics and meteor shower
Phaethon's orbit looks more like that of a cometComet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
than an asteroid. However, it has never been observed to exhibit a coma
Coma (cometary)
frame|right|The [[153P/Ikeya-Zhang|comet Ikeya-Zhang]] exhibiting a bright, condensed coma In astronomy, a coma is the nebulous envelope around the nucleus of a comet. It is formed when the comet passes close to the Sun on its highly elliptical orbit; as the comet warms, parts of it sublimate...
, gas jet, or dust tail, typical features of comets. Despite this, shortly after its discovery, Fred Whipple observed that the "orbital elements of 1983 TB shown on IAUC 3879 are virtually coincident with the mean orbital elements of 19 Geminid meteors photographed with the super-Schmidt meteor cameras". In other words, Phaethon is the long-sought parent body of the Geminids
Geminids
The Geminids are a meteor shower caused by the object 3200 Phaethon, which is thought to be a Palladian asteroid. This would make the Geminids, together with the Quadrantids, the only major meteor showers not originating from a comet...
meteor shower
Meteor shower
A meteor shower is a celestial event in which a number of meteors are observed to radiate from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller...
of mid-December.
Phaethon's composition fits the notion of its cometary origin; it is classified as a B-type asteroid
B-type asteroid
B-type asteroids are a relatively uncommon type of carbonaceous asteroid, falling into the wider C-group. In the asteroid population, B-class objects are abundant in the outer asteroid belt, and also dominate the high-inclination Pallas family which includes the second-largest asteroid 2 Pallas...
because it is composed of dark material. Since Phaethon, several other objects showing mixed cometary and asteroidal features have been discovered, such as 133P/Elst-Pizarro
133P/Elst-Pizarro
Comet Elst–Pizarro is a body that displays characteristics of both asteroids and comets, and is the prototype of main-belt comets. Its orbit keeps it within the asteroid belt, yet it displayed a dust tail like a comet while near perihelion in 1996, 2001, and 2007.* As a comet it is formally...
.
Recent close approaches
Phaethon approached to 18.1 GmGigametre
A gigametre is a unit of length in the metric system, equal to one billion meters, the SI base unit of length, hence to 1,000,000 km or approximately 621,370 miles....
of Earth on December 10, 2007. It will draw nearer in 2017, 2050, 2060, and closer still on December 14, 2093, passing within 0.0198 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
(3.0 Gm).
When Phaethon came to perihelion in July 2009, it was brighter than expected. As Phaethon approached perihelion in June 2009, the STEREO
STEREO
STEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...
-A spacecraft detected an unexpected brightening, by a factor of two.
External links
- Orbital simulation from JPL (Java)
- Ephemeris
- (3200) Phaethon discussed on a blog