Trans-Neptunian object
From Freepedia
| TNOs and similar bodies |
|---|
|
A trans-Neptunian object (TNO) is any object in the solar system which orbits the sun at a greater distance on average than Neptune. The Kuiper belt, Scattered disk, and Oort cloud are names for three divisions of this volume of space. Pluto and its moon Charon are trans-Neptunian objects, and if Pluto had been discovered today, it might not have been called a planet. (See the definition of Planet.)
The orbit of each of the planets is affected by the gravitational influences of all the other planets. Discrepancies in the early 1900s between the observed and expected orbits of the known planets suggested that there were one or more additional planets beyond Neptune (see Planet X). The search for these led to the discovery of Pluto, and since then a few other significant objects have been found. These were too small to explain the discrepancies, however, and revised estimates of Neptune's mass showed that the problem was spurious.
Contents |
Trans-Neptunian objects of note
- Pluto, considered a planet
- Charon, the moon of Pluto
- (15760) 1992 QB1, the prototype cubewano
- (15874) 1996 TL66, a scattered disk object
- (20000) Varuna, a cubewano
- (28978) Ixion, a plutino
- (50000) Quaoar, a cubewano
- (90377) Sedna, as yet unclassified, possibly an Oort cloud object
- (90482) Orcus, a plutino
- 2003 EL61, as yet unclassified ([1], [2]).
- 2003 UB313, a scattered disk object. Currently the largest known trans-Neptunian object.
- 2005 FY9, as yet unclassified ([3])
The hypothetical companion star Nemesis would fall under the definition of trans-Neptunian object, but there is no direct evidence for the existence of this body.
A fuller list of objects is being compiled in the List of trans-Neptunian objects.
Size and composition
Most TNOs are lumps of ice with some organic (carbon-containing) material such as tholin, detected using spectroscopy. They are of the same composition as comets and many astronomers believe them to be just comets. The distinction between comet and asteroid is not yet clear and there is a substantial uncertainty, inhabited by such objects as 2060 Chiron.
It is difficult to estimate the diameter of TNOs. For objects with very well known orbital elements (namely, Pluto and Charon), diameters can be precisely measured by occultation of stars.
For other large TNOs, diameters can be estimated by thermal measurement. If a body has high albedo, it is cold, and hence does not produce much black-body radiation in the infrared. Conversely, a low albedo object produces more infrared. TNOs are so far from the Sun that they are very cold, hence produce black-body radiation around 60 micrometres in wavelength. This wavelength of light is impossible to observe on the Earth's surface: astronomers thus observe the tail of the black-body radiation in the far infrared. This far infrared radiation is so dim that the thermal method is only applicable to the largest KBOs. The diameter of the smaller objects is estimated by assuming an albedo: the diameter of such bodies should be taken to be a rough guess.
Largest discoveries
Currently lying at 97 AU away, the celestial body designated 2003 UB313 is the farthest known object in the solar system, and the third brightest of the TNOs. It was first imaged by Michael Brown of the California Institute of Technology on October 31, 2003 with the Samuel Oschin Telescope at Palomar Observatory near San Diego, California. It is a typical member of the Kuiper belt, but recently it has been argued that its sheer size in relation to the nine known planets mean that it can only be classified as a planet. The discovering astronomer conceded he and his team did not know the exact size of the new object, but its brightness and distance tell them that it is at least as large as Pluto, which measures 2,302 kilometres in diameter. Scientists later estimated that the object was at least 1 1/2 times larger than Pluto. If confirmed, the discovery would be the first of a planet-mass object since Pluto was identified in 1930. 2003 UB313 is 15 terametres (15 billion kilometres) from the Sun, which it orbits every 560 years at an unusual 45-degree angle.
In July, 2005, the American scientists submitted a name for the "new planet" to the International Astronomical Union, re-igniting the debate about whether or not Pluto should be considered a planet at all.
The brightest known TNOs (with absolute magnitudes < 4.0), are:
| Permanent Designation | Provisional Designation | Absolute magnitude | Albedo | Equatorial diameter (km) | Semimajor axis (AU) | Date discovered | Discoverer | Diameter method |
|---|---|---|---|---|---|---|---|---|
| 2003 UB313 | −1.1 | 0.6 (assumed) | ~3000 (> 2300) | 67.7 | 2005 | M. Brown, C. Trujillo & D. Rabinowitz | assumed albedo | |
| Pluto | Planet X | −1.0 | 0.6 | 2320 | 39.4 | 1930 | C. Tombaugh | occultation |
| 2005 FY9 | −0.2 | 0.6 (assumed) | ~1900 | 45.7 | 2005 | M. Brown, C. Trujillo & D. Rabinowitz | assumed albedo | |
| 2003 EL61 | 0.1 | 0.6 (assumed) | ~1600 | 43.3 | 2005 | J.L. Ortiz et al. | assumed albedo | |
| Charon | S/1978 P 1 | 1 | 0.4 | 1205 | 39.4 | 1978 | J. Christy | occultation |
| (90377) Sedna | 2003 VB12 | 1.6 | >0.2 (assumed) | <1800, >1180 | 502.0 | 2003 | M. Brown, C. Trujillo & D. Rabinowitz | thermal |
| (90482) Orcus | 2004 DW | 2.3 | 0.1 (assumed) | ~1500 | 39.4 | 2004 | M. Brown, C. Trujillo & D. Rabinowitz | assumed albedo |
| (50000) Quaoar | 2002 LM60 | 2.6 | 0.10 ± 0.03 | 1260 ± 190 | 43.5 | 2002 | C. Trujillo & M. Brown | disk resolved |
| (28978) Ixion | 2001 KX76 | 3.2 | 0.25 – 0.50 | 400 – 550 | 39.6 | 2001 | Deep Ecliptic Survey | thermal |
| 55636 | 2002 TX300 | 3.3 | > 0.19 | < 709 | 43.1 | 2002 | NEAT | thermal |
| 55565 | 2002 AW197 | 3.3 | 0.14 – 0.20 | 650 – 750 | 47.4 | 2002 | C. Trujillo, M. Brown, E. Helin, S. Pravdo, K. Lawrence & M. Hicks / Palomar Observatory | thermal |
| 55637 | 2002 UX25 | 3.6 | 0.08? | ~910 | 42.5 | 2002 | A. Descour / Spacewatch | assumed albedo |
| (20000) Varuna | 2000 WR106 | 3.7 | 0.12 – 0.30 | 450 – 750 | 43.0 | 2000 | R. McMillan | thermal |
| 2002 MS4 | 3.8 | 0.1 (assumed) | 730? | 41.8 | assumed albedo | |||
| 2003 AZ84 | 3.9 | 0.1 (assumed) | 700? | 39.6 | assumed albedo | |||
| 84522 | 2002 TC302 | 3.9 | > 0.03 | < 1211 | 55.1 | 2002 | NEAT | thermal |
The list has been sorted by increasing absolute magnitude. Estimated diameter is greatly affected by surface albedo which has often been assumed, not measured. Some potentially large Kuiper belt objects have not been included.
External links
- List of Transneptunian Objects
- University of Arizona
- Scientific American magazine
- Diagram of relative sizes of some Transneptunian Objects
See also
| Large trans-Neptunian objectsedit |
| Kuiper belt: Pluto (Charon) | Orcus | Ixion | 2002 UX25 | Varuna 2002 TX300 | 2003 EL61 | Quaoar | 2005 FY9 | 2002 AW197 |
| Scattered disc: 2003 UB313 | Sedna† |
| See also Triton, astronomical objects and the solar system's list of objects, sorted by radius or mass. For pronunciation, see: Centaur and TNO pronunciation. † Current MPC classification. Some consider Sedna an Oort cloud object. |
| The minor planetsedit |
| Vulcanoids | Main belt | Groups and families | Near-Earth objects | Jupiter Trojans |
| Centaurs | Damocloids | Comets | Trans-Neptunians (Kuiper belt | Scattered disc | Oort cloud) |
| For other objects and regions, see: Binary asteroids, Asteroid moons and the Solar system For a complete listing, see: List of asteroids. For pronunciation, see: Pronunciation of asteroid names. |
| Our Solar Systemedit |
| Sun | Mercury | Venus | Earth (Moon) | Mars | Asteroid belt |
| Jupiter | Saturn | Uranus | Neptune | Pluto | Kuiper belt | Scattered disc | Oort cloud |
| See also astronomical objects and the solar system's list of objects, sorted by radius or mass |
