TRANS-NEPTUNIAN OBJECTS (TNO’s)

Planetary astronomers have been looking for other bodies in the outer solar system depths since about 1992, and their numbers continue to increase almost exponentially. Like 134340 Eris, the location of these bodies in the Solar System occupies a region recently termed scattered disc and as they lie beyond the orbit of the most distant planet, Neptune, they are collectively known as trans-Neptunian objects - abbreviated to just TNO’s. Another term for some of these objects are Plutinos, which have a more specialised meaning. It is commonly referred as a trans-Neptunian object whose mean orbit lies in a 2:3 resonance with dwarf planet 134340 Pluto. Examples include the largest, 90482 Orchus, followed by 28978 Ixion, 38083 Rhadamanthus, 38628 Huya, and the first discovered Plutino on 14th September 1993 - the small estimated 92km across 1993 RO. This same region is is inside the Kuiper Belt where the nuclei of billions of comets are thought to reside. As of September 2006, eight large asteroid bodies exist beyond Pluto&38217;s orbit. The largest so far being the dwarf planet Eris.

NOTE : An continuously up-to-date link of all the current known
Trans-Neptunian Objects can be obtained at; [1.]

Before Eris’ discovery in October 2003, several team of observers from 2001 under Michael Brown found several of the largest of these new trans-Neptunian bodies, including Quaoar, Sedna, Orcus, and the presently unnamed and enigmatic, 2003 EL61.

OTHER TRANS-NEPTUNIAN OBJECTS

(134340) P L U T O

PLUTO (See the PLUTO Page)

(134340) E R I S

ERIS (See the ERIS Page)

V A R U N A

VARUNA (20000) or 2000 WR106, which is approximately about the size of Ceres or 936 km across, although recent estimates suggest Varuna is likely not round but ellipsoidal in shape. Varuna was named after the Indian Hundi creation god, and was discovered as another Kupier Belt object by R.Mcmillian on 20th November 2000. This very deep dark yellow body has only a very slightly elliptical orbit with an average distance from the Sun of 43.12 AU, that varies between perihelion and aphelion, 40.9 and 45.3 AU. The orbital inclination is 17.2^o, being about the same as Pluto. Varuna orbital period is 283.20 years. An unusual rapid sidereal rotation was discovered during 2002 from the rapid oscillating brightness in the light-curve, and is presently estimated as either 3.2 or its multiple of 6.34 hours.

Invisible in all amateur telescopes, Varuna presently lies in the zodiac constellation of Gemini, and will stay there until 2015 when it crosses into Cancer. The magnitude presently is hovering between 19.9 and 20.1 magnitude, which will slowly diminish in brightness to 20.2 to 20.4 magnitude over the next few decades. Periastron last occurred on 04th November 1934, and will not again happen until early 2273 AD. Next apastron will be in June 2075.

Q U A O A R

QUAOAR (50000) or 2002 AW197 was discovered by Michael Brown and Chad Trujillo using the 1.2m Oschin telescope at Mt. Palomar Observatory on 04th June 2002. This was almost 3½ years prior to the their most significant find, the dwarf planet Eris. Quaoar is the genderless god of the North American of the Tongva Native tribe, who during the first creation brought into existence all their worship deities used his great singing voice and complex dances.

This large 1260±190 kilometre sized Kuiper Belt asteroid has a near circular orbit, which encircles the Sun once every 282.89 years. Quaoar may still qualify as another dwarf planet, joining Pluto, Ceres and Eris, but more information about the true diameter will be required before it is categorised as such. As of October 2006, it is the fifth largest of the trans-Neptunian bodies. Like Varuna and Ixion, Quaoar is another dark reddish coloured body that poorly reflects light, implying that the surface is not entirely covered with ices. A later spectral analysis made in 2004 contradicts this, finds that Quaoar does have some quantities of frozen crystalline water ice on its surface. This may suggests that Quaoar may have possible ice volcanos caused by internal heat from the inner core or some recent collision.

The next expected periastron for Quaoar is 14th February 2081, whose coinciding aphelion dates are March 1821 and December 2340 AD. Presently (2006) Quaoar lies in northern Ophiuchus as a 19th magnitude star, varing in brightness between opposition and conjunction by merely 0.3 or 0.4 magnitudes. By 2009, Quaoar with move into Serpens, followed by Scutum in Jan 2022 and Sagittarius in December 2028. Over the coming decades the brightness will very slowly increase, where the maximum opposition magnitude of 18.8 will occur within the constellation of Pisces. Regardless, Quaoar will remain invisible to amateur telescopes, though it maybe possible to obtain using an CCD imaging.

S E D N A

S E D N A (90377) or 2003 VB12, is like Eris, as it is a known scattered disk object. Sedna was discovered on 14th November 2003 by the same team lead by Michael Brown who found Eris. Pending the decision by the IAU, in the near future, the 1490±310 km diameter may make Sedna qualify as another dwarf planet, and this will depend on more accurate size determination.

Sedna is quite remarkable because of its extreme elliptical orbit, which can vary between 76.7 AU and an estimated 970 AU or 145 billion kilometers, in an astounding period of around 12 000 years or 4.4 million days! When first found, Sedna just happened to be near perihelion, which is currently expect to occur in early April 2076. Problems exist with how such an object could have formed in the early solar system, and it has been suggested that the orbit has been influenced by passing nearby stars or even another undiscovered large planet. Another possibility is that Sedna was captured by the gravitation of the Sun sometime in the distant past.

Little is really known about this object, but spectroscopy suggests this is a very dark reddish coloured body - in fact rating the reddest in the whole solar system - possibly even beating Mars for the crown! The obtained spectra is radially different than other bodies at these depths, suggesting materials like complex hydrocarbon-like sludge, amorphous carbon, mixed with ices of methanol and methane - the later making up one-third of the material one the surface. Unlike many similar distance objects, little evidence of water ice has been found to exist. From slight changes in brightness over time, an estimated rotational period has been determined as roughly 10 hours 15 minutes.

At present, Sedna lies in Cetus near the border of Taurus, shining as a very faint 21.1 magnitude star. Due to the enormous distance from the sun, the movement against the background sky is very sluggish. After moving into Taurus, Sedna will not reach another constellation until it moves into northern Orion in 2040, then into neighbouring Gemini in 2075. A maximum brightness 20.4 magnitude will be reached in January 2078. When placed near aphelion sometime in 8061 AD, the estimated magnitude drop will be below 30th magnitude, and will be near impossible to see even with the largest of telescopes available today!

O R C U S

ORCUS (90482) or 2004 DW on 17th August 2004 another planetoid body was discovered by the team under Michael Brown. It is named after In 2006, the diameter is estimated to be around 1600 km, though this still remains rather uncertain. The mean distance from the Sun is 39.386, whose perihelion distance is 30.72 AU, which expands at aphelion to 48.05 AU The orbit is highly included to the ecliptic at 20.6^o, having the high orbital eccentricity of 0.220.

2003 EL 61

2003 EL61 (136108) is a most unusual trans-Neptunian object. It was discovered on 28th December 2004 by José Oritiz and Micheal Brown and nicknamed “Santa” because of it was found just prior to Christmas. No official IAU name is presently recognised. A mean diameter of 2003 EL61 is about 1500 km across, though from the variable light curve of 0.44 magnitudes, soon determined that its shape was more like a Rugby or Australian Rules football, and is calculated to be about 1960×1518×996 km. Unlike most of the other trans-Neptunian bodies, the rapid sidereal period is fairly accurate, spinning once every 0.163 days or 3.912 hours.
This distant body orbits the Sun every 285.31 years, averaging 43.34 AU or 6.50 billion kilometres away. The orbit is also moderately elliptical, whose distance varies anywhere between 35.1 and 51.5 AU. Perihelion last occurred in February 1991, with the next perihelion expected sometime in October 2135. Being highly inclined to the ecliptic by 28.2^o, means 2003 EL61 will stray well away from the zodiac constellations along the ecliptic. At 17.5 magnitude at opposition, 2003 EL61 remains one the brightest of these TBO’s and possibly can be seen only in the largest of amateur telescopes. This brightness is only exceeded by Pluto and the object 2005 FY9.

This unusual body also has two known moons, that are also unnamed. Amusingly the brightest was called Rudolph. Provisionally each are currently named as S/2005 (136108) 1 and S/2005 (136108) 2, and orbit 2003 EL61 once every 46.12 and 34.7 days, respectively, at the distances of 39 300km and 49 500km. Separations are estimated as 1.0 and 1.5 arcsec, whose orbits are almost edge-wise to the observers line of sight. The estimated diameters for both moons are around 310km and 170 km, respectively.

2005 FY9

2005 FY9 (136472) is sometimes classified as a so-called Classical KBO that sometimes refered as cubewano, and share the region with the similar plutinos. They are typically 2:3 Neptune resonant KBO’s with significant size. 2005 FY9 is unusually a bright body among all KBO’s, and lies at the mean distance of 45.7 AU, which varies between 38.6 and 52.8 AU. The eccentricity of the orbit is 0.155, and is moderate to highly inclined by 29.0^o to the ecliptic.

I X I O N

IXION (28978) or 2001 KX76, pronounced Ik-sar-on, is a small plutino body similarly placed near to the orbit of Pluto that was discovered on 22nd May 2001. Ixion’s mean distance from the Sun is 39.6 AU, whose highly inclined orbit is 19.6^o to the ecliptic and moderately eccentric (e = 0.382). This caused the distance to vary between 30.1 and 49.2 AU in an orbital period of 248.6 years. Ixion is currently 19.6 and 19.8 magnitude in the zodiacal constellation of Ophiuchus, and is now approaching perihelion in 18th November 2070, having had its last aphelion in May 1945. Between these extremes, Ixion will vary between 18.2 and 20.5 magnitude, and therefore remains invisible to all amateur telescopes.

Little else is known about Ixion itself. It seems to be a fairly small reddish coloured body that is currently estimated to be about 800km across.

Ixion is named in legend after the ancient Greek king of Thessaly, who in an act of vengeance killed his father-in-law by fire. Due to his totally unremorseful attitude, he soon became shunned and eventually exiled from the city. For this he was pitied by Zeus, who brought him into Olympus with the other gods. In some myths, while there Ixion was in Olympus he had an affair with the manifestation of human-shaped spirit in the form of a cloud, named Nephele, whose offspring became the mythical creatures known as Centaurs - half man and half horse. However, Ixion soon acted improperly by making untoward advances to Zeus’s wife, Hera. After firing a thunderbolt at him in anger, Zeus the forced Ixion into Tartarus (Hell) where he was permanently fixed to a burning spinning wheel, which keeps spinning for all time.

Also See :
DWARF PLANET Page.

Disclaimer

The user applying this data for any purpose forgoes any liability against the author. None of the information should be used for regarding either legal or medical purposes. Although the data is accurate as possible some errors might be present. The onus of its use is place solely with the user.

Last Update : 13th October 2006

Southern Astronomical Delights © (2006)

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