28978 Ixion

28978 Ixion

Discovery[2][3]
Discovered by	Deep Ecliptic Survey Cerro Tololo (807)
Discovery date	22 May 2001
Designations
MPC designation	28978 Ixion
Pronunciation	/ɪkˈsaɪ.ən/ ik-SY-ən [note 1]
Alternate name(s)	2001 KX76
Minor planet category	TNO (plutino)[4]
Adjective	Ixionian
Orbital characteristics[2]
Epoch December 31, 2006 (JD 2 454 100.5)
Aphelion	49.269 AU (7,370.503 Gm)
Perihelion	30.091 AU (4,501.495 Gm)
Semi-major axis	39.680 AU (5,935.999 Gm)
Eccentricity	0.242
Orbital period	249.95 a (91,295.847 d)
Mean anomaly	268.546°
Inclination	19.584°
Longitude of ascending node	71.028°
Argument of perihelion	298.779°
Proper orbital elements
Physical characteristics
Dimensions	650+260 −220 km[5]
Albedo	0.12+0.14 −0.06[5]
Temperature	≈44 K
Spectral type	B-V=1.03 ± 0.03 V-R=0.61 ± 0.03[6]
Apparent magnitude	19.6 (opposition) [1]
Absolute magnitude (H)	3.86 ± 0.04[6]
Angular diameter	0.022″

28978 Ixion is a plutino (an object that has a 2:3 orbital resonance with Neptune). It is considered very likely to be a dwarf planet,^[7] although the IAU has not officially classified it as such. Light-curve-amplitude analysis shows only small deviations, which suggests that Ixion is a spheroid with small albedo spots and hence a dwarf planet.^[8] Tancredi (2010) thinks that Ixion is a very probable plutoid.^[9] Its diameter of 650 km estimated by Spitzer makes it about the fifth largest plutino. It is moderately red in visible light and has a surface made of a mixture of tholin and water ice.

It was discovered on May 22, 2001. Ixion was discovered by the Cerro Tololo Inter-American Observatory (807).^[3] It is named after Ixion, a figure from Greek mythology.

Physical characteristics

The diameter of Ixion depends on the albedo (the fraction of light that it reflects).

Other than Pluto, Ixion was the first TNO discovered that was originally estimated to be larger than asteroid Ceres,^[10] Even in 2002, a year after its discovery, Ixion was still believed to be more than 1000 km in diameter,^[11] though the 2002 estimate was a result of a spurious detection at 250 GHz that was not confirmed by later observations.^[12] More recent estimates suggest that Ixion has a high albedo^[13] and is smaller than Ceres. Observations of Ixion by Spitzer Space Telescope in the far-infrared part of the spectrum revealed that its size is about 650 km.^[5]

Ixion is moderately red (slightly redder than 50000 Quaoar) in the visible light.^[14] It also has a higher albedo (>0.15) than the mid-sized red cubewanos.^[12] There may be an absorption feature at the wavelength of 0.8 μm in its spectrum, which is commonly attributed to the alteration of surface materials by water.^[14] In the near-infrared the spectrum of Ixion is flat and featureless. Water ice absorption bands at 1.5 and 2 μm are absent. This is in contrast to Varuna, which has a red spectral slope in the near-infrared as well as prominent water absorption bands.^[15] Both visible and infrared spectroscopic results indicate that Ixion's surface is a mixture of water ice, dark carbon and tholin, which is a heteropolymer formed by irradiation of clathrates of water and organic compounds.^[16] The Very Large Telescope (VLT) has checked Ixion for cometary activity, but did not detect a coma.^[17] Ixion is currently about 41 AU from the Sun,^[1] and it is possible that Ixion could develop a coma or temporary atmosphere when it is closer to perihelion.

Occultation

Ixion may have occulted a relatively bright apparent magnitude 11.5 star in the constellation of Ophiuchus on July 19, 2010.^[18] This event may have been visible from North America.^[18] The RA and DE for this event was in a star-rich region at 16 54 25.8620 −24 24 22.856.^[18] The occultation could have lasted up to 45 seconds,^[18] but the predicted occultation path was likely to miss the Earth. An occultation detection could help refine the diameter of this dwarf-planet candidate.

Orbit and rotation

This diagram shows the orbits of Ixion (green), Pluto (red) and Neptune (grey). The current positions of Ixion and Pluto are indicated (as of April 2006).

Ixion and Pluto follow similar but differently oriented orbits: Ixion’s perihelion is below the ecliptic whereas Pluto's is above it. Uncharacteristically for bodies locked in resonance with Neptune (such as Orcus), Ixion approaches Pluto with less than 20 degrees of angular separation. Ixion is currently crossing the ecliptic heading below, and will reach its perihelion in 2070. Pluto has passed its perihelion (1989) and is descending toward the ecliptic. Ixion's orbital period is almost 250 Earth years, about 0.5% larger than Pluto's. Ixion does demonstrate some regular changes in brightness, which are thought to be caused by its rotation. As of 2010, however, the rotation period of Ixion remains undetermined.^[16]

See also

• Comparison of colours of trans-Neptunian objects

Notes

1. ^ Or as in Latin: Ixīōn, Ancient Greek: Ιξίων. Sometimes erroneously /ˈɪksiən/ IK-see-ən.

References

External links

• AstDys orbital elements
• Orbital simulation from JPL (Java) / Ephemeris