28978 Ixion

28978 Ixion is a plutino (an object that has a 2:3 orbital resonance with Neptune). It is very likely to be a dwarf planet,^[8][9] 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.^[10] It has a diameter of approximately 7005650000000000000♠650 km, making 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 by the Cerro Tololo Inter-American Observatory (807).^[2] It is named after Ixion, a figure from Greek mythology.

Physical characteristics

Different diameters for Ixion depending on its albedo

Other than Pluto, Ixion was the first trans-Neptunian object (TNO) discovered that was originally estimated to be larger than dwarf planet Ceres,^[11] Even in 2002, a year after its discovery, Ixion was still believed to be more than 1000 km in diameter,^[12] though the 2002 estimate was a result of a spurious detection at 250 GHz that was not confirmed by later observations.^[13] More recent estimates suggest that Ixion has a high albedo^[14] and is smaller than Ceres. Observations of Ixion by Herschel Space Telescope and Spitzer Space Telescope in the far-infrared part of the spectrum revealed that its size is about 620 km.^[4]

Ixion is moderately red (slightly redder than 50000 Quaoar) in the visible light.^[15] It also has a higher albedo (>0.15) than the mid-sized red cubewanos.^[13] 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.^[15] 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.^[16] 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.^[17] The Very Large Telescope (VLT) has checked Ixion for cometary activity, but did not detect a coma.^[18] Ixion is currently about 41 AU from the Sun,^[7] and it is possible that Ixion could develop a coma or temporary atmosphere when it is closer to perihelion.

Orbit and rotation

Orbit and position of Ixion (green), Pluto (red) and Neptune (grey) in 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 below the ecliptic 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.^[17]

See also

• 19521 Chaos
• 20000 Varuna
• 50000 Quaoar
• 90377 Sedna
• Trans-Neptunian object § Physical characteristics

Notes

References

External links

• AstDys orbital elements
• Orbital simulation from JPL (Java) / Ephemeris
• 28978 Ixion at the JPL Small-Body Database
  • Discovery · Orbit diagram · Orbital elements · Physical parameters

Dwarf planets
Asteroid belt	IAU: Ceres No longer rounded and therefore not dwarf planets: Vesta (disrupted out of equilibrium)
Centaurs	Possibly: Chariklo Chiron
Centaurs (extended)	Possibly: 1995 SN55 Ceto 2010 TY53
Plutinos	IAU: Pluto Additional objects proposed by Brown and Tancredi: Orcus Ixion 2003 AZ84 2004 UX10 Huya Possibly: 2003 UZ413 2003 VS2 2002 VR128 2004 PF115 2002 XV93 2007 JH43 2001 QF298
Twotinos	Possibly: 2002 WC19
Other resonances/ unknown resonances:	IAU: Haumea Possibly: 2002 XW93 1999 DE9 1999 KR16 2001 YH140 2011 GM27 2010 VK201 2013 FZ27 2014 UM33 1999 CD158
Cubewanos:	IAU: Makemake Additional objects proposed by Brown and Tancredi: 2002 MS4 Salacia Quaoar Varuna Varda 2004 GV9 2002 AW197 2002 TX300 2005 RR43 2003 OP32 2005 RN43 Possibly: Chaos Altjira Sila-Nunam 2002 UX25 2007 JJ43 2005 UQ513 2004 TY364 2003 QW90 1998 SN165 2002 KX14 Praamzius 2004 NT33 2010 FX86 2002 CY248 2010 VR11 Rhadamanthus
Scattered disc	IAU: Eris Additional objects proposed by Brown and Tancredi: 2007 OR10 1996 TL66 2001 UR163 2005 RM43 Possibly: 2002 TC302 2004 XA192 2005 QU182 2006 QH181 2007 UK126 2010 EK139 2010 KZ39 2010 RE64 2010 RF43 2010 TJ 2013 FY27 2008 OG19 1996 GQ21 2012 HH2 1999 CC158 2006 HH123 2010 VZ98
Area uncertain	Captured satellites that were once dwarf planets: Triton (captured by Neptune) Phoebe (captured by Saturn, and was then disrupted out of equilibrium) Possibly: 2011 FW62 (lost) 2000 YW134 V774104
Detached objects	Possibly: 2004 XR190 2010 GB174 2008 ST291 1995 TL8 2005 TB190 2003 QX113 2003 FY128 2004 VN112 2000 CR105
Sednoids	Objects proposed by Brown and Tancredi: Sedna Possibly: 2012 VP113
Former candidates	Pallas Vesta Hygiea Cybele
See also: Charon Vanth Dysnomia Hiʻiaka Mesoplanet Planemo List of trans-Neptunian objects List of possible dwarf planets List of Solar System objects List of Solar System objects by size