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28978 Ixion

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28978 Ixion
28978 Ixion
Discovered by Deep Ecliptic Survey
Discovery time 22 May, 2001
Name 28978 Ixion
Other names 2001 KX76
Group TNO (plutino)[1]
Reference date December 31, 2006 (JD 2 454 100.5)
Longest distance from the Sun 7 370.503 Gm (49.269 AU)
Shortest distance from the Sun 4 501.495 Gm (30.091 AU)
Longest distance from the center of its orbital path
("semi-major axis")
5 935.999 Gm (39.680 AU)
How egg-shaped its orbit is
How long it takes to complete an orbit 91 295.847 d (249.95 a)
Average speed 4.66 km/s
Mean anomaly 268.546°
Angle above the reference plane
Longitude of where it comes up through the reference plane 71.028°
Angle between its shortest distance from what it orbits around and where it comes up through the reference plane
("argument of periapsis")
Size and Other Qualities
Measures ~650+260−220 [3]
< 822 km diameter[4]
Area of its surface < 2.24×106 km²
Volume inside it < 3.15×108 km³
Mass ≈3×1020? kg[5]
Average density 2.0? g/cm³
Gravity at its surface < 0.229 7? m/s²
Slowest speed able to escape into space
("escape velocity")
< 0.434 6? km/s
How long it takes to turn around one time ? d
How much light it reflects 0.15-0.37[4]
Avg. surface temp. ≈44 K
Light-band group
("spectral type")
(moderately red; B-V=1.03, V-R=0.61)
Seeming brightness
("apparent magnitude")
19.6 (opposition)
True brightness
("absolute magnitude")

28978 Ixion is a Kuiper belt object that was found on May 22, 2001. Ixion is a plutino (an object that has a 2:3 orbital resonance with Neptune) and could be a dwarf planet. Astronomers think that it has a diameter of about 800 km, which makes it the third biggest plutino. It is named after Ixion, a figure from Greek mythology. Before it was named Ixion, it had the provisional designation 2001 KX76.


  1. Marc W. Buie (2007-07-12). "Orbit Fit and Astrometric record for 28978". SwRI (Space Science Department). Retrieved 2008-09-29.
  2. 2.0 2.1 "JPL Small-Body Database Browser: 28978 Ixion (2001 KX76)". 2007-07-12 last obs. Retrieved 2008-10-04.
  3. John Stansberry, Will Grundy, Mike Brown, Dale Cruikshank, John Spencer, David Trilling, Jean-Luc Margot (2007). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope". University of Arizona, Lowell Observatory, California Institute of Technology, NASA Ames Research Center, Southwest Research Institute, Cornell University. Retrieved 2008-11-17.
  4. 4.0 4.1 Wm. Robert Johnston. "TNO/Centaur diameters and albedos".
  5. Using the 2007 Spitzer spherical radius of 325 km; volume of a sphere * an assumed density of 2 g/cm³ yields a mass (m=d*v) of 2.8E+20 kg