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28978 Ixion

Discovery[1][2]
Discovered by	Deep Ecliptic Survey Cerro Tololo (807)
Discovery date	22 May 2001
Designations
MPC designation	28978 Ixion
Pronunciation	/ɪkˈsaɪ.ən/ ik-SYE-ən [note 1]
Alternate name	2001 KX76
Minor planet category	TNO (plutino)[3]
Orbital characteristics[1]
Epoch December 31, 2006 (JD 2 454 100.5)
Aphelion	7 370.503 Gm (49.269 AU)
Perihelion	4 501.495 Gm (30.091 AU)
Semi-major axis	5 935.999 Gm (39.680 AU)
Eccentricity	0.242
Orbital period	91 295.847 d (249.95 a)
Average orbital speed	4.66 km/s
Mean anomaly	268.546°
Inclination	19.584°
Longitude of ascending node	71.028°
Argument of perihelion	298.779°
Physical characteristics
Dimensions	650 +260−220 km[4] < 822 km diameter[5] 1055 ± 165 km (IRAM)[6]
Surface area	< 2.24 × 106 km²
Volume	< 3.15 × 108 km³
Mass	≈3 × 1020? kg[7]
Mean density	2.0? g/cm³
Equatorial surface gravity	< 0.229 7? m/s²
Escape velocity	< 0.434 6? km/s
Rotation period	? d
Albedo	0.15-0.37[5]
Temperature	≈44 K
Spectral type	(moderately red) B-V=1.03; V-R=0.61[8]
Apparent magnitude	19.6 (opposition) [9]
Absolute magnitude (H)	3.2[1]

28978 Ixion is a Kuiper belt object discovered on May 22, 2001. Ixion is a plutino (an object that has a 2:3 orbital resonance with Neptune) and a potential dwarf planet; its Spitzer estimated diameter of 650 km makes it about the fifth largest plutino. It is named after Ixion, a figure from Greek mythology. Ixion was discovered by the Cerro Tololo Inter-American Observatory (807).^[2]

Physical characteristics

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

Ixion is moderately red (slightly redder than 50000 Quaoar) and it has a higher albedo (0.15) than the mid-sized red cubewanos.

The latest spectroscopic results indicate that Ixion's surface is a mixture of dark carbon and tholin, which is a heteropolymer formed by irradiation of clathrates of water and organic compounds (see TNO spectra). Water ice absorption lines (1.5 and 2 μm) were absent (Licandro et al. 2002). Unlike Varuna, Ixion does not show greater reflectivity for longer waves (the so-called red slope) in infrared.

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 1000km in diameter.^[6] Though the 2002 estimate was a result of a spurious detection at 250GHz that was not confirmed by later observations.^[11] More recent estimates suggest that Ixion has a high albedo^[5] and is smaller than Ceres. It is much more likely that either 50000 Quaoar or 90482 Orcus will turn out to the first post-Pluto TNO discovered that is larger than Ceres.

The Very Large Telescope (VLT) has checked Ixion for cometary activity, but did not detect a coma.^[12] Ixion is currently about 41 AU from the Sun,^[9] and it is possible that Ixion could develop a coma or temporary atmosphere when it is closer to perihelion.

Orbit

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 appears as a faint point because it is currently 41 AU away and has an apparent magnitude of about 19.7.^[9] Credit: ESO

See also

• Comparison of colours of trans-Neptunian objects

Notes

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

References

1. ^ ^{a b c} "JPL Small-Body Database Browser: 28978 Ixion (2001 KX76)". 2007-07-12 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Ixion. Retrieved 2008-10-04.  
2. ^ ^{a b} Marsden, Brian G. (2001-07-01). "MPEC 2001-N01: 2001 FT185, 2001 KW76, 2001 KX76, 2001 KY76, 2001 KZ76, 2001 KA77". IAU Minor Planet Center. Harvard-Smithsonian Center for Astrophysics. http://131.142.24.68/mpec/K01/K01N01.html. Retrieved 2010-01-06.  
3. ^ Marc W. Buie (2007-07-12). "Orbit Fit and Astrometric record for 28978". SwRI (Space Science Department). http://www.boulder.swri.edu/~buie/kbo/astrom/28978.html. Retrieved 2008-09-29.  
4. ^ 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. http://arxiv.org/abs/astro-ph/0702538v2. Retrieved 2008-11-17.  
5. ^ ^{a b c} Wm. Robert Johnston. "TNO/Centaur diameters and albedos". http://www.johnstonsarchive.net/astro/tnodiam.html.  
6. ^ ^{a b} Altenhoff, Bertoldi, Junkes (October 7, 2002). "Beyond Pluto: Max-Planck radioastronomers measure the sizes of distant minor planets". Spaceref.com. http://www.spaceref.com/news/viewpr.html?pid=9446. Retrieved 2010-01-06.  
7. ^ 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
8. ^ Doressoundiram (2004). "The Meudon Multicolor Survey (2MS) of Centraurs and Trans-Neptunian objects". http://www.iop.org/EJ/article/1538-3881/134/6/2186/205733.web.pdf. Retrieved 2006-11-06.  
9. ^ ^{a b c} "AstDys (28978) Ixion Ephemerides". Department of Mathematics, University of Pisa, Italy. http://hamilton.dm.unipi.it/astdys/index.php?pc=1.1.3.0&n=Ixion. Retrieved 2009-08-13.  
10. ^ Richard Stenger (2001-08-24). "New object deemed largest minor planet". CNN (space). http://edition.cnn.com/2001/TECH/space/08/24/minor.planet/index.html. Retrieved 2008-02-29.  
11. ^ Altenhoff, W.J.; Bertoldi, F.; Menten, K.M. (2004). "Size estimates of some optically bright KBOs". A&A 415 (2): 771–775. doi:10.1051/0004-6361:20035603.  
12. ^ O. Lorin and P. Rousselot (2007). "Search for cometary activity in three Centaurs (60558) Echeclus, 2000 FZ53 and 2000 GM137 and two trans-Neptunian objects (29981) 1999 TD10 and (28978) Ixion". Royal Astronomical Society 376 (2): 881–889. doi:10.1111/j.1365-2966.2007.11487.x. http://www3.interscience.wiley.com/journal/117974948/abstract. Retrieved 2008-10-04.  

• H. Boehnhardt, S. Bagnulo, K. Muinonen, M. A. Barucci, L. Kolokolova, E. Dotto and G. P. Tozzi (2003). "Surface characterization of 28978 Ixion (2001 KX₇₆)". Astronomy & Astrophysics 415: L17–L19.   Pre-print about Ixion's surface from the Planetary Systems Research group of the University of Helsinki

• J. Licandro, F. Ghinassi, L. Testi (2002). "Infrared spectroscopy of the largest known trans-neptunian object 2001 KX₇₆". Astronomy & Astrophysics 388: L9. doi:10.1051/0004-6361:20020533.   Pre-print on arXiv

• W. J. Altenhoff, F. Bertoldi and K. M. Menten (2004). "Size estimates of some optically bright KBOs". Astronomy & Astrophysics 415.  

External links

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