This retrograde TNO has the largest known semi-major axis of any of the retrograde non-cometary objects: 966.4274 ± 2.2149 AU. Our only hope will be to back-calculate the positions of future asteroids discovered to these dates to see if it matches the WISE positions. However, our knowledge of its orbit is extremely uncertain, as shown below, and it has been lost. Nominally, 2010 EQ 169 orbits the Sun at nearly a right angle to the ecliptic plane once every 2.9 years, between the orbits of Mars and Jupiter. We have only a three-day arc of 17 astrometric observations of 2010 EQ 169 between March 7-9, 2010 from which to determine its orbit. Unfortunately, it was discovered after the fact by analyzing past data from the Wide-field Infrared Survey Explorer ( WISE) space telescope, and has not been seen since. It is also the retrograde asteroid with the smallest semimajor axis (2.05 AU) and lowest orbital eccentricity (0.10). This retrograde asteroid holds the distinction (at least temporarily) of being the most highly-inclined main-belt asteroid (91.6°), relative to the ecliptic plane. It is a dark object with a reflectivity only around 3% and is estimated to be about 9 miles across. It takes nearly 117 years to orbit the Sun once. Its orbital inclination (relative to the ecliptic) is 160°, which is a 20° tilt from an anti-ecliptic orbit. Dioretsa is both a centaur and a damocloid. Objects in cometlike orbits that show no evidence of cometary activity are often referred to as damocloids. It is a centaur in a highly eccentric orbit (0.90), ranging between the orbits of Mars and Jupiter out to beyond the orbit of Neptune. The only named retrograde asteroid to date, Dioretsa is an anadrome of the word “asteroid”. The first retrograde asteroid to be discovered was 20461 Dioretsa, in 1999. Let’s now take a look at some of these 98 retrograde objects in greater detail. *asteroids between the orbits of Jupiter and Neptune are often referred to as centaursĪt least some of these objects may be captured interstellar objects. Of these 98 retrograde objects, only 14 have orbits well-enough determined to have received a minor planet number, and only one has yet received an official name (20461 Dioretsa).
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