Wednesday 23 October 2013

The nature and history of 'Quasi-Hilda Object' 2000 YN30.

The Asteroid 2000 YN30 was discovered by the Near Earth Asteroid Tracking (NEAT) group in December 2000 (the name 2000 YN30 implies the 763rd asteroid discovered during the second half of December 2000 - period 2000 Y). It is a 1.7 km diameter object in a Hilda Group orbit, in a 2:3 orbital ration with Jupiter. Hilda Group Asteroids complete three orbits for every two orbits of Jupiter, with their aphelion (the furthest point in their orbit from the Sun) moving in succession through the L₄, L₅ Lagrangian points (60º ahead and behind Jupiter) and the opposite point on its orbit (180º ahead and behind). 2000 YN30 does not appear to be in a stable orbit, and is therefore referred to as a 'Quasi-Hilda Object'.

The motion of the Hilda Group Asteroids. Even though each asteroid is in an elliptical orbit, the resonance of their aphelions with the Lagrangian points of Jupiter makes gives the group an apparent triangular shape. Cosmographica.

In a paper published on the online arXiv database at Cornell University Library on 6 May 2013, Yu-Chi Cheng of the Institute of Astronomy at National Central University in Taiwan and and Wing-Huen Ip, also of the Institute of Astronomy, as well as the Institute of Space Science, also at National Central University and the Space Science Institute at Macau University of Science and Technology, discuss the results of a study of 2000 YN30 as it passed through perihelion (the closest point on it's orbit to the Sun) in January 2009 using the LOT One Meter Telescope at Lulin Observatory in Taiwan.

Cheng & Ip detected a dust tail emerging from 2000 YN30 in January 2009, which they were able to track through till March of the same year. Such dust tails typically form as a comet approaches its perihelion, when ice at the surface sublimates away (turns directly from a solid to a gas - liquids do not form in a vacuum), releasing particles of silica trapped in the ice. For this reason they conclude that 2000 YN30 should be considered to be a Jupiter Family Comet (a comet with an orbital period of less than 20 years; in this case 2842 days, or 7.78 years), and rename it 212P/NEAT (2000 YN30), a designation which indicates it is the 212nd periodic comet discovered, that it was discovered by NEAT and that it was formerly known as asteroid 2000 YN30.

The orbit of 212P/NEAT (2000 YN30) and its position around perihelion in January 2009. JPL Small Body Database Browser.

Cheng & Ip next attempted to model the history of 212P/NEAT (2000 YN30)'s orbit, in order to determine how it reached its current trajectory. They conclude that in the most likely history of events, 212P/NEAT (2000 YN30) was captured into a short-period orbit (an orbit taking less than 20 years) by a close encounter with Jupiter around 46 800 years ago, when it reached 0.0063 AU from Jupiter (i.e. 0.63 of the distance between the Earth and the Sun, about 942 500 km), and that a second close encounter with Jupiter, around 18 250 years ago, when it reached 0.021 AU (3 142 000 km) from the planet, moved it into a quasi-Hilda orbit. As noted previously, quasi-Hilda orbits are not stable, and this orbit is calculated to have grown in eccentricity until it achieved a perihelion distance of around 0.8 AU from the Sun (i.e. 80% of the distance between the Earth and the Su, inside the orbit of Earth, but still outside that of Venus). This degree of eccentricity would have been maintained for about 250 years, since when 212P/NEAT (2000 YN30) has been moving steadily towards a more stable Hilda type orbit, something that Cheng & Ip calculate it will continue to do for the foreseeable future.

See also The dust tail of 3200 PhaethonThe perihelion of Comet 103P/Hartley 2The ejecta of Main-Belt Comet P/2012 T1 (PANSTARRS)The Main-Belt Comet P/2012 T1 (PANSTARRS) and The dust-tail of Asteroid P/2010 A2.

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