Saturday 11 February 2012

The composition of Comet 10P/Tempel 2.

10P/Tempel 2 is a Jupiter Family Comet (a comet with a period of under 20 years; the time a comet takes to orbit the sun is referred to as a 'period', the term 'year' being reserved for planets) that was discovered by Ernst Wilhelm Leberecht Tempel in 1873. It has a period of 5.382 years. At its closest it comes in to 1.427 AU, or 1.427 times as far fro the sun as the Earth, slightly within the orbit of Mars; its orbit is tilted 12% from the plain of the Solar System. At its furthest it reaches 4.716 AU, still within the orbit of Jupiter. 10P/Temple 2 is thought to have a nucleus roughly 16.3 × 8.6 × 8.6 km, and a rotational period (day) of 8.6 hours.

The orbit of 10P/Temple 2. From the Kometeninfo Website.

Comets were once thought to be essentially similar objects originating in the outer reaches of the Solar System, but they are now known to be chemically distinct from one-another, leading scientists to believe that they do not share a common origin. Current thinking suggests that comets are left over pieces of the original proto-planetary disk from which the Solar System formed, and that the different chemical compositions of the comets relates to where about in this disk they formed; i.e. how far from the sun.

In a recent paper published on the arXiv online database at Cornell University Library, and also accepted for publication in the planetary science journal Icarus, a team of scientists lead by Lucas Paganini of the Goddard Centre for Astrobiology, describe a spectral analysis of 10P/Temple 2 made from the W. M. Keck Observatory on Mauna Kea in 2010.

Paganini et. al. established the abundances of compounds in the halo and tail of 10P/Temple 2 relative to the abundance of water (H₂O), the most abundant molecule in the comet.

Based upon this Paganini et al. deduce that the majority of the comet's formation occurred in a relatively warm part of the protoplanetary disk; with a temperature of about 30K (i.e. 30 °C above absolute zero), still considerably outside the orbit of Jupiter, but that the presence of hydrogenated hydrocarbons such as ethane suggests that the comet first started to form in a cooler, more distant part of the disk, where the temperature was around 20K, then was thrown further into the forming Solar System.