23 Aug 2011

 

2007 OR10, all but Snow White!

 

In 2007 a team of astronomers led by Mike Brown (California Institute of Technology, Caltech) discovered a dwarf planet belonging to the Kuiper Belt. It was provisionally called 2007 OR10 and was the fifth largest dwarf planet (about half the size of Pluto), and Brown hypothesised that it was similar to the icy dwarf planet Haumea, and was therefore a very white body. The object was accordingly nicknamed "Snow White", while an official name was decided.
Later observations of 2007 OR10 revealed however that its surface was not white at all, but rather a distinctly reddish colour, so much so that it is actually one of the reddest objects in the Solar System.
To understand the origin of this colour, that could have excluded the possibility of water ice on the surface, Brown's team, unable to use the recently decommissioned Near Infrared Camera (NIRC) at the Keck Observatory (Hawaii), made a new instrument, the Folded-port Infrared Echellette (FIRE), for use on the Magellan Baade Telescope (Chile).
The results obtained with this instrument, to be published in the Astrophysical Journal Letters, have confirmed the red colour of the surface, but also show that the surface is actually covered in water ice. This is surprising, given that water ice is not red!
The mystery is likely to be explained by the presence of methane, a remnant of an atmosphere that has been lost to space over the last 2-3 billion years, a small part of which was precipitated onto the surface. A thin deposit of methane then may cover the water ice, just like on Quaoar, a dwarf planet that appears to be very similar to Snow White.

 

by Michele Ferrara & Marcel Clemens

credit: Caltech,NASA