13 May 2011

 

 

The crystalline surface of Haumea

 

Haumea is one of the four dwarf planets so far discovered beyond the orbit of Neptune; the others are Pluto, Eris and Makemake. There are other candidates, such as Quaoar, but it seems that this is too small to qualify.
Of these dwarf planets Haumea is the strangest (illustrated above). Having dimensions of approximately 2000x1500x1000 km it's shape is closer to a rugby ball than a sphere. It is also one of the fastest spinning bodies in the solar system, completing a turn in only 3.9 hours. According to some models, the elongated shape and very short "day" could both be the result of a glancing impact in the remote past with another transneptunian object. As a result of the impact Haumea would have initially broken into pieces but then re-assembled under the influence of the self-gravity of the fragments.
The angular momentum transferred to the system in the impact caused it to rotate, so that the fragments collected in an elongated shape rather than a sphere. Not all of them though; some pieces remained in orbit, and these are the two satellites of Haumea, Hi'iaka and Namaka, with diameters of 400 and 200 km respectively.
The presence of the two moons has made possible an estimate of the mass of the system (28% that of the Pluto system and 6% that of the Moon), and therefore an estimate of the density, 3.5
g/cm3. This suggests that Haumea is 90% rocky with the remaining 10% likely to be water ice, mostly at the surface.
The most interesting new results come from this icy surface, that according to models should have an amorphous, disorganised structure due to the action of solar radiation, but instead is seen to be crystalline. The results come from a study by an international team of researchers using the SINFONI instrument on ESO's Very Large Telescope, under the direction of Christophe Dumas.
The results, published in Astronomy & Astrophysics, indicate that the ice on Haumea must be continuously re-ordered into a crystalline state (but not necessarily melted) by an internal heat source, perhaps the decay of radioactive elements such as potassium-40, thorium-232 and uranium-238.
A region of enhanced heating may coincide with a warm patch on the surface, already observed in the infrared. The surface of Hi'iaka also has crystalline ice, but in this case the heat source is more likely to be the tidal forces exerted by Haumea. The surface of Namaka remains relatively un-studied however, due to its smaller size and resulting fainter magnitude.

 

by Michele Ferrara & Marcel Clemens

credit: ESO, SINC/José Antonio Peñas