Haumea isn’t a household name like its fellow Kuiper-Edgeworth belt object Pluto, but it is a little bigger along its long axis and maybe even more interesting. I say it is bigger along its long axis, that is the object is egg shaped. Whereas normally forming blobs of protoplanetary material turns spherical under gravity once a certain critical mass is achieved, this one seems to have been spun up, perhaps by an impact, and ended up longer in one direction than in all others it measures approximately 2,000 by 1,600 by 1,000 kilometres and spins in 3.9 hours.
At these distances, the best we can hope to do is see the dot of light, make measurements of its orbit to obtain its mass and take a look at the light it reflects from the Sun to get all other information. Spectroscopy tells us that the minor planet is covered with ice. Knowing from that how reflective it is, and knowing from other observations how far it is means the other thing that determines its apparent brightness – its size – can be obtained. As the egg shaped thing tumbles through space, however, its size from our perspective seems to change. Measurements of this change tell us how long the minor planet is and how wide it is.
Pedro Lacerda of Queen’s University Belfast and colleagues were performing such measurements when it became apparent something else was affecting the overall brightness. There seemed to be an additional dark spot. They measured the spot in different colours and then mapped the brightnesses onto a computer model to show the spot would appear red.
This might be due to an enrichment of organic compounds, or ices or maybe even the remains of something that slammed into the body. Observations are now planned using ESO’s Very Large Telescope in Chile in 2010.