Newswise — Steve Desch is a professor of astrophysics in the School of Earth and Space Exploration at Arizona State University.
Desch’s theoretical research concentrates on star and planet formation, using meteoritic and planetary data to constrain models, in particular of the proto-planetary disk from which our solar system formed. He has developed models of the internal structure and geochemistry of icy dwarf planets such as Pluto's moon, Charon, the largest asteroid, Ceres, and the dwarf planet Haumea.
The recently reported occultation observations of Haumea by Ortiz et al. are very intriguing on many levels, Desch says. It is rare that objects as small, distant and slow moving as Haumea pass in front of a star. Although Haumea is a dwarf planet, its radius is still only 800 km, and it is 6 billion kilometers away and takes 284 years to orbit the Sun. Opportunities like this happen only once every decade or so.
Occultations are the most powerful technique for determining the size of a small object. We can't see Haumea's width in a telescope, and using its brightness to tell its size requires assumptions about its reflectivity. The size of Haumea's shadow as it blocks the light of a distant star is definitive. What made this observation even more intriguing was that it revealed a thin ring orbiting Haumea. This is the only solar system object with rings, besides the giant planets and the small 'centaur' object called Chariklo.
Getting the size of Haumea right is important for understanding it’s composition. Haumea has moons, and their orbits provide a mass, but we also need the size to infer Haumea's density. It appears to be a mix of ice and rock, with more ice and less rock than previously thought. Haumea seems to have suffered a giant collision in the past – it spins very fast, there are fragments from it in similar orbits around the Sun, it has two small moons and now the ring provides further evidence of this. The new density indicates how much ice was knocked off during the collision. It also constrains how much the rock might have chemically reacted with liquid water inside Haumea, and tells us how long liquid water might have existed inside Haumea, with important implications for planetary science and astrobiology.
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