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Moons are icy all the way through: bodies likely chipped from Haumea in cataclysmic event.

You'd need a mighty tall glass to hold two space objects that researchers have now identified as ice cubes at the fringes of the solar system. The larger of the icy bodies is about the width of Ohio, the smaller about twice the length of Rhode Island. Both bodies are moons of the dwarf planet Haumea. Members of the trio were discovered in late 2004 and in 2005 and reside in the Kuiper Belt, a reservoir of objects beyond the orbit of Neptune.

Spectra taken of the larger and outermost of the two moons, dubbed Hi'iaka, had indicated that its surface, unlike most Kuiper Belt objects, is made of nearly pure crystalline water-ice. Now, new spectra taken with the Hubble Space Telescope not only confirm the composition of Hi'iaka, but for the first time also show that the surface of the smaller moon, Namaka, has the same composition. Because both moons are too small to have undergone heating and cooling that would have caused heavier elements to sink to the cores, the icy surfaces are likely to be fair representations of the moons' interiors.

"These things could be, essentially, ice cubes," says Michael Brown of the California Institute of Technology in Pasadena, a codiscover of Haumea and its moons. Brown and Caltech colleague Wesley Fraser describe the new observations online (arxiv.org/abs/0903.0860) and in the April 10 Astrophysical Journal Letters.

The frozen findings aren't just a cosmic curiosity. Haumea, whose rapid spin is thought to have reshaped it into a squashed football, is glazed with water-ice. (The dwarf planet's interior, in contrast, is made up of much denser material.) The similarity between the surface of Haumea and its moons strongly suggests that these satellites were not Kuiper Belt residents that happened to be captured by Haumea, but were chipped off the dwarf planet as a result of a cataclysmic event. Haumea is already the only Kuiper Belt object known to be part of a collisional family--other chunks, besides the moons, are known to have been created when a large impactor, perhaps 500 kilometers in diameter, struck the once-larger dwarf planet in the distant past, Brown says.

In Hawaiian mythology, Hi'iaka and Namaka are daughters of Haumea, the goddess of fertility. The findings provide evidence that these moons are indeed offspring of the planet, Brown says.

"At face value, it looks like Haumea's collisional family and the moons are one and the same--the product of some extraordinary event" early in the history of the solar system, comments Daniel Fabrycky of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

In a separate study, Brown and Caltech colleague Darin Ragozzine report that, as seen from Earth, Namaka and Haumea began transiting, or passing in front of each other, a few years ago. The team posted the findings online (arxiv.org/ abs/0903.4213), and the report will appear in an upcoming Astronomical Journal. The degree of dimming Namaka causes as it journeys across different sections of Haumea will reveal the exact shapes and sizes of the bodies, Ragozzine says.

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Title Annotation:Atom & Cosmos
Author:Cowen, Ron
Publication:Science News
Geographic Code:1USA
Date:Apr 25, 2009
Words:509
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