By Ron Cowen
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. The trio, discovered in late 2004 and 2005, reside in the Kuiper Belt, a reservoir of objects beyond the orbit of Neptune whose most famous denizen is Pluto.
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.