— The Kuiper Belt is a vast ring of icy objects beyond Neptune (Illustration: NASA/JPL-Caltech/T Pyle)
Astronomers have caught their first glimpse of the innards of an icy asteroid 7.5 billion kilometres away in the Kuiper belt region of the outer solar system.
Mike Brown of the California Institute of Technology in Pasadena and his team discovered that five small Kuiper belt objects were travelling in similar orbits to 2003 EL61, the third-largest KBO ever found. The discovery hinted that the five pieces are fragments that split off after an ancient collision.
Such families of objects are common in the asteroid belt between Mars and Jupiter, but this is the first one seen out in the Kuiper belt. Brown's team found that the fragments all had a similar colour and proportion of water ice to 2003 EL61. This makes their association even more likely.
The fragments each reveal surfaces that were once internal regions of the original object. By analysing the subtle differences in composition between the fragments, astronomers can figure out the internal structure of the original body, in effect putting it back together, like archaeologists reconstructing a smashed pot. "It will give us a fresh insight into the Kuiper belt," says Alan Fitzsimmons of Queen's University Belfast in the UK.
Journal reference: Nature (vol 446, p 273 and 294)