An itinerant interstellar asteroid may actually be a comet in disguise.
Known as ‘Oumuamua, the object was detected in October and is the first visitor from another star spotted touring our solar system (SN: 11/ 25/17, p. 14). Early observations suggested the vagabond was rocky. But after additional analysis, a team of researchers suggests December 18 in Nature Astronomy that the object might have an icy core.
In general, comets are icy and asteroids are rocky. Ice gives comets their characteristic tails: As a comet passes near the sun, the heat warms the ice, causing it to sublimate, releasing gas and dust. Because no tail appeared despite ‘Oumuamua’s passage by the sun, the mysterious visitor was dubbed an asteroid — a surprising conclusion since the vast majority of objects ejected from star systems are expected to be icy.
“Everybody’s been assuming that this is just a lump of rock,” says astronomer…
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