IT SEEMS comet Wild 2 lives up to its tough-guy name, at least in one respect. Turns out it’s made of a hard, rocky material rather than the fluffy dust typical of comets.
In 2004, NASA’s Stardust mission swung by Wild 2 to capture particles shed by the object and return them to Earth. Hope Ishii and colleagues at the Lawrence Livermore National Laboratory in California analysed these microscopic fragments and found the comet is much closer to an asteroid in composition (Science, vol 319, p 447).
It is unlike an asteroid in that it throws off gas and…
