253 Mathilde

253 Mathilde is a large, exceptionally dark asteroid in the main belt between Mars and Jupiter. On 27 June 1997, NASA’s NEAR Shoemaker spacecraft passed within about 1,200 kilometres of it on its way to the asteroid Eros, capturing the first close-up views of a world that reflects only around four percent of the sunlight that falls on it — about as black as fresh asphalt.

Mathilde is a C-type asteroid, a primitive body rich in carbon-bearing and clay-like minerals little changed since the Solar System formed. It measures roughly 66 kilometres across its longest axis, yet weighs surprisingly little: its density is only about 1.3 grams per cubic centimetre, lighter than many rocks on Earth. That figure tells us Mathilde is not a solid object at all but a loose rubble pile, with up to half of its interior made of empty space.

The most startling feature is its craters. Several gouges, including ones tens of kilometres wide, are nearly as large as the asteroid itself — impacts that should have shattered a solid rock but were instead absorbed by the porous interior. Spinning just once every seventeen days, far slower than most asteroids, Mathilde offered scientists their first detailed look at one of these ancient, battered carbonaceous bodies that helped build the planets.