An unusual pair of craters on Mars formed when a moon broke apart before crashing into the planet's surface about a billion years ago, a new study suggests.
The craters could hint at what lies in store for Phobos, a potato-shaped moon that is expected to smash into Mars millions of years from now.
The two craters, which lie about 12.5 kilometres apart, share the same oval shape and nearly the same west-east alignment.
© NASAThe alignment of two oval-shaped craters – one spanning 10 km (right) and the other, 3 km – hints they might have been gouged out by a fallen moon that broke apart in Mars's atmosphere.
Similar crater pairs are seen elsewhere, including a duo called "Messier" on the Moon (scroll down for image). The Messier craters may have formed from a pair of orbiting asteroids that crashed to the surface together at a low impact angle.
But John Chappelow and Rob Herrick of the University of Alaska, Fairbanks, say there is only a 2% chance that the two craters on Mars formed that way.
They say the original asteroids in such a pair could have orbited each other in any configuration, making the craters' observed alignment unlikely. "In such a case, the craters should be oriented randomly," Chappelow told
New Scientist.
Instead, their calculations suggests that a moonlet about 1.5 km wide was pulled into a 'death spiral' by the planet's gravity. It then broke apart in the atmosphere, where atmospheric drag separated the pieces so that they struck the ground at different points. They say the pieces probably hit the surface at an oblique angle of 10° or less.
Comment: That sounds very interesting: an ancient fungus, half billion years old, is re-appearing and contributes to the decline in frogs' populations. Is it possible that this fungus has any relationship to impacts from outer space, as we speculated few months ago?