ORBIT OF FLUFF

Rovers get stuck on moon due to a softer surface

- BY STEPHEN BEECH

ROBOTIC space rovers keep getting stuck because the surface of the Moon is "fluffier" than on Earth, suggests a new study.

Researchers reckon they've finally worked out why the multi-million dollar extraterrestrial vehicles get bogged down in soft sand or gravel on the lunar surface and Mars.

They say it's because gravity on Earth, where the rovers are tested, pulls down on sand much more strongly than the gravity on the red planet or the Moon.

When a space rover gets stuck in soft sand or gravel - such as the Mars rover Spirit in 2009-engineers issue a series of commands that move its wheels or reverse its course in a delicate, timeconsuming effort to free it and continue its exploratory mission.