Broken wheel of discovery.

PhysOrg reports on one of 2007’s most dramatic moments of serendipity, when Mars rover Spirit discovered evidence of life by breaking down. As the researchers reported at the recent American Geophysical Union annual meeting, the frozen wheel dragging behind the rover turned up some very interesting mineral traces:

Spirit, which has been driving backward since its right front wheel stopped turning in March 2006, was exploring near a plateau in the Gusev Crater known as Home Plate when scientists noticed that upturned soil in the wake of its dragging wheel appeared unusually bright.

Measurements by the rover’s alpha particle X-ray spectrometer and mini-thermal emission spectrometer showed the soil to be about 90 percent amorphous silica — a substance associated with life-supporting environments on Earth.

“This is one of the most powerful pieces of evidence for formerly habitable conditions that we have found,” said Squyres, Cornell’s Goldwin Smith Professor of Planetary Science, in a Dec. 11 interview with the BBC.

Read more about Spirit’s accidental breakthrough at Astrobiology Magazine and a report on the initial discovery of silica in May in New Scientist, in which study leader Steven Squyres uses the phrase “inadvertent trenching tool.”