A rock-inspecting rover hurtled toward Mars for a perilous landing on Saturday on what NASA hopes will become a historic mission to answer the age-old question of whether life existed on the red planet.
The robotic explorer's arrival on Mars would be the climax of a weekend of interplanetary discovery after a US spacecraft on Friday gathered particles from a comet in a first that could give scientists clues about how Earth began.
Scientists from the US space agency anxiously monitored the Spirit rover's approach to the rugged Martian landscape for a bouncing landing scheduled for 8:35 pm PST (11:35 pm EST/0435 GMT on Sunday).
A second rover, nicknamed Opportunity, is expected to land on the other side of the Red Planet in three weeks.
As each lander heads toward the planet's surface by parachute, it should jettison the shell and inflate the air bags, allowing the craft to bounce safely for up to half a mile (one km) before coming to a stop. But the landing is not without risk.