Spirit (MER-A)

Spirit launched on June 10, 2003, and bounced to a landing in Gusev Crater in January 2004, beginning what was planned as a 90-day mission. The golf-cart-sized rover instead drove for six years and nearly five miles, climbing Husband Hill — the first summit ascent on another planet — and surviving dust storms, failing wheels, and three brutal Martian winters.

Spirit’s stubborn dragging wheel produced its most important discovery: churned-up soil rich in silica, evidence of ancient hot springs or steam vents — exactly the kind of energetic, watery environment where life on Earth thrives. The rover finally fell silent in 2010, embedded in soft sand, having redefined what a Mars rover could be.