Four billion years ago, when the inner Solar System was still being pelted by wayward rocks and the young Earth had barely formed a crust, Mars had lakes — and perhaps even oceans. Today, a six-wheeled robot the size of a car is slowly driving through the remnants of that world. NASA's Perseverance rover has been exploring Jezero Crater, an ancient lakebed, and the rocks it is examining are older than any sample ever studied on Earth's surface. "It's the first time we've been able to investigate this terrain in situ, and that's been very exciting," said Vivian Sun, a scientist on the Perseverance team.

The rover is gathering data from a period known as the Late Heavy Bombardment, when asteroid impacts were still reshaping planetary surfaces across the inner Solar System. Scientists believe that Mars during this era may have resembled the Mojave Desert, but with rivers running through it — though that comparison remains contested, and the debate over how wet and warm early Mars truly was has not been settled. What makes Perseverance particularly well-suited for this long investigation is its engineering. After Curiosity, its predecessor, showed significant wheel wear within a few years of landing in 2012, engineers redesigned the wheels entirely.

So far, Perseverance shows no appreciable wear. The only component being closely monitored is the wheel actuators, which were originally certified for just 20 km of driving; NASA is now working to certify them for at least 100 km, and potentially far beyond that. Unlike solar-powered spacecraft, Perseverance runs on a radioisotope thermoelectric generator and carries no consumables or lubricants that could run out.