Spirit and Opportunity rovers

Each rover had six wheels and weighed about 185 kg. Solar panels made its electricity, and a set of six science instruments let it photograph and study the rocks around it.

Their job was to search for rocks and soils that hold clues to water on Mars long ago.

They were not fast. Spirit's top speed was about 3.75 cm per second. But they were patient, and they kept going for years longer than anyone had planned.

Spirit landed first, on 4 January 2004, inside Gusev crater. Scientists chose Gusev because it looks like a dried-up lake bed.

Opportunity landed on 25 January 2004 on the other side of Mars, on a flat plain called Meridiani Planum. It hit the ground at about 50 km/h, bounced and rolled, and came to rest inside a small crater only about 20 metres wide. The crater was named Eagle.

In March 2005, dust devils (small spinning whirlwinds) passed over the rover and swept dust off its solar panels. Its power jumped from the usual 60% to 93%, which helped it keep working much longer.

In 2006, its right front wheel stopped turning. Spirit carried on, dragging the stuck wheel along. In 2007 that lucky accident scraped up bright white soil that was nearly pure silica, the main ingredient of window glass. It suggested that there were once hot springs or steam vents there. Scientists call it one of the most important finds of either rover.

In 2009, Spirit broke through a thin crust into soft, slippery sand, at a place scientists called Troy, next to a low plateau called Home Plate. It could not get free. Its last message came on 22 March 2010, as the Martian winter approached and its solar power dropped. NASA stopped trying to contact it on 25 May 2011.

Then it went crater to crater. It climbed out of Eagle crater in March 2004 and explored Endurance crater. In 2007 it drove into Victoria crater and stayed inside for almost a year. In August 2011, after a trip of nearly three years, it reached Endeavour crater. There it found signs of ancient water similar to the drinkable water of a pond or lake on Earth.

In March 2015, NASA announced that Opportunity had driven more than a marathon: 42.195 km. Nothing from Earth had ever travelled that far on another world. It also set a one-day Mars driving record of 220 metres, and climbed slopes as steep as 32 degrees.

In June 2018, a dust storm covered the whole planet and blocked out the sunlight Opportunity needed. Its last message came on 10 June 2018. Engineers sent more than a thousand commands to wake it up. None were answered, and on 13 February 2019 NASA declared the mission over. Opportunity's last stop was Perseverance Valley, on the rim of Endeavour crater.