In January 2004, not just one but two NASA exploration vehicles of identical construction landed on Mars. The Mars rover Opportunity landed near the Mars equator, and the Mars rover Spirit closer to the north pole, in the Gusev crater. The aim of the mission was to undertake the geological investigation of areas on Mars where there might have been water in the past. The rovers, 1.6 metres long and 1.5 metres high, weigh 185 kilograms. Originally they were intended to travel across Mars for 90 days, but they have now been in operation for more than five years.