July 4 marks the twentieth year that NASA has had a robot working on the surface of Mars.
In 1997, the Mars Pathfinder landed on the planet and explored the surface for three months, analyzing the Martian atmosphere and climate and assessing the composition of its rocks and soil. (Learn about efforts to send humans to Mars in “Mars: Inside the High-Risk, High-Stakes Race to the Red Planet.”)
Since Pathfinder, eight other NASA robots have explored Mars.
Both the Spirit and Opportunity rovers touched ground in 2004 with the mission of finding evidence of water. Together, they took thousands of pictures of the rocky Martian terrain and collected data that led researchers to believe Mars was indeed once a wet planet. While Spirit has since died, Opportunity continues to function.
Curiosity, the biggest and most advanced rover to be sent to Mars, landed in August 2012. It is equipped with 17 cameras, a laser, and a drill that collects powdered rock samples, in the hopes of finding rocks that originally formed in water. Most recently, Curiosity has delivered new details back to NASA about an ancient lake environment in Mars’ Gale Crater. (See more photos from Curiosity’s incredible journey.)
NASA will launch the InSight mission in spring 2018 to study the interior of Mars, and has plans to launch another rover in 2020 to study an environment that may have once been optimal for microbial life.