The fourth planet from the Sun, Mars is a dusty, cold, desert world with a very thin atmosphere. The Latest NASA's Mars 2020 Mission Drops in on Death Valley This dynamic planet has seasons, polar ice caps and weather and canyons and extinct volacanoes, evidence of an even more active past. Mars is one of the most explored bodies in our solar system, and it's the only planet where we've sent rovers to roam the alien landscape. NASA currently has three spacecraft in orbit, one rover on the surface and another rover under construction here on Earth. India and ESA also have spacecraft in orbit above the Mars.