Three spacecraft currently are collecting data in orbit around Mars: Nasa's 2001-launched Mars Odyssey, Europe's 2003-launched Mars Express and Nasa's 2005-launched Mars Reconnaissance Orbiter.
Two rovers are on the surface, still working: Nasa's 2003-launched Opportunity and 2011-launched Curiosity.
Nasa plans to launch a robotic geologist named InSight in 2016; the lander will penetrate the Martian surface with a seismometer and heat probe.
The next Nasa wheeled rover will fly in 2020, collecting rock samples for potential return to Earth. A human expedition is not anticipated until the 2030s.
