Factbox: Mars and its missions

(Reuters) - Here are some facts about Mars and about missions to the Red Planet, as Russia's first planned interplanetary mission in more than two decades went wrong on Wednesday.

MISSIONS TO MARS:

-- Last month, NASA unveiled $10 billion plans to build a giant deep-space rocket to carry astronauts beyond low-Earth orbit after 2017 for missions to the Moon, an asteroid or Mars.

-- NASA's $2.5 billion Mars Science Laboratory, a robotic science laboratory being prepared for a November 25 launch, is to land in August 2012 near a mountain in a crater on the planet.

-- One of a pair of Mars rovers that arrived on the planet in January 2004 is still working. Its twin succumbed to the harsh environment in 2010. They returned evidence that Mars was once far wetter and warmer than the dry, cold desert that exists today.

-- In November 2008, the Phoenix Mars Lander, which made history by finding definitive proof of water on Mars, lost contact with Earth, effectively ending its more than five-month mission.

RUSSIA'S 2011 MISSION:

-- Russia, hoping to end a 20-year hiatus from deep space, launched an ambitious three-year mission to scoop a soil sample from the surface of the Martian moon Phobos early on Wednesday from the Baikonur launch pad on a Zenit-2SB rocket.

-- The mission was for Phobos-Grunt to reach Mars in 2012 touch down on the larger of Mars' two tiny moons in 2013, collect a sample from the surface and fly back to Earth in 2014.

-- However Russian space agency chief Vladimir Popovkin said that an engine failed to fire on the probe after it reached Earth's orbit, leaving space officials just three days to jolt it out of orbit before its batteries run out.

KEY FACTS ON MARS AND EARTH:

MARS EARTH Average Distance from Sun 142 million miles 93 million miles Average Speed Orbiting Sun 14.5 miles per sec. 18.5 miles/sec. Diameter 4,220 miles 7,926 miles Length of Year 687 Earth Days 365.25 Days Length of Day 24 hrs 37 mins 23 hrs 56 mins. Temperature Average -81 degrees F 57 degrees F

* MARS EXPERIMENT:

-- An isolation experiment in Russia simulated a 520-day manned mission to Mars. Six volunteers were locked away in windowless cells in June 2010. The $15-million Mars500 experiment, which ended last week, was the first full-duration simulation of a manned flight to Mars.

DURING THE MISSION:

* The crew was hermetically isolated.

* After 250 days the crew was divided in half, three sent to a Martian surface simulator and three kept in the 'spacecraft'.

* Crew lived and worked like astronauts on the International Space Station.

* Crew were monitored and their psychological, medical and physical signs recorded.

* 2009 MISSION:

-- In 2009 four Russians, a Frenchman and a German ended a simulated 105-day space trip in Moscow designed to test how they responded to long-term isolation.

Sources: Reuters/NASA/www.esa.int (Reporting by David Cutler, London Editorial Reference Unit)