As Earth's closest neighbor and with an atmosphere more similar to Earth's than any other planet in the solar system, Mars has long been a subject of great interest to astronomers and the public. NASA began exploring Mars with unmanned spacecraft in the 1970s, and the space agency hopes to eventually send a human to the Red Planet. In March 2009, NASA and Microsoft partnered under a Space Act Agreement to make images of Mars and other planets available through Microsoft's WorldWide Telescope, an
Valles Marineris, or Mariner Valleys, is the largest known canyon in the solar system, larger than any on Earth. Its name comes from the Mariner 9 Mars orbiter that discovered it. Mariner 9 orbited the planet from 1971 to 1972.
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