America’s love affair with Mars can be traced to astronomer Percival Lowell, who turned his telescope to the Red Planet in the 1890s and thought he saw an intricate system of canals that must have been built by intelligent beings. He never found them, of course, but Martians became a science fiction mainstay.
Earthlings got their first up-close view of Mars’ rocky surface in 1965, when Mariner 4 flew by and photographed a surface that appeared as dead as the moon’s — lacking water or active geology, two prerequisites for life.
But later missions, from the Mariner 9 orbiter to Spirit and Opportunity, helped establish Mars as a useful comparative laboratory for studying climate and geophysics on Earth. They demonstrated that the planet was once warmer and wetter than it is now. Long ago, it may have been a hospitable cradle for life.
When planetary scientists assembled recently at the behest of the National Academies to set research priorities for the next decade, the search for conditions that would allow life to emerge on Mars topped the list.
“If there’s life or past life on Mars, it means the chances that life exists somewhere else are much higher,” said David Paige, who studies the moon and terrestrial planets at UCLA. If Mars is barren, “it might make Earth more unique than we thought.”
Some experts question the wisdom of focusing so intently on a single planet. Jupiter’s moon Europa, which is covered with an ice-encrusted ocean, could have the potential to harbor life; Saturn’s moon Titan, rich in organic chemistry, might as well.