New Mars rover will look for signs of liquid water

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An enhanced-color image of the Gale crater (Credit: NASA/Steven Hobbs)

Scientists at NASA’s Mars Science Laboratory have selected the crater ‘Gale’ as the landing site of the rover, Curiosity, when it visits the Red Planet next year to search for signs of historical liquid water.

This will mark the 15th time the U.S. has visited Mars since it was first photographed by the Mariner 4 orbiter in 19651. Mars is of great interest to scientists, not only because of its proximity to Earth (it’s our second-closest planetary neighbor after Venus), but because the Red Planet has been the subject of intense speculation about the presence of alien life for over 200 years.

Speculation about Martian life started in the late 1700s with German-British astronomers and siblings, William and Caroline Herschel, who observed the Red Planet and noticed that it had some features in common with Earth, including axis tilt, length of day, and seasonal changes in its appearance. Moved by these similarities, William speculated that Mars had inhabitants. From his address to the Royal Society in 1784:

It appears that this planet is not without considerable atmosphere; for besides the permanent spots on the surface, I have often noticed occasional changes of partial bright belts; and also once a darkish one… These alterations we can hardly ascribe to any other cause than the variable disposition of clouds and vapors floating in the atmosphere of the planet… Mars has a considerable but modest atmosphere, so that its inhabitants probably enjoy a situation in many respects similar to our own.

In the late 1800s, Italian astronomer Giovanni Schiaparelli added to this speculation when he observed what he thought were canals on the surface of Mars. Schiaparelli’s observations inspired the construction of the Lowell Observatory in Flagstaff, Arizona to further study the phenomena. Astronomer Percival Lowell, who founded the observatory, became convinced that the canals were signs of advanced, intelligent life on Mars. From there, it wasn’t much of a leap to science fiction stories about Martian life, including H. G. Wells’ dark tale, The War of the Worlds, and C. S. Lewis’ Christian-themed Out of the Silent Planet.

Despite the fervor over possible Martian life, there were astronomers who questioned whether there was any credible visual evidence for the canals. These questions persisted until Mariner 4 was sent to Mars and failed to detect any signs of the infamous canals. Since then, the focus on the search for life on Mars has shifted to evidence for historical, probably much more primitive, forms of life. If such life ever existed on Mars, it would have required the presence of liquid water, which is why scientists are so eager to find signs of the stuff.

[1] After three more successful Mariner missions, NASA sent two Viking missions, which arrived in 1976 (one of which landed on the surface), two more orbiters in 1993 and 1997, and the first rover, Mars Pathfinder, in 1997. Since that time, NASA has successfully sent several more orbiters, rovers, and flybys to Mars. Other countries, most notably the former Soviet Union, have also visited the Red Planet. NASA has plans to continue visiting Mars through the year 2018 and beyond.

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