But two spacecraft have been rolling around on Mars taking a much closer look for the past year and a half. The Mars Exploration Rover Mission was launched from earth on two separate vehicles on June 15 and July 7, 2003. Spirit and Opportunity landed on January 3 and January 24, 2004, and were expected to have a working life of about 90 sols, or Martian days (about 39.5 minutes longer than ours). Instead, each heroic little vehicle is continuing to do science on the surface of Mars. Spirit has been working for 561 sols and is climbing day by day--sol by sol--to the summit of a formation called the Columbia Hills, sampling rocks and making observations as it goes. Opportunity is on sol 548 and is rolling across the Plains of Meridiani en route to Erebus Crater.
We have a very interesting new book, Roving Mars : spirit, opportunity, and the exploration of the red planet, by Steve Squyres. Squyres is the principal scientific investigator behind the Mars Rover mission, and a lively writer. He details the complicated science involved in designing and operating the two Rover machines, and chronicles the first several months of discoveries made and technical problems surmounted--all done from an ever-changing distance of anywhere from 36 million miles to 250 million miles as Mars and Earth go 'round in their orbits.
Meanwhile, Cassini continues to orbit Saturn. Since it settled into orbit on July 1, 2004, it has been working its way through a series of flybys of many of Saturn's moons, the next being another approach to Titan on August 22.
NASA has a handy page detailing all its current missions. Have we mentioned lately what a boon the web is for science freaks? Unlike entertainment, science is a realm where the practitioners are happy to give their work away.
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