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The mysteries of Mars are slowly unraveling — one rover at a time.

At a talk Thursday evening held at the Peabody Museum of Natural History, Steven Squyres, professor of astronomy at Cornell University and the principal investigator of the Mars Exploration Rover Mission, offered an in-depth look into the construction and history of the Spirit and Opportunity robotic explorers.

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“These robots are our surrogates,” Squyres said. “We experience Mars through their eyes.”

The twin rovers landed on the Red Planet in January 2004 and were expected to last for three months. But they have outlasted dust devils, hostile temperatures and even the scientists’ own ‘suicide missions’ — commands to enter steep craters on the pockmarked surface of the planet — and survived more than five years.

“Today is day 1,825 of our 90-day mission,” Squyres said.

But the rovers’ sojourn on Mars has not been without its problems. In 2007, Spirit was plagued by dust storms that covered its solar arrays and nearly rendered it inoperable. Moreover, the rover’s right front wheel motor broke halfway through its mission, requiring it to travel backwards across the planet’s surface.

Flipping through photographs of crashed and capsized rovers that were met with laughter from the audience, Squyres quipped, “That’s what you call a bad day on Mars.”

Meanwhile, in 2005, Opportunity became trapped in a sand dune — now casually dubbed “Purgatory Dune” by alarmed scientists working on the mission.

“If you ever need to get the attention of NASA headquarters, get a $450 million vehicle stuck in a sand dune on Mars,” Squyres said.

After two and a half weeks of soil simulations, engineers concluded that the best solution would simply be to “put it in reverse and gun it.” The risk paid off — Opportunity escaped and headed for Mars’ Victoria Crater.

Squyres also took time to debunk several widely held misconceptions about Mars, particularly its status in popular culture as a possible host for extraterrestrial life.

“No one has ever detected liquid water on Mars,” he said, adding that water is a prerequisite for life as we currently know it. “But we have powerful evidence indicating that in the past, it did exist.”

The talk concluded with a look at the future of Martian exploration: the Mars Science Laboratory, a NASA rover with advanced tools that is set to launch in fall 2011, and Opportunity’s ongoing trip to the Endeavor Crater — a journey estimated to take two years.

The lecture received general acclaim from the audience, many of whom enjoyed learning about the long and difficult process leading up to the rovers’ launch in 2003.

“I was very impressed,” Zandra Ruiz GRD ’06 said. “It’s amazing that they could build machines that were able to travel so far and survive in these adverse conditions.”

Others praised Squyres’ energetic presentation style.

“The talk was really good — both interesting and fun,” said Ashley Elliott, a New Haven high school student. “He was a very dynamic speaker.”

The speech, which was free and open to the public, was the first of two in the lecture series being offered this semester by the Hall of Minerals, Earth and Space at the Peabody in honor of the Hall’s new multimedia mineral gallery. The second, a presentation by Peabody curator and professor of geology and geophysics Jay Ague, is scheduled for Thursday, April 16.