Opportunity Scores Again; Scientists Very Pleased

If you go exploring the neighborhood, you never know what you'll find. Especially if you're NASA's incredible, overachieving Mars rovers, Spirit and Opportunity. This week Opportunity, cruising the Meridiani Plain, poked around looking at,and photographing, one of the heat shields that it jettisoned on descent to the planet. Then it moved on to a basketball-sized rock that rover program scientists had been calling "Heat Shield Rock" for its proximity to the discarded shield. The conclusion: the rock was a meteorite, fallen from space, and made mostly of an alloy of iron and nickel.

Now, this is not as big as the historic discovery that Mars once ran with liquid water, which was also made by Opportunity on the Meridiani (and confirmed by Spirit on the other side of the Red Planet). But it is very significant science nonetheless. It's the first identified, confirmed meteorite on any planet but Earth.

"This is a huge surprise, though maybe it shouldn't have been," said Dr. Steve Squyres of Cornell University, who is the lead scientist for the experimental instruments the rovers carry.

"I never thought we would get to use our instruments on a rock from someplace other than Mars," Squyres added. He explained that the meteorite came from "a destroyed planet or planetesimal that was big enough to differentiate into a metallic core and a rocky mantle." (We're not principal science investigators on NASA projects, so "planetesimal" was a new word to us, also. It refers to small celestial bodies that are believed to have existed in large quantities during the formation of the solar system).

Aren't there plenty of meteorites on Earth to study? Squyres explains that it's not what we can learn about meteorites, but what we can learn about the Meridiani and about Mars. Planetary scientists would like to know whether the surface is being eroded, or being built up. The numbers and condition of meteorites on the planet's surface maybe the clue needed to answer this question.

NASA Chief Scientist Jim Garvin suggests another benefit from the meteorite discovery: it "opens new research possibilities, including further incentives for robotic and then human-based sample-return missions."

The Mars Exploration Rover project began in 2000, and has exceeded all expectations. The Rovers have proven to be unexpectedly durable. They were only supposed to last 90 days -- in which case they'd have gone silent after April, 2004. Opportunity has survived 352 "sols," or Martian days, and Spirit, which landed first in the Gusev crater on the other side of the planet, has survived 372. They have traveled a total of more than 3.8 miles, have sent back 66,000 pictures, and have taken countless spectrographic measurements. The rovers have been up and running for over four times their expected duration, and have covered over five times their initially planned distance.

A very satisfied Jim Garvin summed it up: "Mars continues to provide unexpected science 'gold,' and our rovers have proven the value of mobile exploration with this latest finding."

FMI: www.marsrovers.jpl.nasa.gov/home/