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This just in...

April 2004

April 16, 2004

Well, the Battle of Bounce Rock is over.

A little while after we landed at Meridiani with Opportunity and took our first look around, we noticed that there was only one object anywhere outside Eagle crater that looked even remotely like a decent-sized rock. We named it "Bounce Rock" because we could see that the airbags had bounced right on top of it as the landing took place. (It figures that if there was only one rock for what seems like miles in every direction, we'd find a way to hit it!) So once we climbed out of Eagle Crater and before we headed for Endurance Crater, it made sense to go over and check Bounce Rock out.

(It's worth noting, by the way, that not everybody on the team was even convinced that it was a rock at first. There was some speculation that it might actually have been one of the airbag covers, shaken off during the landing by a particularly sharp jolt. Before we got to it we had a little guessing game going, with the votes about evenly split between "Mars rock" and "flight hardware", along with a few brave souls who thought it might be a meteorite.)

It was fun, and it sure was interesting, but it was a bit of a struggle. What had us going for awhile there was a very nice Mini-TES spectrum that seemed to show a lot of hematite in the rock. We knew there was hematite in the soil at Meridiani, but this was the first time we'd gotten a hematite signal from rock... so it looked very interesting. We rolled up to it, whipped out the Moessbauer Spectrometer, took some good data, and to our surprise we found no hematite in the rock at all. In fact, the only mineral that the Moessbauer detected was pyroxene, which made this rock look very different from anything we'd ever seen, at either landing site. We put a hole in it with the RAT, looked again, and saw the same thing -- lots of pyroxene and no hematite.

So what was going on? Turns out we'd been faked out on the Mini-TES data. We had been pretty far away from the rock when we had first looked it, and the Mini-TES field of view had also included a particularly hematite-rich patch of soil immediately behind the rock. Once we got close enough to see the rock better with Mini-TES, the Mini-TES data confirmed the absence of hematite, confirmed the pyroxene, and also showed some plagioclase, another mineral, in the rock. So the story was coming together.

Then came the most interesting part of all, the APXS data. The APXS measures elemental chemistry, and what we found was that, chemically, Bounce Rock is almost a dead ringer for a rock called EETA 79001-B. Odd name for a rock; 79001 actually is a rock from Mars that was found in Antarctica back in 1979. It was knocked off of Mars long ago, orbited the sun for awhile, and eventually hit the Earth in Antarctica, where it was found many years later by an expedition sent there to collect meteorites. There are more than a dozen such rocks that are believed to be from Mars on Earth. But until Bounce Rock, nobody had ever found a rock that was actually on Mars and that matched the chemistry of one of these rocks. Now we have.

We're not quite sure where on Mars Bounce Rock came from, but we suspect that it might have been thrown out of a big impact crater that's about 50 kilometers southwest of our landing site. So it's not a meteorite, but it probably did fall from the sky. And it turned out to be a very interesting stop on our drive across Meridiani Planum.


The martian rock nicknamed "Bounce."