About four months ago, the Mars Rover Opportunity was driving around Mars at about 50% power, as five years of accumulated Martian dust on its solar panels was disastrously affecting its ability to acquire power:
But a fortuitous, powerful gust of wind knocked much of the dust off, boosting Opportunity’s power by about 40%. Because of this, Opportunity was able to continue making its way towards Endeavor crater — the largest Martian crater that will ever be examined by any rover — with an added power boost:
Well, a few weeks ago, Opportunity was cruising along the Meridiani Planum when it passed this unusual-looking rock, named “Block Island”:
After looking at the pictures, the scientists working on the mission had determined that the rock was about two feet by one foot (the size of an old tombstone) with a bluish color to it. So, back Opportunity went to take a closer look. The findings? This thing doesn’t look like it comes from Mars:
And, in fact, it doesn’t. It isn’t made of the same stuff that Mars is made of, and members of the Opportunity team unequivocally state:
“There’s no question that it is an iron-nickel meteorite,” said Ralf Gellert of the University of Guelph in Ontario, Canada. “We already investigated several spots that showed elemental variations on the surface. This might tell us if and how the metal was altered since it landed on Mars.”
There’s plenty of evidence other than composition to back up the claim that this is a meteorite. Take a close-up look at the patterns found in this rock:
See those triangular shapes? Those shapes are smoking-gun evidence that this is a meteorite. Not only do we see meteorites on Earth with those same patterns:
We see those triangular shapes in Tunguska fragments as well. How did these patterns get exposed?
“Normally this pattern is exposed when the meteorite is cut, polished and etched with acid,” said Tim McCoy, a rover team member from the Smithsonian Institution in Washington. “Sometimes it shows up on the surface of meteorites that have been eroded by windblown sand in deserts, and that appears to be what we see with Block Island.”
This makes Block Island the largest meteorite we’ve ever found on another planet, which is impressive in its own right. But what we learn from this is even more impressive. You see, Mars’ atmosphere, the way it is right now, isn’t thick enough to allow meteorites this large to land:
The atmosphere is so thin that a meteorite this big would have hit the Martian surface at too great a speed, and would have broken apart from the impact. What does this tell us (and the bold emphasis is mine)?
“Consideration of existing model results indicates a meteorite this size requires a thicker atmosphere,” said rover team member Matt Golombek of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Either Mars has hidden reserves of carbon-dioxide ice that can supply large amounts of carbon-dioxide gas into the atmosphere during warm periods of more recent climate cycles, or Block Island fell billions of years ago.”
That’s right, this is more evidence that — billions of years ago — Mars had a thicker atmosphere. This meteorite, which has theoretically been on the Martian surface for billions of years, could help unlock the secrets of the climate history on Mars. As Albert Yen, another Opportunity scientist, says,
We’re using this meteorite as a way to study Mars. Before we drive away from Block Island, we intend to examine more targets on this rock where the images show variations in color and texture. We’re looking to see how extensively the rock surface has been altered, which helps us understand the history of the Martian climate since it fell.
Opportunity is only about 4 km into its 20 km journey from Victoria to Endeavor crater, and already it’s discovered the largest extraterrestrial meteorite to date, complete with evidence for a denser, thicker atmosphere in Mars’ past. Remember, a denser, thicker atmosphere means a past with liquid water on Mars, which may mean a distant past with life. Not bad for a mission that started in January, 2004, with an expected life of 90 days!