An impact crater on Mars, with darker material exposed beneath the reddish dust
NASA/JPL-Caltech/University of Arizona
Six Martian meteorites have been traced back to the craters they were ejected from on Mars millions of years ago. Finding the original sources of these alien rocks will allow us to place them in context, yielding insights about the history of the Red Planet.
“Being able to identify the impact launch sites for any Martian meteorites has been a challenging goal for a long time,” says Hap McSween at the University of Tennessee, Knoxville, who wasn’t involved in this work. “There have been numerous published attempts before, but none have been very convincing until now.”
When a rock smashes into Mars or another planet, it causes a spray of debris, some of which can float away through space and eventually hit Earth as a meteorite. Anthony Lagain at Curtin University in Australia and his colleagues used a sophisticated model that matches what we know about the ages of the millions of Martian craters and of the six meteorites that were chipped off the planet’s surface.
“On Mars, you’ve got about 80,000 craters larger than 3 kilometres, so about 80,000 craters that might be the source of these meteorites,” says Lagain. The researchers’ model narrowed this down to about 20 possible sources. Then, they studied the structure of the rocks to find out how much force they had been suddenly subjected to when they were blasted into space, feeding that into another model of the craters themselves. This led them to the original sources of the meteorites and how deep they were probably buried before the impacts that sent them to Earth.
The meteorites are all igneous rocks, meaning they are pieces of solidified lava. Pete Mouginis-Mark at University of Hawai’i at Mānoa says that while there are some questions about whether the properties of the lava flows in these craters completely match the meteorites, if these craters are truly the sources of the rocks, we can learn a great deal about Martian volcanic activity from them.
In particular, two of the meteorites that seem to have come from the same crater imply that the area was volcanically active for longer than was previously thought to be likely. “We will have to rethink what we believe to be the internal ‘plumbing system’ of volcanoes on Mars and how they can stay molten for these extended periods of time,” says Mouginis-Mark.
There are only about 200 known Martian meteorites on Earth and they are the only Mars rocks that researchers can examine in detail. NASA’s planned mission to bring back samples directly from Mars is facing serious issues that may lead to its significant delay, so these rocks might be our only chance to study Martian material in state-of-the-art laboratories for a long time. “Here, we’ve got six Martian meteorites coming from five places, so it’s like five sample return missions that you get for free,” says Lagain. Studying these samples further could not only teach us about the evolution of Mars, but also help guide future exploration to the most scientifically interesting spots on the surface.