A small meteorite found in Algeria in 2012 has led scientists to conclude that one or more ancient volcanoes on Mars erupted continuously for as long as two billion years.
The 6.9-ounce (0.2-kilogram) meteorite, dubbed Northwest Africa (NWA) 7635, is one of 100 meteorites known to have come from Mars and one of ten belonging to the same individual meteorite group.
An analysis of the 11 meteorites in this group shocked scientists by revealing NWA 7635 to be 2.4 billion years old, in contrast with the other ten, all of which were revealed to be approximately 500 million years old.
These meteorites are all rock fragments produced by Martian volcanoes that erupted long ago. Because Mars has a thin atmosphere and weak gravity, fragments of volcanic rock were blown off the planet during subsequent asteroid and comet impacts.
Laboratory tests confirm all 11 meteorites were exposed to cosmic rays in space for about 1.1 million years. Those that ended up on Earth were eventually perturbed when they came close to a planet, comet, or asteroid.
According to research team member Marc Caffee of Purdue University, “All 11 were knocked off Mars at the same time, but this one was different than the others.”
The age difference between NWA 7635 and the other 10 meteorites indicates at least one ancient Martian volcano erupted continuously for two billion years or longer.
“What this means is that for two billion years, there’s been sort of a steady plume of magma in one location on the surface of Mars,” Caffee explained. “We don’t have anything like that on Earth, where something is that stable for two billion years at a specific location.”
Olympus Mons, Mars’ largest volcano, with a height of 17 miles, may be the source of the meteorites.
Martian volcanoes, of which there are many, are larger than those on Earth and erupt for longer periods. They grow to extreme sizes because the Red Planet has no plate tectonics.
Tectonic plates, which form volcanoes and craters by grinding past one another, are active on Earth and were once active on Mars when the Red Planet was warmer and wetter.
When Mars cooled, molten rock underneath its plates became solid, and formation of the plates stopped.
With no geological activity, eruptions on Mars are now rare.
The research team published their findings in the journal Science Advances.