Mt Stromboli, off the north coast of Sicily, has been erupting almost continuously for more than 2,000 years, but that's a sneeze compared to the ancient volcanic activity of Mars. According to new geological surveys made possible by studying Martian meteorites, at some point in the past, a volcano on the Red Planet may have erupted non-stop for more than 2 billion years.
Humans are yet to set foot on Mars, but scientists have been able to study the geology of the planet with the help of instruments like the Mars Reconnaissance Orbiter and the Curiosity rover. But sometimes, samples of rock from the Red Planet can be found closer to home: over 100 Martian meteorites have been found over the years, with most being uncovered in either Antarctica or North Africa.
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"Even though we've never had astronauts walk on Mars, we still have pieces of the Martian surface to study, thanks to these meteorites," says Marc Caffee, one of the researchers on the study. "Between Antarctica and other deserts we add more than 1,000 meteorites per year, but only a few of those are interesting, including those originating from Mars and the moon. The standard ones are sent to the Smithsonian, but the unusual ones are sent to NASA and the community of scientists is informed in case they want to request samples."
Caffee and his team analyzed about 30 of the 100 Martian meteorites in the Purdue Rare Isotope Measurement (PRIME) Laboratory, which measures long-lived radionuclides in rock samples to determine when they formed, and – by studying their exposure to cosmic rays – how long they spent whizzing around in space before crashing to Earth. These results suggested that groups of the meteorites that had spent the same amount of time in space were likely blasted off the Martian surface by the same event, such as a larger impact.
A group of 11 meteorites, and one of those in particular, caught the team's attention. This group had all been exposed to cosmic rays for 1.1 million years, but while 10 of them formed around 500 million years ago, one was significantly older. Northwest Africa (NWA) 7635 is a 6.9-oz (196-g) meteorite discovered in Algeria in 2012, but it appears to be 2.4 billion years old – almost 2 billion years older than the other samples kicked off Mars at the same time.
"What this means is that for 2 billion years there's been sort of a steady plume of magma in one location on the surface of Mars," says Caffee. "We don't have anything like that on Earth, where something is that stable for 2 billion years at a specific location."
The difference is that Mars isn't tectonically active like Earth, where our constantly-moving plates would interrupt an erupting volcano long before it hits its 2 billionth birthday. That also allows Martian volcanoes to grow to much larger sizes, with the most obvious example being Olympus Mons, the largest volcano in our solar system.
"We don't know at this point where this particular meteorite came from, whether it was Olympus Mons or some other location," says Caffee. "These meteorites are allowing us to conduct geologic science on the surface of Mars, and we haven't even been there yet."
The research was published in the journal Science Advances.
Source: Purdue University