A long-lived source of magma on Mars has fueled volcanic eruptions for billions of years, clues in a rock ejected from the Red Planet show.
The newly discovered rock belongs to a group of meteorites called shergotites, which originate from of the same Martian volcanic system researchers report on February 1 in Science Advances . But the new stone is much older than its brothers. While previously discovered shergottites solidified from Martian magma between 427 million and 574 million years ago, the new rock formed about 2.4 billion years ago, chemical analysis shows.
Such a wide age range means that the volcanic system on Mars has been spewing hot rocks from a stable magma source for nearly half of the planet’s history, said study co-author Thomas Lapen, a geologist at the University of Houston. This endurance could help scientists better understand the interior of Mars. “These are some of the longest-lived volcanoes in the solar system,” Lapen says.
Lapin and his colleagues studied the elements inside a Martian meteorite discovered in the Algerian desert in 2012. Some of these elements serve as stopwatches that record the breed’s history. Isotopes of beryllium and aluminum formed when exposed to cosmic rays show that the stone has been traveling in space for about 1 million years. The persistent decay of carbon-14 left over from cosmic ray collisions suggests that the rock landed on Earth about 2,300 years ago. By combining these two measurements, the researchers found that the meteorite likely fell from Mars along with other shergottites just over a million years ago. This escape probably followed a powerful impact in Mars’ volcano-filled Tharsida region.
Researchers have discovered that the rocks have more in common than a way out. The chemical similarity between the meteorites suggests that they all came from the same source of hot rock deep within the Red Planet. That’s surprising, given that the mix of radioactive elements in the newly discovered meteorite suggests it solidified 1.8 billion years earlier than the next-oldest, shergottite, Lapen says.
It is known that there are many volcanic systems on the surface of Mars, all fed by magma rising from the depths of the planet. Studies have previously suggested that some of these systems have been operating for billions of years. Although little is known about the Martian subsurface, many scientists have speculated that the magma fueling this volcanism changed over time as the Martian subsurface mixed. The absence of any difference in the composition of shergottites suggests that the interior of Mars is relatively stagnant. This could be a result of Mars’ lack of plate tectonics, a process that helps mix Earth’s interior, Lapin said. Understanding the differences between Earth and Mars can help explain why the two planets took such different trajectories, since Earth is much more habitable than Mars.
The similarity between the shergottites may have another explanation, says planetary scientist Stephanie Werner of the University of Oslo. Strong impacts can melt rocks, resetting their age. She suggests that the shergottites may have formed around the same time billions of years ago, before the age of some of them changed due to exposure over time.
Future missions will help shed light on what’s going on beneath the surface of Mars, says James Head, a planetary scientist at Brown University in Providence. NASA’s InSight lander, currently scheduled for launch in 2018, will use seismic activity to map the Red Planet’s interior.