An unusual mineral deposit found in the Nili Fossae region on Mars may be the product of ancient volcanoes on the Red Planet, new research suggests. This discovery shows rare evidence of explosive volcanic explosions on Mars, and could help rewrite the geological history of the planet.
Explosive volcanic eruptions occur when gases, like water vapor, are dissolved in magma trapped underground. When pressures build up to the point where material can no longer be held in place by rock on the surface, an explosive release of magma may result. Long ago, Mars was home to explosive volcanic eruptions, although evidence for these events is rare. But, in the modern age, only effusive magma flows took place, in which magma escapes to the surface in slow streams of molten rock.
“This is one of the most tangible pieces of evidence yet for the idea that explosive volcanism was more common on early Mars. Understanding how important explosive volcanism was on early Mars is ultimately important for understand the water budget in Martian magma, groundwater abundance and the thickness of the atmosphere,” said Christopher Kremer, a graduate student at Brown University.
With Olivine, Shaken, not Stirred
Nili Fossae has long been of interest to astronomers, as the region is covered in the mineral olivine. This material is common in the interior of planets, but rare on the surface of worlds, leading researchers to question how the deposit reached the Martian surface. One theory stated the olivine was dredged up in large effusive eruptions, while other researchers believe the material was brought to the surface as a result of the asteroid impact that formed the Isidis Basin in which Nili Fossae sits.
Kremer and his team studied the region in great detail, using high-resolution images from the Mars Reconnaissance Orbiter (MRO). Researchers found the deposits are spread evenly over hills, valleys, and craters, lending credence to the idea that a major eruption took place, rather than a low-speed lava flow. The layer of olivine in the crater sits on top of features known to have formed after the Isidis event, showing the mineral deposit was made well after the impact that formed the crater on Mars. In addition, the olivine deposit shows significant alteration by water, providing further evidence for an origin as ashfall.
“We found that the explosive volcanism and ashfall explanation ticks all the right boxes, while all of the alternative ideas for what this deposit might be disagree in several important respects with what we observe from orbit,” Kremer stated.
Who Wants a Closer Look?
The Mars 2020 rover is scheduled to land in the Jezero crater, which sits within the olivine deposit. Once it lands in the crater, Mars 2020 could answer the mystery of how the olivine found there came to sit on the Martian surface.
NASA is still accepting names to fly to the Red Planet with the Mars 2020 rover, and millions of people supporting the mission have already signed up (even our cat, Max) — so you too have a chance to join the journey to visit this exciting geological formation on Mars.