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Debris from ancient explosive volcanoes found at Mars rover landing site
A previously unknown rock type at the future landing site of the European Space Agency’s new Mars rover is revealing more about the red planet.
The rock is believed to have come from an ancient volcanic eruption that once blanketed the site in ash billions of years ago.
In the search for life on Mars, scientists have discovered more about the planet’s explosive past.
The future Mars rover landing site called Oxia Planum, may have once been covered in ash by a highly explosive volcanic eruption hundreds of kilometres away.
Scientists have been using images taken from orbiting spacecraft to map the geology of the site. Understanding more about the rocks can help us learn more about the ancient climate of Mars and whether it could have once supported life.
Emma Harris, a scientist at the Natural History Museum, has been examining a previously unknown rock type and believes it may have formed from an ancient volcanic ashfall.
“There are no known volcanoes at this site, which means the debris probably came from hundreds or maybe even thousands of kilometres away,” Emma says. “It likely came from a really explosive volcano which launched ash high into the atmosphere and travelled this huge distance before settling at this site.”
Remains of this ashfall are now only found within old craters from meteor impacts and other irregular patches across the Oxia Planum site. Emma believes this could be because these areas were once filled with water.
“The likely explanation for the location of these rocks is that upwelling of groundwater from within the crust once filled the bottom of these impact craters,” explains Emma. “When the ash fell on these patches of water, it made it stickier and more cemented. The rest of the ash which landed on the surrounding rock may have just blown away and never preserved.”
The results of this research have been published in the Journal of Geophysical Research: Planets.
Preserved volcanic debris, shown here in purple, was found at the bottom of ancient meteorite craters that may have once been filled with water. © 2024. E. Harris
Martian volcanoes
Volcanoes were very common on Mars, which is home to some of the largest volcanos in the solar system. The largest is Olympus Mons, which is two and a half times the height of Mount Everest.
Active volcanos on Earth have a lifespan of a few million years. But on Mars, some were active for over a billion years. This is because Mars doesn’t have plate tectonics like we see on Earth.
“The Hawaiian Islands in the Pacific formed because of a hot spot in the middle of the Pacific plate, which caused volcanic eruptions,” Emma explains. “The hot spot remains in the same place, but as the plate moved over the top, it created a chain of islands.”
“These hotspots also occur on Mars, but because the plates don’t move, volcanic material can build up over a long period of time. This is why we see huge volcanos like Olympus Mons.”
The volcano that deposited the ash at Oxia Planum is not thought to have been one of these giant volcanos but was most likely a different type of highly explosive volcano. These eruptions didn’t produce any lava but imploded on themselves, leaving behind huge misshapen craters.
As we don’t currently have samples from Mars, it is difficult for scientists to date when the ashfall at Oxia Planum may have settled. Instead, scientists estimate the age of rock by counting the number of craters. Older surfaces of Mars have accumulated more impact craters over time compared to younger rock surfaces.
The Oxia Planum ashfall is thought to have occurred between two periods in Mars’ history known as the Noachian and the Hesperian, which was around four to three and a half billion years ago.
“These rocks are extremely old, but this is the time in Mars’ history we want to be looking at,” says Emma. “If life ever existed on Mars, it would have been a very long time ago because the planet has been arid and fairly inactive for the past three billion years. So we want to look at rocks before this period to see if there are traces of water or microbial life.”
The largest volcano in the solar system is Olympus Mons, which is two and a half times higher than Mount Everest. © NASA/JPL-Caltech/USGS
The search for life on Mars
Despite decades of research, we are still looking for definitive signs that life existed on Mars.
As human travel between planets is still a distant reality, we must rely on rovers to explore the surface of Mars. There have been six successful Mars rovers.
NASA’s Perseverance rover, launched in 2020, has been collecting samples from what is thought to have been an ancient water-filled crater. The samples are waiting to one day be flown back to Earth.
The ExoMars programme will include the European Space Agency’s first Mars rover, called the Rosalind Franklin. Planned for launch in 2028, the main goal of the mission is to search for signs of life.
The rover will be drilling two metres into the surface of Mars, which is the deepest we will have ever drilled into the planet’s surface. Scientists believe this may be deep enough that the Sun wouldn’t have caused any radiation damage to ancient living material.
“Although we can’t study this rock in person, these rovers will be taking images for closer analyses of the material,” says Emma. “It can also use lasers on the rocks so we can get their chemical composition, which we can then compare with rocks on Earth to help work out what it is.”
“The ExoMars rover is not allowed to drive on these ancient volcanic rocks at Oxia Planum because it is too jagged, but I’m hoping that a few boulders have fallen off these formations so we can analyse it in more detail and see if the ashfall hypothesis is correct”
