I feel like I probably had a childhood astronomy phase, but if I did, all I really remember was the feeling of existential dread upon learning that the sun was expanding and would eventually consume the entire Earth. When it comes to Mars, my primary interest was that time Calvin and Hobbes went there in their cardboard box. Later, my father spent a brief time as a consultant biologist on some part of NASA’s search for signs of life, but my understanding of the place, following the science, was that it was not only dead in terms of life, but also in terms of geological activity. The main evidence for that that I knew of was that Mars doesn’t have a magnetosphere. Earth does have one, and our current understanding is that it’s generated by activity in our planet’s molten core. It provides a great deal of protection from solar radiation, which is part of why we’re able to have such low radiation levels and such a nice atmosphere. Mars, or so the thinking goes, lost all of its heat, because it’s such a small planet. It cooled off, lost its core activity, and so lost its magnetosphere along with the capacity to shelter life.
Well, it turns out there’s a bit more going on down there than we thought. Those of you who follow science news will probably have heard about this in recent days, but there’s evidence of new movement deep within the red planet:
In a study published in Nature Astronomy, scientists from the University of Arizona challenge current views of Martian geodynamic evolution with a report on the discovery of an active mantle plume pushing the surface upward and causing earthquakes and volcanic eruptions. The finding suggests that the planet’s deceptively quiet surface may hide a more tumultuous interior than previously thought.
“Our study presents multiple lines of evidence that reveal the presence of a giant active mantle plume on present-day Mars,” said Adrien Broquet, a postdoctoral research associate in the UArizona Lunar and Planetary Laboratory and co-author of the study with Jeff Andrews-Hanna, an associate professor of planetary science at the LPL.
Mantle plumes are large blobs of warm and buoyant rock that rise from deep inside a planet and push through its intermediate layer – the mantle – to reach the base of its crust, causing earthquakes, faulting and volcanic eruptions. The island chain of Hawaii, for example, formed as the Pacific plate slowly drifted over a mantle plume.
“We have strong evidence for mantle plumes being active on Earth and Venus, but this isn’t expected on a small and supposedly cold world like Mars,” Andrews-Hanna said. “Mars was most active 3 to 4 billion years ago, and the prevailing view is that the planet is essentially dead today.”
“A tremendous amount of volcanic activity early in the planet’s history built the tallest volcanoes in the solar system and blanketed most of the northern hemisphere in volcanic deposits,” Broquet said. “What little activity has occurred in recent history is typically attributed to passive processes on a cooling planet.”
The researchers were drawn to a surprising amount of activity in an otherwise nondescript region of Mars called Elysium Planitia, a plain within Mars’ northern lowlands close to the equator. Unlike other volcanic regions on Mars, which haven’t seen major activity for billions of years, Elysium Planitia experienced large eruptions over the past 200 million years.
“Previous work by our group found evidence in Elysium Planitia for the youngest volcanic eruption known on Mars,” Andrews-Hanna said. “It created a small explosion of volcanic ash around 53,000 years ago, which in geologic time is essentially yesterday.”
Ok, so I was already off before this plume showed up – that’s much more recent activity than I would have guessed. Still, it seems like my surprise at an active mantle plume is shared by scientists. From what I can tell, this doesn’t affect our lives in any way – it’s not going to re-start the Martian magnetosphere, so Elon Musk’s supposed plans for colonization still have to account for the radiation problem. From the perspective of people studying Mars, however, this is a major discovery.
Mantle plumes, which can be viewed as analogous to hot blobs of wax rising in lava lamps. give away their presence on Earth through a classical sequence of events. Warm plume material pushes against the surface, uplifting and stretching the crust. Molten rock from the plume then erupts as flood basalts that create vast volcanic plains.
When the team studied the features of Elysium Planitia, they found evidence of the same sequence of events on Mars. The surface has been uplifted by more than a mile, making it one of the highest regions in Mars’ vast northern lowlands. Analyses of subtle variations in the gravity field indicated that this uplift is supported from deep within the planet, consistent with the presence of a mantle plume.
Other measurements showed that the floor of impact craters is tilted in the direction of the plume, further supporting the idea that something pushed the surface up after the craters formed. Finally, when researchers applied a tectonic model to the area, they found that the presence of a giant plume, 2,500 miles wide, was the only way to explain the extension responsible for forming the Cerberus Fossae.
“In terms of what you expect to see with an active mantle plume, Elysium Planitia is checking all the right boxes,” Broquet said, adding that the finding poses a challenge for models used by planetary scientists to study the thermal evolution of planets. “This mantle plume has affected an area of Mars roughly equivalent to that of the continental United States. Future studies will have to find a way to account for a very large mantle plume that wasn’t expected to be there.
“We used to think that InSight landed in one of the most geologically boring regions on Mars – a nice flat surface that should be roughly representative of the planet’s lowlands,” Broquet added. “Instead, our study demonstrates that InSight landed right on top of an active plume head.”
The presence of an active plume will affect interpretations of the seismic data recorded by InSight, which must now take into account the fact that this region is far from normal for Mars.
“Having an active mantle plume on Mars today is a paradigm shift for our understanding of the planet’s geologic evolution,” Broquet said, “similar to when analyses of seismic measurements recorded during the Apollo era demonstrated the moon’s core to be molten.”
My first thought, when hearing about these findings, was that this activity also increases the chance of there being active microbial life in Mars’ crust, similar to what we’ve found on Earth. Reading this article, it seems that I’m also not alone in that. I don’t know how long it’ll be before we get clear answers, but it feels like actually finding that life might be closer than I thought. Once scientists have done their recalculations, accounting for these new data, my guess is that they’ll have a better idea of where to look for life, based on current geological activity.