Mars is perhaps the best candidate world in our solar system for a settlement off Earth. Venus is too inhospitable. The Moon is a lot closer, but the extremely low gravity (.166 g) is a problem for long-term habitation. Mars gravity is 0.38 g, still low by Earth standards but better than the Moon. But there are some other differences between Earth and Mars. Mars has only a very thin atmosphere, less than 1% that of Earth’s. That’s just enough to cause annoying sand storms, but not enough to avoid the need for pressure suits. Mars lost its atmosphere because it was stripped away by the solar wind – because Mars also does not have a global magnetic field to protect itself. The thin atmosphere and lack of magnetic field also exposes the surface to lots of radiation.

Mars’ smaller size also means that it cooled faster than the Earth. While there are ancient volcanoes on Mars, the surface crust looks solid, without plate tectonics. This has led astronomers to believe that Mars is a quiet planet, with heat at the core, but a solid crust and mantle and no geological activity. That also means there are no recent volcanic eruptions that might replenish its depleted atmosphere. However – that view is changing.

There is one region of Mars, Elysium Planitia, which may be geologically active. In fact, there is now good evidence of a giant mantle plume under the surface. A mantle plume occurs when hot magma from the core rises up through the mantle and pushes up against the overlying crust. There are more than 18 such mantle plumes on Earth. One is right below the Hawaiian islands – as the Pacific plate moves over this plume it creates a chain of volcanoes and resulting volcanic islands. What is the evidence for a mantle plume beneath Elysium Planitia?

One line of evidence that we already knew about is evidence of geologically recent volcanic eruptions, as recent as 53,000 years ago. A layer of volcanic ash was deposited in the region dating to that time. Add to this recent data that shows that Elysium Planitia is being pushed up, about a mile above the surrounding lowlands. Measures of gravity intensity show that this uplift is not superficial – it is supported by a deep uplift in the mantle. Further, when scientists map the craters in the area that are all tilting toward the middle of this region, which means that the crust was pushed up after these craters were made. Further still, all Marsquakes seem to originate in this region, indicating it is geologically active.

The simplest explanation for all of these features is that there is a large mantle plume beneath Elysium Planitia, about 4,000 km wide. This means that Mars is not as cold and dead as we thought.

This is all cool planetary science, but I want to know what the implications of this are for building a permanent settlement on Mars. A few thoughts come to mind, some good and some bad. One concern, of course, would be that if we built a settlement on Elysium Planitia, or close to it, it may fall victim to a volcanic eruption. Such an eruption may not happen for thousands of years, but it could happen a lot sooner. It’s very unlikely that the very last eruption on Mars was 53,000 years ago, which in geological terms is practically current. But it probably won’t be difficult to mitigate such risks by just building at a safe distance.

How could a mantle plume be exploited? First, it could be a source of geothermal energy both for electricity and direct heating. We may need to drill deep, but we are developing that technology for deep geothermal plants on Earth. Further, if the ground beneath Elysium Planitia is warm enough that could mean any ice will have melted. So there may be underground pockets of liquid water in the region. This also, of course, raises the specter of extant underground life on Mars. Such areas are teeming with life on Earth. This should therefore be a research priority.

In the extreme, could be use the mantle plume as a mechanism for terraforming Mars? I don’t know how technically feasible this is, but could we drill down specifically to release not only heat but volatiles into the atmosphere? Could we trigger volcanic eruptions by exploding a few atomic bombs deep under ground in the Elysium Planitia (after checking for life, of course)? How much CO2 and other gases would be released? I suspect, probably not enough to matter, but it’s a fascinating thought. Interestingly, humans can survive in as little as 6% Earth’s atmosphere, from just a pressure perspective. We would still need supplemental oxygen, but would not need a pressure suit just to survive. If we could get Mars’ atmosphere up to about 10% Earth’s, that could make life on Mars much easier. The low pressure would not be deadly, the blanket would warm the surface and provide a little more protection from space radiation.

It’s unlikely that terraforming Mars in this way will work or will happen, but it’s an interesting thought experiment.