The hunt for past life on Mars has been an astrobiological obsession for the last three decades. But to truly understand any planet, we first need to grasp both the internal geophysics and planetary geology that can enable life to evolve.
To that end, NASA’s InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission which in 2018 landed on the flat equatorial plains of Elysium Planitia, some 600km north of NASA’s Curiosity rover, spent four years taking data on the geophysics of Mars’ interior. But one crucial experiment —- The Heat Flow and Physical Properties Package, HP3 —- primarily designed and built by the German Aerospace Center (DLR), failed to reach its intended subsurface drilling depth.
HP3 was thus unable to provide the kind of data related to heat flows from Mars’ deep interior that would ultimately enable our understanding of Mars’ geophysical Evolution.
Failure To Penetrate
When we tried to insert our penetrator to dig down to five meters, it turned out the soil behavior at the landing site was completely different to any other soil we had seen previously, Guenter Kargl, a planetary geophysicist at the Austrian Academy of Sciences’ Space Research Institute and a co-investigator on HP3, told me in Graz, Austria.
Known as ‘the Mole,’ HP3 began to hammer itself under the surface but encountered different soil properties than expected and was unable to reach the desired depth, says NASA.
The soil crumbled around the Mole and there was no more side friction to enable the penetrator to move further down into Mars’ subsurface.
The authors of a 2022 paper appearing in the journal Advances in Space Research note that the Mole did not penetrate more than 40cm and may have encountered ejecta from a nearby crater or it may have self-densified the soil during its over 8000 hammer strokes, the authors note. All efforts related to the Mole ended on January 9th, 2021, when a final test to see if the Mole could penetrate without assistance from InSight’s robotic arm failed, they write.
HP3 was designed to help researchers determine whether Mars formed from the same stuff as Earth and the Moon as well as give them a sneak peek into how the planet evolved, says NASA.
Even though we may think of Mars as a small dead planet on the surface, heat in the core of Mars is thought to be at least half that of our sun.
To measure the heat flow of a planet tells us how fast the planet is losing energy from the formation process, Kargl told me at the European Astrobiology Network Association’s 2024 Conference in Austria. We know that the interiors of planets are really hot, sometimes even hotter than the surface of the sun, he says.
But if you want to know about plate tectonics, magnetism, and how volcanism works, you need to know how much energy is in these planetary interiors and how fast the planet is losing this energy, says Kargl. And the only way to measure that is planetary heat flow, he says.
How does understanding the interior of Mars help us interpret exoplanetary systems?
If you want to understand the formation process of a planet, how it evolves and how it will evolve in the future, you need to learn how they tick in their interior, says Kargl. Thus far, we have only one planet where we have fairly decent understanding, that’s Earth, he says.
Understanding Interiors
If we want to understand any other planet or exoplanets, we need to have a complete understanding of all the physics and chemistry going on inside the planet, says Kargl. That’s because the surface is not isolated from the interior; there’s a lot of surface-interior interaction, even on a planet which seems to be as dead as Mars, he says.
Sadly, it’s not likely that we will have another opportunity to measure Mars’ internal heat flow anytime soon. But to get to the bottom of NASA’s astrobiological credo —- Where Do We Come From? What Are We? Where Are We Going? —- more geophysics missions to Mars are a crucial part of what’s needed.
