Knowing that Mars had water isn’t a new thing. As mentioned in the previous story, we’ve seen evidence of river beds, stream flows, and lakes. The water was there, and now it’s not. That’s definitely not a question. The question is what made the water disappear?

It turns out that early in Mars’ history when there was a northern ocean and precipitation and wetter conditions, there was also a magnetic field similar to what we have here on Earth. That magnetic field helped protect Mars’ atmosphere, which kept the water on the surface. Then the magnetic field disappeared, and in new research published in Nature Communications, a team has possibly solved just why that magnetic field went away.

Co-author Kei Hirose explains the logic behind these recent simulations: Earth’s magnetic field is driven by inconceivably huge convection currents of molten metals in its core. Magnetic fields on other planets are thought to work the same way. Though the internal composition of Mars is not yet known, evidence from meteorites suggests it is molten iron enriched with sulfur. Furthermore, seismic readings from NASA’s InSight probe on the surface tell us Mars’ core is larger and less dense than previously thought. These things imply the presence of additional lighter elements such as hydrogen. With this detail, we prepare iron alloys that we expect constitute the core and subject them to experiments.

And once again, we see scientists getting to play with diamonds and lasers. They created a sample of material containing iron, sulfur, and hydrogen. These are the elements they think Mars’ core used to be made from. They then placed the sample between two diamonds, compressed it, and hit it with an infrared laser. Observations were taken with X-ray and electron beams, and the team was able to see what happened as the sample melted under pressure and how the composition changed over time.

Basically, the material separated into two liquids, which would have given Mars the convection currents necessary to make a magnetic field. Eventually, however, the two liquids completely separated, the currents went away, and with those, the magnetic field disappeared. Without the magnetic field, the atmosphere got blown out to space by the solar winds, and the water vapor in the air broke down and escaped, followed by the surface water as it evaporated over time.

So life could have developed, but it likely only had a narrow window to do so, even if that window is slightly longer than we originally thought.

More Information

The University of Tokyo press release

“Stratification in planetary cores by liquid immiscibility in Fe-S-H,” Shunpei Yokoo et al., 2022 February 3, Nature Communications