So you want to go live on Mars. It is smaller than Earth, but still has a lot of real estate. Where is the best place to call home?
NASA’s mantra has been to follow the water: they look for evidence of past life, but for once and for future humans, it’s still a good idea. Water is heavy and almost incompressible, so it is very difficult and expensive to bring it to Mars. That means finding it in situ, on Mars, is critical to success. In addition, water is not just for drinking: it can decompose into hydrogen and oxygen to form both breathable air and rocket fuel. It is the single most valuable thing for a future human presence on the planet.
And now a team of scientists has mapped out the most likely location.
Mars is cold (a high daily temperature of -60 ° C is common), so it is likely that any water is ice (with some profound exceptions). Frozen water has been mapped in different ways for different missions, and most research has focused on single-mission data or ice at isolated points. So the team put together what they call SWIM: the Mars Subsurface Water Ice Mapping project, to analyze data from many missions in a large area of the planet.
The goal was to create a system that could quantify the consistency of multiple independent observations so that they could make a solid prediction of where that water was. Note that we know that there is some enclosure in the polar layers of ice, but that they are difficult to get by spacecraft: landing requirements make it much easier to land near the equator or in middle latitudes. In addition, the ice cannot be more than a few meters deep, so it is possible to dig it up. In other words, it has to be accessible.
With this in mind, they examined observations ranging from the equator of Mars to about 60 ° north, and around the planet covering about 80% of the surface in length. Data have been obtained by various methods, including neutron flux (these subatomic particles are absorbed by hydrogen from water, so their prevalence can be used to map ice locations), thermal inertia (at night, rocks release heat accumulated during the day in a different way than water ice, so it can be used to map where water is), geomorphology (structures and characteristics in the surface indicating that water is nearby, such as glaciers) and radar (water ice and rock reflect radar impulses differently again allowing water to be mapped).
Applying a mathematical algorithm to the data, they came up with a number they call ice consistency, where a positive value is consistent with the presence of ice and a negative value incompatible with it. Higher values mean stronger results.
The result: a map where there is likely to be accessible ice (and, most importantly, probably non-existent) over a large sample of the Martian surface.
The sites with the highest values are in Arcadia Planitia, a wide, gentle plain of ancient volcanic flows, and in another region called Deuteronilus Mensae which is known to have glaciers. Both are located at mid-latitudes (around 45 ° north), so they are relatively easy to access.
To assess their predictions, one thing the team did was examine the new impacts on the surface, where small asteroids were able to traverse the air and hit the ground. If the ice is just below the surface, these impacts can dig it up, which makes it pretty obvious. In recent years, cameras aboard orbiting spacecraft have found 13 such craters. The team found that of these, 12 were where their maps predicted that ice would exist with great confidence. This is reassuring.
NASA, other space agencies and even private companies are looking to send people to Mars. I imagine you will read this article with great interest.
Technology is advancing rapidly and a human foot on Mars is not as much science fiction as it used to be. It is possible that the first person to do so is already walking on Earth. And now we can start planning realistically where that first boot impression might be.