So you want to live on Mars. It’s smaller than the Earth, but still has a lot of real estate. Where’s the best place to call home?
NASA’s mantra was to follow the water – they look for evidence of a past life, but for once and future people it’s still a good idea. Water is heavy and almost incompressible, so it is very difficult and expensive to bring to Mars. That means finding it in situ, there on Mars, is critical to success. Water isn’t just for drinking, either: it can break down into hydrogen and oxygen to make both breathable air and rocket fuel. It is most valuable for a future human presence on the planet.
And now a team of scientists has mapped the most likely place.
Mars is cold – a daily high temperature of -60 ° C is normal – so any water is likely to be ice (with some deep exceptions). Frozen water has been mapped in different ways by different missions, and most research has focused on data from a single mission or ice in isolated places. So the team put together what they call SWIM: the Mars Subsurface Water Ice Mapping project to look at the data from many missions over a wide area of the planet.
The goal was to create a system that can quantify the consistency of multiple independent observations, so that they can make a robust prediction of where that water is located. Mind you, we know there is quite a bit trapped in the polar ice caps, but they are difficult to reach with spacecraft – landing requirements make it much easier to land near the equator or in mid latitudes. Also, the ice should be no more than a few meters deep so that it is possible to excavate it. In other words, it has to be available.
Therefore, they looked at observations extending from the equator of Mars to about 60 ° north latitude and around the planet covering about 80% of its surface in longitude. The data was obtained using several methods, including neutron flux (these subatomic particles are absorbed by the hydrogen in water, so their prevalence can be used to map the locations of ice), thermal inertia (at night, rocks give off heat that is built up during the day in a different way than water ice, so it can be used to map where water is), geomorphology (structures and features on the surface that indicate water is close, such as glaciers), and radar (water ice and rock reflect radar pulses differently, again allowing water to be mapped).
By applying a mathematical algorithm to the data, they came up with a number to call ice cream consistency, where a positive value is consistent with the presence of ice and a negative value is inconsistent with it. Higher values mean stronger results.
The result: a map on which accessible ice probably exists (and, most importantly, probably doesn’t exist) over a wide swath of the surface of Mars.
The places with the highest values are Arcadia Planitia, a wide, smooth plain of ancient volcanic flows, and another region called Deuteronilus Mensae that is known to have glaciers. Both are in the middle latitudes (about 45 ° north latitude) and thus are relatively easy to access.
To evaluate their predictions, the team looked for new impacts to the surface, where small asteroids could pass through the thin air and hit the ground. If ice is just below the surface, those impacts can dig it out, making it pretty obvious. In recent years, cameras onboard spacecraft have found 13 such craters. The team found that 12 of those were located where their maps predicted with a high degree of certainty that ice would exist. That is reassuring.
NASA, other space agencies, and even private companies want to send humans to Mars. I imagine they will read this newspaper with great interest.
Technology is advancing quickly, and a human setting foot on Mars isn’t as much sci-fi as it used to be. The first person to do this may already be on Earth. And now we can realistically start planning where that first boot print might be.