It’s the Mars Life Explorer, also known as MLE. This exciting new concept got a boost in April 2022 when it was prioritized by the U.S. National Academies Planetary Science and Astrobiology Decadal Survey. Regarded by NASA as a "to-do" direct from the planetary science community, the report recommended that MLE should be the next medium-class mission in NASA’s Mars Exploration Program (MEP).
MLE is slated to cost $1.1 billion and could go to the red planet as early as 2033. It could help answer whether Mars’ mid-latitudes have or recently had life in its near-surface ice by drilling deep into it.
Should MLE become a reality, the search for life on Mars could be going underground.
From InSight to MLE
NASA’s InSight lander is in its death throes after being on Elysium Planitia since Nov. 26, 2018. Since then, InSight has been using its seismometer to measure "Marsquakes," but it’s about to succumb to dust: the lander’s pair of 2.2 meter-wide (7.2 foot-wide) solar panels are caked with the stuff and by May 2022 were producing less than a tenth of the power they did when InSight landed. InSight is expected to stop responding by Dec. 2022 at the latest.
“There are discussions about ways to modify the solar array so that you can do dust clearing,” said Amy Williams, assistant professor, Geological Sciences at the University of Florida and "science champion" on the mission concept study for MLE. “People are feeling more confident that we can engineer around that in the future.”
What is the Mars Life Explorer?
We know there was once water on Mars. A lot of it. But as a planet, it’s undergone profound climate change. Do any habitable environments remain? Are they inhabited? MLE should be able to explore these questions and more.
A fixed landing platform launching in the early-to-late 2030s, it’s a “high heritage” mission based on InSight and the Phoenix lander, which in 2008 confirmed the presence of water ice in Mars’ polar regions. MLE would drill 2 meters (6.5 feet) into Mars looking for water ice to take samples and study them in situ.
InSight's “mole” — its burrowing heat probe — was designed to take temperature measurements 3 meters (10 feet) beneath the Martian surface. “Clumpy” ground meant it couldn’t get any deeper than just a few centimeters, so MLE will use Honeybee Robotics’ The Regolith and Ice Drill for Exploration of New Terrains (TRIDENT) — a much larger rotary-hammer drill that will be tested on the Moon during the VIPER and PRIME-1 robotic missions in 2022 and 2023, respectively. TRIDENT will drill into the lowest latitude ice deposits on Mars.
Underground ice on Mars
Why go underground?
“Mars’ surface is pretty sterilizing to life as we know it, but just a few millimeters into the subsurface there’s protection from UV radiation and meters down there’s more protection from gamma radiation,” said Williams. “When the ice melts and you have liquid water present it can likely form a habitable environment if a couple other conditions are met.”
Even if the ice doesn’t contain life itself it will contain a record of what happened to the Martian climate. MLE will also explore what’s in the ice — such as organics, trace gasses, and isotopes — and explore its chemistry. It will also examine how the ice changes over a Martian year (687 Earth days).
MLE vs. NASA’s Perseverance rover
It might be tempting to think that by being merely a platform and not a rover like Perseverance or a drone like Ingenuity — and a much lower-cost mission — that MLE isn’t as ambitious. But if successful, it could be a landmark moment in the search for life because it would be the first mission to look for life that exists right now.
“Perseverance looks in the ancient rock record at a time they were lakes, rivers, and hydrothermal systems,” said Bethany Ehlmann, vice chair of the Decadal Survey Mars panel, member of MLE Steering Group, and president of The Planetary Society. “The science of astrobiology has matured to the point that we can think about searching for modern habitats and modern life on Mars – and Mars Life Explorer is explicitly focused on modern habitability.”
Perseverance may have ancient Mars covered, but modern Mars is becoming more interesting.
“There’s evidence for recent salt deposits, mid-latitude ices, trace gasses exchanging methane, volatiles exchanging water and gasses coming and going seasonally,” said Ehlmann. “Mars teeters right on the edge of habitability so the idea behind Mars Life Explorer is to investigate whether there are habitats on modern Mars.”
Let there be light
The mission must identify from orbit where to land in the mid-latitudes of Mars in a region where ground ice is accessible within a meter of the surface. Where MLE lands on Mars is everything, not only because it has to land where there is accessible ice close to the surface, but because its location will drastically affect light levels.
“The further north you go, the more likely you are to have water ice within one meter of the subsurface,” said Williams. “But you also can substantially impact your power and energy usage, so it's a balance.” In the north it also gets colder for longer, which means more energy is needed to stay alive.
“The goal is for the prime mission to last for one Martian year,” said Williams. “We've got to make it through a winter.”
Life on the edge
Mars is hard even for robots, which persuades astrobiologists that maybe if life exists on Mars it’s often in a vegetative or spore state, perhaps reanimating itself when conditions allow. “It might be right on the edge of what we expect life to be able to do,” said Williams. “If Martian life ever arose it will have evolved to thrive in what we consider to be an extreme environment.”
Landing somewhere with ice close to the surface is, of course, essential, but the mid-latitudes of Mars are seen as the sweet spot for the possible existence of life.
“If you do have episodic warming and melting of the ground ice you could have liquid water, which is vital for life as we know it as the universal solvent,” said Williams. “From an astrobiological perspective that might be enough to enable life, if it exists, to get liquid water when it needs it.”
One proposed landing zone for MLE is Arcadia Planitia, a dusty plain in mid-northern latitudes that is thought to have ice just below the surface.
A logical next step?
MLE could land on Mars in 2033, which is the same year NASA expects the Mars Sample Return mission to deliver the first rocks to Earth from the red planet. They could possibly contain traces of ancient extinct life on Mars.
“The Mars Exploration Program has searched for water, for organic carbon with Curiosity, and for extinct life with Perseverance,” said Williams. MLE seems the next logical step.
If MLE teases out habitable conditions, 2033 could be a big year in the search for life beyond Earth.