It’s almost a mantra these days: find life on the Red Planet. That’s why we’ve sent so many probes to Mars since the early 1960s. Each orbiter, lander, and rover was sent to look for evidence of Mars life in places like the scene above. This is the Octavia E. Butler Landing site for the Perseverance rover. The rocky outcrop in the short distance is a sedimentary deposit that was once part of a river delta. On Earth, this would be a perfect place to look for life.
Since the Martian surface is so barren-looking, the search for evidence of life—or, for life itself—has to be painstaking. There are no trees or plants or Martians waving at our cameras. All we see are rocks, plains, craters, mountains, and ice caps. Yet, those areas all hold clues to the Mars of the past. Those clues may even point to the existence of life there today. We just have to keep collecting data to find it.
It’s interesting to think about how we’d do the same search on Earth if we were, in fact, Martians. First, we’d train telescopes on Earth and try to figure out what the markings on the surface were. The blue color is a pretty strong hint of water on the planet. The clouds would also provide clues about the atmosphere and how “wet” it is. On the landmasses, some areas do change color with the seasons, but you’d need stronger proof than that. So, we theoretical Martians would send spacecraft with cameras, spectrometers, and other instruments, to get “up close” images and data.
Looking for Life in Hard Places
What if we theoretical Martians happened to land our spacecraft on Earth and managed to totally miss the oceans? There are some really barren parts of Earth that look totally devoid of life. Imagine showing up at the dry Antarctic valleys or the high altitude deserts of Chile. What conclusions would we come to about the possibility of life on the planet? What would we be looking for there in terms of life?
Such extreme environments would not necessarily be barren, particularly if there’s any water available. According to Nathalie Cabrol, director of the Carl Sagan Center for Research at the SETI Institute, life-hunters from another world would probably be searching out microbes. There are extreme environmental conditions in some of Earth’s areas that seem barren to us but definitely support thriving microbial colonies. “You can walk on the same landscape for miles and find nothing,” she points out. “Then, maybe…the slope changes by a fraction of a degree. Or, the texture or the mineralogy of the soil is different because there is more protection from solar ultraviolet light. And, all of a sudden, life is here.”
Getting back to Mars, then, is to consider that the Red Planet is a whole world of extreme environments that are similar—but much harsher than—what we see on Earth. And, what matters on Mars, is to look for clues that life might exist there now. The first clue is the existence of water. The second clue might be to look in a relatively protected area. That might be just underneath the surface regolith. Or, perhaps, underground in a hydrothermal system rich with water or in subsurface ice. Microbes might even be hidden away in something as unexpected as a crack in the crystalline structure of a rock.
Life is Tenacious
On a world full of extreme environments such as Mars has, it makes much more sense to analyze it as an extreme biosphere. You can’t assume that Mars life will be like it is on Earth or that life will just migrate to places based on what we know about Earth.
Think of it this way: if you grow up in a wet climate, you’re going to think about safe places to live in a way that’s very different from a being that grew up in a very dry, inhospitable climate. Desert-dwellers here on Earth know this all too well and they can find sustenance in places that rain-forest dwellers wouldn’t even notice. Maybe Mars life has experienced such a change in environments through no fault of its own.
Past Mars and Current Mars
We all know that Mars was very different in the ancient past. The ancient Martian biosphere was warmer and wetter, at least for a time. But, it had to change when the conditions changed that supported that life. Today, any microbial colonies are living under vastly different conditions than they did in the past. When the environment shifted on Mars, so did the habitats. That change happened about 3.5 billion years ago. Before that, any life that existed was dispersed around the planet through the actions of rivers and oceans, windstorms, and other actions. Today, wind and dust storms still exist, and they could be an active transport mechanism for whatever life is eking out an existence.
Cabrol thinks that there is, indeed, Mars life today. However, it’s obviously not on the surface. That means the habitats are underground. If this is correct, then the ongoing observations of Mars by our spacecraft and landers will certainly give us good data on the surface conditions, but we’ll have to modify our definition of what are called “special regions” (where life could exist).
Understanding Mars Life and Habitats
What’s it going to take to understand the existence of microbial life on Mars, given that it’s hidden from our view? Mars scientists need a lot more data about Mars on a global scale, particularly the environment. That’s a big first step towad understanding the Martian biosphere. Even more crucial, they don’t yet have a way to “see” the regions where microbes could be existing now. That’s going to take ever-more specialized missions, and eventually, a “bootprints on Mars” human exploration approach to the search for life there. For the time being, however, we are learning more each day from rovers such as the Perseverance craft, which is just beginning its exploration of the Red Planet.