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.

Did you know that a meteorite can tell us about ancient titanic explosions and collisions that occurred long before the Sun existed? It’s true—and, according to scientists at the Facility for Rare Isotope Beams at Michigan State University, studies of these meteorites can give important clues to that long-ago time in galaxy history.

Meteorite: a Space Rock from the Past

Every day, material falls from the sky and lands on the surface of Earth. It can be as small as a speck of dust or a boulder-sized (or, rarely, a larger) object. When a space rocks lands on the surface of our planet, we call them “meteorites.” They come from asteroids and even from other planets. There’s a whole class called “Mars meteorites” that actually DO come from Mars. They started their trips to Earth when something plowed into the surface of Mars and craters. Some of the rocks blasted out to space and made their way to our planet. Others come from asteroids that collided, sending showers of debris hurtling through space.

Each asteroid carries minerals and crystals, for example. Scientists can study them to understand interesting things about conditions when the asteroids formed. Since they formed early in the history of the solar system, we can get fascinating clues before and during the birth of the Sun and planets. And, some asteroids also contain elements that could only form in cataclysmic events that predated the solar system.

A Little Cosmic Chemistry

Space rocks, the planets, even our own bodies, contain elements that were made in stellar explosions. We contain a lot of hydrogen, too. But, that all came from the Big Bang. But, the elements such as silver or iron or carbon come from the bellies of stars. These are called the “heavy” elements. They form in a process called “nucleosynthesis.” It occurs inside the stars when atoms of elements are slammed together to form new ones.

In our Sun, the process is currently taking hydrogen atoms and making helium. In the future, helium will become the dominant fuel in the solar core. However, in the far future, after the Sun has become a white dwarf, conditions in its core will cause it to produce carbon. For more massive stars, the process goes further, all the way to the creation of iron in the core.

But, as scientists now know, not all the elements are created inside stars exclusively. There’s a special process that makes some of the heavier elements. These are such elements as iodine, gold, platinum, uranium, plutonium, and curium. It’s called the “rapid neutron capture process,” or “r-process” and it occurs in extremely catastrophic events. These would be the explosions of the largest stars, the violent collisions of neutron stars, or a mashup between a neutron star and a black hole. These events are fairly rare in the universe, but when they do happen, the r-process takes place. Resulting neutrons gather in nucleus of atoms of certain elements and then converted into protons. The r-process builds up heavier nuclei as more neutrons are captured. (Keep in mind that in the periodic table the number of protons in an element’s nucleus defines its atomic number and “weight”).

Radioactivity Tells a Tale

It turns out that some of the nuclei produced by the r-process are radioactive. That means they spontaneously emit energy and subatomic particles. This process can take millions of years for the “parent” substance to decay to create stable nuclei. So, what kind of radioactive nuclei get created?

Iodine-129 and curium-247 are two good examples. They came from some event shortly before the Sun formed. Eventually, they became part of materials that coalesced to form space rocks, and eventually planetesimals that existed in the solar nebula. Some collided to create planets and moons. Others remained in interplanetary space over the next billions of years. Eventually, those space rocks fell to Earth as meteorites.

All this time, inside these meteorites, the radioactive decay generated an excess of stable nuclei. Scientists in laboratories can measure those nuclei to figure out the exact amounts of iodine-129 and curium-247 that were present before the solar system formed.

The existence of certain elements in meteorites tells us that something happened just before the Sun and planets were born. But what? That’s more of a challenge. It’s somewhat like trying to remember what your parents were like before you were born. You can’t. You can only look at pictures of them, but that’s not a first-hand experience.

Meteorite Clues Inform Models

At the moment, scientists don’t know exactly what happened to produce the elements in the meteorites. They just know that to get those elements the event was massive and energetic. But, was it a collision of neutron stars? Did a massive star die somewhere in the region near where our solar system formed? Did a black hole and a neutron star get too close together and merge? All those are possibilities for the creation of the elements that eventually ended up in meteorites.

I find it pretty cool that scientists can now “diagnose” a long-ago event from the existence of isotopes in meteorites. It’s all good knowledge that can be used in simulations of star death and massive collisions. In turn, their work will give us more insight into those kinds of events and their effects on nearby regions of space.