What if we aren’t alone in the universe? People have been speculating about the possibility of alien life forms at least since Lucian’s A True Story, some 1,800 years ago. In modern times, much of that has centered on our near neighbor Mars.
Sometimes those life forms are dangerous, probably never more so than in the various versions of The War of the Worlds. Sometimes they’re more congenial, as in the ’60s sitcom My Favorite Martian. Either way, we can’t stop wondering, what if?
The fiction is fun, but it’s science that will answer the question more definitively. And the science has been getting closer to the mark since astronomer Percival Lowell theorized in 1890 that intelligent life built a series of canals on the red planet.
Nowadays we have landers and rovers on the Martian surface, and spacecraft making observations from orbit. We may even get boots on the ground in the years ahead, whether through NASA’s eventual follow-ons to the Artemis moon missions or courtesy of would-be Mars colonizer Elon Musk (though he has missed his original target of 2025).
It helps that Mars is the nearest planet that isn’t a toxic hellscape with surface temperatures hot enough to melt lead. There are theories about life on Venus, but until scientists can create something that survives longer than 2 hours on the surface, Venus isn’t really in the conversation.
So where do we stand, exactly, on finding life other than on Earth?
It’s a complex question because many factors have to align for a planet to support life. It has to be in the habitable zone of a star, close enough to support liquid water but far enough away to not get scorched. It also needs an atmosphere to hold in some of that heat and a rocky surface so that life has somewhere to live. That rocky surface could be covered in water, but the point is that it can’t be a gas giant like Jupiter.
Once you get that right, the planet needs the right mass and gravity and a molten core of liquid metal to generate a magnetic field, which protects the surface against the most harmful rays that come from the host sun. The correct chemical ingredients must also be present, since life can’t exist without the fundamental building blocks, such as carbon, hydrogen, nitrogen, oxygen and phosphorus. All of these elements have to work in balance with one another to create an ecosystem that is just right for supporting life.
It puts into perspective just how special Earth is when it comes to supporting life, as it has maintained this delicate balance for billions of years.
Mars doesn’t have all of those ingredients anymore, but according to 60 years of research, it used to, so it remains Earth’s best lead for finding signs of extraterrestrial life, even if it has long since gone extinct.
There is no shortage of research about Mars. A study in 2025 counted a little over 10,000 studies published between 2001 and 2024, and that’s just what’s being used to train AI. Here’s a rough look at what decades of scientific projects have revealed about our neighboring planet.
For centuries, humans expected to find water on Mars. Astronomers were able to see ice caps on Mars through telescopes long before we became a spacefaring species. This was confirmed in 2002 by NASA’s Odyssey spacecraft.
The discovery of Mars’ atmosphere was first made in 1947 by Gerard P. Kuiper, just a few years before he discovered his namesake asteroid belt where Pluto sits. Kuiper found that there was carbon dioxide in the atmosphere, and later studies found oxygen, nitrogen and other molecules. But by that point the atmosphere was too thin to support any sort of life on the surface.
In the 1970s, NASA’s Mariner 9 orbital mission photographed Mars and found ancient water beds that implied that the red planet was once warm enough to host liquid water. This was a big discovery because planets need a thicker atmosphere to have liquid water.
Since it is already in the habitable zone of the sun, and it’s a rocky planet, that thicker atmosphere and liquid water evidence means life was possible on Mars at some point. Later studies even showed that Mars may have once had an ocean the size of Earth’s Arctic Ocean. Science is still figuring out where all that water went, but the reigning theory is that some of it became ice, some escaped through the thinning atmosphere, and the rest likely became trapped in the crust.
Edwin Kite, a planetary scientist at the University of Chicago, told CNET in an email that Mars’ climate allowed for rivers and lakes but that it might have been sporadic.
“The evidence suggests that early Mars was only intermittently warm and wet, making it a less hospitable planet for the persistence of surface life than Earth, which has been continuously habitable for at least the last 3.5 billion years,” Kite said.
Science says that Mars had all the right ingredients to make life on a wide scale, like an atmosphere and water. It also needed a special mix of other things, like the right pH levels, nutrients and chemical compounds to foster life.
This topic is particularly challenging because no Martian samples have ever returned to Earth, so most of this work is done via the various Mars rovers, satellite measurements with specialized instruments, and other methods.
These studies are promising. The Phoenix Mars Lander did a pH test in 2008 and found that the soil there was right around 8 or 9, which is pretty close to neutral and suitable for microbes and plant life. In fact, the chemical makeup of the soil studied in those tests found that Mars has soil similar to the surface soils in the upper dry valleys in Antarctica.
There is also evidence that Mars was once more geologically active. NASA research scientist Marc Neveu told CNET that the surface of Mars has evidence of “volcanism churning elements” similar to Yellowstone National Park that would have created “pools of warm or hot water,” which could have been suitable for life. Neveu also notes that Mars used to be “bombarded by meteorites, asteroids and comets”, which might have brought organic material to the surface that microbial life could have used as food.
Mars soil in its current form isn’t suitable for plant life without some work, and the few samples analyzed showed no evidence of organic life. Researchers believe this is potentially a side effect of a process called photocatalyticoxidation, a process where oxygen combines with metal to form a metal-oxide that reacts with UV light to wipe out any organic material.
Meanwhile, Mars’ red color is most likely caused by ferrihydrite, a compound that only forms in cold, wet conditions, showing that there’s more evidence Mars was warmer and wetter once upon a time. The Mars Curiosity Rover has found nearly two dozen organic molecules. Those molecules may or may not have been formed by geological or biological processes, but their presence supports the notion that Martian soil was, at one point at least, suitable for life.
The key here is getting samples of Martian soil back to Earth for further study. Martian soil has never been studied using the far more advanced instruments here on Earth.
“Return of samples from Mars will be very useful in determining the ancient temperature, atmospheric pressure, and liquid water availability,” Kite said. “This and other evidence will be useful in figuring out why Mars had a river-forming climate, and why the environment deteriorated.”
The first mission planned to return samples from Mars to Earth is China’s Tianwen-3, set to launch in 2028.
Research sometimes follows tantalizing clues that don’t pan out. Fragments of Mars that landed on Earth from an asteroid or comet impact on the red planet showed what appeared to be fossilized bacteria inside the meteorite. It took almost 20 years but scientists eventually figured out that geological processes could cause similar wormlike structures in rock.
But there are still plenty of mysteries to solve on Mars. One such example is a seasonal fluctuation of methane near Mars’ Gale Crater that peaks in the warmer summer months and drops in the winter. This seasonal breathing, paired with the organic molecules found by the Mars Curiosity rover, could point to life on Mars, but further study is needed.
Mars also houses patches of dusty ice water. This is relevant because dust particles can absorb heat from the sun, sink into the ice, and form tiny pockets of water that can house entire ecosystems of simple lifeforms. Researchers also believe that dusty ice can let in enough light for photosynthesis, which could mean that life still exists on Mars today.
“It’s very possible that microbial life still exists on Mars, trapped in shallow ice or deeper in underground pockets of water,” said Neveu. “Microbes could have migrated there once the surface of Mars became too cold and irradiated to be hospitable, or life could have simply originated there. Microbes are found in these kinds of environments on Earth.”
NASA’s Perseverance rover collected a sample from a dried riverbed in the Jezero Crater in 2025 that contains compounds that contain biosignatures – that is, substances or structures in a sample that might have been made by a lifeform. Proving it is beyond the capabilities of Perseverance, so for now, it’s another maybe.
Neveu also notes that it’s possible that Mars and Earth flung meteorites at each other long ago, and that microbes and spores could’ve hitched a ride during these exchanges. That means if Mars had life, it could’ve come from Earth or even vice versa. This theoretical process is known as lithopanspermia.
LHS 1140b apparently has everything it needs to support life. Science hasn’t observed any there yet.
Scientists also have spotted planets outside our solar system that are candidates for further inquiry into the potential for supporting life. These are the three best ones:
TOI-700 d: TOI-700 d is about 20% larger than Earth and orbits in the habitable zone of its host star, which is a red dwarf. Researchers haven’t yet confirmed that it has an atmosphere, and it’s likely tidally locked like LHS 1140 b. It’s not a great candidate, but simulations, at least, give some hope.
Trappist-1e: This planet is about 70% the size of Earth and orbits in the habitable zone of its host star located about 40.7 light-years away. It is the only planet in its solar system that has any potential of having liquid water, but researchers haven’t yet confirmed if it has an atmosphere.
LHS 1140 b: This is the first exoplanet ever discovered that exists in the habitable zone of its star, is a rocky planet and also has an atmosphere. It’s roughly 70% larger than Earth and tidally locked to its sun (it doesn’t rotate as Earth does).
