The universe is just too big and planets too common for Earth to be the only place where life evolved. The search for life beyond our world is varied, from trying to spot the transmission of an alien civilization to looking for biosignatures on Mars.
The answer to the question of whether we are alone in the Universe might come from anywhere and in ways that we have not anticipated. The way we experience and understand life might not be universal: requirements such as water and DNA might be simply quirks of our planet, rather than standard blueprints in the cosmos for anything living.
We believe that life requires liquid water, suitable elements and molecules, and a source of free energy. Now that our biases on life are clear, let’s have a look at the most promising places for life to exist in the Solar System.
Moons with oceans and geothermal activity
If you are a betting person, this is where your money should go. Europa and Enceladus are, respectively, the active icy moons of Jupiter and Saturn. They have a deep ocean under a relatively thin ice shell. Enceladus has geothermal activity at the bottom of its ocean, and this is also believed to be the case for Europa. Their geological makeup indicates molecules that could be useful to lifeforms. So you have plenty of water, energy, and interesting chemistry – if this is not a great recipe for life, we don’t know what is.
At the same time, it is not a sure bet. On Earth, the source of free energy is photosynthesis. There, it would have to be related to the hydrothermal vents, and calculations suggest that is far below what you can get with photosynthesis. There is still so much we do not know about these moons and it could be possible for a world to have all the right ingredients but not have had the luck for life to find a way to exist.
Deep within the Martian soil
Mars is the next obvious option. The Red Planet is now a frigid desert bombarded by ultraviolet light and radiation. Most certainly not a welcoming place for life, at least Earthly life. But the planet used to have a lot more water flowing on its surface, a denser atmosphere, a magnetic field, and a slightly warmer climate.
That might have been enough for ancient microbes to evolve and thrive in that peculiar environment. There are certainly enough organic molecules for them to have done so. And if they used to exist, could it be possible that some have adapted to the terrible conditions the planet ended up with? Could they have escaped deeper into the soil, safer from temperature changes and cosmic radiation? We do not know yet. But planetary scientists and the many robots we have sent there are certainly looking.
Floating through the rivers of Titan
Looking at Earth from space, the dominating feature is the water. Rivers, lakes, seas, and oceans make our little rock blue. That’s where life started and where it continues. Maybe it is not strictly about water, it could be about any fluid that cycles, bringing chemicals and aiding movements.
If that were the case, then there is only one other place in the Solar System where you can find rivers, lakes, and seas: Titan. The largest moon of Saturn has a dense atmosphere rich in clouds that rain on the world below. The only minor issue is that it is not water, it’s liquid methane.
The composition might be weird but there is still a liquid solvent (albeit not water), and there is energy otherwise you wouldn’t have all these atmospheric changes, and you have an overabundance of organic molecules. So why not consider Titan a candidate? NASA is taking this seriously and will be sending a flying mission called Dragonfly to sample and examine multiple sites around the chilled moon. The mission is expected to arrive in 2034.
In the hellish clouds of Venus
The most surprising finding in the Solar System in the last several years is the phosphine in the atmosphere of Venus. On Earth, this molecule is a byproduct of life and the discovery of it on Venus has obviously got people considering: could life survive in the clouds of Venus? Venus is after all a terrible place. On its surface, the temperature is high enough to melt lead and the pressure is high enough to crush you. Clouds might be better but they are very acidic. Could there be a niche there?
There’s no liquid water in those clouds, but there is chemistry and energy. The amount of phosphine is surprisingly stable, suggesting that it is a substance produced continuously rather than from a more variable source. In our exclusive interview with the discoverer Professor Jane Greaves, we discussed how the life hypothesis is strengthened by the latest observations. Perhaps upcoming missions to the planet might provide clarity and new insight into this possibility.
Because if life could exist on Venus, it opens the possibility that maybe life is a lot more flexible than we had thought.
Trapped deep within icy worlds
Having embraced Venus as a possible site for life, we might as well go all in! Still considering the combination of chemistry, liquid, and energy, why not look at deep-buried oceans? Scientists think they are incredibly common. Several large moons of all the gas giants as well as dwarf planets like Ceres and Pluto have stuff going on under the surface.
Could there be life trapped under tens or hundreds of kilometers of ice? The possibility seems remote at first but researchers are not ready to discount it. Missions include the European Space Agency’s JUICE, which is taking a trip to Jupiter to study if there are oceans deep inside icy moons like Ganymede and Callisto and investigate how habitable those two and Europa are.
There are clearly a lot of places around us where life might have started, somewhere it might have continued to survive and thrive. But we are yet to find out where these places are and what life truly needs to exist.
Source Link: This Is Where Life Could Exist Elsewhere In The Solar System
