Four billion years ago, the surface of Mars was apparently quite habitable. Rivers and lakes flowed along it, there was even a deep ocean. Some astrobiologists view ancient Mars as a cradle for life, even more suitable than Earth, and suspect that life on our planet may have originated a long time ago on Martian rocks and was thrown into space by a powerful impact.
Everything changed when Mars lost its global magnetic field. The charged particles emanating from the Sun were able to carry away the Martian atmosphere, and it gradually depleted. This process turned Mars into the cold, dry world that we see today, 3.7 billion years ago. The Earth still has a global magnetic field, which explains the suitability of our planet for life.
But this turn of events does not at all mean that Mars today is a dead planet.
“If life was on Mars 4 billion years ago, life is on Mars now. Nothing has happened on Mars to destroy life,”says Michael Finney, co-founder of The Genome Partnership, a non-profit organization that hosts conferences on advances in biology and genome technology.
“If there was life on Mars, it would go somewhere, maybe hide, but it probably would still be there,” says Finney.
Life on Mars underground
One of the most promising shelters for life will be the underground part of Mars. Although there is no liquid water on the surface of the Red Planet these days - apart from, perhaps, temporary streams on warm slopes - underground aquifers are likely to have a lot of moisture. Observations of the Mars Express orbiter in Europe indicate that a large lake may be hiding under the South Pole of the Red Planet.
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The motley inhabitants of the Earth speak of their presence in a very obvious way; an advanced alien civilization could probably quickly figure out the existence of life on our planet by simply scanning our atmosphere.
We don't see such obvious traces in the Martian air, but scientists have recently found some interesting things. NASA's Curiosity rover passed through two jets of methane in the 154 kilometers wide Gale crater. This crater has been explored by a six-wheeled robot since landing in 2012. The rover mission also determined that the concentration of methane in the air in Gale Crater varies with the season.
More than 90% of the methane in the Earth's atmosphere is produced by microbes and other organisms, so it is possible that this gas speaks of modern Martian life.
But disputes on this topic are still ongoing. Methane can also be produced by lifeless processes, such as the reaction of hot water with certain rocks. And even if the Martian methane is of biological origin, the creatures that created it may be long dead. Scientists believe that methane geysers on the Red Planet have escaped from the ground and no one knows how long the gas layer remained trapped below before breaking through to the surface.
Searching for Martian DNA
NASA's rover, which will travel to the planet in 2020 next summer, will look for signs of long-dead life. The European-Russian rover ExoMars will do the same, and its mission will begin at about the same time.
But some scientists want to extend this hunt to life, which may still exist today. One of them is molecular biologist Gary Ruvkun, who works at Massachusetts General Hospital and Harvard Medical School.
Ruvkun is one of the three main researchers in the Search for Extraterrestrial Genomes (SETG) project, which is developing a tool to detect past or present life based on DNA or RNA on Mars and other alien worlds.
Part of this idea is based on panspermia, the idea that life has spread widely throughout the solar system and possibly throughout the galaxy, naturally or artificially. If life really came to Earth from somewhere else, chances are high that it once flourished on Mars. The red planet could become the sources of life, or it was "seeded", like the Earth.
Ruvkun views panspermia as a very plausible theory. He believes that the main argument in its favor is the very early appearance of ATP synthase, an enzyme that ensures the appearance of the adenosine triphosphate molecule.
ATP synthase, according to Ruvkun, goes back entirely to the foundation of the tree of life on Earth, which means that this complex molecule appeared about 4 billion years ago.
“It's not just that life appeared at all. The point is that it has developed too quickly. This is why the idea of panspermia is so appealing."
If panspermia is correct, any life forms we find on Mars - or anywhere else in our solar system - are likely to be associated with us. That is, such organisms will use DNA or RNA as their genetic molecule. So we must look for this material.
“It would be foolish not to look for DNA on Mars,” says Ruvkun. "This is an experiment worth doing."
Not only Mars
Mars is not the only place in our solar system where alien life could flourish today. Most astrobiologists would place the Red Planet at the bottom of the list, placing Jupiter's moon Europa and Saturn's moons Enceladus and Titan in front.
Deep oceans of salty liquid water hide under the ice sheets of Europa and Enceladus. Titan is also believed to have a water ocean, and on the surface of this satellite, lakes and seas with liquid hydrocarbons have been found.
Even a red-hot Venus could have quite habitable spaces.
Like Mars, Venus was once rich in water on the surface, but the unstoppable greenhouse effect roasted everything and left the planet with temperatures at which lead melts. However, it is quite possible to live at an altitude of 50 kilometers above the surface of Venus.
What planet do you think the first extraterrestrial life will be found on?
Ilya Khel