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The search for life on other planets has fascinated humanity for decades.
But the reality may be a little less like Hollywood blockbusters, scientists have revealed.
They say that if there was life on the red planet, it will likely present itself as fossilized bacteria and have proposed a new way to look for it.
Here are the most promising signs of life so far:
water
When looking for life on Mars, experts agree that water is the key.
Although the planet is now rocky and arid with water encased in the polar caps, there may have been water in the past.
In 2000, scientists first identified evidence of water on Mars.
NASA Mars Global Surveyor found gullies that may have been created by running water.
Debate is ongoing as to whether these recurrent slope lines (RSLs) may have formed from the flow of water.
Meteorites
Earth has been hit by 34 meteorites from Mars, three of which are believed to have the potential to bring evidence of past life to the planet, writes Space.com.
In 1996, experts found a meteorite in Antarctica known as ALH 84001 that contained formations similar to fossilized bacteria.
However, in 2012, experts concluded that this organic material was formed from volcanic activity without the involvement of life.
Signs of life
Close-ups of the planet were taken from the 1964 Mariner 4 mission.
These initial images showed that Mars has morphologies that could have formed when the climate was much wetter and therefore home to life.
In 1975, the first Viking orbiter was launched which, although inconclusive, paved the way for other landers.
Many rovers, orbiters and landers have now revealed traces of water under the crust and even occasional rainfall.
Earlier this year, NASA’s Curiosity rover found potential building blocks of life in an ancient Martian seabed.
Organic molecules stored in a 3.5 billion-year-old bedrock in Gale Crater – which is believed to have once contained a shallow lake the size of Florida’s Lake Okeechobee – suggest that conditions then may have been conducive to life.
Future missions to Mars plan to bring samples back to Earth for more thorough testing.
Methane
In 2018, Curiosity also confirmed strong seasonal increases in methane in the Martian atmosphere.
Experts said the methane observations provide “one of the most compelling cases” for life today.
Curiosity’s methane measurements occurred over four and a half Earth years, covering parts of three Martian years.
Seasonal peaks were found in late summer in the northern hemisphere and late winter in the southern hemisphere.
The magnitude of these seasonal peaks – by a factor of three – was far more than scientists expected.
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