The search for life on other planets has captivated mankind for decades.
But the reality could be a little less like the Hollywood blockbusters, scientists have revealed.
They say if there was life on the red planet, it probably will 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 key.
Although the planet is now rocky and barren with water locked up in polar ice caps there could have been water in the past.
In 2000, scientists first spotted evidence for the existence of water on Mars.
The Nasa Mars Global Surveyor found gullies that could have been created by flowing water.
The debate is ongoing as to whether these recurring slope lineae (RSL) could have been formed from water flow.
Meteorites
Earth has been hit by 34 meteorites from Mars, three of which are believed to have the potential to carry evidence of past life on the planet, writes Space.com.
In 1996, experts found a meteorite in Antarctica known as ALH 84001 that contained fossilised bacteria-like formations.
However, in 2012, experts concluded that this organic material had been formed by volcanic activity without the involvement of life.
Signs of Life
The first close-ups of the planet were taken by the 1964 Mariner 4 mission.
These initial images showed that Mars has landforms that could have been formed when the climate was much wetter and therefore home to life.
In 1975, the first Viking orbiter was launched and although inconclusive it paved the way for other landers.
Many rovers, orbiters and landers have now revealed evidence of water beneath the crust and even occasional precipitation.
Earlier this year, Nasa’s Curiosity rover found potential building blocks of life in an ancient Martian lakebed.
The organic molecules preserved in 3.5 billion-year-old bedrock in Gale Crater — believed to have once contained a shallow lake the size of Florida’s Lake Okeechobee — suggest conditions back then may have been conducive to life.
Future missions to Mars plan on bringing samples back to Earth to test them more thoroughly.
Methane
In 2018, Curiosity also confirmed sharp seasonal increases of methane in the Martian atmosphere.
Experts said the methane observations provide ‘one of the most compelling’ cases for present-day life.
Curiosity’s methane measurements occurred over four-and-a-half Earth years, covering parts of three Martian years.
Seasonal peaks were detected 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.