Scientists think that, in the past, water may have flowed across the surface in rivers and streams, and that vast oceans covered the planet. Over time, the water was lost into space, but early conditions on the wetter planet could have been right for life to evolve.
With water, comes life. And if Mars has any stores of water beneath its surface–or water covering a percentage of its surface in the past–that means life might be possible.
In June of 2018, NASA's Mars rover, Curiosity, identified a number of organic molecules, which are the "carbon-based building blocks of life." Space.com reports:
'These results do not give us any evidence of life,' stressed study lead author Jennifer Eigenbrode, a scientist at the Solar System Exploration Division at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
'But there is a possibility that [the organics] are from an ancient life source; we just don't know,' Eigenbrode told Space.com. 'And even if life was never around, they [the molecules] tell us there was at least something around for organisms to eat.'
Now that InSight has landed, NASA will only improve its understanding of the planet, continue to compare its similarities to Earth, and learn whether or not life is possible—or present.
According to scientists at Oxford, this case is already closed; there is no life on Mars. The rocks on Mars' surface absorbed its water billions of years ago, rendering life on the planet impossible. The Independent's Josh Gabbatiss reports:
Mars was made uninhabitable when its surface water was absorbed into the planet’s crust...The Red Planet was covered in water until around three billion years ago, much like Earth. But modern-day Mars is barren and dry, precluding the existence of Martians anywhere other than in science fiction.
'On Mars, water reacting with the freshly erupted lavas that form its basaltic crust resulted in a sponge-like effect,' said Dr Jon Wade, who led the study, published in the journal Nature.'This water-rock reaction changed the rock mineralogy and caused the planetary surface to dry and become inhospitable to life,' he said.