'Hundred times' more probability of finding water on exoplanets, says new study

Their theory was presented at the Goldschmidt Geochemistry conference in Lyon. 

Water on exoplanets 

For this new study, the team analyzed planets that orbit stars called M-dwarfs. These stars are far smaller and cooler than our Sun. Moreover, M-dwarfs are commonly found in our galaxy. 

And the majority of rocky and Earth-like exoplanets have been discovered to orbit M-dwarfs. 

Following the identification of a suitable star candidate, the team developed a computer model to investigate the possibility of creating and maintaining liquid water on exoplanets. The model included the parameter of heat generated within the planet for the water to remain liquid. 

“We found that when one considers the possibility of liquid water generated by radioactivity, it is likely that a high percentage of these exoplanets can have sufficient heat to sustain liquid water– many more than we had thought,” added Ojha. 

“The new model shows that if the conditions are right, this could approach 1 planet [with liquid water] per star. So we are a hundred times more likely to find liquid water than we thought. There are around 100 billion stars in the Milky Way Galaxy. That represents really good odds for the origin of life elsewhere in the universe,” explained Ojha.

The scientists speculate that a similar scenario might allow for the existence of subsurface liquid water in Saturn's or Jupiter's frozen moons. The continual interior churning caused by the gravitational influences of the big planets they orbit might heat up the interior under their frozen surface. 

“This is similar to the effect of our Moon on tides but much stronger. This makes the moons of Jupiter and Saturn prime candidates for finding life in our Solar System and many future missions have been planned to explore these bodies,” added Ojha. 

The study is published in the journal Nature Communications.

Study abstract:

Liquid water is a critical component of habitability. However, the production and stability of surficial liquid water can be challenging on planets outside the Habitable Zone and devoid of adequate greenhouse warming. On such cold, icy exo-Earths, basal melting of regional/global ice sheets by geothermal heat provides an alternative means of forming liquid water. Here, we model the thermophysical evolution of ice sheets to ascertain the geophysical conditions that allow liquid water to be produced and maintained at temperatures above the pressure-controlled freezing point of water ice on exo-Earths. We show that even with a modest, Moon-like geothermal heat flow, subglacial oceans of liquid water can form at the base of and within the ice sheets on exo-Earths. Furthermore, subglacial oceans may persist on exo-Earths for a prolonged period due to the billion-year half-lives of heat-producing elements responsible for geothermal heat.