A new analysis shows that there are probably many more Earth-like exoplanets with water in the liquid state than previously thought. The work finds that even where conditions are not ideal for the existence of water in the liquid state on a planet’s surface, water could be present beneath the planet’s surface.
Presenting the work at the Goldschmidt Geochemistry Conference in Lyon, lead researcher Dr. Lujendra Ojha (Rutgers University, New Jersey, USA) said, ” We know that the presence of water in the liquid state is essential for life. Our work shows that this water can be found in places we had not sufficiently considered before. This greatly increases the chances of finding environments where life could, in theory, develop.”
The researchers found that even if a planet’s surface is frozen, there are two main ways to generate enough heat to allow water to liquefy underground. Lujendra Ojha said, “As Earthlings, we are currently lucky because we have the right amount of greenhouse gases in our atmosphere to make water stable in a liquid state on the surface. However, if Earth were to lose its greenhouse gases, the average global surface temperature would be about -18 degrees Celsius and most of the water on the surface would freeze completely. A few billion years ago, this really happened on our planet and the water on the surface froze completely. However, this does not mean that water was completely solid everywhere. For example, the heat of radioactivity in the depths of the Earth could have heated the water enough to keep it liquid. Even today, we see this happening in places like Antarctica and the Canadian Arctic, where despite the freezing temperature, there are large underground lakes, sustained by the heat generated by radioactivity. There is also some evidence to suggest that this could also be the case – currently – at the south pole of Mars.”
Dr. Ojha continued, “Some of the moons found in the solar system (e.g., Europa or Enceladus) have significant amounts of water in the liquid state underground, even though their surfaces are completely frozen. This is because their interiors are continually stirred by the gravitational effects of the large planets around which they orbit, such as Saturn and Jupiter. An effect similar to that 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 celestial bodies.”