Over the past decade, we have been able to peer beyond the solar system and search for planets in systems beyond ourselves, having discovered more than 4,000 exoplanets in total. The next challenge for understanding these distant worlds is to know if they can be habitable, as many will likely be outside the habitable zone in which liquid water may be present on their surfaces.
Now, new research aims to go beyond the concept of a habitable zone and understand the habit of exoplanet based on planetary geology.
“We usually expect to find these planets in the so-called ‘Goldilocks’ or habitable zone, where they are at the right distance from their stars to support liquid water on their surface,” lead author Brendan Dyke, University Assistant Professor of Geology in British Columbia said in a statement.
But his research aims to go further. “Just because a rocky planet can contain liquid water doesn’t mean it,” he explained. “Take a look at our own solar system. Mars is also within the habitable zone and although it once supported liquid water, it has long since dried up. “
A major objective for many exoplanet researchers is to discover rocky planets similar in structure and size to the Earth. “The discovery of any planet is very exciting, but almost everyone wants to know if there are small Earth-like planets with iron cores,” Dyke said.
To understand the core of the planets, the team looked for clues to the formation of the planets. Rocky Earth-like planets with an iron core typically have a similar iron-to-star ratio that they orbit, but how much this iron core can vary in mantle versus mantle. It is this core versus mantle issue that can determine the presence of water and whether a planet will have plate tectonics, which can be an important determination of habitat potential.
“As the planet builds, those with larger cores will form thinner crusts, while those with smaller cores make thicker layers of iron like Mars,” he explained. This knowledge of geology can be applied to planets outside our solar system to help narrow down potential candidates for habitable exoplanets.
“Our findings suggest that if we know the amount of iron present in a planet’s particle, we can estimate how thick its layer will be and, in turn, whether liquid water and an atmosphere can exist.” They said. “This is a more accurate way of identifying a possible new Earth-like world than relying on its position in a habitable zone alone.”
This research has been published in the Astrophysical Journal Letters.