A lot of time has been spent talking about the so-called Goldilocks Zone when it comes to the search for Earth 2.0. The Kepler mission was designed basically to do just that – stare at stars similar to our Sun and look for rocky planets in that region where liquid water could exist. But we still haven’t found an exoplanet that matches our conditions. And it’s not even about the possibility of liquid water anymore. After all, we have liquid water beneath icy crusts on worlds in our solar system that definitely aren’t in the Goldilocks Zone.

So now, researchers at the Southwest Research Institute have led new work on narrowing down candidates for other Earths. Their results were published in The Astrophysical Journal Letters and reason that younger planets make better targets because they still have the right amounts of radioactive isotopes to keep the planet warm. And that would happen through a process called mantle degassing, where the radioactive heat causes convection in the mantle, and that convection allows carbon dioxide to vent from volcanoes.

A carbon dioxide blanket would warm the planet, and that could help support a habitable climate.

Of course, determining if an exoplanet has the right abundance of elements is difficult, especially considering we’re just starting to grasp what the atmospheres are made of. But we can spectroscopically measure the host star to determine what elements are in the upper layers, and from there, infer the composition of the planets.

Again, we’ll need younger planets for this type of heating. As lead author Cayman Unterborn explains: Under the most pessimistic conditions we estimate that this critical age is only around 2 billion years old for an Earth-mass planet and reaching 5–6 billion years for higher-mass planets under more optimistic conditions. For the few planets we do have ages for, we found only a few were young enough for us to confidently say they can have surface degassing of carbon today…”

The team is hoping that a certain newly aligned space telescope will help provide some more data in our quest for Earth 2.0.

More Information

SwRI press release

“Mantle Degassing Lifetimes through Galactic Time and the Maximum Age Stagnant-lid Rocky Exoplanets Can Support Temperate Climates,” Cayman T. Unterborn et al., 2022 May 3, The Astrophysical Journal Letters