Younger exoplanets are better candidates when looking for other Earths

(ORDO NEWS) — While the scientific community is looking for worlds orbiting nearby stars that could potentially harbor life, a new study led by the Southwest Research Institute shows that younger, rocky exoplanets are more likely to support a temperate, Earth-like climate.

In the past, scientists have focused on planets located within a star’s habitable zone, where it is neither too hot nor too cold for liquid surface water to exist. However, even within this so-called “Goldilocks Zone”, planets can develop climates inhospitable to life.

Maintaining a temperate climate also requires the planet to have enough heat to power a planetary carbon cycle. The key source of this energy is the decay of radioactive isotopes of uranium, thorium and potassium.

This critical heat source could power a rocky exoplanet’s mantle convection – a slow creeping movement of the region between the planet’s core and crust that eventually erupts on the surface.

Surface volcanic degassing is the main source of CO2 into the atmosphere, which helps keep the planet warm. Without mantle degassing, planets are unlikely to be able to maintain a temperate, habitable climate, as on Earth.

“We know that these radioactive elements are needed to regulate the climate, but we don’t know how long these elements can do this because they decay over time,” said Dr. Cayman Unterborn, lead author of the Astrophysical Journal Letters paper on the study.

“In addition, radioactive elements are distributed unevenly throughout the Galaxy, and as planets age, they can become depleted and degassing stops. Since planets can have more or less of these elements than on Earth, we wanted to understand how these differences can affect How long can rocky exoplanets sustain temperate Earth-like climates?

The study of exoplanets is a difficult task. Today’s technologies do not allow measuring the composition of the exoplanet’s surface, much less its interior.

However, scientists can measure the abundance of elements in a star spectroscopically by studying how light interacts with elements in the star’s upper layers. Using this data, scientists can infer what a star’s orbiting planets are made of, using the stellar composition as a rough proxy for its planets.

“Using host stars to estimate the amount of these elements that could have been incorporated into planets over the course of the Milky Way’s history, we calculated how long planets can be expected to have enough volcanism to sustain a temperate climate before the energy runs out.” Unterborn said.

“According to our estimates, under the most pessimistic conditions, this critical age is only about 2 billion years for terrestrial mass planets and reaches 5-6 billion years for larger planets under more optimistic conditions.

For those few planets for which we have a measured age , we found that only a few of them are young enough that we can say with certainty that they may be undergoing surface carbon degassing today, when we observe it, say,

This study combined direct and indirect observational data with dynamical models to understand which parameters most influence an exoplanet’s ability to sustain a temperate climate.

Additional laboratory experiments and computational modeling will allow a reasonable range of these parameters to be quantified, especially in the era of the James Webb Space Telescope, which will provide deeper characterization of individual objects.

With the help of the Webb telescope, it will be possible to measure three-dimensional changes in the atmospheres of exoplanets.

These measurements will deepen our knowledge of atmospheric processes and their interactions with the planet’s surface and interior, allowing scientists to better assess whether a rocky exoplanet in habitable zones is too old to be Earth-like.

“Exoplanets without active outgassing are more likely to be cold, snowy planets,” Unterborn said. While we cannot say that other planets are not degassing today, we can say that they would require special conditions such as tidal heating or plate tectonics to do so. These planets include the rocky exoplanets found in the TRAPPIST-1 star system. From this, younger temperate planets may be the easiest places to look for other lands.”


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