A team of U.S. astronomers has calculated internal heating rates for 53 terrestrial exoplanets and found that all of them are likely to have volcanic activity at their surfaces, and that at least 26% could be ocean worlds, with a majority similar in structure to the icy moons of our Solar System’s giant planets.
An artist’s impression of a water-world exoplanet. Image credit: Sci-News.com.
“Plumes of water erupt from Europa and Enceladus, so we can tell that these bodies have subsurface oceans beneath their ice shells, and they have energy that drives the plumes, which are two requirements for life as we know it,” said Dr. Lynnae Quick, a planetary scientist at NASA’s Goddard Space Flight Center.
“So if we’re thinking about these places as being possibly habitable, maybe bigger versions of them in other planetary systems are habitable too.”
Dr. Quick and colleagues from NASA’s Goddard Space Flight Center, Planetary Science Institute and the University of Idaho decided to explore whether there are planets similar to Europa and Enceladus in the Milky Way. And, could they, too, be geologically active enough to shoot plumes through their surfaces that could one day be detected by telescopes.
To look for possible ocean worlds, the researchers selected 53 planets with sizes most similar to Earth, though they could have up to 8 times more mass.
They then sought to determine how much energy each one could be generating and releasing as heat.
They considered two primary sources of heat. The first, radiogenic heat, is generated over billions of years by the slow decay of radioactive materials in a planet’s mantle and crust. That rate of decay depends on a planet’s age and the mass of its mantle.
They applied the decay rate to their list of 53 planets, assuming each one is the same age as its star and that its mantle takes up the same proportion of the planet’s volume as Earth’s mantle does.
Next, they calculated heat produced by something else: tidal force, which is energy generated from the gravitational tugging when one object orbits another.
One exit route for this heat is through volcanoes or cryovolcanoes. Another route is through tectonics, which is a geological process responsible for the movement of the outermost rocky or icy layer of a planet or moon.
Whichever way the heat is discharged, knowing how much of it a planet pushes out is important because it could make or break habitability.
For instance, too much volcanic activity can turn a livable world into a molten nightmare. But too little activity can shut down the release of gases that make up an atmosphere, leaving a cold, barren surface. Just the right amount supports a livable, wet planet like Earth, or a possibly livable moon like Europa.
“Forthcoming missions will give us a chance to see whether ocean moons in our Solar System could support life,” Dr. Quick said.
“If we find chemical signatures of life, we can try to look for similar signs at interstellar distances.”
The team’s results appear in the Publications of the Astronomical Society of the Pacific.
_____
Lynnae C. Quick et al. 2020. Forecasting Rates of Volcanic Activity on Terrestrial Exoplanets and Implications for Cryovolcanic Activity on Extrasolar Ocean Worlds. PASP 132, 084402; doi: 10.1088/1538-3873/ab9504
This article is based on text provided by the National Aeronautics and Space Administration.
