New research suggests planets that have a companion nearby could have a longer life as a result.
As Earth-sized planets age their molten cores tend to solidify, interfering with its ability generate heat and regulate carbon dioxide, the University of Washington reported. Researchers found if a companion planet is nearby its gravitational pull could prevent this internal cooling through a process known as tidal heating. The research was published in the July issue of Monthly Notices of the Royal Astronomical Society.
Tidal heating is a result of the push and pull of outer companion planets. The effect is believed to occur on Jupiter's moons Io and Europa, but the researchers demonstrated it can also happen outside of our solar system.
The team used computer models to look at tidal heating in two Earth-sized exoplanets with non-circular orbits in the habitable zone (the distance from a host star in which liquid water can exist). A circular orbit would never change shape, leaving a constant gravitational pull from the nearby planet and preventing tidal heating from occurring.
"When the planet is closer to the star, the gravitational field is stronger and the planet is deformed into an American football shape. When farther from the star, the field is weaker and the planet relaxes into a more spherical shape," Barnes said. "This constant flexing causes layers inside the planet to rub against each other, producing frictional heating."
The researchers suggested any Earth-sized planets within the habitable zone of older, smaller stars should be followed by scientists. These planets could hold some of the longest-lived surface habitats in the entire universe.
"Perhaps in the distant future, after our sun has died out, our descendants will live on worlds like these," Barnes said.
The research was done through the Virtual Planetary Laboratory, a UW-based interdisciplinary research group. The research was funded through the NASA Earth and Space Science Fellowship Program and the National Science Foundation.
