It turns out having a companion to grow old with is good for both people and planets. In a paper published in the July volume of the Monthly Notices of the Royal Astronomical Society on Friday, August 1st, a group of astronomers at the University of Washington and the University of Arizona have discovered that for some Earth-like planets, the gravitational pull of a companion planet creates sufficient tidal heating to offset the natural internal cooling process of mid-size planets.

companion planets

This means that the inner planet of the companion planets has a greatly extended period of time in which it could possibly host life, which makes these planets excellent candidates in the search for extraterrestrial life.

Details on the companion planets study

The astronomers applied computer models to determine where the companion planets effect was likely to occur. The results indicated that tidal heating could happen on older Earth-sized planets in noncircular orbits in the habitable zone of low-mass stars (below one-quarter of the mass of the sun).

This means that now all discoveries of Earth-sized planets in the zone of habitation of older, small stars will include a follow up search for companion planets. Planetary researchers say this will make it easier to narrow down which planets could potentially host life.

Statement from astronomer Rory Barnes

“When the planet is closer to the star, the gravitational field is stronger and the planet is deformed into an American football shape,” commented Rory Barnes, one of the lead authors of the new paper, in a press release today. “When farther from the star, the field is weaker and the planet relaxes into a more spherical shape. This constant flexing causes layers inside the planet to rub against each other, producing frictional heating.”

The effect of the old planet’s own tectonics and tidal heating produced by the outer companion, Barnes went on to explain, make such planets potentially the longest-lived surface habitats in the universe. “Perhaps in the distant future, after our sun has died out, our descendants will live on worlds like these.”