Companion Planets May Increase a Planet's Chances of Hosting Alien Life

Astronomers continue their hunt for life on other planets. Yet part of that search depends on narrowing down which locations are most likely to host favorable conditions. Now, scientists have taking another step toward discovering life; they've found that companion planets may extend the chance for life on Earth-sized planets in the cosmos.

As they age, planets cool and their molten cores solidify. This makes them less able to host life, since the lack of inner heat-generating activity makes it more difficult for the planets to regulate carbon dioxide in order to prevent runaway heating or cooling. Yet for certain Earth-sized planets, it turns out that the gravitational pull of an outer companion planet could help matters.

Gravitational pull can actually generate heat in a process called tidal heating. This process involves the gravitational push and pull of the outer companion planet on its closer-in neighbor. This effect can actually be seen on Jupiter's moons Io and Europa, and could also take place on exoplanets, generating heat.

"When the planet is closer to the star, the gravitational field is stronger and the planet is deformed into an American football shape," said Rory Barnes, the second author of the new paper, in a news release. "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 researchers used computer models in order to see where this effect could occur. They found that tidal heating could happen on older Earth-sized planets in noncircular orbits in the habitable zone of low-mass stars, or those less than one-quarter the mass of the sun.

 The findings reveal that any discoveries of Earth-sized planets in the habitable zone of old, small stars should be followed by searchers for companion planets. This could be a way to help narrow down which planets might host life and could, eventually, lead to the discovery of life.

The findings are published in the journal Monthly Notices of the Royal Astronomical Society.