Twin Alien Planets Could Boost Chances for Extraterrestrial Life

Alien planets could host life well into their old age if they have companion worlds tugging at them, researchers say.

Such exoplanets could potentially be the longest-lived life-friendly areas in the universe, enduring for up to 10 trillion years, scientists added.

As planets age, they cool, with their hot molten cores solidifying over time. This probably makes them geologically active and therefore less habitable for life as we know it, scientists say. On Earth, life depends on the geological activity of plate tectonics to circulate rocks that can absorb or release carbon dioxide, a greenhouse gas that absorbs heat. Without plate tectonics, the planet might experience runaway heating or cooling, and thus potentially become uninhabitable.

In a new study, scientists have found that if a world has a companion planet that gravitationally tugs on it, this could prevent that world from cooling, and thus extend its chances of hosting life.

Strange twin worlds

The researchers analyzed red dwarfs stars, also known as M dwarf stars. These stars are up to 50 times dimmer than the sun and up to less than 10 percent as massive. Red dwarfs are the most common kind of star, making up to 70 percent of the stars in the universe, and this fact has made scientists wonder if these red dwarfs might be the best places to look for alien life.

Because there is life nearly wherever there is water on Earth, scientists typically define planets as potentially habitable if their surfaces are warm enough to sustain water on their surfaces. Red dwarfs are cold stars, which means their habitable zones are closer than Mercury is to the sun — sometimes less than 0.1 astronomical units (AU), or one-tenth the average distance from Earth to the sun. The average distance between Earth and the sun is about 93 million miles (150 million kilometers).

Red dwarfs are colder than the sun, which means they burn fuel more slowly and live far longer. Prior research has suggested that the most readily discoverable Earth-size habitable-zone planets are likely to be about 10 billion years old — more than twice the age of 4.6-billion-year-old Earth.

Ordinarily, plate tectonics ends due to cooling long before a planet reaches 10 billion years in age. However, the researchers found that if this old world has a companion planet orbiting a bit farther away from the star, this outer planet can pull the old world into an orbit that will keep it warm enough for plate tectonics.