The new study considers how other exoplanets in a red dwarf solar system might keep the geophysical fires lit inside of a habitable planet, courtesy of the influence of gravitational tides.
If a habitable planet were kept in an elliptical orbit around its star, owing to the gravitational tugging of another planet sharing its solar system, the star could warp the habitable planet’s shape.
Unlike oval-shaped elliptical orbits, which subject their planets to varying gravitational forces and thus tidal heating, circular orbits translate to a constant gravitational influence, and therefore no tidal heating.
“If another planet’s gravitational effect keeps the habitable-zone planet on a slightly eccentric orbit, that would promote internal tidal heating,” said Greenberg. The team looked for what combinations kept the habitable zone planet in a range of internal heating levels that were neither too nor hot nor cold. The Earth-like planet’s tidal heating could vary over time owing to the convoluted gravitational interactions of its planetary neighbors.
Our various SETI efforts, such as listening for radio transmissions or searching for signs of life in exoplanetary atmospheres, might want to focus on habitable worlds with outer planets around ancient red dwarfs.