Our familiar, warm, yellow sun is a relative rarity in the Milky Way. By far the most common stars are considerably smaller and cooler, sporting just half the mass of our sun at most. Billions of planets orbit these common dwarf stars in our galaxy.
To capture enough warmth to be habitable, these planets would need to huddle very close to their small stars, which leaves them susceptible to extreme tidal forces.
In a new analysis based on the latest telescope data, University of Florida astronomers have discovered that two-thirds of the planets around these ubiquitous small stars could be roasted by these tidal extremes, sterilizing them. But that leaves one-third of the planets – hundreds of millions across the galaxy – that could be in a Goldilocks orbit close enough, and gentle enough, to hold onto liquid water and possibly harbor life.
UF astronomy professor Sarah Ballard and doctoral student Sheila Sagear published their findings the week of May 29 in the Proceedings of the National Academy of Sciences. Ballard and Sagear have long studied exoplanets, those worlds that orbit stars other than the sun.
“I think this result is really important for the next decade of
“The distance is really the key piece of information we were missing before that allows us to do this analysis now,” Sagear said.
Sagear and Ballard found that stars with multiple planets were the most likely to have the kind of circular orbits that allow them to retain liquid water. Stars with only one planet were the most likely to see tidal extremes that would sterilize the surface.
Since one-third of the planets in this small sample had gentle enough orbits to potentially host liquid water, that likely means that the Milky Way has hundreds of millions of promising targets to probe for signs of life outside our solar system.
Reference: “The orbital eccentricity distribution of planets orbiting M dwarfs” 29 May 2023, Proceedings of the National Academy of Sciences.