Hundreds of millions of planets in galaxy could be habitable, study finds

A third of the most common planets around small stars throughout the galaxy could be in conditions that could hold liquid water and likely support life. We are potentially talking about hundreds of millions of planets. This is described in a study by astronomers at the University of Florida, writes Phys.org.

Astronomy professor Sarah Ballard and doctoral student Sheila Sagear published their findings in the journal Proceedings of the National Academy of Sciences. They have long studied exoplanets – worlds that revolve around stars other than the Sun.

During the study, astronomers measured the eccentricity of a sample of more than 150 planets around M dwarf stars, which are roughly the size of Jupiter. The more oval the orbit, the more eccentric it is.

If a planet orbits close enough to its star, at about the distance that Mercury orbits the sun, an eccentric orbit can subject it to a process known as tidal heating. As the planet is stretched and deformed by changing gravitational forces on its irregular orbit, friction heats it up. At the extreme end, this could bake the planet, removing all chance for liquid water.

Data came from NASA’s Kepler telescope, which captures information about exoplanets as they move in front of their host stars. To measure the planets’ orbits, Ballard and Sagear focused especially on how long the planets took to move across the face of the stars. Their study also relied on new data from the Gaia telescope, which measured the distance to billions of stars in the galaxy.

“The distance is really the key piece of information we were missing before that allows us to do this analysis now,” Sagear said.

Experts have found that stars with several planets most likely have circular orbits that allow them to hold liquid water. Stars with one planet are most likely to experience extreme tides 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.

It was previously reported that scientists discovered a rocky planet named LP 791-18 d which is Earth-sized with some extreme features. The planet’s elliptical orbit causes it to deform slightly each time it passes close to the dwarf star, creating friction within the planet. This can cause volcanic activity over its entire surface.