A third of the most common planets in the galaxy could be in the habitable zone

A third of the planets orbiting the galaxy’s most common stars may be far enough away for liquid water to exist, one of the criteria associated with harboring life.

The data is from a new study conducted by astronomers at the University of Florida, in the United States, published in the journal Proceedings of the National Academy of Sciences (PNAS).

Researchers investigate the characteristics of exoplanets that are around stars smaller and cooler than our Sun. It is estimated that the rest of the planets probably present inhospitable scenarios for the existence of life.

University doctoral student Sheila Sagear says the results offer new avenues for researching planets outside our solar system. “These stars are excellent targets to look for small planets in an orbit where it is conceivable that the water is liquid and, therefore, the planet could be habitable”, says Sheila, in a statement.

Considering that dwarf stars are cooler than our Sun, a planet would need to be closer to receive enough heat to harbor liquid water. However, according to the study, the close orbits leave the planets susceptible to extreme tidal forces caused by the gravitational effect of the star.

In the study, astronomers estimated how oval the orbits of a sample of more than 150 planets are around stars about the size of Jupiter. According to research, an eccentric orbit can lead to a phenomenon called tidal heating. In the process, as the planet is deformed by changing gravitational forces from the irregular orbit, friction leads to heating. At extreme points, the temperature would be so high that it would wipe out the chances of liquid water.

“It’s only for these small stars that the habitability zone is close enough for these tidal forces to be relevant,” explained university astronomy professor Sarah Ballard in a statement.

Kepler data

To estimate the orbits of planets around dwarf stars, the researchers measured the time it took for planets to move across the face of stars. Data from the Kepler telescope, from the US space agency, NASA, and from the Gaia telescope, which measured the distance of billions of stars in the galaxy, were used.

“Distance is really the key information that we were missing before and that allows us to do this analysis now”, said Sheila.

According to the study, 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.

The researchers reckon that the discovery that a third of the planets in the small sample had orbits smooth enough to potentially host liquid water likely means that the Milky Way has hundreds of millions of promising targets for investigating signs of life outside our system. solar.