Unveiling Hidden Worlds: Watery Exoplanets Concealed by Invisible Stars
Dwarf stars, invisible to the naked eye, may hide a wealth of exoplanets that contain liquid water and suitable conditions for life, according to a new study. Pale red stars make up about 58 of the more than 100 billion stars in the Milky Way, so the new findings greatly expand the prospects for planet hunting.
Scientists already knew that red dwarfs host planets, but the new study estimates what percentage of their planets orbit in a way that preserves liquid water and the chances of life.
What are the chances of life?
About a third maintain a Goldilocks orbit, according to the study, which is suitable for water. This makes numerous habitable new exoplanets – many hundreds of millions – seen as a past study estimates that each red dwarf boasts an average of three planets.
“This result is really important for the next decade of exoplanet research, because the eyes are turned on this population of stars,” says PhD student and co-author Sheila Sagier in a press release.
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Why focus on red dwarfs?
Astronomers look for red dwarfs in part because they are 3.5 times more likely than solar stars to host planets that are smaller than Neptune and closer to Earth in size.
“These stars are excellent targets for searching for small planets,” Sager said in the press release.
Red dwarfs burn at about 60 percent of the sun’s temperature, so planets with liquid water must stay close to avoid freezing (but not too close). Their orbits also cannot be too elliptical, as eccentric orbits exert tidal forces on the planet and frictionally heat it. As such planets spin around, changes in gravitational forces tear the planet apart, cooking it Jupiter’s moon Io.
How did the survey track down exoplanets?
Astronomers have two main methods to study the motions of exoplanets, the most common of which is the observation of a planet “passing” through or passing in front of a star. The second most common involves studying how planets cause their stars to wobble under the influence of gravity.
For the new study, the researchers examined transit data from Kepler mission, a now-defunct space telescope that NASA launched in 2009 to search for exoplanets. Kepler took repeated snapshots of 150,000 stars, looking for changes in brightness and evidence of planets, until NASA retired it in 2018. During its lifetime, the telescope led to the discovery of more than 2,600 planets, and the new study looked at 150 of them in orbit around red dwarfs.
Analyzing the transits of the planets, they calculated the distance and shape of their orbits and ruled out two-thirds as too hot or cold. A third fall into the liquid water zone, although astronomers cannot confirm that the planets contain water.