2023-06-03 12:07:06
New research indicates that most of the stars in our Milky Way are M-class known as red dwarfs. Red dwarfs are smaller and redder than the sun, and many of them may be able to host life.
A new analysis of data from the planet-hunting Kepler mission has found that a third of planets around red dwarfs could be habitable, meaning there are hundreds of millions of habitable planets in the Milky Way alone.
For the analysis, astronomers at the University of Florida collected new data from the European Space Agency’s Gaia satellite, which precisely measures the distances and motions of stars, to fine-tune measurements of the orbits of exoplanets.
For each orbit, the scientists wanted to determine an indicator called the eccentricity (or eccentricity), which measures the length of a planet’s path around its star.
“Distance is really a key piece of information that we missed previously that allows us to do this analysis now,” University of Florida astronomy graduate student Sheila Sager and lead author of the study said in a statement.
Planets around red dwarfs with large eccentricities — extremely long elliptical orbits — redden the star if they are close enough, in a process called tidal heating.
Tidal heat is caused by the planet’s wobbly orbit, causing gravitational expansion and contraction of the star. Just like rubbing your hands together, all of these motions create frictional heat.
If there is too much heat, the planet will lose water, along with the potential for life on its surface. Because it is essential to life as we know it, water in general is at the center of the search for habitable worlds beyond Earth.
If a planet orbits a red dwarf, that distance might prevent tidal warming, but then the planet would be too cold and not warm enough for life.
Therefore, exoplanets around red dwarfs must live close to their stars to have a chance of getting hot enough for life, which puts them at risk of tidal overheating if their orbits are not perfectly circular.
“Only for these young stars is the habitable zone close enough for tidal forces to be relevant,” Sarah Ballard, a University of Florida astronomer and study co-author, said in the post.
With their new and improved measurements of the large number of exoplanets detected by the Kepler space telescope, Sager and Ballard found that two-thirds of the planets around red dwarfs are affected by the heat of their host stars, burning their chances of life.
But that would put a third of the planets in the so-called Goldilocks Zone, where liquid water could theoretically exist — along with the possibility of life.
The team found that star systems with multiple planets are more likely to have circular orbits that allow them to hold liquid water. Stars containing more than one planet are thought to be subject to strong tidal forces that remove the effects of biofluids, and the findings are published in the journal PNAS.
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