Astronomers have discovered a type of exoplanet called a “super-Earth” located in the habitable zone of its small star, and it’s right in our cosmic backyard, just 137 light-years away. The planet, named TOI-715 b, is intriguing to astronomers who are increasingly interested in the possibility of habitable planets orbiting stars quite different from our sun.
Although it might seem to make sense to look for potentially habitable planets when looking for Earth-like planets orbiting sun-like stars, those aren’t the only targets that astronomers are interested in. One issue is that most discovered exoplanets are much larger than Earth, partly because it is so hard to detect smaller planets. Another issue is that the most common star in our galaxy by far is not a yellow dwarf star like our sun, but a smaller, dimmer, redder type called a red dwarf. When researchers discover rocky planets orbiting around red dwarfs, a few of which have been identified to date, that increases the pool of potentially habitable worlds that could be out there.
As red dwarf stars give off much less heat than stars like our sun, the habitable zone around them is tighter. The habitable zone refers to the distance from a star at which water could exist as a liquid on a planet’s surface — i.e. when the planet’s surface temperature is between 0 and 100 degrees Celsius. However, it takes much more than being in the habitable zone for a planet to be truly habitable. Other facts are important in determining habitability, like how much atmosphere the planet has, how much radiation it receives from its star, and whether it has a mix of oceans and land.
This particular exoplanet is located right in prime territory of its star’s habitable zone. It orbits the star in just 19 days, sitting right close to it. That helped astronomers to discover the planet because it frequently passes in front of its star as seen from Earth. That was how the NASA spacecraft Transiting Exoplanet Survey Satellite, or TESS, was able to identify it.
At around one and a half times the diameter of Earth, it is the smallest planet in the habitable zone discovered by TESS so far. To learn more about whether it is,, in fact,, habitable, astronomers need to use another tool, such as the James Webb Space Telescope, to observe its atmosphere and see if it can detect water there.
The research is published in the journal Monthly Notices of the Royal Astronomical Society.