In the hunt for life beyond the Solar System, several things are key. First, we need to find worlds that are similar in size to our own. Second, they need to be close enough for us to study. And third, they need to pass in front of their star relative to us, so we can study their atmospheres.
With that being the case, the star GJ 9827 just might be one of Kepler’s most important discoveries yet. Scientists have found three super-Earths transiting the star, just 98 light-years away. This makes them prime targets for atmospheric study.
“Our preliminary analysis shows the GJ 9827 planets are excellent candidates for atmospheric observations,” the team, led by Prajwal Niraula from Wesleyan University in Connecticut, writes in their paper. It has been submitted to the American Astronomical Society for publication.
GJ 9827 is roughly 70 percent the size and mass of our Sun. The planets (b, c, and d) were found to orbit the star in 1.2, 3.6, and 6.2 days respectively (a perfect ratio of 1:3:5). The innermost planet, b, has a radius of 1.75 times that of Earth. The middle, c, is 1.36, and the outer planet is 2.1.
It’s thought that 1.5 times the radius of Earth might be the threshold at which planets become gaseous. Thus, not only do these planets transit their star, they might allow us to glimpse how planets evolve – all in one system.
They are the closest planets found by NASA's Kepler mission. While other planets have been found by other telescopes that are closer, mostly by noticing the wobble in the star from the gravity of the planets, these are the closest found to be transiting their star.
“This is one of the best targets for atmospheric characterization, because it's relatively bright,” Niraula told IFLScience. “It's in the top five candidates, according to our calculations.”
We'll be able to see the star's light coming through their atmospheres, analyze its spectra, and thus work out what's in the atmospheres. This is one of the best ways to search for biosignatures of life on other worlds.
These planets are unlikely to be habitable, being far too close to the star and thus far too hot. But Niraula said it's possible they have still retained their atmospheres despite their proximity, just like Venus has done in our own Solar System.
Scientists have already used telescopes like Hubble to study the atmospheres of more distant worlds. That these planets are so close makes them extremely exciting targets not just for Hubble, but upcoming telescopes like the James Webb Space Telescope (JWST).
“It is precisely in these nearest systems where the atmospheric measurements will be the most sensitive to and the question of habitability will be examined in the greatest detail in the decades to come,” the team wrote in their paper.
Our Solar System is a bit of an oddity in that it doesn’t contain any super-Earths, whereas most other systems do. Future studies of GJ 9827, then, seem like a bit of a no-brainer.