For the John Templeton Foundation, I wrote about the innovative quest to uncover habitable planets around M-type stars.
On October 30, 2018, after its maneuvering fuel was finished, the Kepler Space Telescope retired. This date marked the end of its nine-year mission, during which it aided the discovery of 2,662 exoplanets. (The first confirmed exoplanet was discovered only in 1992.) “Kepler broke open the galactic treasure chest of smaller earth-size planets and we learned how common they were,” says David Charbonneau, a professor of astronomy at Harvard University and an expert in planetary discovery. “We now know that exoplanets are incredibly common, that most if not all stars have planets — it’s sort of an inevitable part of making a star. But the actual stars that Kepler looked at were very far away, so it was good for getting population statistics but not actually for providing the very best targets that we could go and study in detail.”
In search of better targets, Charbonneau, together with David Latham at the Harvard-Smithsonian Center for Astrophysics, has launched a new project to look for earthlike planets — and eventually, possible signs of life on them. They are focusing on the most common type of star in our galaxy, so-called M-type stars or red dwarfs, which are between 10 and 60 percent of the mass of the Sun. M-type stars are dim and relatively cool, which makes them harder to observe, but they have other useful qualities for planet-hunters: their lower intensity means that such earthlike planets, which have a rocky surface and liquid water, can have smaller and faster orbits than those in larger star systems. Because most exoplanet detection depends on observing transits when a planet comes between the surface of its star and the observer, the geometry and timing of smaller, faster orbits makes it much easier for astronomers to observe transits and extrapolate data about the planets’ size and density.