When searching for life elsewhere in the universe, it’s a natural inclination to go looking for Earth-like planets capable of supporting Earth-like biology. After all, finding life as we know it is hard, but that’s nothing compared with even imagining life as we don’t know it. But the best candidates for life might be in solar systems very different from our own. As NASA astronomer Elisa Quintana, most famous for the first ever detection of an Earth-sized planet in a star’s habitable zone, explained Saturday at the Star Trek: Mission New York event, the best place to look might be around tiny, dim red dwarfs.
Some of this just comes down to basic math. It’s estimated red dwarfs account for more than 70 percent of the galaxy’s stars, meaning there are a whole lot more of them than there are Sun-like Class G stars. Quintana also pointed out red dwarfs burn for billions, maybe even trillions of years, meaning they give their planets far, far more time to develop than our star’s piffling few billion years. The habitable zones of such dimly burning stars would be much closer than Earth’s orbit, with the whole thing comfortably fitting inside Mercury’s orbit.
Quintana described what life might be like on a planet orbiting such a star, beginning with the fact red dwarfs emit light in the infrared spectrum. “Any life that would form on these planets would have to adapt to a much different environment, living under this infrared light,” she said. “What would the plants look like? We think that maybe you would have planets that are cast in a reddish glow from their sun. But you can also imagine that some plants, because you don’t have all this light, that they’d have to soak up a lot of the light and might even be black. Things would look a lot different than they do here on Earth.”
Being so close to a star, even a relatively small one, would create unique challenges for life on such planets, and we have no way of knowing whether life could survive such hardships. The red dwarf’s gravitational forces would be a particular problem. Quintana described tidal heating, in which the star’s gravity would constantly reshape the planet from spherical to football-shaped as it orbited the planet, with potentially devastating consequences for the planet’s internal heat. Such planets might also be tidally locked, with one side always facing the star and the other always facing away, leaving only a narrow band on the boundary between the two that might be neither too hot nor too cold to support life.
“Planets are thought to form from a disc of material from newly formed stars,” Quintana went on. “And they grow by small rocks colliding and growing, and eventually you have these planets. When you have this process occurring so close to a star, you have things going much faster, you have higher collisions. So maybe a planet can form, but if it accretes an atmosphere or water, it might not be able to maintain it from being bombarded constantly.”
Given all that, the odds might well be low that life — let alone intelligent life — could arise on planets orbiting red dwarfs. But since those stars are so ridiculously abundant in our galaxy, the odds could be low and still plenty of these planets could sustain life. This is particularly worth exploring because, as Quintana concluded, many of our closest neighbors are red dwarfs. If we do have neighbors, even of the microbial variety, they might well have been born in the dim, infrared glow of a red dwarf.