To paraphrase the old line about beetles, God sure must love red dwarf stars, because she made so many of them.
About three out of four stars in our galaxy are red dwarfs — “the dim bulbs of the universe,” in the words of Seth Shostak, senior astronomer at the SETI Institute in Mountain View, Calif.
But although these small, relatively gloomy stars are all over the place, they’ve historically been discounted as targets for SETI — the search for extraterrestrial intelligence. Most SETI efforts have looked at larger stars like our own Sun.
The reason has to do with orbital dynamics, geometry and heat. Red dwarfs, with their relatively low mass, have narrow habitable zones as traditionally defined. That’s the Goldilocks orbit in which a planet won’t be too hot or too cold. The precise dimensions of HZs are debatable, but more massive stars have bigger ones. In our own solar system, Venus is too close to the Sun and Mars too far away, but Earth is just right.
A typical red dwarf has a narrow HZ — and it’s so close to the star that an orbiting planet would become tidally locked, meaning one side of the planet always faces the star and the other always is dark. The word on the street is that such a planet couldn’t support life because the daylight side would be roasted and the dark side totally frozen.
But Shostak and his SETI colleagues have a sunnier view of red dwarfs. Yes, the tidal lockage is a bummer, but oceans and atmospheres can do a lot of the heavy lifting in transporting heat from the hot side to the cold side and allowing the planet to retain at least some portion of habitability.
The SETI Institute has put out a press release saying it would use an array of telescopes in California to look at 20,000 red dwarfs.
“Red dwarf stars are not as bad as they first seemed,” Shostak told The Washington Post.
Indeed they have obvious search advantages:
1. They’re close, on average. That’s because there’s so many of them. It’s a numbers game. And close does count, because a (very hypothetical) alien radio signal sent from twice as far away is going to be four times fainter when it reaches Earth.
2. They’re old, on average. The Sun is built to last about 10 billion years, Shostak said. But a red dwarf star can last 100 billion years. The entire universe is only about 13.8 billion years old, but in general a red dwarf is more likely to be ancient than a yellow Sun-like star.
