Are the Red Dwarfs Ready for SETI?
There are oodles of M-type red dwarf stars. Before now, most SETI researchers didn’t pay them much attention, because their habitable zones are narrow. Also, because the habitable zones are closer in, any planets in the lucky radius would most likely be tidally locked to the star, leaving one hemisphere in darkness and the other scorched in ceaseless heat and light – if not sterilized by deadly flares. Those constraints appear to be loosening, according to a SETI Institute article on Space.com.
The advantage of M-type stars is their long life. Presumably, this gives intelligent life more time to evolve and mature. They are also the most common stars. It’s hard for SETI scientists to overlook all that potential real estate, even if not as suitable as the zone around our sun. Edna DeVore, public outreach director for the SETI Institute, wrote:
There’s considerable interest in the question of whether M-Stars could host habitable planets. Would the planets be tidally locked with one face always directed toward the M-Star? Would flares wipe out life on the local planet? If M-Stars could host habitable planets, life may be much more widespread that we’ve previously thought. Thus, M-Stars are of interest to astrobiologists including SETI scientists who are searching for life beyond Earth.
A study just published in the Feb. 2007 Astrobiology journal includes papers from the NASA Astrobiology Program about the habitability of planets around M-type stars. If DeVore’s summary is representative, the papers focused on the long lifetime of the stars as the major reason for exploring their environments. Though their habitable zones are narrow, potential warming from CO2 in the atmospheres of terrestrial planets was considered, and some of the drawbacks and hazards were re-evaluated. This particular issue is free for download at the Astrobiology journal site.
Wishing upon a star does not make SETI dreams come true. Ms. DeVore’s article did not delve into the problems: flares, narrow zones, tidal locking. Notably, she remarked that initial hopes that solar systems would be arranged like ours have been dealt a blow. “We also expected to find solar systems like our own with small terrestrial planets near the star, and larger gaseous planets farther out,” she said. “This particular pre-conception was discarded with the discovery of hot Jupiters on 4-day orbits about their stars.” There’s the fallacy of extrapolating from a sample of one.
Choosing M-Stars as a backup plan, though, may not be a cause for joy. It might turn out like the following hypothetical bad-news, good-news joke. Two pioneers crossing a mountain range hope to live off the bounty of fruit trees on the other side. Upon arriving, the trees that haven’t been destroyed are very few and far between. “But look,” the younger one chimes in, trying to be helpful. “There’s an endless supply of poison oak.”
Research Project: Some of the free papers in the Astrobiology journal deal directly the problems of flares, tidal locking and other habitability issues of M-Stars. Perhaps one of our readers would like to evaluate the claims and see if their hopes are plausible. Keep in mind, though, that finding billions of suitable zones does not imply they have renters. That’s a different question.