Just when we started getting excited about the habitability of alien planets in our galaxy, pesky old astrophysical research comes along and take us down a peg. Based on models created of planets orbiting in the habitable zones of red dwarf stars, researchers from the Harvard-Smithsonian Center for Astrophysics suspect the chances of them being able to support life are slim. These findings are an especially big bummer since red dwarf stars make up the lion’s share of stars in our galaxy. If their planets can’t be habitable, our chances of finding extraterrestrial life may have just become significantly smaller. The study appeared June 2nd in arXiv.
Before we get into why they may suck to live next to, let’s talk about what red dwarf stars are. Like our sun, red dwarfs are main sequence stars. Main sequence stars are at a period in their stellar evolution where they are converting hydrogen into helium and releasing massive amounts of energy. About 90% of the stars in our galaxy are main sequence stars.
One difference between red dwarf stars and stars like our sun is that red dwarfs are much smaller. Red dwarf stars are categorized by having a mass that is anywhere between 50% and 7.5% the size of our sun and emit as little as 0.1% as much energy. Both characteristics give red dwarfs a dim glow and relatively chilly core temperatures: 5,000 degrees Fahrenheit. Comparatively, our sun’s core burns at around 27 million degrees Fahrenheit. But stars like ours aren’t even close to the most massive on the galactic block. That title belongs to “hypergiants”–stars which can be over 100 times bigger than our sun and emit hundreds of thousands of times more energy.
Despite their small size, red dwarfs are far more numerous than stars like our sun, making up 80% of the stars in the Milky Way galaxy. They also live longer. The low temperature of red dwarf stars means that they burn through their hydrogen more slowly. Stars like our sun live to around 10 billion years old, but red dwarfs can live for trillions of years.
The binary Gliese system consists of two red dwarf stars. Gliese 623b is right of center.
For the cooler red dwarfs to support life, their orbiting planets would have to be much closer to be considered residents of the “habitable zone.” The habitable zone is the section of a solar system far enough away from its sun that a planet’s water wouldn’t boil away and close enough that a planet wouldn’t freeze. If a system has a big sun, the habitable zone can be further away. If the system has a smaller sun, a planet would need to snuggle up with it to stay in that liquid-water friendly region. The latter is the case with red dwarf systems, but it poses some problems for their planets’ practical habitability.
Being that close to a sun means getting hammered with solar wind.
To simulate the effect of solar wind on nearby planets, researchers simulated what would happen to three planets circling in the habitable zone of a middle-aged red dwarf star. In short, they found that life would be screwed. Since these red dwarf planets don’t have the same kind of strong gravitational field that we have here on Earth, their atmospheres would probably be blasted away into space. Researchers suspect that even if these red dwarf planets did have a sturdy gravitational shield like ours, their proximity to the star would still make the weather less than favorable.
“The space environment of close-in exoplanets is much more extreme than what the Earth faces,” explained study co-author Jeremy Drake in a press release. “The ultimate consequence is that any planet potentially would have its atmosphere stripped over time.”
Despite the dangers of solar radiation, it doesn’t eliminate the possibility of life altogether. “We state that these planets may not sustain an atmosphere. We do not claim that [this makes] them uninhabitable but it would have to be a life form that is very different than that we expect based on the assumption that we need liquid water for life,” study author Ofer Cohen told Nerdist in an email. “We find extreme life forms on Earth in places and form we did not expect.” Indeed, with critters like those living around deep sea vents and in geothermal areas of Yellowstone National Park, we’d be unwise to hastily assume life couldn’t hack in it in a given harsh environment.
Researchers enthusiastically pointed out another interesting fact about red dwarf planets in their press release: these planets would have some killer auroras. Researchers say that the auroras on a red dwarf planet would be 100,000 times more powerful than those on Earth. “If Earth were orbiting a red dwarf, then people in Boston would get to see the Northern Lights every night,” added Cohen.
Imagine catching a night game at Fenway under the spectacular glow of the not-so-northern lights…