Harsh space weather dooms life on red-dwarf planets

Life in the universe might be even rarer than we thought. Recently, astronomers looking for potentially habitable worlds have targeted red dwarf stars because they are the most common type of star, comprising 80 percent of the stars in the universe. But a new study shows that harsh space weather might strip the atmosphere of any rocky planet orbiting in a red dwarf’s habitable zone.

“A red-dwarf planet faces an extreme space environment, in addition to other stresses like tidal locking,” says Ofer Cohen of the Harvard-Smithsonian Center for Astrophysics.

Cohen presented their findings this week in a press conference at a meeting of the American Astronomical Society.

This artist's conception shows a hypothetical alien world orbiting a red dwarf star. Although it is in the star’s habitable zone, this planet faces an extreme space environment that is stripping its atmosphere and generating powerful aurorae. Since they are subjected to such harsh physical conditions, red-dwarf planets may not be habitable after all, so life in the universe might be even rarer than we thought. (Image by David A. Aguilar, CfA)

This artist’s conception shows a hypothetical alien world orbiting a red dwarf star. Although it is in the star’s habitable zone, this planet faces an extreme space environment that is stripping its atmosphere and generating powerful aurorae. Since they are subjected to such harsh physical conditions, red-dwarf planets may not be habitable after all, so life in the universe might be even rarer than we thought. (Image by David A. Aguilar, CfA)

Earth is protected from solar eruptions and space weather by its magnetic field. Just like the shields of the Starship Enterprise, Earth’s magnetic field deflects incoming energy blasts. We also are protected by distance since Earth orbits 93 million miles from the Sun.

Red dwarf stars are smaller and cooler than the Sun. To be in the star’s habitable zone, where the temperature is warm enough for liquid water, a planet would have to be much closer to its star than the Earth is to the Sun. As a result, such a planet would be subjected to severe space weather.

Previous work has looked at the impact of stellar flares from a red dwarf on a nearby planet. In contrast, the new research examines the effect of the red dwarf’s constantly blowing stellar wind. The team used a computer model developed at the University of Michigan to represent three known red-dwarf planets circling a simulated, middle-aged red dwarf.

They found that even an Earth-like magnetic field could not necessarily protect a habitable-zone world from the star’s continuous bombardment. Although there were moments when the planet’s magnetic shields held firm, it spent far more time with weak shields than strong shields.

“The space environment of close-in exoplanets is much more extreme than what the Earth faces,” explains co-author Jeremy Drake (CfA). “The ultimate consequence is that any planet potentially would have its atmosphere stripped over time.”

The extreme space weather also would trigger spectacular aurorae, or Northern Lights. The aurora on a red-dwarf planet could be 100,000 times stronger than those on Earth, and extend from the poles halfway to the equator.

“If Earth were orbiting a red dwarf, then people in Boston would get to see the Northern Lights every night,” adds Cohen. “Oh the other hand, we’d also be in constant darkness because of tidal locking, and blasted by hurricane-force winds because of the dayside-nightside temperature contrast. I don’t think even hardy New Englanders want to face that kind of weather.”

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

 

 

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  • 12rw

    jovian planets have big magnetosphere which can protect there moons hence it doesnt really matter.

  • BioWebScape

    Well there goes the Type I or the Type II’s for those stars. I can’t remember they were guessing( educated of course ) about what was it 50% of them might have planets? So a huge number of Goes flipped to the No Go side. So where will we find the other Folks in the night sky? But the big Jovian like Planets have their own Space noise and even maybe thier own killer space weather locally. I have this feeling that we might be the only ones out here in the space lanes, but even if we aren’t Till we get to the point of not trying to kill ourselves off, and can get to space further than our own solar system it might not matter. Is there anyone out there, the song lines go

  • John Kierein

    Water covered planets could well have oceanic life with water shielding it like on the severe radiation environment of Europa.

  • Java55

    If these close orbiting planets are tidally locked, one would suspect that all the volatiles will have condensed upon the cold unlit side — those which were not stripped off by the stellar winds.

  • alliwant54

    Maybe it will take a higher greenhouse gas content to push the edge of the habitable zone out to where the solar winds are not too violent. Would be nice if the heliopause is not close enough to frequently get compressed until a prospect planet is exposed to the full blast of cosmic rays too. I guess this is just further evidence that long term habitability is no trivial issue; a lot of ways things can go wrong.

  • Liberty Max

    Huge complex data factors about Sun and Earth are extremely unique with probability of zero to form without intelligent power outside our dimension. We shouldn’t be here, yet here we are.

    • AstronomyGuy

      I agree with your statement, but not your upside down US flag.

  • Veni Vidi Vici

    Most super earths are larger, possibly with larger iron cores and combined with a thick Venus like atmosphere maybe life is possible at the farthest edge of the goldilocks zone…

  • alexis

    i think this article is very interesting and important to society so the people know what going on.