Astrobiology Hopes Dim with Exoplanet Findings
Harsh “space weather” around dim red dwarf stars may make planets uninhabitable. “Godzilla Earths” may not fare much better.
“Life in the universe might be even rarer than we thought,” begins a Harvard press release. That’s because the weather on most planets is awful:
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 (CfA).
This is not really news; it’s been worried about before, and was mentioned in the film The Privileged Planet. What’s new is a model that explores the impact of stellar winds on a potentially habitable planet around a known red dwarf star, one that is medium sized.
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.
Earth’s magnetic field protects our home from the sun’s wind and flares, but our sun is a G-type star. M-type red dwarf stars are the most plentiful. Because of the lower temperature, a planet around an M star would have to be closer to the star, and therefore more exposed to the onslaught of charged particles. Being closer to a star also creates stronger tides that would force the planet into tidally locking, with one hemisphere always facing the star. If it’s any consolation, dying aliens would be treated to aurorae 100,000 times stronger than those seen on Earth.
“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.”
The “Godzilla of Earths” is a name given to a new class of giant rocky planets announced by Space.com, with Kepler-10c being the first representative. “Super Earths” a few times larger than our planet are known (see PNAS), but this one is about 17 times bigger than Earth. These giant planets were not thought possible: according to planetary formation theories, larger planetesimals should have gathered gas and become gas giants. Surprisingly, Kepler-10c appears to have no atmosphere, even though it’s massive enough to have held onto one since its inception. According to the PNAS paper, most super-Earths (or mini-Neptunes) show the presence of an atmosphere.
Astronomers inferred from its mass that Kepler-10c is rocky, not gaseous. It orbits its star every 45 days, making it too close to its host star to be habitable. That isn’t stopping some from speculating about life.
How you could cook up life on hot rocks without water was not explained by Dr. Sasselov. News sites like Fox News that republish these stories don’t ever seem to ask those kinds of questions. PNAS admitted of known super-Earths, “we remain ignorant of the origins of, and existence of, exobiology, leaving the location of the habitable zone uncertain.”
What SETI said
Space.com also announced that SETI researchers are intensifying their searches for alien radio signals coming from earth-class planets discovered by the Kepler spacecraft. Result: “no alien transmissions detected” so far.
Diamond in the sky
There may be many planets made entirely or partially of diamond, Yale News says. Unfortunately, it’s unlikely anyone would live there to enjoy them. Diamonds might even be boring on a planet where that’s all there is to look at.
Studying stars and exoplanets is exciting and worthwhile; we have a lot of data about extrasolar planets now. But there is zero data about life on any of them. If you have no data, you have no science; you only have imagination, wishing, and dreams. If they find a perfect Earth-like exoplanet in its star’s habitable zone, with an atmosphere, will that make astrobiology a science at last? No; it will prove an Earth-mass planet exists in an orbit around a star where water might exist in a liquid form. Habitability is not the same as habitation, any more than prime vacant real estate is the same thing as a city. Oh, but if an alien signal is detected, what then? It will prove intelligent design.