PSR B1257+12: Deadly Pulsar Could Still Support Planetary Life

An artist's depiction of a pulsar, at right, and its exoplanet. Institute of Astronomy, University of Cambridge

Scientists think that planets may be able to stay friendly to life even around the most violent, deadly stars we know of, according to a new study published in the journal Astronomy & Astrophysics.

Those stars are pulsars, so-called "stellar corpses" that form under special conditions when a star runs out of fuel and explodes in a supernova. Pulsars get their name because from Earth, they appear to pulse—a phenomenon caused by the star spinning along one axis as it shoots out powerful streams of particles like a two-way searchlight along another axis. In addition to this dangerous radiation, pulsars also produce heavy so-called winds of highly charged electrons.

Even a relatively tame star like our sun can be just as hostile to life as it is hospitable: If it weren't for our atmosphere blocking the worst of the ultraviolet light that gives us sunburns, our DNA would rack up more mutations and damage too quickly for our cells to repair it.

So scientists had pretty much written off exoplanets orbiting pulsars as far too harsh an environment for life to survive. But in the new paper, a pair of European astronomers revisit that assumption and suggest that with the right size and the right atmosphere, a planet could still host life.

There aren't a whole lot of pulsars with planets around them, but there are a handful, including the pulsar PSR B1257+12, which is home to the very first two exoplanets scientists ever spotted. In the new paper, the scientists focused on these two planets, which are each about three times the mass of Earth, and their tiny cousin that's just 2 percent the mass of Earth.

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A cocooning atmosphere protects its planet by absorbing radiation and turning it into heat, which usually stays at whatever level of the atmosphere at which it is created. The more energetic a particle of radiation is, the deeper it can usually slip into an atmosphere.

The researchers behind the new paper calculate that pulsar planets could survive their host's violent outbursts if they are equipped with atmospheres about a million times as thick as Earth's. In order to hang on to that atmosphere, they would also need to be at least as large as Earth but no more than 10 times as massive.

That magical combination, the researchers calculate, would put the two larger planets around PSR B1257+12 in the habitable zone, where water at the planet's surface would remain liquid rather than freezing or boiling away. And with 200,000 known pulsars in the Milky Way, that's a lot more potential alien suns for scientists to study.