[LINK] "Dark Matter Heat Could Make Exoplanets Habitable"

[rfmcdonald]

Lisa Grossman's Wired Science article reminded me of a "Earths are over-rated. It's the un-earthly worlds that will shake us to the core.".

In a new paper posted on arXiv.org and submitted to the Astrophysical Journal, physicists Dan Hooper and Jason Steffen of Fermilab in Illinois suggest an exotic internal radiator for cold, rocky planets: dark matter. In certain parts of the galaxy, they say, dark matter could effectively outshine the sun.

“It’s not something that’s likely to produce a lot of habitable planets,” Hooper said. “But in very special places and in very special models, it could do the trick.”

Dark matter is the name given to the mysterious stuff that makes up about 83 percent of the matter in the universe, but generally ignores regular matter. No one knows exactly what dark matter is, but one of the most popular theories says it’s made of hypothetical particles called WIMPs — weakly interacting massive particles — that interact with regular matter only through the weak nuclear force and gravity. WIMPs are also their own antiparticles: Whenever one WIMP meets another, they annihilate each other in a burst of energy.

If those explosions happen inside a planet, they could warm the world enough to melt ice, Hooper and Steffen suggest.

Physicists are still waiting for WIMPs to show themselves by colliding with detectors in deep underground mines. But the fact that the detectors haven’t seen anything conclusive yet puts limits on how heavy and large the particles can be. If WIMPs were bigger or heavier than a certain theoretical limit, physicists reason, the particles would have shown up by now.

Hooper and Steffen considered two possible model WIMPs that interact as often as they possibly can while still being consistent with the experiments, one particle that’s 300 times heavier than a proton and one that’s just 7 times the proton’s mass. Then they calculated how much energy the explosions from colliding these hypothetical dark matter particles would contribute to the planet’s overall warmth.

On Earth, they found, dark matter doesn’t make a difference. Earth lies in a part of the Milky Way where dark matter is relatively thin, so it contributes at most one megawatt of energy to Earth’s internal thermostat. By contrast, the Earth absorbs about 100 petawatts, or 100 quadrillion watts, from the sun.

But in the dark matter-rich centers of galaxies, WIMPs could be a contender. The researchers considered rocky planets that lie within 30 light-years of the galactic center, and found that planets with masses 10 times greater than Earth’s could scoop up enough dark matter to generate 100 petawatts of energy. That could be enough energy to keep liquid water on their surfaces, even without the aid of a nearby star.

These wouldn't be very Earth-like planets, but they would be heated for very long periods of time.