The Five Ages

The current state of the distant future

Archive for April 2011

Degenerate Era plate tectonics

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Reporters were calling me last week about a paper that turned up on astro-ph, Dark Matter and the Habitability of Planets, by Hooper and Steffan.

Their thesis is that in regions where the density of non-baryonic dark matter is high, an abundance of dark matter particles scatter off the nuclei in the planetary interiors, and get trapped inside a planet, where they wheel on rapidly precessing orbits through the near-transparency of the rocky firmament. Weakly interacting dark matter likely constitutes its own anti-particle, and so when trapped WIMPS encounter each other, they annihilate, producing heat. In The Five Ages, we drew on this process to keep the white dwarfs and the neutron stars shining weakly through the dark expanses of the Degenerate Era.

In Hooper and Steffan’s picture, WIMP annihilation isn’t wimpy at all. In fact, they lean on the process to produce enough heat to keep the water liquid and the planetary surfaces habitable, even in the absence of a parent star.

Sounds like a long-shot to me, but where the WIMP annihilation mechanism might be quite useful is in powering geological activity for the duration. There are plenty of potentially habitable planets orbiting low-mass M-dwarf stars which have staggeringly long main-sequence lifetimes. The long-term habitability hitch for the planets orbiting these stars is not the loss of stellar radiation, but rather cooling of the planetary interior and the attendant shut-down of mantle convection. A cold planet like Mars doesn’t maintain a dynamo, it has no magnetic field to speak of, and its atmosphere is therefore subject to the ravages of solar coronal mass ejections. It’d really be quite nice if WIMP annihilation could keep things ticking long after the heat of formation and the heat of radioactive decay have e-folded into oblivion.


Written by Greg Laughlin

April 4, 2011 at 12:01 am

Posted in Uncategorized