Did you ever ride a Tilt-A-Whirl, one of those cheap carnival rides that makes you dizzy and sick?  Our planet would be like that (in slow motion) if its inclination were out of control.  Without tilt stability, a new study reveals, we wouldn’t be sick, we’d be dead, or never alive in the first place.   It’s not enough to be in the Habitable Zone.  Would-be inhabited planets need to avoid a new problem, called “tilt erosion.”

The new constraint on habitability is described in an article by Adam Hadhazy on NASA’s Astrobiology Magazine, “Loss of Planetary Tilt Could Doom Alien Life.”  Astronomers considering the factors needed to sustain life already knew that inclination was important.  They knew that it provides for alternating seasons, distributing the temperate zones so that the equator is not eternally hot and the high latitudes eternally frozen.  They also knew that red dwarf stars (the majority of stars), with their narrower habitable zones closer in, tend to tidally lock one face of a planet toward its star, dramatically reducing its habitable real estate (2/09/2006).

The new study by René Heller, a postdoctoral research associate at the Leibniz Institute for Astrophysics in Potsdam, Germany, shows that stable inclination is far more important for life than previously assumed.  Cheerful astrobiologists envisioning life everywhere are going to have to worry about this new constraint; “The findings do not bode well for planets residing in the habitable, or ‘Goldilocks’ zones around red stars smaller than the Sun,” the article said.  Here’s a summary of Heller’s findings and the implications:

  1. Time limit:  “According to computer simulations, red dwarf stars quickly erase the axial tilt of habitable, Earth-like exoplanets. This temperature-moderating tilt is nullified in such a short time that life may never have a chance to get going.”
  2. Far out:  Habitable planets around sun-like stars suffer far less tilt erosion.  So far, so good – provided they have at least 5 degrees of tilt.  If not, watch out:
  3. Gasping for air:  “In theory, bands of habitability in temperate, mid-latitude zones could persist. In a worst-case scenario, however, the entire atmosphere of a zero-obliquity planet could collapse, Heller said. Gases might evaporate into space around the planet’s blazing middle and freeze to the ground in the bleak north and south.  Life, had it ever emerged, would be stopped dead in its tracks.”….

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