by GOVERT SCHILLING
However, Jack Lissauer, a theoretical astrophysicist at NASA’s Ames Research Center in Moffet Field, California, is much more optimistic. Together with Jason Barnes, a physicist at the University of Idaho, Moscow, and John Chambers, a theoretical astrophysicist at the Carnegie Institution’s Department of Terrestrial Magnetism in Washington, D.C., he has carried out large numbers of detailed numerical simulations of “moon-less Earths,” which show that the consequences are less dire than is generally assumed.
That’s because really big changes in a planet’s tilt would occur only after a very long time, so there would be more than enough time for the evolution of life, Lissauer reported yesterday here at the summer meeting of the American Astronomical Society. “The variations in Earth’s axial tilt would indeed be substantially larger if there was no large moon,” Lissauer says, “but really big excursions from the current value would only occur on time scales of billions of years.” That would leave ample time for advanced land life to evolve under relatively stable climatic conditions—although what would happen to such life during an axial shift remains unclear.
When a planet rotates in the opposite direction to its orbital motion (which happens to be the case for Venus), the effect of gravitational perturbations on its spin axis would be even smaller, the simulations indicate. And, of course, if a planetary system contains only one planet, there are no perturbations at all. Nobody knows how common such single-planet system might be.
Not everybody is overwhelmed by the importance of the new results. “I don’t think [changes in a planet’s axial tilt] would be a problem for the development of advanced life,” as any type of life would adapt to changing circumstances anyway, says planetary scientist Sara Seager of the Massachusetts Institute of Technology in Cambridge.
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