Earth from Saturn

I should have posted this for Earth Day. It’s a spectacular photo taken by Cassini from next to Saturn. The little dot outside the main rings on the right is Earth, and the top left is a zoom-in of the planet.

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Just a little more astronomy

This is a bit much astronomy for a primarily biology blog, I know. Unless something great pops up, this will be the last astronomy post for at least a little while.

Some new research into the tidal forces of stars and their planets has yielded some interesting results.

Planets around small mass stars may only have a billion-year window during which life can form. This is the implication of research into the tidal forces that can pull a planet into a tighter orbit around a star.

The so-called habitable zone around a star is loosely defined as planetary orbits in which water would be liquid, not vapor or solid, on the planets’ surface. These orbits are closer-in for smaller (less bright) stars.

However, habitability is not a permanent property of a planet.

“For some planets around low mass stars, they are not going to hang around in the habitable zone forever,” says Rory Barnes of the Lunar and Planetary Institute at the University of Arizona. “They are going to be pulled out.”

The pulling is due to tidal forces that arise because the gravitational attraction between planet and star is not uniform over their surfaces.

Barnes and his colleagues have shown that the tidal forces around a small mass star can draw a planet from the habitable zone on the order of a billion years, as reported in a recent issue of Astrobiology Journal.

If some of these migrating planets can be detected, they could provide a test of the Gaia hypothesis, which says that life can force changes to a planet in order to keep it in a habitable state.

So basically life may only have a 1 billion year window to form. That certainly isn’t the case across the board since this research applies specifically to low mass stars. But is it at all surprising that life on Earth originated somewhere between 200 million and 1,000 million years ago, i.e., within the first billion years of the planet’s existence?