A new theory, based on computer simulations, questions whether life-bearing planets really need a galactic habitable zone (GHZ) such as the one Earth occupies (a zone that protects the planet from the usual harshness of space).
Modelling the idea that our sun might be an "immigrant star" from another part of the galaxy, Rok Roskar of the University of Washington and colleagues argue,
"Our view of the extent of the habitable zone is based in part on the idea that certain chemical elements necessary for life are available in some parts of a galaxy's disk but not others," said Rok Roskar, a doctoral student in astronomy at the University of Washington.However, they qualify,
"If stars migrate, then that zone can't be a stationary place."
If the idea of habitable zone doesn't hold up, it would change scientists' understanding of just where, and how, life could evolve in a galaxy, he said.
"Our simulated galaxy is very idealized in the formation of the disk, but we believe it is indicative of the formation of a Milky Way-type of galaxy," he said. "In a way, studying the Milky Way is the hardest thing to do because we're inside it and we can't see it all. We can't say for sure that the sun had this type of migration."In other words, under ideal conditions, there might be more than one type of galactic habitable zone.
Or else perhaps the zone should be thought of as a checklist of necessary conditions rather than a specific place ...
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Note: The image is from NASA, and is an artist's conception of the Milky Way.