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Tuesday, July 02, 2013

60 billion terrestrial planets oribiting Red Dwarf stars?

What this means is that un-Sol-like suns are hosting earth-like worlds. Worlds similar to our own, with of course the necessary distinct differences orbit suns very different from our own sun.

Astronomers theorize that red dwarfs, which make up 75% of all main sequence stars in our galaxy, feature circumstellar habitable zones (HZ) that are considerably more interior than those of G stars (of which our sun is one). And in fact, owing to the low energy output of these stars, their HZs are about as close as Mercury is to our sun. But it’s within these sweet spots that water can remain in its liquid state — an important precursor to life.



Previous estimates have suggested that there may be as many as 4.5 billion potentially habitable planets in orbit around red dwarfs in our galaxy. But earlier this year, data from the ESO’s HARPS planet finder indicated that upwards of 40% of all red dwarf stars have a super-Earth orbiting in the HZ. This upped the number to tens of billions of such planets. What’s more, astronomers believe that virtually every red dwarf is host to at least one terrestrial planet.
And now, owing to a new calculation of the influence of cloud behavior on climate, the number has been extended even further, reaching 60 billion habitable zone planets. And the reason for the latest revision has to do with a newfound sense of the size of red dwarf habitable zones — a zone that’s now much larger, and more interior, than previously thought.
As noted, red dwarf HZs are very interior. These close orbits cause planets to be tidally locked with their sun (i.e., the same side of the planet always faces the parent star, much like how our moon features a side that always faces Earth).
Mind you that the planets' apparently don't revolve is a tad hard for me to envision. "Tidally locked" sounds like a frightening state of affairs.

The author makes this point in the comments:
Studies of exoplanetary "habitability" typically combine chemistry with astronomy to determine whether or not water can exist in liquid form. There's virtually no biology being done further than that. Consequently, the term "potentially habitable" almost always needs to be take with a considerable grain of salt.

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