Astrobiologists give Earth at least 1.75 billion years before Earth becomes uninhabitable

According to a new study published in the journal Astrobiology, we have a minimum of 1.75 billion years before the Earth becomes uninhabitable, and if we can make it out of the solar system before then, the 'super-Earth' planet Gliese 581d would be a great place to relocate.

With all the planets that astronomers have been spotting orbiting around other stars, there's been a lot of talk about a star's 'habitable zone' . This is the band of space surrounding a star that's kind of a 'Goldilocks zone', where the temperature is just right — not too hot or too cold — so that a planet could have liquid water. A planet being in this habitable zone doesn't guarantee that it's going to have life on it, but we have a pretty good example of that with our very own planet, Earth.

You might think that since Earth is teeming with life that we're right smack-dab in the middle of our Sun's 'Goldilocks zone', but we're not. Looking at the image to the right, whether we use a more 'forgiving' version of the zone (light green) or a more 'restrictive' one (dark green), either way Earth is closer to the inner edge of it. It's obvious that we're in a good position right now, of course, but according to the latest research, it's not always going to stay that way. This is because the position of the 'Goldilocks zone' depends on the output from the star, and that changes as the star ages.

As our sun gets older, it will get hotter, and this will push its habitable zone further out. Somewhere between 1.75 and 3.25 billion years from now, the zone will move far enough outward that Earth will slip out of its inner edge. Our home planet, whatever state it's in at the time, will heat up to the point where all the liquid water will boil off the surface. Given that the age of our planet is around 4.5 billion years, that means that the minimum length of time that Earth is habitable — at least to us or life forms like us — is over 6 billion years.

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That's pretty good, given that some planets out there aren't as lucky. Kepler 22b, a 'super-Earth' planet orbiting a star about 600 light away, apparently has roughly 6 billion years, at the most. We're apparently not sure yet how old this planet is, so there's no telling how much longer it has from now, but there are others that are even better off that are probably worth focusing more attention on.

Another 'super-Earth' called Gliese 581d is probably the best one. It orbits a small, cool star that's only around 20 light years from here (so right in our local neighbourhood), and it's expected to be habitable for at least 40 billion years! Since that's nearly three times the current age of the universe, it'll still be habitable when Earth is a burned-out cinder!

So, if we're still around at the time, we might want to check in to see if our neighbours can put us up for awhile.

(Images courtesy: National Science Foundation/Zina Deretsky, Wikimedia Commons)

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