News broke a couple of days ago  of the first planet ever found outside our solar system that might actually be habitable:

The estimated equilibrium temperature of GJ 581g is 228 K, placing it squarely in the middle of the habitable zone of the star and offering a very compelling case for a potentially habitable planet around a very nearby star.

Simply stunning. While we know nothing about the actual prospects for life on the planet (and won’t unless we somehow figure out whether there’s water on it or not),  knowledge of a planet that exists in the habitable zone does actually change the picture. We did not have evidence of a single such planet until now. And the fact that it’s a mere 20 light years away means that an unmanned probe that could approach .5 lightspeed would be sending us information about it in 40 years (which would take another 20 to reach us). But let me allow the discovers to explain what the true significance of this discovery is:

That a system harboring a potentially habitable planet has been found this nearby, and this soon in the relatively early history of precision RV surveys, indicates that eta_Earth, the fraction of stars with potentially habitable planets, is likely to be substantial. This detection, coupled with statistics of the incompleteness of present-day precision RV surveys for volume-limited samples of stars in the immediate solar neighborhood suggests that eta_Earth could well be on the order of a few tens of percent. If the local stellar neighborhood is a representative sample of the galaxy as a whole, our Milky Way could be teeming with potentially habitable planets.

In less than two hundred years we may well have humans living on other planets. Does that not blow your mind? In case you need visuals, here’s an artist’s depiction from NASA’s Astronomy Picture of the Day.