What would an Earthlike exoplanet look like up close?S

Once upon a time it was big news when any planet outside our solar system was discovered. Now the search is on to find Earth-like exoplanets... and such planets are being discovered on a regular basis.

Of course, this does depend somewhat on how one defines "Earth-like". It doesn't always mean a pleasant little blue ball like our own. To an astronomer, it might be enough that the planet is solid instead of being an enormous gas giant like Jupiter. So an "Earth-like" planet might still be a sterile, red-hot sphere of iron and rock three or four times larger than our planet. Earth-like, maybe — but not picnic, either.

But they keep coming closer to the mark. One of the nearest to hit the bull's eye is HD 85512b.

It's 3.6 times the mass of the Earth and orbits an orange dwarf star... but at just the right distance so that liquid water might exist there. The relative coolness of its star is balanced by the planet orbiting closer to it than the Earth does the Sun...at roughly the distance of Venus. Even better yet, HD 85512b has a nearly circular orbit, so it's not bothered by radically changing temperatures, and HD 85512, the star, is a peaceful one, sparing the planet the tempests of disruptive solar storms.

Astrophysicist Lisa Kaltenegger and her colleagues believe that HD 85512 is potentially habitable. If it has at least a 50 percent cloud cover—-to provide the proper greenhouse effect—-it would be perfectly suitable for life. Since the Earth averages 60 percent, this isn't an unreasonable expectation. For these reasons, Kaltenegger and others think that HD 85512 is not only a candidate for habitability, it's the best one found to date.

What would an Earthlike exoplanet look like up close?S

So, what, I wondered, might a future visitor find there? A warm world, I think, with a sky filled with heavy water vapor clouds. There'd be water, perhaps in abundance, but the waves in the lakes and seas would be dampened by a gravity half again greater than Earth's. I didn't really want to speculate on life, so to bring a little liveliness to the scene I thought it not unreasonable to feature a hot spring, pouring mineral-laden water into the sea and warm water vapor into the atmosphere.

Read more about HD 85512 via Arxiv