How often the Universe has planets truly like the earth - true earth twins, planets the size of the earth, rocky planets with a surface that supports liquid water - well, we don't have that number yet, but I'm optimistic we'll figure it out.

BBC: From counting to characterising exoplanets

The severity of the laboratory test was equivalent to an oblique collision with the rocky surface of the Earth - a comet coming in at an angle of less than 25 degrees from the horizon, rather than head on (perpendicular to the Earth's surface).

BBC: Comets could have seeded life on Earth

Neutrons ejected from a watery surface move much more slowly than those from a rocky one, because the hydrogen nuclei in water are light enough for an exiting neutron to knock around much like one billiard ball hitting another a process that slows the neutron down.

ECONOMIST: Divining water

On Thursday, NASA released a sweeping color panorama of the planet's surface, showing the rocky, reddish desert surrounding it and the mountain it will explore in the coming months.

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It's unlikely any aliens call Kepler-37b home: it's thought to be rocky, with no atmosphere, and hugs its sun in a 13-day orbit cycle, meaning surface temperature is terribly high.

ENGADGET: NASA's Kepler telescope spies smallest planet to date, no aliens