Astronomers have reached a milestone in the search for potentially habitable planets by discovering water vapor on a planet over 700 trillion miles away from Earth.

This planet, dubbed, HAT-P-11b, is the smallest planet yet we've been able to analyze for chemical composition. Previously, small planets like this one have a lot of cloud cover, making analysis of their atmospheres and composition nearly impossible. Hat-P-11b, though, has nothing but clear skies, making such a reading possible.

Why is detecting water on other planets so important? Water is one of the key ingredients for the basis of life, at least as we know it. Planets with water are potentially more habitable and could have both the ability to host life and sustain it.

Hat-P-11b is five times bigger than Earth, with a gaseous atmosphere, similar to Neptune in our Solar System. It's also close to its sun, so much so that it's temperature is around 1,100 degrees Fahrenheit. This suggests that Hat-P-11b probably doesn't host life, but the discover of water vapor in its atmosphere is still an important one.

"Eventually, we'll be able to study smaller, Earth-like planets, but if we can pin down the properties of larger planets and perfect our observing techniques, we'll be ready," says Knicole Colon, an astronomer at Lehigh University in Bethlehem, Pennsylvania.

The previous method of finding evidence of water on a planet involves something called "transiting." This happens when a planet moves in front of its star. This process gives off light around the planet. A powerful telescope's spectrometer measures the light and searches for a particular signature within it that denotes the presence of water.

This method works well with large planets, but not so much with smaller ones, many of which have cloudy atmospheres around them. And finding water on smaller planets is key because we're looking for planets similar to Earth's size.

However, fortunately for astronomers, two telescopes working together, the Hubble and Spitzer Space Telescopes, picked up Hat-P-11b's water vapors, thanks to the planet's clear skies. That means we may soon discover other planets of similar size with clear skies, perhaps more potentially habitable than Hat-P-11b.

"We need to find, like, 20 more of these before we're happy," says Jonathan Fraine, one of the study's authors. "The great thing is that now we know that clouds aren't blocking all of the light on every single one of these planets."