A Neptune-sized exoplanet, which lies some 729 trillion miles away (122 light-years), has water vapor in its atmosphere. While it's a promising sign for astronomers in search of distant life, exoplanet HAT-P-11b with its water-filled atmosphere is not the kind of place you'd want to live -- or where anything could live.

The water in the planet's atmosphere is scaldingly hot, existing at a temperature of over 1,000 degrees. Furthermore, there's no solid surface where water or life could rest; HAT-P-11b is a big ball of gas with only a small solid core.

Nonetheless, scientists are encouraged by their new discovery, as it's the smallest exoplanet whose atmosphere astronomers have been able to observe. Scientists have found water in the atmospheres of other gas giants, but smaller planets typically have cloud cover too thick to allow scientists to understand what's going on.

Water vapor, as well as any other atmospheric molecules, absorbs specific wavelengths of light but not others. Scientists can therefore analyze the rays of light passing from a planet's host star through the planet's atmosphere in order to detect the presence of water vapor.

That is, as long as satellite telescopes can pick up the light rays, and the new study into the atmosphere of HAT-P-11b is proof that they can.

Lead researcher and University of Maryland astronomy professor Drake Deming says discoveries like this aren't just about finding water or the potential for life, but understanding how faraway planets and solar systems form and evolve.

"Our ideas about the formation of planets have been developed to match our solar system," said Deming, "and we don't know whether other planetary systems behave the same way. We want to test the fundamental question of whether small planets are rich in heavy elements, like the oxygen in water vapor."

The work of Deming and his research team is detailed in the latest issue of the journal Nature.