An exoplanet about the size of Neptune has been discovered to have clear signs of water vapor in its atmosphere, a rarity among planets that small.

According to Space.com, scientists have typically had far greater luck finding traces of water and water vapor in the atmospheres of planets more similar in size to Jupiter. HAT-P-11b orbits a star in the Cygnus constellation some 124 light years from Earth and would be the smallest exoplanet with traces of water vapor.

"This discovery is a significant milepost on the road to eventually analyzing the atmospheric composition of smaller, rocky planets more like Earth," John Grunsfeld, an assistant administrator of NASA's Science Mission Directorate, said in a news release. "Such achievements are only possible today with the combined capabilities of these unique and powerful observatories."

The scientists were also encouraged to have such a clear view of the planet and hope to get the same kind of visibility with similar exoplanets.

Jonathan Fraine, a graduate student at the University of Maryland, led a new study on HAT-P-11b published in the journal Nature.

"When astronomers go observing at night with telescopes, they say 'clear skies' to mean good luck," he said in the release. "In this case, we found clear skies on a distant planet. That's lucky for us because it means clouds didn't block our view of water molecules."

Though the exoplanet is about the same size as Neptune, it orbits its star at a slightly lesser distance, making a trip around in roughly five days. The researchers determined it must be a warm planet because of its gaseous atmosphere and rocky core.

"Water is the most cosmically abundant molecule that we can directly observe in exoplanets, and we expect it to be prevalent in the upper atmospheres of planets at these temperatures," Fraine told Space.com. "Detecting it is both a confirmation of our theories and revealing for the bulk of the spectrum that we can observe."