Astronomers have spotted water vapor and evidence of exotic clouds in the atmosphere of an alien planet known as HAT-P-26b.

The researchers also determined that HAT-P-26b's atmosphere is dominated by hydrogen and helium to a much greater degree than that of Neptune or Uranus, the alien world's closest counterparts in our own solar system in terms of mass.

"This exciting new discovery shows that there is a lot more diversity in the atmospheres of these exoplanets than we have previously thought," David Sing, an astrophysics professor at the University of Exeter in England, said in a statement. [Gallery: The Strangest Alien Planets]

"This 'warm Neptune' is a much smaller planet than those we have been able to characterize in depth, so this new discovery about its atmosphere feels like a big breakthrough in our pursuit to learn more about how solar systems are formed, and how it compares to our own," added Sing, the co-leader of a new study about HAT-P-26b that was published online today (May 11) in the journal Science.

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