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NASA's Space Place

Clear Skies in Cygnus

Alex H. Kasprak
National Aeronautics and Space Administration

When astronomers set out to use an observatory or telescope on the surface of our planet, they are always hoping for a clear sky. How else are they going to see through those clouds and into space? That’s a big benefit of orbiting telescopes like the Hubble Space Telescope. Since they are already in space—well above the clouds—they aren’t affected by Earth’s weather.

Why then, you might ask, would a group astronomers using three orbiting space telescopes worry about cloud cover? Simple: It’s not Earth’s clouds they worry about. Instead, it’s the clouds of planets in faraway solar systems. These planets are called exoplanets.

One planet, named HAT-P-11b, is 120 light-years away in the swan-shaped constellation Cygnus. Scientists had a goal to detect water vapor in HAT-P-11b’s atmosphere. The planet, which is roughly the size of Neptune, has a rocky core and gassy atmosphere.

It was the possibility of clouds in that atmosphere that had these scientists concerned. And unfortunately, you can’t turn on the Weather Channel and get a forecast for a place like HAT-P-11b. Clouds would have been a problem because they get in the way of light passing through the planet’s atmosphere. The way that scientists detect water vapor is by looking at how light from the planet’s star changes when it passes through the atmosphere of the planet. Put a cloud in the way and all bets are off!

Luckily it was nothing but clear skies for the scientists, so they were able to find the water vapor they were looking for! HAT-P-11b is the smallest exoplanet for which a molecule of any kind has been identified. This discovery is an important stepping-stone. The ultimate goal is even more challenging—finding water vapor on an Earthlike planet. Finding planets like Earth with water vapor will be key in our hunt for life on planets outside of our own solar system.

Don’t let HAT-P-11b’s clear skies fool you, though. This super-hot exoplanet is no place for life, let alone a picnic.

Want to learn more about the wild world of planets elsewhere in the universe? Check out “What is a planet?” at NASA’s Space Place.http://spaceplace.nasa.gov/planet-what-is.

Artist’s conception of exoplanet HAT-P-11b, shown with a visible atmosphere, passing in front of its star. Image Credit: NASA/JPL-Caltech


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