SCIENCE

After cataloging nearly a thousand worlds beyond our solar system, astronomers can now for the first time forecast cloudy skies on a distant exoplanet. (National Geographic News)

Use our resources to better understand planets—from out-of-this-world to the one you’re on.

Discussion Ideas

• Read our short encyclopedic entry on “planet.” The entry says “Most of the exoplanets discovered so far are gas giants.” Is Kepler-7b a gas giant? What gases do you think are present on Kepler-7b?
  • Here’s the part where I’d link you to NASA’s information page on Kepler-7b, but due to the government shutdown, I can’t. Thanks, Congress!
  • Yep, it’s definitely a gas giant! Big exoplanets like Kepler-7b are nicknamed “hot Jupiters,” because they share so many characteristics with the largest planet in our own solar system, the beautiful gas giant Jupiter. Hot Jupiters are usually much hotter and much larger than the gas giants in our solar system, however. In fact, the radius of Kepler-7b is 1.5 times the radius of Jupiter!
  • The swirling clouds of gases that make up Kepler-7b probably include hydrogen, helium, water vapor, ammonia, and methane. Jonathan Fortney, professor of astronomy and astrophysics at the University of California at Santa Cruz and co-author of a paper on the cloud map of Kepler-7b, has more exotic ideas: “These clouds may well be composed of rock and iron, since the planet is over 1,000 degrees Fahrenheit,” he says. (Iron clouds!)

• Why do you think Kepler-7b is so much hotter than Jupiter, even though it shares so many other characteristics with the gas giant?
  • Kepler-7b is much, much closer to its parent star, Kepler-7, than Jupiter is to the sun. In fact, Kepler-7b is much, much closer to Kepler-7 than the Earth is to the sun! In fact, Kepler-7b is much, much closer to Kepler-7 than Mercury—our innermost planet—is to the sun!
  • A good measure of this distance can be seen by tracking the planets’ orbits, or how long they take to circle their parent star. A “year” on Kepler-7b is just under 7 days, according to the NG News blog. A “year” on Jupiter, however, is more than 11 (Earth-defined) years!

• Despite being so much larger than Jupiter, Kepler-7b has only about half Jupiter’s mass. Does this make Kepler-7b more or less dense than Jupiter?
  • Much less dense! Kepler-7b is one of the least dense exoplanets ever discovered. Its density is about the same as polystyrene (Styrofoam)!

NASA, come back, we miss you!