Artist’s conception of the clouds on Kepler-7b, compared for size with Jupiter (right). The western side is cloudy, while the east is largely cloud-free. (credit: NASA/JPL-Caltech/MIT)

Of the 2,000-plus planets discovered orbiting alien stars, only one has been found to have clouds. The planet, Kepler-7b, is one of the earliest exoplanets discovered. If you were hoping the clouds could be a sign of life, you’re likely to be disappointed. Kepler-7b, like other early exoplanets, is a gas giant larger than Jupiter.

And like many exoplanets, Kepler-7b is a “Hot Jupiter,” meaning it orbits very close to its star. It’s about 44 percent the mass of Jupiter but about 1.6 times its size and orbits its host star at about 0.6 astronomical units from its star (Earth is one AU from the Sun).

The planet is unusual in a few ways. Its large size and small mass mean that it has a low density, lower than is predicted by current models of planetary interiors. It’s about as reflective to light as Jupiter, which is also not expected for a planet so close in to its star. That’s because the star is close enough that its light should strip away the clouds and leave the planet dark.

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