Kepler-7b

Lore & Background

Kepler-7b was confirmed during the first 34 days of Kepler's science operations and announced at a meeting of the American Astronomical Society on January 4, 2010. It orbits a star slightly hotter and significantly larger than the Sun, which is expected to soon reach the end of the main sequence. The planet orbits its host star every 4.8855 days at a distance of approximately 0.06 AU, making it the furthest-orbiting planet among the first five discovered by Kepler. Its orbit is almost edge-on as seen from Earth, with an inclination of 86.5°.

Kepler-7b has a mass of only 0.433 that of Jupiter but has expanded to a radius of 1.478 Jupiter radii, giving it a mean density of 0.166 g/cm³—about the same as expanded polystyrene. Such low densities are not predicted by current standard theories of planet formation. Its equilibrium temperature is nearly 1540 K, making it over twelve times hotter than Jupiter, though it is the second coolest of the first five Kepler planets.

Astronomers used data from NASA's Kepler and Spitzer space telescopes to create the first cloud map of a planet beyond the Solar System. Kepler's visible-light observations of the planet's Moon-like phases revealed a bright spot on its western hemisphere, and Spitzer data helped determine that the bright spot came from clouds rather than heat. The clouds may be composed of rock and iron, and the planet's cloud patterns appear remarkably stable over time.

Reader's Guide

Kepler-7b holds significance as one of the first five exoplanets confirmed by the Kepler spacecraft, marking an early milestone in the mission's planet-hunting success. Its discovery helped demonstrate Kepler's ability to detect transiting planets and led to follow-up observations that confirmed its planetary nature. The planet's extremely low density challenged standard theories of planet formation, as such diffuse worlds were not predicted by existing models. Most notably, Kepler-7b became the first extrasolar planet to have a crude map of its cloud coverage, achieved through combined observations from Kepler and Spitzer. This cloud mapping represented a breakthrough in characterizing exoplanet atmospheres, showing that reflective features on distant worlds could be interpreted as cloud patterns. The planet's relatively high geometric albedo of 0.3, detected through reflected starlight, further contributed to understanding its atmospheric properties. Kepler-7b's legacy includes providing early evidence that hot Jupiters can have stable, long-lasting cloud features, unlike the changing cloud patterns on Earth.

Did You Know?

• Its mean density of 0.166 g/cm³ is about the same as expanded polystyrene.
• The planet's clouds may be composed of rock and iron due to its high temperature.