Kepler-6b

Lore & Background

Kepler-6b was initially identified as a transit candidate around the star KOI-017 by NASA's Kepler satellite, which trails Earth and continuously monitors a region between the constellations Cygnus and Lyra. After the detection of a transit signal, follow-up observations confirmed its planetary nature. Speckle imaging with the WIYN Telescope helped account for background starlight that could have skewed the planet's size estimate. Radial velocity measurements using HIRES on the Keck I telescope determined the planet's mass, while the Spitzer Space Telescope observed occultations and phase curves at infrared wavelengths of 3.6 and 4.5 micrometres. The confirmation of Kepler-6b was announced alongside planets Kepler-4b, Kepler-5b, Kepler-7b, and Kepler-8b at the 215th meeting of the American Astronomical Society on January 4, 2010.

The host star, Kepler-6, is a sunlike star in the Cygnus constellation, about 20.9% more massive and 39.1% larger than the Sun. With an effective temperature of 5647 K, it is cooler than the Sun and is estimated to be 3.8 billion years old. Kepler-6 is notably metal-rich, with an iron abundance 2.18 times that of the Sun ([Fe/H] = 0.34). Kepler-6b is the only known planet in this system.

Kepler-6b is a hot Jupiter with a mass 0.669 times that of Jupiter and an orbital period of 3.23 days. Its average distance of 0.046 AU places it nearly ten times closer to its star than Mercury is to the Sun. The intense stellar irradiation heats its atmosphere to 1660 K, causing the planet to puff up to 1.3 times Jupiter's size. The planet is likely tidally locked to its star, and its atmosphere may exhibit a thermal inversion where temperature increases with altitude. In 2015, the nightside temperature was estimated at 1719 K.

Reader's Guide

Kepler-6b holds significance as the third planet discovered by the Kepler mission, demonstrating the satellite's ability to detect transiting exoplanets and paving the way for subsequent discoveries. Its confirmation, along with four other planets announced at the same American Astronomical Society meeting, marked an early milestone in Kepler's planet-hunting campaign. The planet's inflated radius, despite its sub-Jupiter mass, illustrates the dramatic effect of stellar irradiation on close-in gas giants, a key characteristic of hot Jupiters. The detection of its occultation and phase curves by the Spitzer Space Telescope provided insights into its atmospheric properties, including the possibility of a thermal inversion. The unusually high metallicity of its host star, Kepler-6, adds to the understanding of planet formation in metal-rich environments. Kepler-6b remains the only known planet in its system, and its study continues to inform models of planetary atmospheres and tidal locking.

Did You Know?

• Kepler-6b was the third planet discovered by the Kepler spacecraft, but the sixth planet observed by the satellite.
• Its host star, Kepler-6, has 2.18 times more iron than the Sun, making it unusually metal-rich.
• The planet's atmosphere is heated to 1660 K, causing it to expand to 1.3 times Jupiter's size despite having only 0.669 Jupiter masses.
• In 2015, the nightside temperature of Kepler-6b was estimated to be 1719 K.