Kepler-11g

Lore & Background

Kepler-11g was originally flagged as KOI-157 by the Kepler space telescope, which detected periodic dimming events as the planet transited its star. Because it orbits much farther from Kepler-11 than the inner five planets, fewer transits were observed, and gravitational interactions with the other planets could not be detected. To confirm its planetary nature, the Kepler team used multiple observatories including the Keck 1 telescope, the Shane and Hale telescopes, telescopes at WIYN and Whipple observatories, the Nordic Optical Telescope, the Hobby-Eberly and Harlan J. Smith telescopes, and NASA's Spitzer Space Telescope. The team ran numerous models to rule out false positives such as an eclipsing binary star in the background, finding a 0.18% probability that Kepler-11g is not a planet. The planet's designation follows alphabetical order by distance from the host star, with 'g' assigned as the sixth and farthest planet.

Reader's Guide

Kepler-11g is notable as part of the flattest and most compact planetary system discovered by NASA's Kepler mission at the time of its announcement. Its large orbital distance relative to the inner five planets made it the most challenging to confirm among the Kepler-11 planets, requiring exhaustive modeling to eliminate alternative explanations. The planet's mass could not be directly measured from transit data; only an upper limit of 25 Earth masses could be placed, with formation models suggesting a mass not much greater than about 7 Earth masses. Its radius of 3.33 Earth radii is comparable to Neptune's, and its gaseous envelope is estimated to comprise about 10% of its mass. With an orbital inclination of 89.8°, it is seen nearly edge-on from Earth. The system's discovery demonstrated the Kepler telescope's ability to detect multiple transiting planets in a single system and highlighted the challenges of confirming planets at greater orbital distances.

Did You Know?

• Kepler-11g orbits its star every 118.37774 days at a distance of 0.462 AU.
• Its radius is 3.33 times that of Earth, similar in size to Neptune.
• The probability that Kepler-11g is a false positive was determined to be 0.18%.
• Kepler-11g is the outermost of six planets in the Kepler-11 system.