Kepler-553 is a star in the northern constellation of Cygnus, approximately 2,430 light-years from the Solar System. It is a G-type subgiant that hosts two known exoplanets.
Planetary system Two exoplanets are known to orbit Kepler-553, both gas giants. The inner planet, Kepler-553b, is between Neptune and Saturn in size; the outer, Kepler-553c, is a super-Jupiter in the habitable zone. The planets were discovered by NASA's Kepler space telescope using the transit method, and were confirmed in 2016 by a study that used statistical validation to confirm over 1,000 Kepler candidates. They were later characterized with radial velocity measurements.
Kepler-553 b Kepler-553 b is a super-Neptune-sized planet (or a sub-Saturn) orbiting close to its host star. Its mass remains unconstrained beyond an upper limit due to the challenges in detecting its weak radial velocity signal.
Kepler-553 c Kepler-553 c is a massive gas giant with a moderate orbital eccentricity, orbiting within the system's habitable zone. Its equilibrium temperature of approximately 251 K makes it a cold giant, potentially analogous to Jupiter but with higher metallicity. The planet's bulk composition is estimated to be about 8% heavy elements by mass, consistent with expectations for a gas giant of its mass. Prior to its confirmation, this planet was known as KOI-433.02, and a 2011 article from the Planetary Habitability Laboratory included it in a list of exoplanet candidates that could hypothetically host potentially habitable exomoons. There is as yet no evidence of any moons around this planet.
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