Kepler-51 is a star with 1.04 times the mass of the Sun, and 0.94 times its radius. It is located 2556.51 light years away from the solar system and is estimated to be 0.3 billion years old, as compared to the Sun which is roughly 4.6 billion years old.
Kepler-51 is known to have 3 exoplanets in orbit around it.
Kepler-51 b was discovered by the Kepler observatory, in 2013-01, using the transit method. Its semi-major axis is 0.25 astronomical units, as compared to Earth's which is 1 astronomical unit. The mass of Kepler-51 b is 2.226 times the mass of Earth. The radius of Kepler-51 b is 7.100 that of Earth. With a mass below 5 Earth masses, a density of 0.03, and a semi-major axis of 0.2514 astronomical units, Kepler-51 b could, potentially, be an ocean world - a planet with no dry land.
Kepler-51 c was discovered by the Kepler observatory, in 2013-01, using the transit method. Its semi-major axis is 0.38 astronomical units, as compared to Earth's which is 1 astronomical unit. The mass of Kepler-51 c is 4.134 times the mass of Earth. The radius of Kepler-51 c is 9.000 that of Earth. With a mass below 5 Earth masses, a density of 0.03, and a semi-major axis of 0.384 astronomical units, Kepler-51 c could, potentially, be an ocean world - a planet with no dry land.
Kepler-51 d was discovered by the Kepler observatory, in 2014-03, using the transit method. Its semi-major axis is 0.51 astronomical units, as compared to Earth's which is 1 astronomical unit. The mass of Kepler-51 d is 7.632 times the mass of Earth. The radius of Kepler-51 d is 9.700 that of Earth. At more than 10 Earth masses, Kepler-51 d is an ice giant, a planet that is made up mostly of volatiles like water, amonia and methane, and enveloped by a dense hydrogen and helium atmosphere, much like Uranus and Neptune in our solar system.