HR 8799 and Its Four Giant Planets

HR 8799 is a star 135 light-years from Earth with a spectral type of A5 and a very young age class, its age measured at 0.03 billion years. Its temperature is 7400 K, hotter than the Sun's, and four planets are known to orbit it: HR 8799 b, c, d, and e.

All four are Jupiter-like planets, a class that exceeds 4 times Earth's radius, and all were found by imaging. The first three were announced in 2008, while HR 8799 e followed in 2010.

HR 8799 b has a mass of 2000 Earth masses, roughly 6.29 times Jupiter's mass, and a radius of 13 Earth radii, larger than Earth's. Its mean density is 5.02 g/cm³, 0.91 times Earth's, and its orbital period is 170000 days. Among the listed planets, it has the smallest reported mass.

HR 8799 c and HR 8799 d share several measured properties. Each has a mass of 3000 Earth masses, roughly 9.44 times Jupiter's mass, and a radius of 13 Earth radii, larger than Earth's. Their estimated mean densities are each 7.52 g/cm³, 1.37 times Earth's. The two differ in orbital period: 69000 days for HR 8799 c and 37000 days for HR 8799 d.

HR 8799 e has a mass of 3180 Earth masses, roughly 10 times Jupiter's mass, and a radius of 13.1 Earth radii, larger than Earth's. Its mean density is 7.76 g/cm³, 1.41 times Earth's. Among the listed planets, it has the largest reported mass and the largest radius by reported estimates. No orbital period is reported for HR 8799 e.