HD 28109 and Its Three Known Planets

HD 28109 is a star located 455 light-years away with three known planets. The host is an F8 star with an age of 3.2 billion years, a mass of 1.23 solar masses, a radius of 1.43 solar radii, and a temperature of 6190 K. Its mass, radius, and temperature are all reported as larger or hotter than the Sun's.

All three planets were discovered by transit in 2022, the method in which a planet passes in front of its star from our viewpoint and causes a small dip in observed brightness. HD 28109 b is Neptune-like, with a mass of 6.2 Earth masses, a radius of 2.69 Earth radii, and an orbital period of 22.9 days. Its mean density is 1.76 g/cm³, 0.319 times Earth's. HD 28109 c is Jupiter-like, with a mass of 9.2 Earth masses, a radius of 4.13 Earth radii, and an orbital period of 56 days. Its mean density is 0.72 g/cm³, 0.131 times Earth's. HD 28109 d is Neptune-like, with a reported upper limit of 5.8 Earth masses, a radius of 3.11 Earth radii, and an orbital period of 84.3 days. The reported radius estimates for all three planets are larger than Earth's, as are the reported mass estimates for b and c.

Among the listed planets, HD 28109 b has the shortest year by reported estimates, at 22.9 days, and the smallest radius, at 2.69 Earth radii. HD 28109 c has the second-shortest year, at 56 days, and the largest radius, at 4.13 Earth radii. HD 28109 d has the longest year, at 84.3 days, and the second-smallest radius, at 3.11 Earth radii.