HIP 9618: A Cooler, Smaller Sun with Two Neptune-like Worlds

HIP 9618 is a star 220 light-years away, and it hosts two known planets, both found by transit in 2023. The star is 5.6 billion years old and has a reported mass of 0.942 solar masses, a reported radius of 0.959 solar radii, and a temperature of 5650 K. Its mass and radius are smaller than the Sun's, and it is cooler than the Sun.

Both planets are Neptune-like, a class that reaches up to 4 times Earth's radius. HIP 9618 b has a reported upper limit of 8.3 Earth masses, a radius of 3.83 Earth radii, and an orbital period of 20.8 days. HIP 9618 c has a reported upper limit of 7 Earth masses, a radius of 3.43 Earth radii, and an orbital period of 52.6 days. Both planets are larger than Earth, and their years last 20.8 and 52.6 days. Among the listed planets, HIP 9618 b has the shortest year and the largest radius, while HIP 9618 c has the longest year and the smallest radius.