XO-2 S and Its Three Known Planets

XO-2 S is a G8 V star 494 light-years away. Its spectral type marks it as a G-type main-sequence dwarf, a class that includes the Sun. The star is estimated to be 7.1 billion years old, and its measurements include a mass of 0.982 solar masses and a radius of 1.02 solar radii. Its reported temperature of 5400 K is cooler than the Sun's. Three planets are known to orbit this host, all discovered by the radial velocity method, which detects the wobble a planet's gravity induces in its star's motion; repeated wobbles reveal the planet and its orbital period.

XO-2 S b was discovered in 2014. Its minimum mass, a lower bound on its true mass, is 82.6 Earth masses, larger than Earth's, and its orbital period is 18.2 days. XO-2 S c was also discovered in 2014. Its minimum mass is 439 Earth masses, larger than Earth's and roughly 1.38 times Jupiter's mass, and its orbital period is 120 days. XO-2 S d was discovered in 2024. Its minimum mass is 1180 Earth masses, larger than Earth's and roughly 3.71 times Jupiter's mass, and its orbital period is 4700 days.

Among the listed planets, XO-2 S b has the shortest year by reported estimates and the smallest minimum mass. XO-2 S c has the second-shortest year and the second-smallest minimum mass. XO-2 S d has the longest year and the largest minimum mass.