Struve 2398
Struve 2398 is a binary star system in the northern constellation of Draco. Struve 2398 is star number 2398 in the Struve Double Star Catalog of Russian-German astronomer Friedrich Georg Wilhelm von Struve. The astronomer's surname, and hence the star identifier, is sometimes indicated by a Greek sigma, Σ; hence, this system can be listed with the identifier Σ 2398. Although the components are too faint to be viewed with the naked eye, this star system is among the closest to the Sun. Parallax measurements by the Gaia spacecraft give them an estimated distance of away.
Both stars are small red dwarfs, with each having around a third the Sun's mass and radius. They are each sources of X-ray emission. They are orbiting with a period of about 871 years, at a separation of about 63 astronomical units with an orbital eccentricity of 0.29.
The pair has a relatively high proper motion of 2.2 arc seconds per year. The system is on an orbit through the Milky Way that has an eccentricity of 0.05, carrying them as close as 8 kpc and as far as 9 kpc from the Galactic Center. The plane of their galactic orbit carries them as far as 463−489 pc away from the galactic plane.
Planetary systems
Both stars of the Struve 2398 system are known to host planets.Struve 2398 A has one known planet, a likely super-Earth discovered in 2024 using the radial velocity method. This planet has a minimum mass 2.8 times that of Earth, and has a close orbit with a period of 11 days; it is too close to its star to be in the habitable zone. TESS observations show that the planet likely does not transit its host star.
Struve 2398 B also hosts one known planet, a super-Earth orbiting within the habitable zone, circling its host star every 37.9 days. An additional planet with an orbital period of 4.765 days is suspected. Both were detected using the radial velocity method and announced in 2025. Other planetary candidates had previously been proposed around star B, but were not confirmed.