TOI-1803: A Cool Dwarf with Two Close-Orbiting Planets

TOI-1803 is a star located 389 light-years away. It is cooler than the Sun at 4690 K, and its reported mass and radius estimates are both smaller than the Sun's, at 0.756 solar masses and 0.715 solar radii. The star's age is 1.4 billion years. Two planets are known to orbit this host: TOI-1803 b and TOI-1803 c. Both were discovered in 2025 by the transit method, in which a planet passes in front of its star from our viewpoint and causes a small dip in observed brightness.

TOI-1803 b is a Neptune-like planet with a radius of 2.99 Earth radii and a mass of 10.3 Earth masses, both larger than Earth's corresponding values. Its mean density is 2.13 g/cm³, 0.386 times Earth's. It completes one orbit in 6.29 days.

TOI-1803 c is a Jupiter-like planet with a radius of 4.29 Earth radii and a mass of 8 Earth masses, both larger than Earth's. Its mean density is 0.558 g/cm³, 0.101 times Earth's. It completes one orbit in 12.9 days, the longest orbital period among the two listed planets, while TOI-1803 b has the shortest at 6.29 days. TOI-1803 c also has the largest radius among the listed planets at 4.29 Earth radii, while TOI-1803 b has the smallest at 2.99 Earth radii. Among the listed planets, TOI-1803 b has the largest reported mass at 10.3 Earth masses, and TOI-1803 c has the smallest at 8 Earth masses.