KOI-351 b, also known as Kepler-90 b, is the innermost planet of Kepler-90, a Sun-like star about 2,800 light-years away that has eight known planets, tied with our own solar system for the most around a single star. It crosses in front of its star every 7.01 days. NASA's Kepler space telescope found the system by catching the small dips in starlight as each planet passes across the star.
It was first reported in 2013 by a team led by Juan Cabrera, who reported four new planets around the star, b, c, e and f, and validated three that had been listed before. Cabrera's team noted that b and its neighbour c, both smaller than twice Earth's size, orbit within half a percent of a 4 to 5 ratio, which means their gravity regularly nudges each other. They also pointed out that the system resembles a compressed version of ours, with small planets close in and giant planets farther out.
Kepler-90 b is about 1.3 times Earth's radius, according to the NASA Exoplanet Archive. Its mass of about 2.3 Earth masses in the archive is an estimate from its size, not a measurement. It is extremely hot: so close to a Sun-like star, it receives more than 300 times the light Earth gets, and its equilibrium temperature is estimated at over 1,000 kelvin.