Kepler-10 is a planetary system made of a star and at least two planets. Its apparent visual magnitude, 11.16, makes it visible only with a telescope or binoculars.
The star is similar to the Sun on many aspects: 1.065 solar radii, 0.91 solar mass, a temperature of about 5435 °C (5500 °C for the Sun) and its spectral type is G (as the Sun). It is however much older (about 10.6 billion year old; the Sun is 4.57 billion year old) and contains about 30% less metals (elements heavier than hydrogen and helium).
Both planets were first spotted by the Kepler telescope (transits), and then detected using the radial-velocity technique. While the radii of the planets are undisputed, their masses are much more controversial. Indeed, in 2014, Dumusque et al. found masses of 3.3 and 17 Earth masses (what would make Kepler-10 c the heaviest known rocky planet and a so-called “mega-Earth”) by using HARPS data, while in 2016 Weiss et al. using HIRES-only data found very different masses of 4.6 and 5.7 Earth masses, with a combined (HARPS+HIRES) estimate at 3.7 and 14 Earth masses.