Voyager 1 at the speed it moved outward over the year to 2026-10-25 (JPL Horizons). Driving: nonstop, never refuelling.
Facts
K2-18 b has an equilibrium temperature between −50 and +50 °C.
How it was found
First planet found in 2015, by transit and radial velocity (NASA Exoplanet Archive).
Its planets
K2-18 b — 2.4 times Earth's width, a 'sub-Neptune' — bigger than Earth, smaller than Neptune; its year lasts 33 days; about 11 °C, between freezing and boiling; found in 2015 by transit.
K2-18 c — 2.7 times Earth's width (estimated from its mass, not measured), a 'sub-Neptune' — bigger than Earth, smaller than Neptune; its year lasts 9 days; about 90 °C, between freezing and boiling; found in 2017 by radial velocity.
NASA Exoplanet Archive, Planetary Systems Composite Parameters (fetched 2026-11-02). Composite values: where a planet's size or mass was not measured, the archive estimates it from the other.
This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with NASA under the Exoplanet Exploration Program.