Voyager 1 at the speed it moved outward over the year to 2026-10-25 (JPL Horizons). Driving: nonstop, never refuelling.
How it was found
First planet found in 2012, by transit timing variations and transit (NASA Exoplanet Archive).
Its planets
Kepler-51 e — 2.2 times Earth's width (estimated from its mass, not measured), a 'sub-Neptune' — bigger than Earth, smaller than Neptune; its year lasts 260 days; found in 2024 by transit timing variations.
Kepler-51 d — 9.7 times Earth's width, Neptune-sized; its year lasts 130 days; about 110 °C, hotter than boiling water; found in 2014 by transit.
Kepler-51 c — 9 times Earth's width, Neptune-sized; its year lasts 85 days; about 170 °C, hotter than boiling water; found in 2012 by transit.
Kepler-51 b — 7.1 times Earth's width, Neptune-sized; its year lasts 45 days; about 270 °C, hotter than boiling water; found in 2012 by transit.
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.