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 2017, by radial velocity (NASA Exoplanet Archive).
Its planets
tau Cet f — 1.8 times Earth's width (estimated from its mass, not measured), a 'sub-Neptune' — bigger than Earth, smaller than Neptune; its year lasts 640 days; about −71 °C, below freezing; found in 2017 by radial velocity.
tau Cet g — 1.2 times Earth's width (estimated from its mass, not measured), about Earth-sized — probably rocky; its year lasts 20 days; about 370 °C, hotter than boiling water; found in 2017 by radial velocity.
tau Cet h — 1.2 times Earth's width (estimated from its mass, not measured), about Earth-sized — probably rocky; its year lasts 49 days; about 200 °C, hotter than boiling water; 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.