Voyager 1 at the speed it moved outward over the year to 2026-10-25 (JPL Horizons). Driving: nonstop, never refuelling.
Facts
HD 191939 g has an equilibrium temperature between −50 and +50 °C.
How it was found
First planet found in 2020, by radial velocity and transit (NASA Exoplanet Archive).
Its planets
HD 191939 f — 13 times Earth's width (estimated from its mass, not measured), a giant, Jupiter-sized or more; its year lasts about 8 Earth years; about −150 °C, below freezing; found in 2022 by radial velocity.
HD 191939 d — 3 times Earth's width, a 'sub-Neptune' — bigger than Earth, smaller than Neptune; its year lasts 38 days; about 270 °C, hotter than boiling water; found in 2020 by transit.
HD 191939 c — 3.2 times Earth's width, a 'sub-Neptune' — bigger than Earth, smaller than Neptune; its year lasts 29 days; about 330 °C, hotter than boiling water; found in 2020 by transit.
HD 191939 e — 13 times Earth's width (estimated from its mass, not measured), a giant, Jupiter-sized or more; its year lasts 100 days; about 120 °C, hotter than boiling water; found in 2022 by radial velocity.
HD 191939 b — 3.4 times Earth's width, a 'sub-Neptune' — bigger than Earth, smaller than Neptune; its year lasts 9 days; about 610 °C, hotter than boiling water; found in 2020 by transit.
HD 191939 g — 3.7 times Earth's width (estimated from its mass, not measured), a 'sub-Neptune' — bigger than Earth, smaller than Neptune; its year lasts 280 days; about 5 °C, between freezing and boiling; found in 2022 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.