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 2022, by radial velocity (NASA Exoplanet Archive).
Its planets
HD 153557 b — 4.8 times Earth's width (estimated from its mass, not measured), Neptune-sized; its year lasts 7 days; about 500 °C, hotter than boiling water; found in 2022 by radial velocity.
HD 153557 d — 12 times Earth's width (estimated from its mass, not measured), a giant, Jupiter-sized or more; its year lasts about 110 Earth years; about −230 °C, below freezing; found in 2022 by radial velocity.
HD 153557 c — 4.4 times Earth's width (estimated from its mass, not measured), Neptune-sized; its year lasts 15 days; about 330 °C, hotter than boiling water; 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.