Kepler-186

Kepler-186

system

Kepler-186 is a red dwarf about 580 light-years away in Cygnus, with a compact family of five small planets. It is famous for the outermost, Kepler-186 f — announced in 2014 as the first Earth-size planet in another star's habitable zone. That planet's confirmation has since been disputed, so it is shown here plainly labelled as likely-but-unconfirmed rather than quietly left out.

Open in 3D viewSee Kepler-186 in the live, interactive 3D map

Key facts

Type
Red dwarf + 5 planets
Distance
580 light-years
Confirmed
4 (b–e)
Disputed but shown
Kepler-186 f

Science

Classification

Type
Single red-dwarf system
Central star
Kepler-186 — M1 red dwarf, ~3788 K, 0.48 M☉

Planets

Confirmed
4 · b, c, d, e — all transiting, all secure
The famous fifth
Kepler-186 f — shown, disputed

Distance

Distance
580 light-years · in Cygnus, the Swan

How we know

Note
The four inner planets (b–e) are securely confirmed and transiting, so their sizes are measured; their masses are only size-estimated, so no density is quoted. Kepler-186 f was announced in 2014 as the first Earth-size planet in a star's habitable zone — a landmark — but its confirmation has since been disputed, and the doubt has grown: a 2019 re-analysis (Burke et al.) put its false-positive probability near 4% (~96% confidence), and a 2025 reassessment (Robnik & Seljak, PNAS) put it at 20% (~80% confidence), calling it marginal — both below the strict under-1% bar used to certify a planet, so the NASA Exoplanet Archive flags it controversial (checked 2026-07-07), and it has never been independently mass-confirmed. It IS shown here — the planet that made the system famous — but clearly labelled as likely-but-unconfirmed, not passed off as secure. Placed at its real position, 580 light-years away.

Discovery & history

Name
A designation from NASA's Kepler mission (the 186th planet-hosting star it confirmed); the star has no proper name.

NASA's Kepler telescope found this system in 2014. Four small transiting planets (b–e) are securely confirmed. A fifth, Kepler-186 f, was announced as a landmark — the first Earth-size planet in a habitable zone — but its statistical validation has since been questioned, and the doubt has grown (a 2019 re-analysis put it near 96% confidence, a 2025 one near 80%, both below the strict bar to certify a planet), and it was never mass-confirmed. It is shown here as the famous disputed world it is — rendered, but labelled honestly rather than passed off as secure.

Images

Artist's concept of Kepler-186 f — imagined as a landscape under its red-dwarf sun. An artist's impression, not a photograph; the planet's detection is disputed and its real surface is unknown.
Gemini Observatory / AURA / Danielle Futselaar — CC BY 4.0 · Wikimedia Commons
NASA's comparison of Kepler's small habitable-zone planets — including Kepler-186 f and Kepler-442 b — with the Solar System (a NASA diagram).
NASA/Ames/JPL-Caltech (public domain) · Wikimedia Commons
Where to find it — in Cygnus, the Swan (IAU constellation chart). To the eye it is a single point of light; no telescope has imaged its surface.
IAU / Sky & Telescope, R. Sinnott & R. Fienberg (CC BY 3.0) · Wikimedia Commons

Images from open archives · credit shown per image