55 Cancri
system
55 Cancri (Copernicus) is a Sun-like star 41 light-years away in Cancer, circled by five planets — from a scorching super-Earth to a cold gas giant. Its innermost world, 55 Cnc e (Janssen), transits the star, so its size and rocky density are measured: a dense, lava-covered world barely twice Earth's width, orbiting in just 18 hours.
Open in 3D viewSee 55 Cancri in the live, interactive 3D map
Key facts
Type
Sun-like + 5 planets
Distance
41.0 light-years
Confirmed planets
5
55 Cnc e
Transiting lava super-Earth
Science
Classification
- Type
- Single Sun-like system (with a distant red-dwarf companion)
- Central star
- 55 Cancri / Copernicus — K0V (~5172 K, 0.9 M☉)
Planets
- Confirmed planets
- 5 · e (lava super-Earth), b, c, f, d (a cold Jupiter at 5.6 AU)
- 55 Cnc e
- Transiting — real size + density (rocky)
- Others
- True masses; radii model-estimated (no transit)
Distance
- Distance
- 41.0 light-years · just visible to the naked eye (V 6.0)
How we know
- Note
- Five confirmed planets (NASA Exoplanet Archive, checked 2026-07-05). Only the inner planet e transits, so only it has a measured radius and density; the four giants have true (radial-velocity) masses but model radii, so no density is quoted for them. Map distance is symbolic; the real gap is 41.0 light-years.
Discovery & history
- Name
- A Flamsteed number in Cancer; the star's IAU name is Copernicus.
Its first planet was found in 1996; the count reached five by 2007, and the inner planet e was caught transiting in 2011.
Images
Images from open archives · credit shown per image