55 Cancri
Star
55 Cancri (Copernicus) - a Sun-like star 41 light-years away in Cancer, circled by five planets: a family ranging from a scorching super-Earth to a cold gas giant. Its innermost world, 55 Cnc e, transits the star, so we know its size and density - 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
Mass
1.80 × 10³⁰ kg
0.905 M☉
Radius
656,045 km
94% of the Sun's radius
Surface temperature
5,172 K (4899 °C)
Luminosity
2.43 × 10²⁶ W
Spectral type
K0V (Sun-like, slightly cooler)
Science
Physical
- Mass
- 1.80 × 10³⁰ kg · 0.905 M☉
- Radius
- 656,045 km · 94% of the Sun's radius
- Density
- 1,522 kg/m³ · 1.5× water
- Spectral type
- K0V (Sun-like, slightly cooler)
Rotation
- Note
- Rotates about once every 40 days; a mature, fairly quiet star.
Composition
- By mass
- A hydrogen/helium star a little cooler and less luminous than the Sun and notably metal-RICH, which may have helped build its five planets. It has a distant red-dwarf companion (55 Cancri B) far out at ~1,000 AU.
Temperature
- Surface
- 5,172 K (4899 °C)
Radiation & temperature
- Luminosity
- 2.43 × 10²⁶ W · 0.635 L☉
- Surface temperature
- 5,172 K (4899 °C)
- Peak wavelength
- 560 nm · green-yellow visible light
Discovery & history
- Name
- '55 Cancri' is a Flamsteed number in Cancer; the star's IAU name is Copernicus and its planets carry names of famous scientists and instrument-makers.
The first planet here (55 Cnc b) was found in 1996, among the earliest exoplanets; the count grew to five by 2007, one of the richest systems then known. In 2011 the inner planet e was caught transiting, turning it into one of the most-studied rocky exoplanets. The star and planet e were named Copernicus and Janssen in the 2015 IAU public campaign.
Images
Images from open archives · credit shown per image