55 Cnc e
55 Cnc e is a super-Earth orbiting the G8 V star 55 Cnc in the constellation Cancer. It lies about 41 light-years from Earth and was discovered in 2004 using the radial velocity method.
How Big Is 55 Cnc e?
55 Cnc e has a radius of 1.88 times that of Earth. Its mass is 8.0 times that of Earth, giving it a density of 6.66 g/cm³ — comparable to rocky planets like Earth (5.51 g/cm³).
Is 55 Cnc e in the Habitable Zone?
55 Cnc e orbits inside the inner edge of the habitable zone of 55 Cnc. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of 55 Cnc: 0.615–1.476 AU (conservative: 0.779–1.399 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Orbit and Year Length
A year on 55 Cnc e — one full orbit around 55 Cnc — lasts just 17.7 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.015 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.05).
How Was 55 Cnc e Discovered?
55 Cnc e was discovered in 2004 using the radial velocity method, with observations from McDonald Observatory.
The radial velocity method measures the subtle wobble of a star caused by the gravitational pull of an orbiting planet, visible as periodic shifts in the star's light spectrum. The size of the wobble reveals the planet's minimum mass.
How Far Away Is 55 Cnc e?
55 Cnc e is 41.0 light-years (12.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 1985. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 721,600 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. 55 Cnc e scores 0.26, ranking #2,830 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: 55 Cnc
55 Cnc e belongs to a system of 2 stars; it orbits 55 Cnc.
55 Cnc
- Spectral type
- G8 V
- Surface temperature
- 5,198 K (Sun: 5,772 K)
- Mass
- 1.01 M☉
- Radius
- 0.98 R☉
- Age
- 10.0 billion years (Sun: 4.6)
The 55 Cnc Planetary System
55 Cnc e is one of 5 known planets in the 55 Cnc system. Its siblings:
55 Cnc e — Complete Data
| Radius | 1.875 Earth radii (0.167 Jupiter radii) |
|---|---|
| Mass | 7.99 Earth masses (0.025 Jupiter masses) |
| Density | 6.66 g/cm³ (Earth: 5.51) |
| Orbital period | 0.74 days |
| Orbital distance | 0.015 AU |
| Eccentricity | 0.050 |
| Earth Similarity Index | 0.26 |
| Distance from Earth | 41.0 light-years (12.6 parsecs) |
| Constellation | Cancer |
| Discovery method | Radial Velocity |
| Discovery facility | McDonald Observatory |
| Discovery year | 2004 |
Data: NASA Exoplanet Archive, last updated 2021-02-05. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About 55 Cnc e
Is 55 Cnc e habitable?
No — 55 Cnc e orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is 55 Cnc e?
55 Cnc e is about 41 light-years from Earth in the constellation Cancer. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 721,600 years to get there.
How big is 55 Cnc e compared to Earth?
55 Cnc e has 1.88 times the radius of Earth and about 8.0 times its mass.
How long is a year on 55 Cnc e?
One orbit around 55 Cnc takes 0.7 Earth days — short enough that 496 of its years would fit into one Earth year.
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