pi Men c
pi Men c is a mini-Neptune orbiting HD 39091 in the constellation Mensa. It lies about 60 light-years from Earth and was discovered in 2018 using the transit method.
How Big Is pi Men c?
pi Men c has a radius of 2.02 times that of Earth.
Is pi Men c in the Habitable Zone?
The position of pi Men c relative to the habitable zone of HD 39091 cannot be precisely determined from the available orbital data.
Habitable zone of HD 39091: 0.934–2.188 AU (conservative: 1.183–2.074 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Orbit and Year Length
A year on pi Men c — one full orbit around HD 39091 — lasts 6.27 Earth days, shorter than Mercury's 88-day year.
How Was pi Men c Discovered?
pi Men c was discovered in 2018 using the transit method, with observations from Transiting Exoplanet Survey Satellite (TESS).
The transit method watches a star for the tiny, regular dip in brightness that occurs when a planet crosses in front of it. The depth and timing of these dips reveal the planet's size and orbital period.
How Far Away Is pi Men c?
pi Men c is 59.6 light-years (18.3 parsecs) from Earth. Light arriving here tonight left the planet around the year 1967. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 1,048,960 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. pi Men c scores 0.26, ranking #2,973 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 39091
HD 39091
- Surface temperature
- 5,998 K (Sun: 5,772 K)
- Mass
- 1.07 M☉
- Radius
- 1.17 R☉
- Age
- 3.9 billion years (Sun: 4.6)
The HD 39091 Planetary System
pi Men c is one of 3 known planets in the HD 39091 system. Its siblings:
- HD 39091 b
- pi Men d (Neptune-like)
pi Men c — Complete Data
| Radius | 2.019 Earth radii (0.180 Jupiter radii) |
|---|---|
| Orbital period | 6.27 days |
| Earth Similarity Index | 0.26 |
| Distance from Earth | 59.6 light-years (18.3 parsecs) |
| Constellation | Mensa |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2018 |
Data: NASA Exoplanet Archive, last updated 2025-09-25. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About pi Men c
Is pi Men c habitable?
pi Men c is not known to orbit within the habitable zone of HD 39091, and as a mini-Neptune it is an unlikely candidate for life as we know it.
How far away is pi Men c?
pi Men c is about 60 light-years from Earth in the constellation Mensa. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 1,048,960 years to get there.
How big is pi Men c compared to Earth?
pi Men c has 2.02 times the radius of Earth.
How long is a year on pi Men c?
One orbit around HD 39091 takes 6.3 Earth days — short enough that 58 of its years would fit into one Earth year.
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