YZ Cet d
YZ Cet d is a terrestrial planet orbiting the M4.5 V star YZ Cet in the constellation Cetus. It lies about 12 light-years from Earth and was discovered in 2017 using the radial velocity method.
Is YZ Cet d in the Habitable Zone?
YZ Cet d orbits inside the inner edge of the habitable zone of YZ Cet. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of YZ Cet: 0.038–0.102 AU (conservative: 0.049–0.096 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on YZ Cet d
The equilibrium temperature of YZ Cet d is about 357 K (84 °C) — hotter than anywhere on Earth. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 2.70 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on YZ Cet d — one full orbit around YZ Cet — lasts 4.66 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.029 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.07).
How Was YZ Cet d Discovered?
YZ Cet d was discovered in 2017 using the radial velocity method, with observations from La Silla 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 YZ Cet d?
YZ Cet d is 12.1 light-years (3.7 parsecs) from Earth. Light arriving here tonight left the planet around the year 2014. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 212,960 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. YZ Cet d scores 0.67, ranking #77 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: YZ Cet
YZ Cet
- Spectral type
- M4.5 V
- Surface temperature
- 3,151 K (Sun: 5,772 K)
- Mass
- 0.14 M☉
- Radius
- 0.16 R☉
- Luminosity
- 0.0022 L☉
- Age
- 3.8 billion years (Sun: 4.6)
The YZ Cet Planetary System
YZ Cet d is one of 3 known planets in the YZ Cet system. Its siblings:
YZ Cet d — Complete Data
| Mass (best estimate) | 1.09 Earth masses |
|---|---|
| Orbital period | 4.66 days |
| Orbital distance | 0.029 AU |
| Eccentricity | 0.070 |
| Equilibrium temperature | 357 K (84 °C) |
| Stellar irradiation | 2.70× Earth |
| Earth Similarity Index | 0.67 |
| Distance from Earth | 12.1 light-years (3.7 parsecs) |
| Constellation | Cetus |
| Discovery method | Radial Velocity |
| Discovery facility | La Silla Observatory |
| Discovery year | 2017 |
Data: NASA Exoplanet Archive, last updated 2022-02-15. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About YZ Cet d
Is YZ Cet d habitable?
No — YZ Cet d orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is YZ Cet d?
YZ Cet d is about 12 light-years from Earth in the constellation Cetus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 212,960 years to get there.
How long is a year on YZ Cet d?
One orbit around YZ Cet takes 4.7 Earth days — short enough that 78 of its years would fit into one Earth year.
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