HD 7924 d
HD 7924 d is a super-Earth orbiting HD 7924 in the constellation Cassiopeia. It lies about 55 light-years from Earth and was discovered in 2015 using the radial velocity method.
Is HD 7924 d in the Habitable Zone?
HD 7924 d orbits inside the inner edge of the habitable zone of HD 7924. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of HD 7924: 0.479–1.151 AU (conservative: 0.606–1.092 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on HD 7924 d
The equilibrium temperature of HD 7924 d is about 499 K (226 °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 15.17 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on HD 7924 d — one full orbit around HD 7924 — lasts 24.5 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.155 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.21).
How Was HD 7924 d Discovered?
HD 7924 d was discovered in 2015 using the radial velocity method, with observations from W. M. Keck 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 HD 7924 d?
HD 7924 d is 55.4 light-years (17.0 parsecs) from Earth. Light arriving here tonight left the planet around the year 1971. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 975,040 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. HD 7924 d scores 0.31, ranking #1,177 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: HD 7924
HD 7924
- Surface temperature
- 5,131 K (Sun: 5,772 K)
- Mass
- 0.65 M☉
- Radius
- 0.78 R☉
The HD 7924 Planetary System
HD 7924 d is one of 3 known planets in the HD 7924 system. Its siblings:
HD 7924 d — Complete Data
| Mass (best estimate) | 6.44 Earth masses |
|---|---|
| Orbital period | 24.45 days |
| Orbital distance | 0.155 AU |
| Eccentricity | 0.210 |
| Equilibrium temperature | 499 K (226 °C) |
| Stellar irradiation | 15.17× Earth |
| Earth Similarity Index | 0.31 |
| Distance from Earth | 55.4 light-years (17.0 parsecs) |
| Constellation | Cassiopeia |
| Discovery method | Radial Velocity |
| Discovery facility | W. M. Keck Observatory |
| Discovery year | 2015 |
Data: NASA Exoplanet Archive, last updated 2015-05-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About HD 7924 d
Is HD 7924 d habitable?
No — HD 7924 d orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is HD 7924 d?
HD 7924 d is about 55 light-years from Earth in the constellation Cassiopeia. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 975,040 years to get there.
How long is a year on HD 7924 d?
One orbit around HD 7924 takes 24.5 Earth days — short enough that 15 of its years would fit into one Earth year.
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