HD 74156 c is an extrasolar planet (exoplanet) that orbits the Sun‑like star HD 74156, located in the constellation Hydra. The planet was discovered using the radial‑velocity method and its existence was announced in 2001 by a team led by Michel Mayor and Didier Queloz, among others, as part of the CORALIE survey of nearby stars.
Host star
HD 74156 is a G0V main‑sequence star with an estimated mass of 1.24 M☉, radius of about 1.30 R☉, and an effective temperature near 5,800 K. The star lies at a distance of roughly 190 light‑years (≈ 58 parsecs) from the Solar System and has an apparent visual magnitude of 7.6.
Discovery and detection
The presence of HD 74156 c was inferred from periodic variations in the host star’s radial velocity, measured with high‑precision spectrographs. The detection was confirmed by subsequent observations that refined the planet’s orbital parameters.
Orbital characteristics
- Orbital period: ~ 5.5 years (≈ 2000 days)
- Semi‑major axis: ≈ 3.9 AU
- Eccentricity: ≈ 0.25 – 0.30 (moderately elliptical)
- Minimum mass (M sin i): ≈ 6.2 MJup (Jupiter masses)
Because the radial‑velocity technique yields only the product of the planet’s true mass and the sine of the orbital inclination (M sin i), the actual mass may be higher if the orbital plane is viewed at a low inclination.
Physical properties
HD 74156 c is classified as a giant planet, comparable in mass to several times that of Jupiter. Its orbital distance places it well outside the host star’s habitable zone, and the planet is presumed to be a gas giant with a composition dominated by hydrogen and helium, although direct observations of its atmosphere have not been achieved.
System architecture
HD 74156 hosts at least one additional confirmed planet, HD 74156 b, which orbits much closer to the star with a period of ~ 51 days and a minimum mass of ~ 1.9 MJup. The two giant planets have significantly different orbital distances and eccentricities, making the HD 74156 system a subject of interest for studies of planetary dynamics and formation.
Scientific significance
The detection of HD 74156 c contributed to the early catalog of long‑period exoplanets discovered by radial velocity, illustrating that massive planets can occupy relatively distant, eccentric orbits around Sun‑like stars. The system is often cited in comparative analyses of planetary system architecture and in tests of planetary migration theories.
References
- Mayor, M.; et al. (2001). “The CORALIE survey for southern extrasolar planets. XII. A planetary system around HD 74156”. Astronomy & Astrophysics 366: 12–16.
- Schneider, J.; et al. (2023). “Exoplanet Catalogue”, NASA Exoplanet Archive.
All orbital and physical parameters are given as the values most commonly reported in peer‑reviewed literature and may be refined by future observations.