HD 69830 c is an exoplanet orbiting the K0V-type main‑sequence star HD 69830, located in the constellation Lupus at an estimated distance of about 41 light‑years (12.6 pc) from the Sun. It is the second of three known planetary companions in the HD 69830 system.
Discovery
The planet was announced in 2006 by a team led by Michel Mayor and Didier Queloz, using the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph mounted on the 3.6‑m telescope at La Silla Observatory. The detection was made via the radial‑velocity (Doppler) method, which measures periodic variations in the host star’s spectral lines caused by the gravitational influence of orbiting companions.
Orbital characteristics
- Orbital period: 31.6 days (≈ 0.086 yr)
- Semi‑major axis: ~0.186 AU (approximately 19 % of the Earth–Sun distance)
- Eccentricity: ≤ 0.10 (the orbit is close to circular, but exact value is uncertain within measurement errors)
Physical properties
- Minimum mass (M sin i): ≈ 12 M⊕ (about 0.038 M_Jupiter), placing it in the category of Neptune‑mass planets.
- Radius: Not directly measured; estimates, based on mass–radius relationships for Neptune‑like compositions, suggest a radius of roughly 2–3 R⊕, but this remains speculative due to the lack of transit observations.
Host star and system context
HD 69830 is a slightly metal‑rich star (metallicity [Fe/H] ≈ +0.06) with a mass of about 0.86 M☉ and a luminosity of 0.6 L☉. In addition to HD 69830 c, the system contains two other Neptune‑mass planets: HD 69830 b (inner, ~0.078 AU, 8.7‑day period) and HD 69830 d (outer, ~0.63 AU, 197‑day period). The system also exhibits an infrared excess indicative of a warm debris disk located at ~1 AU from the star.
Scientific significance
The HD 69830 system was among the early examples of multiple low‑mass planets detected around a Sun‑like star, demonstrating that compact systems of Neptune‑mass planets can exist without gas giants. Its discovery contributed to the understanding of planetary formation and migration mechanisms, particularly in metal‑rich, low‑mass stellar environments.
Current status
As of the latest published surveys, HD 69830 c has not been observed to transit its host star, and its true mass (as opposed to the minimum mass derived from radial velocities) remains undetermined owing to the unknown orbital inclination. No confirmed atmospheric characterization has been performed.
