An international team of astronomers, led by Instituto of Astrofísica of Canarias, has identified a new exoplanet orbiting the star HD 176986, located 91 light-years from Terra. The planet, called HD 176986 d, was classified as a super-Earth and has a minimum mass estimated at 6.76 times that of Terra. The discovery increases the number of confirmed worlds in this stellar system to three and is the result of prolonged observations with high-precision spectrographs. The study was published in the journal Astronomy & Astrophysics.
The finding reinforces the importance of long-term monitoring campaigns to detect planets in wider orbits. The previous two planets, HD 176986 b and HD 176986 c, were confirmed in 2018, with short orbital periods of 6.49 and 16.81 days. The host star is a K-type orange dwarf, with a mass and radius slightly smaller than those of Sol, which favors the detection of subtle signals from planetary companions.
Main characteristics of the exoplanet
The planet HD 176986 d completes an orbit around the star every 61.38 days. Ele is positioned approximately 0.28 astronomical units away from the star. Sua minimum mass reaches 6.76 Earth masses, with a margin of error of about 0.9 Earth masses.
The estimated equilibrium temperature of the planet reaches 363 K, considering the radiation received from the star. Esse value indicates warm conditions at the surface, although it does not directly determine the presence of an atmosphere or habitability.
Planetary system details
The HD 176986 system now has three superearths confirmed by the radial velocity method. HD 176986 b has a minimum mass of 5.36 Earth masses. HD 176986 c has a minimum mass of 9.75 Earth masses.
All planets orbit in a compact configuration. The star exhibits magnetic activity with a cycle of approximately 2,432 days. Stellar rotation is estimated to take about 36 days.
Main data of HD 176986 system
- Star: HD 176986 (type K, mass ≈ 0.84 M☉, radius ≈ 0.83 R☉, age ≈ 4.3 billion years)
- Planet b: orbital period 6.49 days, minimum mass 5.36 M⊕
- Planet c: orbital period 16.81 days, minimum mass 9.75 M⊕
- Planet d: orbital period 61.38 days, minimum mass 6.76 M⊕
- System distance: 91 light years from Terra
These parameters were refined based on more than 330 combined observation nights.
Detection methods and challenges overcome
The HARPS spectrographs, on Chile, and HARPS-N, on Ilhas Canárias, recorded variations in the star’s radial velocity with high precision. The analysis required advanced modeling to separate planetary signals from the noise caused by stellar activity. Planet d’s signal emerged subtly and was only isolated after integrating data collected over 18 years.
The combination of historical and recent sets allowed greater confidence in detection. Ferramentas multidimensional Gaussian modeling was instrumental in filtering stellar contributions and confirming the existence of the third planet.
Relevance to exoplanet science
Super-Earths with orbital periods over 50 days and masses less than seven times that of Terra are still relatively rare in the current catalogue. Cada discovery of this type adds crucial information about the distribution of masses and orbits in multiplanetary systems around orange dwarfs. The HD 176986 system demonstrates that compact architectures can include worlds in outer orbital zones.
Researchers use this data to test models of planetary formation and dynamic migration. The frequency of super-Earths in K-type stars suggests that this type of planet is common in Via Láctea.
Opportunities for future studies
The system offers promising targets for next-generation telescopes. Additional Observações can refine the masses and search for evidence of atmospheres. The relative proximity facilitates detailed spectroscopic analyzes and investigations into possible gravitational interactions between the planets.
Continuous monitoring programs continue to reveal new worlds in familiar systems. The advance highlights the need for long baselines to detect planets in moderate orbits.
