By analysing observational data, researchers have gleaned new insights into the best places to search for habitable extrasolar planets (known as exoplanets) orbiting Sun-like stars in the Milky Way1. These insights can inform future space missions designed to search for exoplanets that may potentially harbour life.
The habitable zone of a star is defined as the region around the star in which liquid water can exist on the surface of a rocky planet. The existence of water may allow carbon-based, photosynthetic life forms, similar to those on Earth, to evolve. These life forms could modify the planet’s atmosphere to an extent that it could be detected from Earth.
To identify exoplanets in the habitable zones of stars, the researchers analysed planets and planet candidates discovered by NASA’s Kepler space telescope, the Observatoire de Paris in France and the High Accuracy Radial Velocity Planet Searcher at the European Southern Observatory in Chile. They considered habitable exoplanets orbiting F, G and K stars (G stars are similar in size to the Sun, whereas F and K stars are bigger and smaller than the Sun, respectively), as the lifetimes of such stars generally exceed two billion years — long enough for life to evolve on orbiting planets.
The researchers detected the highest occurrence of exoplanets in the habitable zones around G stars; F stars showed 9.5% lower occurrence of exoplanets in their habitable zones than G stars, while K stars had the lowest occurrence of exoplanets in their habitable zones. The researchers also found that the occurrence of exoplanets in the habitable zone increased with the increasing star lifetime.
“The findings of this study will be useful for space missions dedicated to the detection of habitable exoplanets,” says Anirban Pathak, a senior author of the study.
[The authors of this work are from: Jaypee Institute of Information Technology, Noida, India, Palacky University, Olomouc and Regional Centre for Special Optics and Optoelectronics Systems – TOPTEC, Turnov, Czech Republic.]
