Nearest super-Earth in habitable zone orbit discovered

Astronomers have identified three new planets orbiting the K-type star HD 48948, located about 55 light-years from Earth in the constellation Camelopardalis. Of these, the most distant, HD 48948 d, appears particularly promising for the search for extraterrestrial life. Indeed, it is located in the habitable zone of its star, a region where temperature conditions could allow the presence of liquid water on its surface.

A star and its planets

K-type stars, like HD 48948, are less massive and less luminous than our Sun, but they are more massive than M-type stars (or red dwarfs). They are often called “orange dwarfs” because of their characteristic color. HD 48948 has about 67% of the mass of the Sun and is 1,000 years old. 11.5 billion years. The planets discoveries around HD 48948 have orbital periods of 7.3, 38 and 151 days respectively. Due to their proximity to the star, the first two planets are much too hot to be considered habitable. However, with an orbital period of 151 days, HD 48948 d is located at a much more interesting distance.
HD48948 hosts three probable super-Earths, one of which is the closest example of this class we know of orbiting in its star’s habitable zone. Credits: Soumita Samanta

A habitable super-Earth?

HD 48948 d has some intriguing features. Its orbital distance is comparable to that of Venus relative to the Sun, but due to the lower luminosity of HD 48948, the temperature on this planet would be closer to that of Earth. In addition, it is far enough from its star to avoiding the destructive effects of stellar flaresa common problem for planets around red dwarfs. Estimated to be about 10.59 times the mass of Earth, HD 48948 d is classified as a super-Earth. However, this classification is based solely on mass estimates based on gravitational effects observed on the star, because none of the planets in the system transit HD 48948 from our perspective. Without these transits, it is impossible to directly measure their size and confirm their composition. Doubts therefore remain as to its true nature. HD 48948 d could in particular be a mini-Neptune, a planet with a thick gaseous envelope, rather than a rocky planet. Although further research is needed to confirm the composition of HD 48948 d, this planet remains a promising candidate for the search for extraterrestrial life. Astronomers therefore hope that future observations, perhaps by next-generation space telescopes, will help determine whether this object has conditions favorable to life. Continued study of this system could also reveal other as-yet-undiscovered planets, enriching our understanding of distant star systems.