mass of Mars around Gliese 876 b and c could be stable on timescales above the Hubble time. CHEOPS and ESPRESSO could detect exomoons around the four candidates. However, both methods require a transiting exoplanet, which is not the case for HIP 12961 b, HIP 57050 b, Gliese 876 b and Gliese 876 c. In culture In the fictional universe of Avatar, the Pandoran biosphere is the biosphere of the habitable exomoon Pandora, orbiting the gas giant Polyphemus. See also Exomoon Habitability of natural satellites Habitable exoplanet List of potentially habitable exoplanets Superhabitable planet References Planetary habitability Exoplanetology Astrobiology Exomoons Types of planet