In the search for Earth’s siblings, astronomers often focus on rocky planets, and for good reason: in our Solar System, planets similar to Earth are located only in the habitable zone. But this does not have to be the case in other solar systems. There, gas giants as big as Jupiter or even bigger could be located in the habitable zone of their host star. The habitable zone might even be larger in these systems, because these giant planets could also provide energy to the moons in their orbit.
Researchers now argue in the Astrophysical Journal that such gas giants should not be excluded from the search for life. They have published a list of giant planets that were discovered with the Kepler telescope and whose moons could potentially harbor life. According to the model of our Solar System, it seems likely that these planets have moons – of the 175 currently known moons orbiting the eight planets of our Solar System, the gas giants have 172.
The list, which could be added to in the future by the James Webb telescope, includes a total of 121 gas planets that are all at least three times as large as the Earth. Astronomers have not yet identified a single exomoon with certainty, but there are at least a few candidates.