The possible exomoon candidate orbits a planet orbiting a Sun-like star about 5,700 light-years away from Earth. Dubbed Kepler 1708 bi, this satellite has a radius of about 2.6 times that of Earth and orbits a Jupiter-sized exoplanet, completing its orbit around its parent star about once every two Earth years.
Exomoons could be common
The astronomers used a database of more than 4,000 exoplanets detected by NASA’s Kepler Space Telescope (now retired). Since large planets orbiting far from their parent star are more likely to have moons large enough to detect, the team focused on a subset of just 70 exoplanets. They all take more than 400 Earth days to orbit their star or have an estimated average surface temperature of around 27° Celsius, slightly higher than Earth’s.
This for now mysterious object orbits the planet called Kepler 1708b in another solar system, 5,500 light-years from Earth.
Taking into account that the existence of a supermoon has not been officially confirmed yet , this finding would give more weight to the hypothesis that it would not be so strange to also find moons outside our own solar system. Kepler 1708 bi is the second exomoon candidate. The previous one (Kepler 1625b) was identified four years ago and is still waiting to confirm this detection.
“Astronomers have found more than 10,000 exoplanet candidates so far, but exomoons are much more challenging,” explains David Kipping of Columbia University, who has spent the last decade searching for exomoons. “They are terra incognita, ” he says.
Both moons are located far from their host star , where there is less gravity to pull on the planets and ‘tear’ off their satellites.
Of course, if it is finally a real satellite, it has a radius of 2.6 times that of the Earth, which probably shows that it is a gaseous moon instead of a rocky one. By comparison, Jupiter’s satellite Ganymede (the largest moon in our solar system), is 60% smaller than Earth and not much larger than Neptune’s moon Triton, so it’s a bit confusing to think of a moon so big
We need more data. Confirmation will perhaps require the use of the recently launched James Webb telescope, but it will not be an easy task, since the opportunity to detect it only comes every two years, when Kepler-1708b transits in front of the star and that all bodies are lined up to allow detection. The next appointment would be March 24, 2023, the researchers calculate.
How is a moon detected outside the solar system?
Since we cannot photograph them directly, their presence is inferred by the transit method , that is, when they pass in front of a star, momentarily dimming its light.
The detection of exomoons is a fascinating field in astronomy, because they have the potential to reveal how and where life might have arisen in the universe. Also the fact of finding out how these exomoons were formed, if they can support life or if they have some role in this important step, makes them elements of high astronomical interest.
Referencia: Kipping, D., Bryson, S., Burke, C. et al. An exomoon survey of 70 cool giant exoplanets and the new candidate Kepler-1708 b-i. Nature Astronomy, 2022 DOI: 10.1038/s41550-021-01539-1
