Researchers may have found the first exomoon

So far, researchers have discovered 6000 planets orbiting stars outside our solar system. At least one of them also has a moon: a team led by French astronomer Quentin Kral has presumably discovered the first exomoon.

The moon orbits the planet HD 206893 b, discovered in 2021. According to the researchers, it is very large: it has 0.4 Jupiter masses, the team writes in a paper to be published in the journal Astronomy & Astrophysics, which is available as a preprint on the arXiv document server. This corresponds to more than seven Neptune masses. It orbits the planet in about three-quarters of a year.

However, the planet itself is also a giant: HD 206893 b is a gas planet with 1.25 times the radius of Jupiter but 28 times the mass. It orbits the star HD 206893, a spectral class F star 133 light-years from Earth, along with another planet. The planet orbits the star at a distance of 9.6 astronomical units, about 1.4 billion kilometers, and takes over 25 years to complete one orbit.

The moon was discovered using the VLTI/GRAVITY instrument at the European Southern Observatory on Cerro Paranal mountain in the Atacama Desert in northern Chile. The team used a method called astrometry, which records spatial fluctuations between stars and planets or planets and moons.

6000 confirmed exoplanets

According to the US space agency National Aeronautics and Space Administration (NASA), 6000 exoplanets are currently confirmed. In addition, there are over 8000 candidates that still need to be confirmed. There are also several candidates for exomoons, but they have not yet been confirmed.

According to Kral's team, it is not certain that the newly discovered object is actually a moon of HD 206893 b. There remains "some ambiguity" as to whether the pair could also be a double planet. In any case, there is no definition of what an exomoon is.

(wpl)