Astronomers Find First Evidence of a Moon Outside of Our Solar System

Astronomers, using the NASA’s Hubble and Kepler space telescopeshave, found recently evidence of a moon orbiting a planet outside our solar system. Of course this is not unexpected, but for the first time solid evidence instead of pure speculation.

This moon candidate is app. 8000 lightyears away from Earth and orbits a giant gas-planet.

Since moons outside our solar system, called exomoons, cannot be imaged directly so far, their presence is inferred when they pass in front of a star, momentarily dimming its light - called a transit.

However, exomoons are much harder to detect than exoplanets because firstly they are smaller than their companion planet, and so their transit signal is weaker and secondly because Exomoons also shift position with each transit.

Illustration of the planet/moon pair is transiting is star, src, Credit: NASA, ESA, D. Kipping (Columbia University), and A. Feild (STScI)

In a recent paper published in "Science Advances", the scientists report the candidate moon is unusually large – potentially comparable to Neptune. Such large moons do not exist in our own solar system. The researchers say this may yield new insights into the development of planetary systems and may cause experts to revisit theories of how moons form around planets. Despite its size the candidate exomoon has only 1.5% the mass of its companion planet. The planet is estimated to be several times the mass of Jupiter!

The researchers note that if this is indeed a moon, both it and its host planet lie within their star’s habitable zone. However, both bodies are considered to be gaseous and therefore unsuitable for life - at least as we know it.

The astronomers note as well, that the moon hypothesis is tentative still and must be confirmed by follow-up Hubble observations. Thus they speak of an "exomoon candidate" only.