Given that the majority of the planets in our Solar System have moons, it’s very likely that they exist elsewhere in the universe around exoplanets, too. Of course, as moons are often much smaller than their host planets, it’s difficult to prove that they exist outside the Solar System as we’re observing from thousands of light years away.
But, despite the hurdle, astronomers use a technique known as gravitational microlensing, which takes advantage of chance alignments between stars, in an attempt to uncover any potential candidates. If one of these stars has a planet circling it, the alien world can act as a second lens to brighten or dim the light even more. Sadly, however – and as a team of exomoon hunters has recently discovered – microlensing effects can only usually be seen just the once, which makes declaring a new discovery extremely difficult.
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