Artist's impression of the rings around J1407b (centre) and how the eclipse the star it orbits (J1407, left). [credit: Ron Miller]

First ring system found beyond solar system may hide exomoons

Back in 2012, astronomers uncovered the first ring system in another solar system. Now they have released details of its dimensions and possible evidence of alien moons nestled within.

The rings encircle the planet J1407b. As the planet orbits its star, its set of more than 30 rings periodically blocks out some of the star’s light. Such eclipses can last for several weeks at a time, but the amount of light blocked can alter minute by minute as denser or sparser regions move across the star.

Artist's impression of the rings around J1407b (centre) and how the eclipse the star it orbits (J1407, left). [credit: Ron Miller]
Artist’s impression of the rings around J1407b (centre) and how the eclipse the star it orbits (J1407, left). [credit: Ron Miller]

Building up a picture of how the starlight varies over time gives astronomers something called a ‘light curve’. From that, the team from the Leiden Observatory in The Netherlands and the University of Rochester in the US has inferred that some of the rings must be tens of millions of kilometres wide – trumping Saturn’s rings, which are ‘only’ 250,000 kilometres in extent.

Like the Cassini division in Saturn’s rings, those around J1407b appear to have a sizeable gap too. In the case of Saturn, that gap is kept open by the gravitational tug from Mimas, one of its moons. Perhaps an alien moon (exomoon) is similarly keeping the gap around the exoplanet prised open. If so, it would have a mass between Mars and Earth’s and orbit its planet in around 2 years.

Image of Saturn clearly showing the Cassini division (the gap about halfway out). Could a similar gap around J1407b be kept open by an exomoon? [credit: NASA/ESA/Cassini]
Image of Saturn clearly showing the Cassini division (the gap about halfway out). Could a similar gap around J1407b be kept open by an exomoon? [credit: NASA/ESA/Cassini]

As J1407 is such a young star, these observations give us a wonderful glimpse of how planets, and perhaps their moons, form, providing a window into how our own set of worlds came to be here.