Most of the little moons of Jupiter and Saturn are oddballs. Their orbits are stretched out and tilted at odd angles. And some of them orbit in the opposite direction from the planets’ major moons. A study last year proposed that Jupiter and Saturn captured those moons thanks to a passing star.

Researchers used computers to study the orbits of many objects in the Kuiper Belt – a broad region beyond the realm of the planets. Many of their orbits are odd as well.

The work showed that all of those orbits could be explained by a close approach by a star billions of years ago. The star would have been a little less massive than the Sun. And it would have passed about 10 billion miles from the Sun – a bit more than a hundred times the distance from Earth to the Sun.

That would have taken the star near the edge of the Kuiper Belt. The star’s gravity would have stirred up the millions of objects in that region – chunks of ice and rock that can be quite large. In fact, the largest member of the belt is Pluto.

Many objects were kicked out of the solar system. But others would have been kicked toward the Sun. Some of them might have been captured by the giant outer planets – especially Jupiter and Saturn – giving both worlds big entourages of odd moons.

Jupiter itself is high in the sky at nightfall. It looks like a brilliant star. Binoculars reveal its large moons – but the odd little ones remain hidden.

Script by Damond Benningfield