Jupiter is a colossal ball of gas that sits five times farther from the Sun than Earth. Now imagine a similar ball, but around another star, at a distance tens of times greater. These are called cold Jupiters, and they remain a puzzle: how did they get there?
Astronomers studied four such planets around distant stars. They combined two observation methods: tracking how the star wobbles slightly under the planet's gravitational pull, and how it slowly drifts against the background of other stars over 25 years. It's like watching a swing: by the motion of the seat, you can tell how heavy the child is, even if you can't see them.
By merging the data, scientists calculated the planets' masses and orbital tilts. It turned out that one star has two planets moving in highly inclined planes, as if their orbits had been tilted. This is a rare case that will help test how such systems become so skewed.
The discovery shows that cold Jupiters might be far more numerous than we thought. The Gaia telescope, in the coming years, will likely find hundreds more of these worlds, and then the picture of planet formation will become clearer.
The Jupiter from the first sentence is our neighbor. But these distant giants, found by barely perceptible stellar motions, remind us that planetary systems can be arranged very differently from ours.
One of the found planets has a mass of only 0.37 Jupiter masses — less than Saturn, but it is still considered a cold Jupiter because of its location far from the star.
In Stanislaw Lem's novel 'Solaris', the ocean planet orbits two suns, and its orbit long remained a mystery, just like the orbits of cold Jupiters, which scientists try to decipher from indirect clues.