Once it was enough to find planets outside our Solar System, but with thousands of exoplanets confirmed, it's now possible to learn something about how they are organized. An international team of scientists led by Université de Montréal astrophysicist Lauren Weiss has found that exoplanets revolving around the same star show a pattern of similar sizes and regular orbital spacing.

Using the W M Keck Observatory on Maunakea in Hawaii, Weiss and her team studied 1,035 exoplanet systems that were discovered by NASA's Kepler Space Telescope. These were examined for high resolution spectra that allowed the researchers to make precise measurements of the stars and their planets.

By focusing on 909 planets in 355 multi-planet system located between 1,000 and 4,000 light years away, the scientists were able to apply statistical analysis to the planets and their relationships to one another and two distinct patterns emerged.

First, exoplanets of the same size tended to group together, much in the same way that planets in the Solar System do. In our system, the small, rocky Earthlike planets congregate in the inner Solar System while the outer system is dominated by the great gas giants. Second, the planets are spaced apart regularly in a way that cannot be attributed to random distribution.

The team says that this has a great deal of significance when it comes to our understanding of planetary formation. This is because the classic model of planet formation where the planets form from an accretion disk of gas and dust should cause the sort of regular groups and spacings seen by the Montreal team.

The only problem is that while the Solar System shows a similar grouping, the distances are far from regular. Though the inner planets are rocky and terrestrial, they vary in spacing and size. This indicates that the gravitational fields of Jupiter and Saturn caused major disruptions to the orbits of the inner planets during formation.

To gain a better understanding of this hypothesis, Weiss and her term are taking a closer look at Jupiter-like planets in multi-planet systems. The current batch of planets all had their planets very close to their stars, but the plan is to find giant planets farther out and see how they affect the inner planets. The hope is that this will not only provide a better understanding of system formation, but the ability to predict the presence of potentially life-bearing planets.

The research was published in the Astronomical Journal.