Planetary systems outside our own tend to follow a similar pattern. The planets are usually around the same size and each one spaced at regular intervals. That’s according to a study looking at 909 planets across 355 stars.
“The planets in a system tend to be the same size and regularly spaced, like peas in a pod. These patterns would not occur if the planet sizes or spacings were drawn at random,” says Lauren Weiss, an astrophysicist from the University of Montreal who led the international research team responsible for the study.
That stands in stark contrast to our own solar system. The innermost planets come in a wide range of sizes with large spacing between each.
With the help of the W. M. Keck Observatory, the team found that small planets tend to be followed by more small planets. The same goes for big planets. And there is regular orbital spacing between the two.
So, what makes our solar system different? Evidence points to Jupiter and Saturn having something to do with it. The two gas giants are believed to have disrupted our solar system’s early structure giving us the four widely spaced terrestrial planets we have today.
Weiss plans to look for Jupiter-like planets in multi-planet systems discovered by Kepler in a new study. And see how their presence, or lack of, affect the patterns of inner planetary systems.
But in the grand scheme of things, 909 planets doesn’t even register as a blip. Current telescopes can only see so much. Plus, the transit method (when the planet crosses in front of the star) of discovering planets means we pretty much only detect the innermost planets anyways.
Take Jupiter. It takes 12 years to make a trip around the Sun. It would take almost as long to notice a planet as far out as Jupiter in another solar system. That’s why most exoplanets we hear about orbit absurdly close to their star. They are just easier to detect. It doesn’t take as long to wait for the relatively tiny planet to cross in front of their host star.
Still, this pattern needs an explanation. The more we understand how planetary systems are formed and why, the better we can get at determining which systems are the best bet to have terrestrial planets. Once we know that, we can take a closer look to see if any are good places for life to set up shop. Those are mysteries the next generation of telescopes like the James Webb Space Telescope, and others, will attempt to tackle.