Solar Systems Are Like Peas in a Pod—But Ours Is Wildly Disordered

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A montage image of the solar system pictured against a false-color view of the Rosette Nebula. ASU/JPL/NASA

Scientists combing the skies have found that our solar system is a strange and unusual beast. While other systems are orderly and neat, Jupiter and Saturn might have knocked our planets off-kilter.

The team of researchers used the W.M. Keck Observatory on the Manau Kea volcano in Hawaii to analyze 909 planets in 355 planetary systems. These planets were discovered by NASA's Kepler spacecraft.

Planets in individual systems, the team found, are usually close in size to their neighbors and orbit their stars at regular slots.

Lauren Weiss, astrophysicist and lead author of the study, which was published in The Astronomical Journal, explained in a statement, "The planets in a system tend to be the same size and regularly spaced, like peas in a pod."

Our system's planets are wildly different in size. The radius of Mercury is approximately 1,500 miles, while Jupiter's is more than 40,000 miles. The spaces between the inner planets of our solar system are also particularly large in comparison to the other observed systems.

The Role of Jupiter and Saturn

The size and distribution of planets in systems could be related to their creation. The scientists write, "Perhaps the physics of planet formation set a size to which planets prefer to grow."

Many scientists believe planets form in a disk of gas and dust circling a newborn star. These planets could emerge in patterns like the "peas in a pod" model, the researchers say—close together and relatively uniform in size and orbital spacing.

Weiss and her team suspect that Jupiter and Saturn are to blame for our solar system's haywire structure. There is ample evidence, they say, that these behemoth planets have disturbed our system's order.

To test their theory, Weiss will search for Jupiter-like planets at large orbital distances from their stars. At present, research has focused on planets closer to their stars because of the limited length of the Kepler mission.

By learning more about how planets emerged, the scientists hope to be able to determine which stars might host habitable planets.