Including the new findings, between 25 and 50 percent of all extrasolar planets whose angles of inclination have been measured have tilts exceeding 30 degrees. In Earth's solar system, Earth has the greatest orbital tilt relative to the sun's axis of rotation, at an angle of 7.1 degrees. The newly found tilted planets, Pont says, represent "a spectacular upheaval of the standard view of close-in planet formation ... and probably indicate instead catastrophic encounters between several planets." All this is old hat to Ford and Fred Rasio of Northwestern University in Evanston, Ill., as well as other theorists who have been advocating for years that gravitational encounters between planets play a critical role. Although it will take time for all the new discoveries to be published and compared with models, says Ford, "my impression is that several people at this very meeting were surprised by the findings and began to realize that planet scattering is likely very important for determining the final architecture of planetary systems." Even for the sedate, orderly solar system, planet-planet interactions have been important, Ford says. He cites the violent events responsible for the formation of Mercury and for the formation of Earth's moon, believed to be created when a Mars-sized body crashed into the young Earth. He speculates that what makes the solar system special is not that it entirely avoided planetary pinball, but that it happened relatively early. Early enough, in fact, that the short-lived, massive disk of rocky debris survived after the last strong planet-scattering event. The disk's gravity would have damped back down elongated and inclined orbits, returning the solar system's planets "to the nearly circular and coplanar orbits that we enjoy today," Ford suggests. Related Links: |
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