A planet-size object that possibly once visited the solar system may have permanently changed our cosmic neighborhood by warping the orbits of the four outer planets, a new study suggests. The findings may shed light on why these planets’ paths have certain peculiar features.
For decades, astronomers have debated how the solar system’s planets formed. However, most hypotheses agree on the type of orbit the planets should have: circles that are arranged concentrically around the sun and lie on the same plane. (If you viewed them edge-on, you would see only a line.) However, none of the eight planets, including Earth, have perfectly circular orbits. Plus, the planets’ paths don’t lie precisely on the same plane.
Compared with Mercury (whose orbit, within our planetary family, is the most egg-shaped and tilted), the paths of the four outer giant planets — Jupiter, Saturn, Uranus and Neptune — show minor deviations from the ideal orbits. Yet explaining these niggling discrepancies has been challenging, said Renu Malhotra, a planetary scientist at the University of Arizona in Tucson and a co-author of the new study.
“[T]he puzzle for theoretical astrophysics has long been to figure out how the orbits later became out-of-round and tilted from their mean plane by not too much and not too little,” she wrote in an email to Live Science. While previous research has focused on how interactions between these planets reshaped their orbits, Malhotra said, “these hypotheses are not consistent with certain important details of the observed orbits.”
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