Planetary science

Cassini aids hunt for Planet Nine

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Researchers using the Cassini spacecraft have narrowed down the search for the Solar System's hypothetical ninth planet.

Planet Nine is thought to be orbiting in the far outer Solar System, but has not yet been found. If it exists, its gravity should tug slightly on the outer planets, including Saturn. To determine Saturn's orbit, Agnès Fienga at the University of Nice Sophia Antipolis in Valbonne, France, and her colleagues used data from the ground-based radio-dish network that tracks the position of Cassini, which has been orbiting Saturn since 2004. Using a Solar System model refitted with Planet Nine, the researchers conclude that if it exists, the planet probably lies along a particular 21° slice of its predicted orbit.

If Cassini continues to operate until 2020, data from the spacecraft would further improve the estimate of the planet's location, the team says.

Astron. Astrophys. 587, L8 (2016)

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