The Search for Planet 9 Turns to Saturn and Cassini

Somewhere in the far outer reaches of the solar system lurks the mysterious Planet 9 (sometimes called Planet X), the giant planet CalTech professors Mike Brown and Konstantin Batygin claimed to have found evidence of just last month. It’s too far away to see but astronomers would like to know where to look when it finally makes its return close to the inner circle of planets. A new theory suggests that the key to pinpointing this location is currently in the vicinity of Saturn – the Cassini space probe.

What can a nearly 20-year-old spacecraft tell us about the path of a never-seen planet? Quite a bit, it turns out. Astronomers know that planets leave distinct fingerprints of heat energy behind in the path they take while orbiting the Sun. The amounts of energy left by a cold Planet 9 are tiny – tens of degrees above absolute zero making millimeter-length radio waves – but they’re there. If only there were some way to capture and identify those fingerprints.

Cassini

Cassini

Fortunately, that’s one of the many functions Cassini has performed as it traveled back and forth through Saturn’s rings. Agnès Fienga of the Nice Observatory in France and her fellow astronomers there have analyzed the data collected so far and, while it hasn’t shown where Planet 9 has traveled, it’s revealed plenty of places where it hasn’t. Already, half of the proposed possible Planet 9 orbital paths have been eliminated.

Planet 9 could be anywhere

Planet 9 could be anywhere

Will the definitive proof of Planet 9’s existence and route through the solar system be Cassini’s final moment of glory? The probe is scheduled to self-destruct in a plunge into Saturn’s atmosphere on September 15, 2017. This could convince NASA to extend the mission a few more years to 2020 to collect fingerprints for astronomers to analyze.

The process of elimination has helped many of us pass tests (OK, just me). It looks like it could help astronomers ace the test of proving the existence and path of Planet 9.