The planets are coming! The planets are coming! Only months after announcing the possibility of a ‘Planet X’ 10 times Earth’s mass orbiting 250 times Earth’s distance from the sun, a team of Spanish astronomers think there may be another massive planet hiding even deeper in the inky depths.
In March this year, astronomers reported the discovery of 2012 VP113, an asteroid that orbits farther from the sun than any previously known. 2012 VP113 joins Sedna and a number of other asteroids beyond the outer asteroid belt (Kuiper Belt) whose orbits are aligned in a way that hints at the gravitational influence of a possible planet farther out. Scientists calculate that this world would be about 10 times the mass of Earth and orbit at roughly 250 times Earth’s distance from the sun.
Carlos and Raul de la Fuente Marcos at the Complutense University of Madrid in Spain have taken another look at these distant bodies. As well as confirming their bizarre orbital alignment, the pair found additional puzzling patterns, according to a recent article in New Scientist.
Too small to tug on one another, the team attributes the similarity of their orbits to the ‘shepherding’ influence of a larger unseen body in a pattern called orbital resonance.
We see orbital resonance at play with Neptune and Pluto. The two worlds exert a regular and repeating gravitational attraction on each other causing their orbits to be related by a simple whole number ratio. For every 2 orbits Pluto makes around the sun, Neptune makes 3.
Similarly, 2012 VP113 and friends appear to revolve as a group in lockstep with a distant world with a mass estimated between that of Mars and Uranus and orbiting 200 times Earth’s distance from the sun. Some of these remote asteroids have orbits that take them out to that distance – that’s where a second large planet may play a part.
Since it would be unusual for a distant shepherding planet to orbit so close to its ‘sheep’ unless it too were in resonance with yet another large body, the Spanish team suggests that another ‘Planet X’ 250 times the Earth-sun distance pulls the strings as it were. Their numbers square nicely with the distance predicted in the earlier work on Sedna and 2012 VP113.
Spotting any new Planet Xs will be extremely tricky. The remote asteroids travel along very elongated orbits that periodically take them close enough to the sun for us to photograph them. ‘Close’ is a bit of an exaggeration. Sedna, for example, only pulls up to 76 times the Earth-sun distance at best where it tops out at a feeble magnitude +20.5. Any planets beyond are expected to follow more circular orbits similar to the familiar inner solar system gang and glow ever so faint.
Heat-radiating planets as large as the ones predicted and at the distances suggested, should have been detected by NASA’s WISE space probe’s infrared survey. But WISE’s two complete infrared sweeps of the sky found that no object the size of Saturn or larger exists out to a distance of 10,000 times the Earth-sun distance (10,000 AUs or astronomical units) and no object larger than Jupiter exists out to 26,000 AUs. Still, WISE had its limits. A remote planet colder than about -330 F (-201 C) could escape detection.
Naturally, the results don’t preclude these smaller objects. While hypothetical for the moment, larger telescopes both on Earth and in orbit may one day coax these putative Planet Xs into the light.
For more information on the topic, check out the team’s scientific paper.