A Cornell University Professor’s recalculation of models linking a proposed 9th solar system planet to a slant in the orbital plane around our Sun could help constrain its possible size, mass and orbit.
Artist’s impression of Planet Nine. Image credit: Tom Ruen / ESO.
Earlier this year Batygin & Brown at the California Institute of Technology proposed a strange alignment of icy Kuiper belt objects at our Solar System’s edge could be explained by a 9th planet orbiting eccentrically beyond Neptune.
Last month a follow-up paper from Bailey et al at the same institution, and another from a Brazilian team led by Rodney Gomes, posted within the same week, suggested Planet Nine could also solve a second longer standing solar system puzzle – the misalignment between the Sun’s equator and the orbital plane of the planets around it.
This six degree offset is a problem as our understanding of the Solar System’s formation from a rotating dust cloud requires the equator of our newly formed Sun to be lying in the same plane as the outer disk from which the planets formed, and along which their orbits subsequently followed.
Enter Bailey and Gomes. In both papers Planet Nine’s steep orbit tugs on the other planets, gradually changing their orbital plane. This effect is only negligibly felt by the Sun due to its superior mass, causing a misalignment over time.
In this model the degree of tilt is heavily influenced by the mass of the Planet Nine, a value that Brown and Batygin had estimated to be around 10 times that of the Earth, based on the distribution of Kuiper belt objects.
“We decided to look for the right planetary mass that could cause the orbital inclination to see if it might fit within Brown and Batygin’s range and it did!” Dr. Gomes says.
“Whilst we weren’t validating Batygin & Brown’s hypothesis we have shown that if Planet Nine exists it provides a nice theoretical explanation of our titling Solar System.”
In Cornell, Professor Dong Lai was following events with interest ever since Brown and Batygin’s original paper and was moved to put pen to paper after reading the work from Bailey and Gomes.
“It’s all happened in only a few weeks!” Prof. Lai says.
“Their papers were very good science but rather formal, and I thought they would leave many observational physicists in difficulty when it came to interpreting them. As a result I wrote my paper in a much simpler way whilst still coming up with a broadly similar result.”
“Dong’s paper provides a way to understand the model with only conventional physics,” agrees Dr. Konstatin Batygin, co-author of the original Planet Nine paper.
However Gomes disagrees with Professor Lai’s description of his work as ‘simple’.
“Lai’s paper adds more accuracy to the final results by taking into account the fact that the equator of the Sun was not a fixed over time.”
In future Professor Lai hopes his contribution can provide a useful way of playing around with the mathematics to more easily narrow down properties of Planet Nine such as its mass, shape, or orbit through more accurate measurement of the properties and history of our Solar System’s orbital tilt.
Dr. Batygin agrees it could prove a more useful way of expressing the mathematics though warns of the assumption that even if Planet Nine exists, it is solely responsible for the full 6 degrees of tilt.
“There’s a complex set of variables at play which you have to input in these equations,” he says.
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Dong Lai. 2016. Solar Obliquity Induced by Planet Nine: Simple Calculation. arXiv: 1608.01421
