Planet Neptune Not Guilty of Harassment

New research by a University of Victoria PhD student is challenging popular theory about how part of our solar system formed. At the meeting of the American Astronomical Society’s Division of Planetary Sciences in Pasadena, California, Alex Parker presented evidence that, contrary to popular belief, the planet Neptune can’t have knocked a collection of planetoids known as the Cold Classical Kuiper Belt to its current location at the edge of the solar system.

Parker and his thesis supervisor Dr. J. J Kavelaars (Herzberg Institute of Astrophysics) studied binaries — systems of two objects that, like the Earth and the Moon, travel around the Sun while orbiting around each other. Binaries are extremely common in the Kuiper Belt. “Binaries are really useful tools for astronomers,” said Parker. “Since their orbits can be affected by their environment, we can use them to test what the interplanetary environment is like and what it was like in the past.”

Using computer simulations, the researchers determined that many binary systems in part of the Belt would have been destroyed by the jostling they would have experienced if Neptune did indeed move the Kuiper Belt to its current location. “These binaries with slow, wide orbits are a hallmark of the Cold Classical Kuiper Belt,” said Parker, “and they would not be there today if the members of this part of the Kuiper Belt were ever hassled by Neptune in the past.” This strongly contradicts a popular theory for the origin of the Cold Classical Kuiper Belt, and instead suggests that it formed near its present location and remained undisturbed over the age of the solar system.

The Cold Classical Kuiper Belt lies in a very flat ring between 6 and 7 billion kilometers from the Sun, and contains thousands of bodies larger than 100 kilometers across, roughly one-third of which may be in binary pairs. The Kuiper Belt is of special interest to astrophysicists because it is a fossil remnant of the primordial debris that formed the planets, says Parker. “Understanding the structure and history of the Kuiper Belt helps us better understand how the planets in our solar system formed, and how planets around other stars may be forming today.”

The research will be published in an upcoming edition of Astrophysical Journal Letters. A preprint is available online at http://arxiv.org/abs/1009.3495

Images

Illustration of a primordial Kuiper Belt binary during a close approach with the planet Neptune, similar to the encounters studied by Parker and Kavelaars.

* http://www.astro.uvic.ca/~alexhp/new/figures/Neptune_1500.jpg

* http://www.astro.uvic.ca/~alexhp/new/figures/Neptune_3000.jpg

Diagram illustrating the process that destroys binaries during close encounters. * http://www.astro.uvic.ca/~alexhp/new/figures/Neptune_dia.png

Alex Parker is supported by the National Science Foundation’s Graduate Research Fellowship Program.