## 2009 PIMS-CSC Seminar - 07

- Date: 03/27/2009

Simon Fraser University

Is the Outer Solar System Chaotic?

The stability of our Solar System has been debated since Newton devised

the laws of gravitation to explain planetary motion. Newton himself

doubted the long-term stability of the Solar System, and the question

has remained unanswered despite centuries of intense study by

generations of illustrious names such as Laplace, Langrange, Gauss, and

Poincare. Finally, in the 1990s, with the advent of computers fast

enough to accurately integrate the equations of motion of the planets

for billions of years, the question has finally been settled: for the

next 5 billion years, and barring interlopers, the shapes of the

planetary orbits will remain roughly as they are now. This is called

"practical stability": none of the known planets will collide with each

other, fall into the Sun, or be ejected from the Solar System, for the

next 5 billion years.

Although the Solar System is now known to be practically stable, it may

still be "chaotic". This means that we might---or might not---be able

to precisely predict positions of the planets within their orbits, for

the next 5 billion years. The precise positions of the planets can

effect the tilt of each planet's axis, and so can have a measurable

effect on the climate. For the past 15 years, there has been some

debate about whether the Solar System exhibits chaos or not: when

performing accurate integrations of the planetary motions, some

astronomers observe chaos, and some do not. This is particularly

disturbing because it is known that inaccurate integration can inject

chaos into a numerical solution that would otherwise be stable.

In this talk I will demonstrate how I closed that 15-year debate on

chaos in the solar system by performing the most carefully justified

high precision integrations of the orbits of the outer planets that has

ever been done. The answer surprised even the astronomical community,

and was published in _Nature Physics_.

I will also show lots of pretty (but as yet unpublished) pictures at

the end, demonstrating the fractal nature of the boundary between chaos

and regularity in the Outer Solar System.

2:30pm, Rm. 8500, TASC II