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Frederic Rasio on "Planetary Orbits"

April 14, 2005

Frederic Rasio on "Planetary Orbits"

Astrophysicists at Northwestern University have found direct evidence to explain why planets in other systems have more elongated orbits than the orbits observed in our own solar system. Frederic Rasio, associate professor of physics and astronomy, says the circular orbits of planets in our system seem to be the exception to the rule…

Rasio: Our planets seem to be going around really circular orbits while the planets that have now been detected elsewhere all appear to be going around in a very eccentric, elongated orbits that takes them very close to the center of the star for part of the cycle and then very far away on the other side.

Rasio says the elongated orbits of planets in systems can be explained by perturbations in the orbits of planets occurring over billions of years…

Rasio: In many cases, 2 of the planets will be so close together that they actually kick each other rather strongly. Basically one gets kicked into all the other planets and they start kicking each other out , and basically the whole system of planets goes through a very violent stage of instability and chaos. And, what’s left behind is typically a bunch of survivors. These survivors will typically be on very elongated orbits that resulted from the slingshot mechanism.

Rasio says this planet scattering could potentially occur in our solar system…

Rasio: Computer simulations of planetary systems show that all of them, at some level, are chaotic. It’s only a question of time. It’s probably the case, that something like the solar system just has a much longer life time, the planets can continue to go around their initial circular orbit for a very long time before anything significant happens, in terms of perturbations and scatterings.

Rasio says this discovery questions the long held principle that our solar system is not unique…

Rasio: We should never conclude that we are in a special place, because why should we be special? However, there is something we know is very special about our solar system, we are in a system that obviously had characteristics such that the kind of life we have was able to develop.

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