Mystery Solved: How The Orbits Of Extrasolar Planets Became So Eccentric

[Knight-Dragon]

Bad news for UFO believers...

http://www.sciencedaily.com/releases/2005/05/050510185421.htm

EVANSTON, Ill. --- Except for the fact that we call it home, for centuries astronomers didn't have any particular reason to believe that our solar system was anything special in the universe. But, beginning with the discovery 10 years ago of the first planet outside our solar system, evidence suggests that, as far as planetary systems go, the solar system might be special indeed.

Instead of the nice circular orbits our nine planets enjoy, most of the more than 160 extrasolar planets detected in the last decade have eccentric orbits: so elongated that many come in very close to the central star and then go out much further away. In a paper to be published April 14 by the journal Nature, astrophysicists at Northwestern University are the first to report direct observational evidence explaining the violent origins of this surprising planetary behavior.

"Our results show that a simple mechanism, often called 'planet-planet scattering,' a sort of slingshot effect due to the sudden gravitational pull between two planets when they come very near each other, must be responsible for the highly eccentric orbits observed in the Upsilon Andromedae system," said Frederic A. Rasio, associate professor of physics and astronomy. "We believe planet-planet scattering occurred frequently in extrasolar planetary systems, not just this one, resulting from strong instabilities. So while planetary systems around other stars may be common, the kinds of systems that could support life, which, like our solar system, presumably must remain stable over very long time scales, may not be so common."

Verene Lystad, an undergraduate student majoring in physics at Northwestern, and Eric B. Ford, a post-doctoral fellow at the University of California Berkeley and a former student of Rasio's at the Massachusetts Institute of Technology, are members of Rasio's research team and authors on the Nature paper.

The system they focused on, three huge Jupiter-like planets orbiting the central star Upsilon Andromedae, was the first extrasolar multi-planet system ever discovered by Doppler spectroscopy. (In this technique, planets are detected and studied indirectly by measuring the reflex motion they impose on their parent stars.) The inner planet, a "hot Jupiter" so close to the star that its orbit is only a few days, was discovered in 1996, and the two outer planets, with elongated orbits that perturb each other strongly, were discovered in 1999. As a result, the system now has been well studied for many years and offered the best and most accurate data for the research team's calculations.

"In this system the two outer planets are in a very peculiar orbital configuration, which kept puzzling us for a long time," said Rasio.

To understand this better, Rasio and his collaborators developed a precise computer model of the orbits of the planets as they are today and then evolved them back tens of thousands of years. Their analysis showed that the system evolved over time exactly as would be expected if the initially stable system was suddenly perturbed, with the sudden disturbance affecting the outermost planet only.

They showed that a fourth giant planet, which is no longer in the system, must have come in too close and scuffled with the outer planet in a gravitational feud, eventually kicking the outer planet into the middle one. The fourth planet -- the troublemaker -- was ejected into space. The abrupt kick sent the outer planet into an elliptical orbit, while the middle planet initially remained on a circular orbit. Over time, the outer planet eventually perturbed the middle planet's orbit enough to deform it slowly into an eccentric orbit as well, which is what is seen today, although every 7,000 years or so the middle planet returns gradually to a circular orbit.

"This is what makes the system so peculiar," said Rasio. "Ordinarily, the gravitational coupling between two elliptic orbits would never make one go back to a nearly perfect circle. A circle is very special."

"Originally the main objective of our research was to simulate the Upsilon Andromedae planetary system, essentially in order to determine whether the outer two planets lie in the same plane like the planets in the solar system do," said Lystad, who started working with Rasio when she was a sophomore and did many of the computer integrations as part of her senior thesis. "We were surprised to find that for many of our simulations it was difficult to tell whether the planets were in the same plane due to the fact that the middle planet's orbit periodically became so very nearly circular. Once we noticed this strange behavior was present in all of our simulations, we recognized it as an earmark of a system that had undergone planet-planet scattering. We realized there was something much more interesting going on than anyone had found before."

Understanding what happened during the formation and evolution of Upsilon Andromedae and other extrasolar planetary systems has major implications for our own.

"In these newly discovered systems things have not remained stable for billions of years," said Rasio. "While they may have formed like the solar system, after a while things went catastrophic. Our solar system, it appears, is rather peculiar in its long-term stability."

 

[FearlessLeader2]

If I didn't regard it as a waste of time, I'd point out an obvious correlation between this latest discovery and a fairly popular topic that gets debated frequently here.

But, naaah.

Nice to know science agrees with the Bible though...

 

[Masquerouge]

If I didn't regard it as a waste of time, I'd point out an obvious correlation between this latest discovery and a fairly popular topic that gets debated frequently here.

But, naaah.

Nice to know science agrees with the Bible though...

Could you point where in the Bible the specifity of the eccentricity of the orbits of the planets in our solar system, versus other solar systems, is discussed ? Or did I miss a book ?

 

[FearlessLeader2]

You missed something, that's for sure. Maybe it was the point, maybe it was the little bus you ride to school, but you missed something.

Here's a free hint:

The article above strongly implies that earthlike planets are not only rare, but most of them are in solar systems that are unstable due to the influence of large planets with elliptical orbits. Does that mean anything to you?

 

[Knight-Dragon]

Moderator Action: If you gentlemen don't mind, stop trying to hijack my thread into another religious thread.

 

[Quasar1011]

This is only one planetary system. I don't see how the mystery can be said to have been solved, based on just one system. Solved for the Upsilon Andromedae system itself, perhaps...

 

[Masquerouge]

This is only one planetary system. I don't see how the mystery can be said to have been solved, based on just one system. Solved for the Upsilon Andromedae system itself, perhaps...

Plus they don't look to sure of themselves either, or maybe it's standard scientific caution :
"We believe planet-planet scattering occurred frequently in extrasolar planetary systems, not just this one, resulting from strong instabilities. So while planetary systems around other stars may be common, the kinds of systems that could support life, which, like our solar system, presumably must remain stable over very long time scales, may not be so common."

Anyway I'm really lacking the astrophysical tools here, but to me the sheer number of stars in the Universe is a strong argument for our solar system not to be unique.

 

[col]

I've argued against this line many times. If the chances are small enough - and I think they are for all kinds of reasons - , the number of stars doesnt make it likely that there is life anywhere else in the universe. Its the product that matters.

col (ex-astrophysicist)

 

[The Last Conformist]

Only, small enough is very small. If only one sun-like star in a thousand has a planetary system similar to ours, that's still millions in our galaxy alone.

 

[(+) Influence]

Plus they don't look to sure of themselves either, or maybe it's standard scientific caution :
"We believe planet-planet scattering occurred frequently in extrasolar planetary systems, not just this one, resulting from strong instabilities. So while planetary systems around other stars may be common, the kinds of systems that could support life, which, like our solar system, presumably must remain stable over very long time scales, may not be so common."

Anyway I'm really lacking the astrophysical tools here, but to me the sheer number of stars in the Universe is a strong argument for our solar system not to be unique.

I would assume it's hard for astro-physists to actually be certain of their theories. It would seem arrogant if they were to declare their theory to be right after at most several decades of observation for something that is billions of years old.

 

[Bozo Erectus]

We obviously have a very powerful instinct to see ourselves as unique or somehow special. When we had virtually no information at all and based our views of the universe on religion, we took it for granted that we were the center of the universe and the pinnacle of creation. When Galileo and others began showing that the Earth is just another planet among others and later that the sun itself was just another star and nothing special, and when Darwin showed that even the human race itself is just another animal species, these new ideas were resisted (in fact, theyre still being resisted). Somehow, no matter what we learn, we always manage to adapt to the new data and still reassure ourselves that we're special in some way. So here we are in the 21st century, in an age where science rules, when our instruments are barely beginning to explore the space around us, and still, the common sense consensus among the scientific establishment, along with the population at large, is that not only is our species unique and alone in the cosmos, but our very solar system itself is unique and special! People who say differently are still ridiculed or dismissed as cranks. Ah humanity, gotta love ya, at least youre consistent!:shakehead

 

[Renata]

I think it's a little silly of them to try to draw conclusions about all planetary systems when we can still only observe a very specific subset of possibilities. But it sounds like some interesting work, nonetheless.

Renata

 

[Shaihulud]

I'll like to point out that the extra solar planets we discovered are massive, almost protostars. The primary reason we were able to detect them is due to their mass. Planetery systems could exist aroubd every star we know and we would not know because we can't detect them yet. Those extra solar planets that we discovered, they are the odd ones that stands out!

 

[Eran of Arcadia]

What I want to know is how the existence of life on other planets is a threat to the religious point of view. "We're not alone, ergo God doesn't exist" doesn't make any sense to me. Even knowing we are physiologically similar to other species on this planet isn't really a problem, so why should this be?

 

[Oerdin]

I doubt it is a case of most other solar systems being highly excentric rather the only planets we can detect are ones which cause a great deal of wobble in the star they orbit around. That means the planet in question must be very large and how a very excentric orbit or we won't see it.

This is a bias in our sampling methods and nothing more.

 

[stormbind]

@Eran, no. Life on other planets is no more a threat to religion than life on other continents.

I think the discovery is valuable, because it will at least help us to identify rules for solar systems which are more likely to harbour life. This is surely better than random searching?

If most planets follow a simiar pattern, and are changing temperatures so rapidly, we might find them easier to mine, because just about every planet will offer a window for exploitation

 

[Renata]

I'll like to point out that the extra solar planets we discovered are massive, almost protostars. The primary reason we were able to detect them is due to their mass. Planetery systems could exist aroubd every star we know and we would not know because we can't detect them yet. Those extra solar planets that we discovered, they are the odd ones that stands out!

Or they really could be the vast majority of planetary systems. There's just no way to know.

Renata

 

[betazed]

Or it could be that we detect eccentric orbit planets because they are easier to detect! Seems to me that the doppler shift of star method is specifically easy when the planet has an eccentric orbit.

We will see how the numbers look when we can detect hundreds of planets using the transit approach.

 

[RoddyVR]

i'm curious.
the methods that they use to "find" the planets. which planets in our own system would they see from that distance? would they even see earth? or is jupiter the only one big enough to be detected by "our tech level" at the distance that other stars are to us?

 

[The Last Conformist]

i'm curious.
the methods that they use to "find" the planets. which planets in our own system would they see from that distance? would they even see earth? or is jupiter the only one big enough to be detected by "our tech level" at the distance that other stars are to us?

Jupiter, possibly Saturn, I believe.