Sun Might Have Exchanged Hangers-On With Rival Star

[pmbryant]

From the New York Times:

Sun Might Have Exchanged Hangers-On With Rival Star
By DENNIS OVERBYE

The Sun may have captured thousands or even millions of asteroids from another planetary system during an encounter more than four billion years ago, astronomers are reporting today.

Such an interstellar ballet would explain many mysteries of the outer solar system - including the strange behavior of the recently discovered Sedna, the system's most distant known object, which occupies a strange elongated orbit far beyond Pluto.

The astronomers' calculations, from supercomputer simulations, suggest that gravity from the star at the center of the other planetary system could have kicked Sedna out of a more conventional orbit. In the process, the Sun and the other star would have swapped their outer entourages. Indeed, the astronomers estimate that there is a 10 percent probability that Sedna itself was one of those strangers.

(snip)

"I don't think anyone has considered that extrasolar planets would be in our own solar system," said Scott J. Kenyon of the Harvard-Smithsonian Center for Astrophysics. He is the co-author, with Benjamin C. Bromley of the University of Utah, of a paper being published today in Nature.

Their paper is the latest in a series of efforts to consider an intruding star as a way of explaining the weird properties of Sedna.

"Sedna surprised the hell out of everybody," said Harold F. Levison of the Southwestern Research Institute in Boulder, Colo., who has proposed a slightly different intruder scenario, with Alessandro Morbidelli of the Observatory of the Côte d'Azur in France.

(snip)

More: http://www.nytimes.com/2004/12/02/science/02solar.html?oref=login

[mainegreen]

1. Interesting article. Thanks!

[Warpy]

2. Sounds pretty unlikely to me

given the distances we're talking about and how a close enough encounter with another system would distort orbits enough to destroy both systems.

I find it likelier that there was a planet between Mars and Jupiter that suffered a catastrophic collision of some sort during its formation.

To capture anything into a stable orbit it must be moving slowly enough and it can't come close to any of the existing planets. Quite posibly the outer planets like Pluto and the posited X Y and Z planetoids are from outside the system, and quite possibly whatever destroyed the fifth planet was, but it's highly unlikely that all the material in the asteroid belt is from outside the system. The orbit is just too in line with the other system planets.

[papau]

4. Would not a second Sun establish the single plane orbit we see for 8 of

planets?

[pmbryant]

6. The single plane is established by the way planets are believed to form

Planets are believed form out of clouds of gas and dust that surround young stars. These clouds, due to the collisions between all the dust particles, soon settle into thin disks. (Such disks are seen around many young stars.) Planets presumably form from accretion in such disks.

So a "second Sun" is not necessary to establish a single orbital plane for the planets. (I'm not sure it is even conducive to this process, at least if it is too close.)

Peter

[papau]

7. I agree - but the single plane observation would not be affected was

what I was getting at.

The capture idea was applied to Pluto was it not? - based on the "plane" of the orbit? Or is my memory failing again?

If so, how is this different from the capture of a weakly attached planet that I assume was the Pluto senario?

[pmbryant]

8. Pluto

I guess I don't understand your question about the single plane of the planets.

As for Pluto, its orbit is anomalous compared to the other planets, but not nearly so much as to suggest it was captured. I believe almost all currently believed scenarios suggest that it formed as a regular member of the Solar System (like the smaller Kuiper Belt asteroids).

[papau]

9. I am not keeping up, obviously. Thanks for the heads up on Pluto not

being a captured planet.

I was thinking about the effect on planetary orbits of a pass by of another sun - Is the single plane that I recall now a close to a single plane, with Pluto a little less close to that plane?

Good grief - I do not know if all the other "moons" are in similiar single plans.

Amazing how much I do not know!

The world was easy when there was less knowledge!

:-)

[pmbryant]

10. Single plane

You're right that virtually all the planets and traditional asteroids and Kuiper Belt asteroids etc are all essentially in a single plane (the "ecliptic" for short). Mercury is a bit anomalous, and so is Pluto. But they are still at least "close".

The satellites are different. Most tend to be in the equatorial plane of the planet they circle (except our own Moon, oddly enough, which is actually closer to the ecliptic than to the Earth's equator). So for an extreme example like Uranus, whose equator is tilted roughly 90 degrees to the ecliptic, its moons orbit in a very different plane than the planets.

As for an close encounter with another Sun messing up the orbital plane of the planets, I think it would have to be extremely close to do so.

Indeed, it is hard to keep up with this stuff!

--Peter

[mainegreen]

11. Weird

I always thought that the moons of Uranus still orbited in the same (or almost same) plane as we did and just the planet got knocked over. Its kinda hard for me to imagine the scenario that would end up with the moons in Uranus' equatorial plane unless they all formed from the event that tipped in over in the first place.

Explanations, anybody?

[pmbryant]

12. Uranus's satellites

Weird but true. I just poked around the internet a bit and didn't find much definitive on current theories for the formation of Uranus' satellites. And I don't recall hearing much about it back when I studied this kind of stuff much more closely.

I suspect this is an area where our present knowledge is quite limited.

:shrug:

Peter


PS I did find this abstract of a paper from 2003 that suggests that your scenario is a topic of discussion:

http://edpsciences.nao.ac.jp/articles/aa/abs/2004/01/aa3475/aa3475.html

We study the thermodynamical conditions existing in the Uranian subnebula from which the regular satellites were presumably formed, assuming it was produced by an earth-sized body impact on proto-Uranus (Stevenson 1984; Slattery et al. 1992). ...

[pmbryant]

13. Just found some more info on Uranus' satellites formation (not definitive)

From an Oct 2004 paper by astronomers at the University of Hawaii:

http://arxiv.org/PS_cache/astro-ph/pdf/0410/0410059.pdf

Uranus is noteworthy in the sense that its obliquity exceeds 90 degrees. This compares to the modest obliquities of Jupiter, Saturn and Neptune at 3, 27 and 30 degrees respectively. A possible cause is that a protoplanet of about one Earth mass collided with Uranus near the end of its growth phase (Korycansky et al. 1990; Slattery et al. 1992). Greenberg (1974) argued that the current regular satellites must have formed after Uranus’ obliquity reached 98 degrees because their low inclination prograde orbits would not have adjusted to their current configurations with Uranus. Recently Brunini et al. (2002) suggested that if Uranus’ tilt was created by a giant impact any satellites beyond about 2 × 106 km (i.e. all known irregular satellites of Uranus) would have likely been lost owing to the orbital impulse imparted to Uranus by the impactor. In addition, Beauge et al. (2002) show that any significant migration by Uranus through a residual planetary disk would have caused its outer satellites to become unstable.

So, through all that jargon, it sounds to me like this is a wide-open subject.

--Peter

[mainegreen]

14. Interesting PDF

A bit more intelligible than the other link. Does sound like there is some debate about this. Hopefully they send out some probes to analyze the makeup of the moons.

That is, of course, after we send some repukes to Mars!

[pmbryant]

5. This isn't about the traditional asteroid belt

They aren't proposing that the traditional asteroids are from another Solar System, but rather:

Either encounter would also leave alien planetoids in our solar system (and some of ours in the alien system) orbiting at a steep angle to the plane in which the planets go around. And so the next step is to search for such objects.

So the hypothetical alien asteroids have not been found. And of course, may not even exist, since this is scenario is just a hypothesis to explain the orbit of Sedna.

--Peter

[papau]

3. cool - and original - thanks for posting!

:-)