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sol_g2v
2004-Nov-23, 05:19 AM
Several objects larger than Pluto likely lurking in outermost solar system, Sedna co-discoverer believes: link (http://www.space.com/scienceastronomy/mystery_monday_041122.html)

frogesque
2004-Nov-23, 08:49 AM
Several objects larger than Pluto likely lurking in outermost solar system, Sedna co-discoverer believes: link (http://www.space.com/scienceastronomy/mystery_monday_041122.html)

Interesting speculation but at this point it remains speculation untill more research and observations are made.

Unless of course PX bears down on us, reverses the orbit of Venus and describes daisy chains round the sun :lol:

R.A.F.
2004-Nov-23, 01:51 PM
Interesting speculation but at this point it remains speculation until more research and observations are made.

I agree. Until/unless an object larger than Pluto is observed, I'm real uncomfortable speculating that something larger than Pluto is actually out there.

Paul Mitchell
2004-Nov-23, 02:48 PM
Several objects larger than Pluto likely lurking in outermost solar system, Sedna co-discoverer believes: link (http://www.space.com/scienceastronomy/mystery_monday_041122.html)

I asked Brown if there might be worlds larger than Pluto clear out at the edge of the Oort Cloud, 1.5 light-years away and nearly half the distance to the Alpha Centauri star system.

It does stike me as odd that we should have "planetoids" as far out as half way to Alpha Centauri.

What is to stop objects at that distance from swapping from orbiting one star to another? In which case it would be inappropriate to describe them as part of our solar system, except temporarilly, surely?

frogesque
2004-Nov-23, 03:13 PM
Several objects larger than Pluto likely lurking in outermost solar system, Sedna co-discoverer believes: link (http://www.space.com/scienceastronomy/mystery_monday_041122.html)

I asked Brown if there might be worlds larger than Pluto clear out at the edge of the Oort Cloud, 1.5 light-years away and nearly half the distance to the Alpha Centauri star system.

It does stike me as odd that we should have "planetoids" as far out as half way to Alpha Centauri.

What is to stop objects at that distance from swapping from orbiting one star to another? In which case it would be inappropriate to describe them as part of our solar system, except temporarilly, surely?

Could they orbit both in a figure of eight? Ooooh! Freaky woowoo thought :o

Evan
2004-Nov-23, 04:17 PM
Can't orbit in a figure eight. That is an unstable orbit and will result in the object being ejected. To make a figure eight orbit the object must pass through the L1 point between the two stars. That is a chaotic region where tiny changes in initial conditions result in large changes in outcome.

frogesque
2004-Nov-23, 04:36 PM
Can't orbit in a figure eight. That is an unstable orbit and will result in the object being ejected. To make a figure eight orbit the object must pass through the L1 point between the two stars. That is a chaotic region where tiny changes in initial conditions result in large changes in outcome.

So I guess it's safe to come out from under the table now? :o

sol_g2v
2004-Nov-23, 08:21 PM
Maybe we just lob giant snowballs back and forth with Alpha Centauri and Barnards Star. That would be fun.

Paul Mitchell
2004-Nov-24, 12:22 AM
Can't orbit in a figure eight. That is an unstable orbit and will result in the object being ejected. To make a figure eight orbit the object must pass through the L1 point between the two stars. That is a chaotic region where tiny changes in initial conditions result in large changes in outcome.

Would such an orbit have to pass through the L1 point?

I'm no expert in calculating orbits (and it's about to show :D) but I presume tha it's not possible to have an elongated eliptical orbit about both stars. However could not a figure-eight type orbit that passed either side of the L1 point be possible? Mind you it'd still have to pass through two points of "balance" between the stars' gravities, so the instability may still remain.

Evan
2004-Nov-24, 12:35 AM
For the orbit to switch from one primary to another it would have to pass through the L1 point, but that won't work. If it passed short of the L1 point (reached periapsis) it wouldn't switch to the other star. If it passed further than the L1 point then it must approach the other star with excess velocity and will not come back to the previous periapsis point where it can assume another orbit around the first star. A figure eight orbit is inherently unstable. This does not even consider any proper motion that may occur in the star that does not have influence while the object orbits the other.

Another way to think about it is to try and visualize a figure eight orbit between Earth and Moon. By the time an object loops around the Earth and heads for the Moon the Moon isn't even there anymore.

eburacum45
2004-Nov-24, 12:38 AM
Since Alpha Centauri has a proper motion independent of the Sun no orbit would be stable.

Perhaps some sort of orbit might be possible within a cluster, or between two stars with shared proper motion (for instance between former members of clusters like the stars in the Ursa Major stream)-

but it seems very unlikely.

Evan
2004-Nov-24, 12:53 AM
Any pair of gravitational objects must have a proper motion relative to each other even if it is just diving straight together with no angular momentum.

eburacum45
2004-Nov-24, 01:30 AM
Hmm. that has made me think... the Sun was probably in a cluster of some sort at one point; the Oort clouds of stars in a cluster must often merge and swap members, until the cluster falls apart after hundreds of millions of years. So our cloud might contain a sample of the whole cluster.

I wonder how long an Oort cloud takes to form.