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A.DIM
2010-Mar-12, 10:12 PM
Getting WISE about Nemesis (http://www.astrobio.net/exclusive/3427/getting-wise-about-nemesis), from AstroBio.

A recently-discovered dwarf planet, named Sedna, has an extra-long and unusual elliptical orbit around the Sun. Sedna is one of the most distant objects yet observed, with an orbit ranging between 76 and 975 AU (where 1 AU is the distance between the Earth and the Sun). Sedna’s orbit is estimated to last between 10.5 to 12 thousand years. Sedna’s discoverer, Mike Brown of Caltech, noted in a Discover magazine article that Sedna’s location doesn’t make sense.

"Sedna shouldn't be there,” said Brown. “There's no way to put Sedna where it is. It never comes close enough to be affected by the Sun, but it never goes far enough away from the Sun to be affected by other stars.”

Perhaps a massive unseen object is responsible for Sedna’s mystifying orbit, its gravitational influence keeping Sedna fixed in that far-distant portion of space.

“My surveys have always looked for objects closer and thus moving faster,” Brown told Astrobiology Magazine. “I would have easily overlooked something so distant and slow moving as Nemesis.”


Yep, if such a body were a part of our system, we would not necessarily have discovered it by now.

ToSeek
2010-Mar-12, 11:49 PM
Thread restored with the proviso that any discussion should be based on mainstream sources.

Buttercup
2010-Mar-12, 11:52 PM
I'm from Sedna, ask me anything! :D

A.DIM
2010-Mar-13, 12:13 AM
I'm from Sedna, ask me anything! :D

What is the cause of your dwarf planet's orbit?

:D

BigDon
2010-Mar-13, 01:09 AM
The Oort cloud doesn't have enough mass?

(That's beyond Kuiper belt isn't it?)

A.DIM
2010-Mar-13, 03:26 PM
The Oort cloud doesn't have enough mass?

I'd think Brown has considered this.


(That's beyond Kuiper belt isn't it?)

Yes, there's an inner and outer Oort cloud beyond Kuiper Edgeworth.

flynjack1
2010-Mar-13, 04:27 PM
Nemesis could be out there stirring up Lucifer's Hammer even as we speak. Unscientifically speaking, just when we think we have a handle on the dwarf planets new objects such as Sedna show up. Its a big sky and if this thing is well off the ecliptic it could take awhile to find. Intuitively it seems more likely than not.

A.DIM
2010-Mar-13, 05:01 PM
I tend to think so as well, but we need better evidence.
Cometary wakes, inclined, elliptical orbits, kuiper "cliffs" etc. do not a Nemesis make.

Daniel Whitmire (http://www.ucs.louisiana.edu/~dpw9254/) co author with Matese on some papers, has been looking for it for a quarter century.

I suspect he too, like those of us interested, is looking forward to WISE's results.

Buttercup
2010-Mar-13, 05:11 PM
I have an idea about Sedna, but don't want to mention it for fear of being banned for 24 hours. :(

Maybe it's just one of those things like the bumble bee's ability to fly?

BigDon
2010-Mar-13, 06:01 PM
Thread restored with the proviso that any discussion should be based on mainstream sources.

Well, I heard on this well known, main stream, de-bunking site

http://www.bautforum.com/

That since the Sun could be a big solid ball of incandesent charged iron* it just might be drawing in Sedna electro-statically from the rest of the plasma universe.

OR

or it's really the effects of the chemtrails causing us all to believe that somebody is actually paying people to stay up all night, glued to telescopes looking NOWHERE and hoping something drifts by.

Yeah right.

So they had to come up with something or they'll stop getting paid for cruising the internet all night. Since they are making it up you might as well make it mysterious. Who can tell one heavily cropped long exposure from another? Bip, move a pixil and voila Sedna!

Or

Or this really old english lit professor...

Okay Toseek, put the stick down...I mean it! That's not funny!

I'm old now. My mind wanders.






*Now you didn't say which side of the main stream argument...

EDG
2010-Mar-13, 09:44 PM
I was kinda surprised to see that anyone still too the idea seriously. That said, I don't think it's impossible for a smaller object to be out there stirring things up... I guess the main question (if it's a planet of some kind) is "how did it get out there"? If there wasn't enough mass to form Uranus and Neptune in their current orbits within the solar system, there sure as heck isn't enough mass to form a bigger planet a few thousand of AU further out.

Jens
2010-Mar-15, 04:35 AM
If I understand correctly, the problem isn't that it's there, because it's in a stable orbit, but the problem is rather how it got there in the first place? It seemed strange to me that Brown said it is too far to be affected by the sun. Shirley it is being affected if it is in orbit, right? (apologies in advance for any intentional typos).

01101001
2010-Mar-15, 06:33 AM
If I understand correctly, the problem isn't that it's there, because it's in a stable orbit, but the problem is rather how it got there in the first place? It seemed strange to me that Brown said it is too far to be affected by the sun. Shirley it is being affected if it is in orbit, right? (apologies in advance for any intentional typos).

I'll bet you a coffee that Mike Brown knows Sedna is orbiting the Sun. The article quote, without necessary context was:


"Sedna shouldn't be there,” said Brown. “There's no way to put Sedna where it is. It never comes close enough to be affected by the Sun, but it never goes far enough away from the Sun to be affected by other stars.”

Thankfully there was at least a link to context, the Discover article (http://discovermagazine.com/2006/may/cover/article_print) from which the quote was lifted:


[The discovery of] Sedna was completely unexpected. It's 8 billion miles from the sun—Pluto is 3.6 billion—and in 2004 we had no idea that things in that very outer region of the solar system existed. The fact that they do is going to tell us an incredible amount about the birth of the sun and the earliest history of the solar system.

Sedna shouldn't be there. There's no way to put Sedna where it is. It never comes close enough to be affected by the sun, but it never goes far enough away from the sun to be affected by other stars, which is the case with comets that have been observed in the Kuiper belt. Sedna is stuck, frozen in place; there's no way to move it. And if there's no way to move it, basically there's no way to put it there—unless it formed there. But it's in a very elliptical orbit, and there's no way to form anything in an elliptical orbit like that. It simply can't be there. There's no possible way—except it is. So how, then?

I'm thinking it was placed there in the earliest history of the solar system. I'm thinking it could have gotten there if there used to be stars a lot closer than they are now and those stars affected Sedna on the outer part of its orbit and then later on moved away. So I call Sedna a fossil record of the earliest solar system. Eventually, when other fossil records are found, Sedna will help tell us how the sun formed and the number of stars that were close to the sun when it formed.

Used to be. Has our Nemesis gone off to bother other systems?

What exactly is Nemesis anyway? Depending on who is describing/predicting it, it seems to mass between a small terrestrial and a brown dwarf, even a red dwarf, orbiting up to multiple light years away, still here, or long gone. I've seen so many descriptions. How will we know Nemesis if/when we find it? Or will any non-dwarf body do?

Swift
2010-Mar-15, 06:35 PM
Used to be. Has our Nemesis gone off to bother other systems?
There are some theories that yes, this is exactly what happened (well, sort of).

The November 2009 issue of Scientific American had an article by Simon Zwart (Professor of Computational Astrophysics at Leiden U.), entitled "The long lost siblings of the sun" (http://www.scientificamerican.com/article.cfm?id=the-long-lost-siblings-of-the-sun), where he offers evidence that the sun actually formed in a small cluster of 1500 to 3500 stars (with a diameter of about 10 light years), which has dispersed over the last several billion years. But, if true, early in the solar system's history, it would have had some close neighbors which could have done things like perturb the orbits of the outer bodies in our system (past 50 AU).

EDG
2010-Mar-16, 03:24 AM
Sedna shouldn't be there. There's no way to put Sedna where it is. It never comes close enough to be affected by the sun, but it never goes far enough away from the sun to be affected by other stars, which is the case with comets that have been observed in the Kuiper belt. Sedna is stuck, frozen in place; there's no way to move it. And if there's no way to move it, basically there's no way to put it there—unless it formed there. But it's in a very elliptical orbit, and there's no way to form anything in an elliptical orbit like that. It simply can't be there. There's no possible way—except it is. So how, then?

I really have trouble believing this. Can there really be absolutely no way for a distant body's orbit to be disturbed into an elliptical orbit? Not even a close encounter (or two, or more) with a body of similar mass in the oort cloud? Or a collision? Comets come into the solar system all the time after all, why couldn't the same thing have happened to Sedna?

kzb
2010-Mar-16, 01:07 PM
Here is a new paper on forthcoming close encounters. We had better have developed comet deflection technology in 1.44 million years, because Gliese 710 will approach close enough to disrupt the Oort cloud.

What is ignored by the paper is the possibility of Gliese 710 having a planetary system of its own, that should make it interesting.

http://arxiv.org/abs/1003.2160

IsaacKuo
2010-Mar-16, 02:03 PM
I really have trouble believing this. Can there really be absolutely no way for a distant body's orbit to be disturbed into an elliptical orbit?
If the delta-v involved is low enough, yes. But that's not the case here.

Not even a close encounter (or two, or more) with a body of similar mass in the oort cloud?
Bodies of similar mass have relatively small and weak gravity wells, so a close encounter wouldn't have a strong enough effect. (On the order of 1km/s?)

Also, the probability of such an encounter is very low, due to the low density of objects and the relatively low speeds involved.

Or a collision?
Assuming a nudge of about 1km/s is needed, a single collision strong enough to provide the nudge would instead smash Sedna to bits.

Comets come into the solar system all the time after all, why couldn't the same thing have happened to Sedna?
Comets come from much further out, where even a tiny nudge can send them falling inward. If the aphelion is sufficiently far away, then a small nudge can modify the orbit to have a very different perihelion. Sooner or later, the perihelion gets modified to bring the comet near enough for us to notice.

However, Sedna's aphelion isn't far enough away for this. It still has a decent speed at aphelion, so a tiny nudge has only a tiny effect.