Sedna's Long Orbit: Uncovering the Reasons Behind Its Unusual Path

[aishwaryaj]

What does most evidence point to regarding the reasons for Sedna's looong orbit? I think it highly unlikely that the Sun's gravitation can keep it in place.

 

[nismaratwork]

What does most evidence point to regarding the reasons for Sedna's looong orbit? I think it highly unlikely that the Sun's gravitation can keep it in place.

Why do you believe that, when the Sun is more than enough to constrain long-period comets, with orbits that extend beyond Sedna's? I would add, it has been argued that it is "in place" as an object in the Oort Cloud, and not a scattered disk object.

Here are the various hypotheses on wikipedia which seem to cover the spectrum of believable reasons:

Mathematical speculation
A study done by Hal Levison and Alessandro Morbidelli of the Observatoire de la Côte d'Azur (OCA) in Nice, France, suggested that the most likely explanation for Sedna's orbit was that it had been perturbed by a close (~800 AU) pass by another star in the first 100 million years or so of the Solar System's existence, possibly one of the other stars that formed out of the same collapsing nebula as the Sun.[24][34] They proposed another scenario, which may explain Sedna's orbit more accurately: Sedna could have formed around a brown dwarf about 20 times less massive than the Sun and have been captured by the Solar System when the brown dwarf passed through it.

One commonly accepted hypothesis[35] is that the Solar System was once within an open cluster which gradually dissociated over time.[35][36] A close neighboring star located within the same stellar cluster and which later moved away then could have dragged Sedna out farther from the Sun to its present orbit.[35]

Another possible explanation, advanced by Gomes, involves perturbations of Sedna's orbit by a hypothetical planetary-sized body in the inner Oort cloud. Recent simulations show that Sedna's orbital characteristics could be explained by perturbations by a Neptune-mass object at 2000 AU (or less), a Jupiter-mass at 5000 AU, or even an Earth-mass object at 1000 AU.[27][35] Another object, 2000 CR105, has an orbit similar to Sedna's but a bit less extreme: perihelion is 44.3 AU, aphelion is 394 AU, and the orbital period is 3240 years. Its orbit may have resulted from the same processes that produced Sedna's orbit.

It has also been proposed that Sedna's orbit is the result of influence by and in resonance with Nemesis, a theorized dim companion to the Sun which has been proposed to be responsible for the periodicity of mass extinctions on Earth from cometary impacts, the lunar impact record, and the common orbital elements of a number of long period comets.[26]

The oligarch theory of planet formation suggests that there were hundreds of planet–sized objects, known as oligarchs, in the early stages of the Solar System's evolution. Many of these would have been gravitationally scattered out by larger planets, to distances well beyond the Kuiper belt. Sedna may be the first known example of such oligarch planets.

http://en.wikipedia.org/wiki/90377_Sedna

 

[aishwaryaj]

Why do you believe that, when the Sun is more than enough to constrain long-period comets, with orbits that extend beyond Sedna's? I would add, it has been argued that it is "in place" as an object in the Oort Cloud, and not a scattered disk object

No, I mean, how do you justify the elongation? Considering the average spacing between the orbits of the other planets, Sedna's orbit canNOT be explained by just our Sun.

The Wiki entry does explain the origins of the orbit, but other than the Nemesis hypothesis, is there a valid ground for the continued orbit of Sedna around the Sun, unless you consider it a part of the Oort cloud?

 

[nismaratwork]

No, I mean, how do you justify the elongation? Considering the average spacing between the orbits of the other planets, Sedna's orbit canNOT be explained by just our Sun.

The Wiki entry does explain the origins of the orbit, but other than the Nemesis hypothesis, is there a valid ground for the continued orbit of Sedna around the Sun, unless you consider it a part of the Oort cloud?

I don't know, and I don't think anyone does. I don't believe this necessitates the existence of Nemesis. All of the ones I could think of, and one more are in the wikipedia article. There simply is no answer to your question, only the conundrum itself.

 

[russ_watters]

No, I mean, how do you justify the elongation? Considering the average spacing between the orbits of the other planets, Sedna's orbit canNOT be explained by just our Sun.

The Wiki entry does explain the origins of the orbit, but other than the Nemesis hypothesis, is there a valid ground for the continued orbit of Sedna around the Sun, unless you consider it a part of the Oort cloud?

The way you word a lot of that doesn't make much sense. An orbit is an orbit, highly elongated or not. It doesn't require another object and there is no reason why it wouldn't continue to orbit unless it interacts with another body.

 

[nismaratwork]

The way you word a lot of that doesn't make much sense. An orbit is an orbit, highly elongated or not. It doesn't require another object and there is no reason why it wouldn't continue to orbit unless it interacts with another body.

That interaction could have been a long time ago, and the effects are being seen over time, right? The interaction established an orbit (which evolves over time), but isn't required on a constant basis.

 

[Chalnoth]

No, I mean, how do you justify the elongation? Considering the average spacing between the orbits of the other planets, Sedna's orbit canNOT be explained by just our Sun.

Sure it can! Gravity is an infinite-range force, so if there was no other matter out there beyond our solar system (and no cosmological constant), there could, in principle, be objects with orbits around our Sun that were quadrillions of light years in length. It would obviously take an absurdly long time for such an orbit to occur, but there is no problem with it happening.

So the real thing that limits the size of orbits isn't gravity, but instead other stuff out there that would disturb their orbits. But the nearest star is around 3 light years away, which is so vastly further than Sedna's orbit isn't even funny. So until Sedna passes nearby some other object within our own solar system, it'll just keep orbiting the Sun in its current orbit.