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laurele
2008-Apr-12, 04:57 PM
Is Sedna a Kuiper Belt Object or an Oort Cloud Object? I was under the impression it orbited within the Oort Cloud, but several people have told me that is incorrect, that Sedna is a Kuiper Belt Object.

Also, is the Oort Cloud located before or after the heliopause? My understanding is that the heliopause is the area where the sun's gravity stops having any effect on any objects, aka, the end of our solar system. But recently, I've seen a visual depiction of the solar system that shows the Oort Cloud out past the heliopause. How is this possible? Isn't the Oort Cloud still within the sun's sphere of influence? It's the source of long period comets, which appears to mean there has to be some gravitational influence from the sun pushing these comets further into the solar system. If the Oort Cloud were beyond the heliopause, how could there be any attraction of its comets toward the sun?

antoniseb
2008-Apr-12, 05:02 PM
The Heliopause is well inside the Ooort Cloud.
The Heliopause is NOT something that prevents gravity from affecting things outside it. Oort Cloud objects are still attracted to the Sun.

Sedna is most likely a Kuiper Belt object that got thrown into a higher orbit through some gravitational interaction a long time ago.

laurele
2008-Apr-12, 05:06 PM
So what exactly is the heliopause?

Is Sedna currently orbiting in the Kuiper Belt or in the Oort Cloud?

Amber Robot
2008-Apr-12, 05:19 PM
So what exactly is the heliopause?

The Heliopause is where the Solar Wind meets the Interstellar Medium.

http://en.wikipedia.org/wiki/Heliosphere

Jeff Root
2008-Apr-12, 09:41 PM
Offhand, I think Sedna is a "scattered disk object" (SDO). The disk
referred to is the Kuiper belt. SDOs are thought to be KBOs (Kuiper
belt objects) scattered outward from the Kuiper belt by gravitational
interactions with other large bodies. I don't understand how a large
body in the Kuiper belt could get moved around unless there was an
even larger body in that region. SDOs and KBOs are both TNOs
(trans-Neptunian objects). As of September 2006 (when I looked
through the online lists from the Minor Planet Center, and counted),
over 1000 TNOs had been catalogued.

No actual Oort cloud objects have been seen yet, AFAIK.

-- Jeff, in Minneapolis

George
2008-Apr-12, 10:12 PM
m1omg showed me this illustration (http://en.wikipedia.org/wiki/Image:Oort_cloud_Sedna_orbit.jpg). Sedna is not an Oort Cloud object. I don't think any Oort Cloud object has been seen, but perhaps some long period comets are known to have come from there.

The problem is the vast distance to the Oort Cloud and the fact that their reflected sunlight varies inversely as to the fourth power of their distance. IIRC, Jupiter would be too dim and object even for the HST if it were about 10,000 a.u. distance, which is only 1/5th the outer region for the Oort Cloud.

A.DIM
2008-Apr-12, 11:07 PM
Is Sedna a Kuiper Belt Object or an Oort Cloud Object? I was under the impression it orbited within the Oort Cloud, but several people have told me that is incorrect, that Sedna is a Kuiper Belt Object.

Also, is the Oort Cloud located before or after the heliopause? My understanding is that the heliopause is the area where the sun's gravity stops having any effect on any objects, aka, the end of our solar system. But recently, I've seen a visual depiction of the solar system that shows the Oort Cloud out past the heliopause. How is this possible? Isn't the Oort Cloud still within the sun's sphere of influence? It's the source of long period comets, which appears to mean there has to be some gravitational influence from the sun pushing these comets further into the solar system. If the Oort Cloud were beyond the heliopause, how could there be any attraction of its comets toward the sun?

Attraction or perturbation?

For a plausible scenario see : "A wide binary solar companion as a possible origin of Sedna-like objects" located here (http://www.ucs.louisiana.edu/~dpw9254/).

Jens
2008-Apr-13, 03:48 AM
Also, is the Oort Cloud located before or after the heliopause? My understanding is that the heliopause is the area where the sun's gravity stops having any effect on any objects, aka, the end of our solar system.

Just as something to keep in mind, there is no place, even in the entire universe, where the sun's graviy stops having any effect on objects. Graviy decreases with distance but never becomes zero. So (theoretically, though not usefully in practice) all objects in the universe with mass exert some gravitational effect on all others.

The heliopause is actually (I think) the place where the solar wind stops flowing outward.

Eroica
2008-Apr-13, 03:18 PM
Offhand, I think Sedna is a "scattered disk object" (SDO)
That's what I think.

Sedna's eccentricity is 0.855, which is very eccentric compared to classical KBOs (or Cubewanos), which have eccentricities of about 0.0-0.2.

Sedna semimajor axis is 526 AU, which is again off the scale for KBOs, which mostly have semimajor axes of 40-50 AU.

laurele
2008-Apr-13, 04:18 PM
"If the Oort Cloud were beyond the heliopause, how could there be any attraction of its comets toward the sun?"

"Attraction or perturbation?"

I have to admit I'm somewhat ignorant here. Could you explain the difference between attraction and perturbation?

Thank you to everyone who has taken the time to answer this question. My knowledge of astronomy is still quite limited, and I admit to not having been familiar with some of the concepts raised here, such as the interstellar medium. I appreciate all the links, references, and explanations BAUT members have provided.

George
2008-Apr-13, 06:49 PM
An attraction is a hug, a perturbation a slap. :)

Jeff Root
2008-Apr-13, 06:54 PM
"If the Oort Cloud were beyond the heliopause, how could there be any
attraction of its comets toward the sun?"

"Attraction or perturbation?"

I have to admit I'm somewhat ignorant here. Could you explain the
difference between attraction and perturbation?
A.DIM was not sure whether you were asking about the constant
gravitational attraction of comets toward the Sun, which keeps them
in orbit around the Sun, or the varying gravitational perturbations
caused by the varying distances to planets or other large bodies,
which sometimes makes the comets move closer to the Sun.

A perturbation is just a change in an orbit. The most common cause
of perturbations is gravitational attraction between the body of interest
(in this case, comets in the Oort cloud) and a planet. For comets,
another significant cause of orbit perturbation is outgassing. Gasses
escaping from the surface of a comet act like jets or rockets, pushing
the comet arount, changing its orbit.

As I think you have already learned, the heliopause isn't relevant to
the gravitational attraction between the Sun and comets. The force
of gravity is weak at that distance, but it is enough.

-- Jeff, in Minneapolis