PDA

View Full Version : the Oort Cloud



damienpaul
2004-Jan-06, 12:29 AM
I have just read an article that states that in 1.4 million years time the red dwarf star Gliese 710 will wander through the Oort Cloud, presumably causing chaos and mayhem with the residents therein, not to mention the rest of the solar system.

the article also states that this type of event is relatively common.... does anyone have any more light to shed on this, and also the current position of the Gliese 710 red dwarf?

GOURDHEAD
2004-Jan-06, 11:17 PM
See: http://www.solstation.com/stars2/gl710.htm

damienpaul
2004-Jan-06, 11:26 PM
thank you kindly for that

VanderL
2004-Jan-11, 10:53 AM
Did you ever consider the possibility that the Oort cloud does not exist? It is also one of those theoretical constructs waiting to be confirmed.
Cheers.

damienpaul
2004-Jan-12, 01:43 AM
actually that is an interesting point...has there been direct evidence of the existence of the Oort Cloud?

Matthew
2004-Jan-12, 03:25 AM
Did you ever consider the possibility that the Oort cloud does not exist? It is also one of those theoretical constructs waiting to be confirmed.
Cheers.

The Oort Cloud has been proven to exist.

TheThorn
2004-Jan-12, 04:20 AM
I'd be interested in seeing that proof.

The evidence appears circumstantial but compelling to me, but I wouldn't call it proof.

No comet has been found that had a hyperbolic orbit (ie. came from interstellar space. And a lot of long period comets have aphelia around 50,000 au. Together, those facts strongly suggest a cloud of potential comets out at around that distance, but I don't think that constitutes proof.

Are you aware of further evidence?

Littlemews
2004-Jan-12, 04:25 AM
I wish Pioneer 10 can reach there quickly, therefore we can see the Oort Cloud.

The Oort Cloud of icy bodies is believed to extend out from 20,000 to about 100,000 AU from the Sun.

damienpaul
2004-Jan-12, 08:06 AM
are there any missions planned for the Oort cloud?

Josh
2004-Jan-12, 08:54 AM
No, Matthew. VanderL (et al) are right. The Oort cloud is only inferred to exist because of the orbits of comets.

VanderL do you have any other hypothesis about the Oort cloud or the comets' orbits? Does your theory of plasma universe explain it without the need for an Oort cloud?

A mission to the general area would be very interesting! As I understand it telescopes (even Hubble etc) are able to see the Kupier Belt asteroids, but only jsut and have no chance of seeing the Oort cloud. Why can't some sort of mapping function be used to see if there's anything out there? Even though they are extrodinarily dim can't they still be seen compared to the complete blackness behind them? Why can't some very powerful lasers be used with a telescope (at an angle obviously) to see if there is any interference??

VanderL
2004-Jan-12, 10:01 PM
Hi Josh,

Here at http://www.holoscience.com/news.php?article=ayxpdjcb
there is a whole story about comets and how they fit in an electric model. They are not the supposed dirty snowballs. They are leftovers from the violent history of the planets and their planetary orbits. Comet Borrelly showed us a dry and hot surface, so the return mission of comet Wild 2 should also give us no evidence of water. I hope you have some time to spare to read the whole article, there are many interesting comments.
About learning if there really is an Oort cloud, the only way I see is when we send a spacecraft over there, but I can't see it happening anytime soon.
Cheers.

Tim Thompson
2004-Jan-29, 02:44 AM
As one might expect, the "electric" model for comets does not make physical sense. For instance, the coma is supposed to be a "plasma sheath". But a plasma sheath is only a few Debye lengths (the characteristic distance over which charges are shielded in a plasma) in size, and the Debye length for the solar wind is about 10 meters, plus or minus a few meters. Comet comas are thousands to millions of kilometers in extent, way too large for any kind of plasma sheath.

Furthermore, the large negative charge presumed for the comet should be neutralized, fairly quickly, by the protons in the solar wind. After all, if we are going to be "electrical" about this, we should recall that "unlike charges attract", so what keeps the positive protons from going into the negative comet and making it a neutral comet?

In a laboratory plasma, a sheath forms around a surface with a floating potential, which could be the surface of a charged body, or the surface of a charge neutral conductor (like the metal surface of a spacecraft). In the case of the spacecraft, there is no net charge to negate, only an induced surface charge because it's an electrical conductor. But in the case of the electric model comet, there is a net negative charge on the comet. Plasma sheaths are maintained in a laboratory with probes that are part of an electric circuit. So, when the plasma charge carriers try to negate the probe potential, they are whisked away in the circuit by the EMF (a battery or a power source), which does not get "discharged". However, the comet has no equivalent circuit (otherwise it could not be charged anyway). So there's no place for the positive charge carriers in the plasma to go except into the body of the comet, to neutralize the excess negative charge.

The protons & electrons of the solar wind do not neutralize each other because they have too much kinetic energy to stick together. This is typical for space plasmas, and laboratory plasmas; the particles can't lose their excess energy and stick together (it is very hard for a planet to "capture" a moon for the very same reason). But they can & do lose their excess energy in the case of a large body, like a comet, where the particle kinetic energy would be transformed to thermal energy in the body of the comet, allowing the protons to slow down and neutralize the excess negative charge of the comet. So even if they had the proposed excess negative charge, they could not long stay that way.

And furthermore, the few spacecraft which have encountered comets directly, all carried electric & magnetic field monitors. If indeed the coma was a plasma sheath, then the spaceraft and their field measuring devices are deep inside the sheath, where they should be able to experience and measure the very large electric fields associated with the net charge of the comet. They don't, which is affirmative evidence that the excess charge (and the consequently necessary electric field) is not there.

There are several other large mistakes on that webpage, but this is all I have time for at the moment, though it should be enough.

Manchurian Taikonaut
2004-Mar-08, 02:22 PM
there are many models, some say the Oort cloud is 30,000 Au some say the ort cloud is 1 light year away, others show it as 100,000 + AU

we don't have enough information

Duane
2004-Mar-08, 07:44 PM
The existance of the Oort cloud was the result of measurements done by Jan H. Oort in the 50's. He used the orbital distribution of 19 well measured cometary orbits to establish where these objects had come from.

Two recent Oort cloud objects are Hale-Bopp and Hyakutake. Both had their orbits precisely calculated and were found to be travelers from the Oort cloud.

Oort cloud objects are too small and too far away to be seen in their usual orbit by current technology. It would be impractical to try and send a craft out to them, given we have no orbital characteristics. It would be like shooting a bullet at a forest of trees, where the trees are spaced 1000 km part. In fact, it would be worse.

While there may be millions of these objects, they are spaced millions of kilometers apart. A chance encounter would be most unlikely.

GOURDHEAD
2004-Mar-09, 02:47 PM
:unsure: Has evidence been acquired demonstrating that the galaxy is not permeated with Oort cloud like objects somewhat homogeneously distributed from about 10000 light years from the galactic center out to beyond the galactic halo (secularly speaking)? The cloud would be more galactic than solar. If so, what contribution, assuming densities below current detection thresholds of current electromagnetic detection techniques, would such a population contribute to the dark matter enigma? How can such a wild guess be falsified? :unsure:

antoniseb
2004-Mar-10, 08:45 PM
Originally posted by GOURDHEAD@Mar 9 2004, 02:47 PM
The cloud would be more galactic than solar. If so, what contribution, assuming densities below current detection thresholds of current electromagnetic detection techniques, would such a population contribute to the dark matter enigma? How can such a wild guess be falsified?
First, an earlier post indicated that there hadn't been ANY hyperbolic orbits for comets, but, in fact they are rare but not unheard of. Generally, they are not VERY hyperbolic.

Theory: Current theories suggest that the Oort cloud was formed as objects in the Kuiper belt, and further in were thrown out during the planet formation period. Some objects escaped altogether, and some are within the grasp of Solar gravity. These would all be in highly elliptical orbits with perihelions in the planetary solar system, mostly around Neptune's orbit.

Detection: all the comets in the Oort cloud combined might have the mass of a lump of ice about 1000 miles in diamter [like a large Plutino]. Total number is a wild guess. It could be 100 times more than this, which is still a tiny fraction of the Solar system mass. We may never be able to detect these object via their gravity. The objects spend the vast majority of their time in the outer parts of their orbits. They are very cold and dark, even in the near infrared. If you knew exactly where one was, you could illuminate it with a high powered laser. It might take a year for the reflection to come back.

Galactic Comets: There should be escaped comets from the formation of every planetary system, and these would mostly orbit the galactic center with orbits similar to the parent star system. Once in a while we should, and do, see comets with some excess velocity. So far we haven't seen anything obviously from a grossly different orbit than ours, but they must exist.

Dark Matter: The total unseen baryonic matter is about three or four times the mass of the visible stars. The free comets from the birth of our solar system are probably much less than the mass of the Earth. These things can't come close to making up the difference. The total non-baryonic missing mass according to the current LCDM theory is about six time more than all the baryonic matter [seen and unseen].

Mission: There is a sort-of planned mission called the Interstellar Probe. This thing is sometimes chopped out of the budget, and sometimes put back in. The mission isn't to go to another star, but simply to get to the interstellar medium, and inner part of the Oort cloud within ten years of being launched. There is no concrete plan for how it will get their, they seem to be accepting ideas at this stage, and a launch won't happen for at least ten years, and maybe more. The mission has no plan to specifically look for an Oort Cloud member, as we have no clue where they are.

Duane
2004-Mar-10, 10:00 PM
Thanks antoniseb, that was a nice summary.

TheThorn
2004-Mar-10, 10:26 PM
Originally posted by antoniseb@Mar 10 2004, 08:45 PM
First, an earlier post indicated that there hadn't been ANY hyperbolic orbits for comets, but, in fact they are rare but not unheard of. Generally, they are not VERY hyperbolic.

That was me what said that. Turns out I was wrong again. Thanks for pointing that out. I learn something every day.

Looks like even one of the comets in the current news is on a hyperbolic orbit - Comet Linear (C/2002 T7).

Interesting.

damienpaul
2004-Mar-11, 10:18 AM
At the risk of sounding like a dumb donkey...what exactly is a hyperbolic orbit?

galaxygirl
2004-Mar-11, 11:28 AM
I believe it's an open orbit with an eccentricity that's greater than 1.

antoniseb
2004-Mar-11, 12:30 PM
Originally posted by damienpaul@Mar 11 2004, 10:18 AM
At the risk of sounding like a dumb donkey...what exactly is a hyperbolic orbit?
There's one good answer already, but to put it in more visual terms, it is the path that an object takes on a single pass near a heavy object. Most people use the term trajectory as opposed to orbit for this situation.

The Cassini probe made a hyperbolic trajectory passed Jupiter on it's way to Saturn. A Comet escaped from another star has too much velocity to stay around the sun, but it will certainly not just follow a straight line path if it happens to go near the sun. Without careful measurement, it will look like the path of any comet.

In geometry we talk about the conic sections: circle, ellipse, parabola, hyperbola. In the case of long period comets, their orbits to us look close to being parabolas where we can see them because they are very eccentric [non-circular] ellipses. The hyperbolic [on-shot] comets are also very close to following parabolic trajectories on the tiny part of the path we see.

If a comet, or object were from a star in a colliding galaxy, it might have a huge excess velocity, and it's hyperbolic trajectory would be unmistakeable. It could be a slightly bent arc as it wizzes past the sun. Similarly, photons going through a gravitational lens are on extremely flat hyperbolic trajectories.

GOURDHEAD
2004-Mar-12, 01:00 PM
Detection: all the comets in the Oort cloud combined might have the mass of a lump of ice about 1000 miles in diameter [like a large Plutino]. Total number is a wild guess. It could be 100 times more than this, which is still a tiny fraction of the Solar system mass. We may never be able to detect these objects via their gravity. The objects spend the vast majority of their time in the outer parts of their orbits. They are very cold and dark, even in the near infrared. If you knew exactly where one was, you could illuminate it with a high powered laser. It might take a year for the reflection to come back.

A wild guess indeed; that's all that's available to us since there's no observational evidence. If the Oort cloud is indeed a spherical shell as Oort assumed and of 0.8 light years thickness [say from 0.5 to 1.3 light years], it represents a rather substantial volume [4*pi*(R2^3-R1^3)/3]. This is approximately 2.76 cubic light years or 6.9e+52 cubic miles or 4.6e+73 cubic centimeters. At the equivalent density of one hydrogen atom per cubic meter this yields the mass equivalent of about 7e+36 liters of hydrogen at standard temperature and pressure or 10e+32 grams. The mass of the sun is less than 10e+33 grams. If there were 10e+5 times this much mass in the Oort cloud, it would still be below our current observational detection sensitivity with the mass equivalent of about one million suns. Now I don’t believe that there is anywhere near this much mass in the Oort cloud; my point is that it could exist without our having observed it. An Oort cloud mass of from 0.5 to 4 or 5 solar masses would not be surprising. Extrapolating this guessing throughout galactic and intergalactic space might provide enough mass to account for the “missing mass”.

What makes the theorists so sure that there is not at least 9 times as much unlighted baryonic mass as there is lighted baryonic mass in the universe. Intergalactic space is many times more voluminous than is intra-galactic space. Celestial mechanics does not prohibit the expulsion of material into intergalactic space nor does it require that all the material initially in intergalactic space has been swept up since the birth of the universe.

Duane
2004-Mar-12, 02:03 PM
GOURDHEAD, that is an interesting question, and I too would like to hear the answer.

From what I understand of current models for planetary formation, the ejection of everything from plantismals to gas giants should be fairly common. So, why couldn't normal baryonic matter make up a large percentage (or even all) of the black matter out there?

antoniseb
2004-Mar-12, 02:18 PM
Originally posted by GOURDHEAD@Mar 12 2004, 01:00 PM
If the Oort cloud is indeed a spherical shell as Oort assumed and of 0.8 light years thickness [say from 0.5 to 1.3 light years], it represents a rather substantial volume [4*pi*(R2^3-R1^3)/3]. This is approximately 2.76 cubic light years or 6.9e+52 cubic miles or 4.6e+73 cubic centimeters. At the equivalent density of one hydrogen atom per cubic meter this yields the mass equivalent of about 7e+36 liters of hydrogen at standard temperature and pressure or 10e+32 grams. The mass of the sun is less than 10e+33 grams. If there were 10e+5 times this much mass in the Oort cloud, it would still be below our current observational detection sensitivity with the mass equivalent of about one million suns.
My calculations don't agree with yours, by several orders of magnitude. Please correct me if I am wrong here:

I think light goes 3e8 meters per second, and that there are about 3e7 seconds per year. A light-year is about 1e16 meters long. A cubic light-year is therefore about 1e48 cubic meters.

You said that there was about one hydrogen atom per cubic meter [I assume that was a typo and you meant centimeter for this calculation [values assumed for ISM density vary from about .05 up to 1.0 hydrogens per CC, I'll take the high value for the Oort cloud].

So a cubic light-year has about 1e54 cubic centimeters, and therefore about 1.5e30 moles of hydrogen. This is a little less than the mass of Jupiter, but one tenth of one percent the mass of the sun [2e33 grams].

BTW, as an update to my previous post, there is a theory of some merit that says that Neptune's orbit was moved inward by more than a few percent from the Kuiper belt to its current location by the expulsion of comets into the Oort cloud. This would require about 1e9 to 1e10 comets to be out there, which is still a small mass compared to Jupiter, but MUCH bigger than Pluto.

GOURDHEAD
2004-Mar-13, 01:16 PM
My calculations don't agree with yours, by several orders of magnitude. Please correct me if I am wrong here:

Alas tis I who erred; yours is the more accurate arithmetic.


You said that there was about one hydrogen atom per cubic meter [I assume that was a typo and you meant centimeter for this calculation [values assumed for ISM density vary from about .05 up to 1.0 hydrogens per CC, I'll take the high value for the Oort cloud].

I actually meant cubic meter because my arithmetic errors for computing volume was leading me to way too much mass which I got anyway. Now that you've corrected my calculations let's examine how much mass could be in the Oort cloud and remain below the detection threshold (observational as well as gravitational) conceding that the average density in the Oort cloud is larger than in the ISM. Also, the current assumptions about the ISM density could be equivalently increased and remain below observational detection limits. What is the ISM density guess based on.

Is there a proven method by which to set limits on how much mass could be in the Oort cloud and remain undetected?

antoniseb
2004-Mar-13, 10:50 PM
Originally posted by GOURDHEAD@Mar 13 2004, 01:16 PM
Is there a proven method by which to set limits on how much mass could be in the Oort cloud and remain undetected?
My understanding about this is that from the inside, if the density of the Oort cloud were perfectly uniform it could be *any* density without affecting the celestial mechanics of the planets. I don't know a standard way to express the results for specific ways of being non-uniform.

Note that the ISM density is probably close to the Oort cloud gas density, since the heliopause is far within the Oort cloud.

Note also that at some UV wavelengths we have been able to measure the column density between us and various stars. This has set some limits on the hydrogen density in the local neighborhood.

Planetwatcher
2004-Mar-14, 05:43 AM
Believing in or supporting the arguements for the existence of the Orrt Cloud really isn't difficult if one thinks outside the box just a little, or rather inside the cloud without it clouding one's judgement. :D

I've read here arguements which I am understanding to say that they doubt the existence of the Orrt Cloud simply because they can not directly see it.

But how can you see something as if on the outside when you are in fact inside.
Such is the case here. Our entire solar system is contained within the Orrt Cloud.
In other words, we are inside the thing. So naturally we can't see it as though we were viewing from the outside as we do other stars.

It's much the same with the Milky Way Galaxy. We are inside or part of it. So it looks different to us then it would to an observer in a different galaxy.

I think it is possible that the Orrt Cloud is actually a nebula. Our nebula, the nursery of our Sun. It looks different to us then the other nebulas we view simply because we are within. What would the Crab Nebula look like if we were on a planet inside .

antoniseb
2004-Mar-14, 01:01 PM
Originally posted by Planetwatcher@Mar 14 2004, 05:43 AM
I've read here arguements which I am understanding to say that they doubt the existence of the Orrt Cloud simply because they can not directly see it.

Hmmm, I didn't notice any posts implying it doesn't exist. My read on the posts was that the other writers and myself were saying the Oort cloud is hard to observe and see how dense it is, but that its density is interesting to us. There was also some discussion of how it was formed.

BTW, one item that can lead to some confusion here is the word cloud being used as part of the name. What Oort wrote about was a region in which cold comet nuclei floated around, orbiting the sun at great distance. He was not referring to plasma, gas, or dust, as you would find in the more visible nebula.