oort cloud

[alokmohan]

The Oort cloud is a huge spherical cloud of some 1012 comets surrounding the solar system and extending halfway to the nearest stars. We believe that the Oort cloud comets originated as icy planetesimals between the orbits of Jupiter, Saturn, Uranus and Neptune, and were dynamically ejected to their current distant orbits by gravitational interactions w<br /><br /> <br />The ejection process scatters the comets not only to large orbits but also to moderately large inclinations, on the order of 20 or 30 degrees. Once in the Oort cloud, gravitational perturbations from random passing stars, from encounters with giant molecular clouds in the galaxy, and from the galactic tide continue to modify the cometary orbits. Because these perturbations occur when the comets are close to aphelion (the farthest point from the sun) in their very eccentric orbits, they are most effective at changing the angular momentum of the orbit. The angular momentum figures most importantly in determining the perihelion distance of the comet (the point at which it is nearest to the sun) and its orbital inclination. As a result, the perihelia of the comets tend to diffuse away from the planetary region and the inclinations of the orbits continue to grow. <br /> <br />As an example, a comet with a perihelion distance of about 10 astronomical units (AU), near the orbit of Saturn, and an aphelion distance of 50,000 AU, typical for the Oort cloud, moves at a velocity of only 2.7 meters per second at aphelion. A one-solar-mass star passing at a distance of 1 parsec (206,265 AU) at a velocity of 30 kilometers per second will perturb the velocity of the comet by about 0.29 meter per second. That is enough to raise the perihelion distance to 12.3 AU or to increase the orbital inclination by about six degrees. Because a comet will receive on the order of 40,000 such perturbations over its lifetime, it is easy to see how the inclinations and perihelion distances of the orbits can be completely randomized. The

 

[witgenestone]

actually it was 10^12 comets

 

[vandivx]

interesting reading for me who is not astronomer, thx<br /><br />I wonder if developped Oort cloud can be observed around other stars which could be taken as confirmation of this theory and also as indication of developped/settled planetary system around that star<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[nexium]

About two times Earth mass is the smallest exoplanet we have detected so far, so we need to improve at least 1000 times to detect large comets. May never happen. Neil

 

[vandivx]

I was thinking it might be detected as 'cloud', after all it has got that name because it makes large structure which might be visible or detectable at large distances as some structure<br /><br />sort of like we see gas clouds, you could also never ever see gas particles themselves but their clouds we can, same as we see rings around planets when we couldn't see the parts that make them up<br /><br />however perhaps Oort cloud doesn't have property like gas particles that would make it detectable at large distances as you say, in any case I know we couldn't see individual comets in other star systems<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

I think what makes it very hard is the extremely low densities of objects "out there".<br /><br />The Kuiper belt type disks we find quite often because there are enough particles in an area for us to detect the infrared radiation.<br />But the oort cloud structures are so thin, the excess radiation is too small to be detected above the background.noise level <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[PistolPete]

Well, accoridng to Solstation.com a large dust disk has been detected around Epsilon Eridani, so it may be possible to detect evidence of Oort clouds around other stars. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[MeteorWayne]

As I said, disks are dense enough to be detected, very thinly populated shells do not provide a strong enough signal. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[3488]

Thats true. I think PistolPete referred to Epsilon Eridani's Kuiper Belt, rather than <br />Epsilon Eridani's Oort Cloud.<br /><br />That is a most fascinating link, I quite like SolStation & often use it myself. <br /><br />Also this one from Extrasolar Visions.<br /><br />Epsilon Eridani is shown alongside its planets & Kuiper Belt. Click on the object in question<br />to get information on said object.<br /><br />If you like Asteroid Belts, check this out. HD69830 & Zeta Leporis <img src="/images/icons/laugh.gif" /> .<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[alokmohan]

It is the last point in solar system having lot of comets in it.It must be getting depleted day by day.In the beginning there wre more comets than we see today.

 

[nexium]

The oort cloud likely looses about one millionth of it's comets per thousand years, so there will still plenty 1/2 billion years from now. It might be temporarilly gaining comets from outside our solar system, but likely most just pass though our oort cloud and keep going into the oort cloud of another star. Neil

 

[alokmohan]

Billion years back,more comets were in the sky.I mean more persons saw disasters and havoc.There may be flying dragons in the sky ,per imagination.They hqd fire from face!!Dragons spewed fire and dragons were there in the sky gods face.Ha,ha.

 

[MeteorWayne]

I doubt too many persons saw comets billions of years ago.<br /><br />In fact the rate has been fairly constant as far as we know over at least the last few billion years, based on the evidence we've been able to find.<br /><br />And as far as observed comets go, naked eye comets are rather rare, a few per decade, again a fairly contant rate.<br /><br />Of course now we discover many more than in the past using our binoculars and telescopes. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[alokmohan]

http://www.pibburns.com/catastro/clubenap.htmIn 1982, two British astronomers, S. V. M (Victor) Clube and William Napier, published a book entitled The Cosmic Serpent. Clube and Napier suggested that the outer planets occasionally divert giant comets (more than 50 kilometers in diameter) into the inner solar system into short-period orbits. Debris from the resultant disintegration of these giant comets can adversely affect the environment of the Earth. Dusting can block sunlight, resulting in globally cooler conditions. Impact events in the super-Tunguska class may result in not only heavy localized destruction but also the occasional "impact winter" or dust veil with global climatological effects. <br /><br />Clube and Napier identified the progenitor of the Taurid complex as such a giant comet whose injection into a short-period (about 3.3 year) orbit occurred sometime in the last twenty to thirty thousand years. The Taurid complex currently includes the Taurid meteor atream, Comet Encke (the only known currently active comet in the Taurid complex), "asteroids" such as 2101 Adonis and 2201 Oljato, and copious amounts of dust. All ten of the numbered asteroids in the Taurid complex appear to have associated meteor showers and therefore are likely to be extinct comets masquerading as asteroids. <br /><br />The effects of the disintegration of the Taurid progenitor object in an Earth-crossing orbit should appear in the geological and climatological record. Clube and Napier marshalled evidence for such effects in "The Cosmic Serpent" as well as their later book Cosmic Winter published in 1990. Clube and Napier, following in the footsteps of earlier catastrophists, also sought evidence of catastrophic events in ancient mythology and history. These authors have also written papers in standard peer-reviewed journals about the role giant comets play in constructing a tenable physical theory of coheren

 

[vandivx]

how about this<br /><br />stars with their planets are fairly isolated groupings within galaxy and let us suppose that during the star formation period when the gas clouds coalesced into stars and planets at the locations where we today find the stars there were 'interstellar' regions in between where stars/planets didn't form where the clouds of gas coalesced into only small but many objects like comets... <br /><br />the idea is that there might be no sharply delimited or defined Oort cloud out there but that interstelar space as such is all full of comets and some of those that are found in the region where we say the Oort cloud is located happen to visit our inner solar system once in a long while due to various perturbations, likely those small proto-planetary bodies spend most of their time going about like particles of gas cloud at random, drifting like, and only when they they get cought up in gravitational influence of nearby star system they acquire defined orbits and are called comets<br /><br />what I am saying is that stars/planets are rarish occurences and that some part of the expanse of the primordeal protogalactic gas cluds coalesced only into small bodies scattered all over today's interstelar space with only here and there being spots where big bodies (stars) formed and swept their neigbourhood clean of the cometary material<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[brellis]

<font color="yellow">what I am saying is that stars/planets are rarish occurences and that some part of the expanse of the primordeal protogalactic gas cluds coalesced only into small bodies scattered all over today's interstelar space with only here and there being spots where big bodies (stars) formed and swept their neighbourhood clean of the cometary material </font>- very interesting notion<br /><br />On a broader scale, the empty space between galaxies isn't as empty as we once thought. This CNN Article details observations of so-called 'halo' stars at the fringes of both the Milky Way and Andromeda.<br /><br />Here's a space.com article on the same topic. Somewhere an article quotes a researcher as saying that by the time we pinpoint all the tiny stuff like brown dwarves, drifting planets - and icy comets - we'll confirm that Andromeda and Milky Way may already be "touching" today!<br /><br />That said, it's important to remember that the sum total of the mass of the oort cloud is very slight compared to the planets, and is even more scattered when you consider the scale of distance that far from the sun. Even KBO's are so far apart from each other that between the four spacecraft to reach the Kuiper Belt, they <i>may</i> have been affected by <i>one</i> object out there.<br /><br />We're getting better at seeing the hard-to-see stuff, and it's confirming that on a broad scale, the mass and rotation of material on a galactic level is making sense.<br /><br />Based on these findings and the chaotic interactions between stars as they orbit the galactic center, it should come as no surprise to one day discover that the interstellar 'empty' areas aren't so empty after all.<br /><br />We already know that lots of stuff gets thrown out there. We've thrown a couple of Pione <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>

 

[brellis]

hiya MW<br /><font color="yellow">I doubt too many persons saw comets billions of years ago.<br /><br />In fact the rate has been fairly constant as far as we know over at least the last few billion years, based on the evidence we've been able to find.<br /><br />And as far as observed comets go, naked eye comets are rather rare, a few per decade, again a fairly contant rate.<br /><br />Of course now we discover many more than in the past using our binoculars and telescopes.</font><br /><br />Before we started making planet earth glow at night with our modern technology, comets - and shooting stars <img src="/images/icons/wink.gif" /> - probably looked much more impressive, and threatening to people who thought God was wreaking havoc on us for our sins <img src="/images/icons/frown.gif" /> <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>

 

[alokmohan]

But what exactly is oort cloud.Are you suggesting it is in interstellar space?

 

[vandivx]

the idea is that what we call Oort cloud doesn't extend from those 20,000-50,000 AU but from 20,000 AU all the way to next stars out there (with each star neighborhood being relatively cleared out area)<br /><br />the comets in deep interstelar space move chaotically like gas particles and only acquire cometary orbits if they get cought by star's gravitation for some reason or other<br /><br />I think the upper limit of those 50,000 AU was estimated from cometary orbits but that doesn't mean the 'would be comets' (or cometary bodies) aren't out there farther out, they just are very unlikely to get into well defined orbit and approach star but are just drifting like gas particles at random - individual cometary bodies do not have much any gravitational influence on one another<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[vandivx]

"Before we started making planet earth glow at night with our modern technology, comets - and shooting stars - probably looked much more impressive, and threatening to people who thought God was wreaking havoc on us for our sins "<br />---<br /><br />you could add - before we started to live in houses with permanent lighting and reading and even working by artificial light etc etc... I think our eyes are much less keener than early man's no matter how you adjust your eyes before star gazing, I suspect that's why the early civilizations have had some amazing knowledge of sky and we are like blind lemmings for the most part nowadays compared to them<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[alokmohan]

light pollution is a serious matter.Remote villages are good place to see stars.