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32

Awesome question, especially since we know so little of the answer. Nobody knows for sure how the Oort Cloud formed - I'll put that out there right now - but the current hypothesis is that it was originally part of the Sun's protoplanetary disk. All of the ice and rock coalesced into small bodies - proto-comets, if you will. While these bodies were much ...

17

Here's my answer. I'll try to make it as comprehensive as possible. It's pretty hard to define the edge of the Solar System. Most people would probably define it as where objects are no longer gravitationally bound to the Sun. That just shifts the question a little, though: Where is that dividing line? To try to answer this, I'll go over the regions of the ...

13

Unfortunately, the paper is not available on ArXiv (oh, what hardships we must overcome!), but I have found it here. In it, where the "900" figure is mentioned (2nd page, I believe), the authors (Trujillo and Sheppard) say that they ran simulations with the data already found and their additional findings, and found that 900$^{+800}_{-500}$ bodies larger ...

12

The angular resolution of the telescope really has no direct bearing on our ability to detect Oort cloud objects beyond how that angular resolution affects the depth to which one can detect the light from faint objects. Any telescope can detect stars, even though their actual discs are way beyond the angular resolution of the telescope. The detection of ...

11

Whenever I see this question discussed, it seems that the heliopause, or some variation thereof, is given as an answer -- and then it's mentioned that the Oort Cloud extends beyond it. A more correct answer, therefore, should be that it ends at that distance at which objects are, for all practical purposes, no longer bound to the solar system barycenter. ...

11

I had a chat with a European PhD student who plans to make an attempt to find Oort cloud objects in data from the Gaia space telescope. This could be possible thanks to microlensing events when an Oort object transits (near) a background star and relativistically magnifies the star's light for a moment. Best case is that in a few years we will have a map of ...

11

The idea that belts or spheres of dust might be responsible for (some) microwave emission is not crazy. Indeed we know that dust does emit microwaves and indeed the contribution of such dust has to be removed from the CMB signal before it can be interpreted cosmologically. There is some debate about some of the larger scale anisotropies (particularly the "...

9

Several months after the accepted answer was posted: In 2014, NASA announced that the WISE survey had ruled out any object with Tyche's characteristics, indicating that Tyche as hypothesized by Matese, Whitman, and Whitmire does not exist. The quotation is from the Wikipedia article on Tyche. The article gives the following references for the statement: ...

9

Generally it would be that peers of Matese and Whitmire looking at the statistics and viewing that the results are not conclusive enough to indicate the existence of Tyche. There can also be alternative reasons to explain the results mentioned in the paper other than a Jupiter sized planet in the Oort Cloud. As was mentioned in the comments, it is almost ...

9

The latter. Long-period comets appear to come from random directions.

9

An approach would be to use the Bondi-Hoyle (B-H) accretion rate and then assume that some large fraction of the gravitational potential energy was radiated from the innermost stable circular orbit (ISCO) as the material spiralled into the black hole via an accretion disc. To calculate the B-H accretion rate we need how fast the black hole traverses the ...

7

Most Oort cloud objects stay in the Oort cloud, and we never see them. Comets don't last long. A comet is made of a mixture of ices and dust. A comet that enters the inner solar system has one of a few outcomes: it could pass out of the solar system, and either never be seen again, or enter such a long orbit that it isn't seen again for an extremely long ...

7

The suns gravitational pull extends unlimitedly far and, if the universe were otherwise empty, a body could orbit it (very slowly) at unlimited distance. However, the universe is NOT otherwise empty. The nearest other stars are about 4 light years from the Sun at the moment, so a body more than two lightyears away will typically feel equally strong ...

5

Nobody has "seen" the Oort-cloud (yet). The Oort cloud is simply a concept that can explain why long-period comets appear to come from random directions. With the current instruments, we are not able to detect any of these comets "at the source". It is also not even possible to show with measurements that at that distance there might be a companion-object ...

4

You can exclude the 'considering the distance' piece - of course Oort Cloud objects could transfer between different gravitational fields. However what is it you think will make this transfer? Without some sort of gravitational impetus why would one of these objects leave the solar system? And if you do manage to slingshot one out of the solar system at a ...

4

In addition to Mark's answer, we also have reasons to expect a spherical distribution. The following makes some assumptions on how our solar system formed. They are standard, but we are not completely certain on its correctness. What I use is usually considered noncontroversial--it's how the planets themselves arose that is most problematic, but is not ...

4

There may be Sednoids there. Sednoids are a hypothetical class of "inner Oort Cloud objects" named after their prototype, Sedna. Sedna's aphelion is ~936 AU, bringing it close to the inner boundary of the Oort Cloud. Sednoids may have aphelions ranging from about 100 AU to 1,000 AU. The problem is, only two Sednoids have beet detected to date, 90377 Sedna ...

4

The thing about detecting exoplanets by eclipses is that the eclipses are repeatable. You have the same star, whose light curve dims in the same way with each eclipse, which gives you information about the planet's orbital period and its apparent size relative to the star. The Kepler mission observed many fluctuations in stellar brightness that were not ...

3

There doesn't seem to be such a word. Interstellar space within the Solar System is still just interstellar space. There doesn't seem to be a demand for the word you're looking for either. We distinguish space by its contents; the space within the heliosphere is called the interplanetary medium (it contains solar plasma, dust, etc.), while the interstellar ...

3

The gravitational region around the planets isn't hard to calculate, sometimes called the Sphere of Influence, sometimes called the Hill Sphere. They're calculated differently but they define pretty much the same idea. The actual long term stable region is somewhere around 50% of the Hill Sphere. A gas giant like Jupiter simply doesn't have a large ...

3

The primary source of comets for our solar system comes from the Oort Cloud, a smaller amount coming from the Kuiper belt. The Oort cloud is thought to have originated from the remnants of a proto-planetary disk. This paragraph explains this better: The Oort cloud is thought to be a remnant of the original protoplanetary disc that formed around the Sun ...

3

Since most comets are on a predictable orbit that has them circling the sun (several times), then they cannot be from outside the solar system. Any comet that originates outside the solar system, will pick up enough velocity approaching the sun to be able to leave the solar system. Therefore, we would only see the comet once. It is unlikely that the comet ...

3

Well, given that we can see the stars and that the Oort "cloud" is closer than the nearest star, then the answer to your main question is obviously that the "cloud" is not opaque. I think it is called a cloud because it consists of many individual, small "particles" that don't interact with each other. Also, the term cloud avoids giving the impression that ...

3

The main problem with determining an object's orbit is we only know the position with certainty in two dimensions. The distance to the object is largely unknown. This accounts for the large uncertainty in the period of newly discovered TNOs. Many possible orbits could fit the early observations, and therefore the uncertainty is large. As time goes on, ...

2

Simple answer: the material is just too spread out. Forming a planetary-size object takes LOTS of collisions to build up enough matter to start gravitationally attracting the surrounding stuff. The Oort cloud is very far from the sun (starting at ~1000 AU, compared to a maximum of ~50 AU for Pluto), meaning that the icy fragments are moving very slow in ...

2

And they are then ejected by the orbital changes of giant planets. But why are they ejected to form specifically a local Oort cloud instead of going interstellar and becoming vagabonds? Per multiple models, most comets did become vagabonds. Estimates vary, but the lowest I've seen is 65% being ejected, and some estimate that well over 90% were ejected. ...

2

The composition of the gas from which stars and their planetary systems form is reasonably well known. About 1-2% of this gas is in the form of chemical elements heavier than Helium (the so-called metallicity of the gas). A fraction of these "metals" - the iron, silicon, oxygen etc. is capable of forming dust and then accumulating to form "rocky" material. ...

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