46 votes
Accepted

How is it possible that we haven't discovered anything in the Oort cloud yet?

It's not very surprising that no Oort Cloud objects have been detected via occultations. They're extremely rare, even for our most advanced space-based observatories. According to Ofek & Nakar ...
  • 34.2k
32 votes
Accepted

Do all stars have an Oort cloud or is it a rare occurence?

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 ...
  • 34.2k
22 votes

Where does the Solar System end?

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 ...
  • 34.2k
19 votes
Accepted

Why can't we observe the Oort cloud with a telescope?

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 ...
  • 120k
14 votes
Accepted

Scientific evidence against CMB originating from “Oort Soup”?

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 ...
  • 120k
14 votes
Accepted

Does Halley's Comet travel past the outer bounds of the Oort Cloud?

No. Halley's Comet has an aphelion of 35 AU, which is far less than the believed boundaries of the Oort cloud. Any object on an elliptical orbit with a perihelion of 0.6 AU and an aphelion of 2,000 ...
  • 3,550
13 votes
Accepted

How did scientists determine an estimate of the number of planets greater than Sedna's size to exist in the Inner Oort Cloud?

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 (...
  • 34.2k
12 votes

Where does the Solar System end?

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 ...
10 votes

What reason is there to doubt the existence of the hypothesised planet Tyche in the far distant solar system?

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 ...
9 votes
Accepted

Could a black hole pass quiescently through the Oort cloud?

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 (...
  • 120k
8 votes

Why is the Oort cloud presumed to be spherical?

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

Does Halley's Comet travel past the outer bounds of the Oort Cloud?

Without knowing anything specific about this comet, you can use Kepler's third law to get an idea whether this could be the case. It says that the cube of the semi-major axis is proportional to the ...
8 votes
Accepted

Why didn't passing stars destroy the Oort cloud?

The Oort cloud is disturbed. This is thought to be one of the ways we can get long period comets. It is also depleted of objects over time and it is likely that only a fraction of the original objects ...
  • 120k
7 votes
Accepted

If the Oort cloud has billions of objects larger than 20 km, then why do we have so few comets?

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 ...
  • 93.4k
7 votes
Accepted

How far out can the sun keep celestial objects revolving?

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....
  • 9,928
6 votes

Why is the Oort cloud presumed to be spherical?

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 ...
6 votes
Accepted

Why is the Oort cloud presumed to be spherical?

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 ...
6 votes

Could more objects from the Oort cloud with highly elliptical orbits be discovered in the future?

If you consider "objects" to include comets, then yes, they will be, probably within a few months. Extremely long-period comets are continually being discovered by various space telescopes ...
  • 3,550
6 votes

Could more objects from the Oort cloud with highly elliptical orbits be discovered in the future?

Although, there hasn't been a confirmed direct observations of the Oort cloud, it is confirmed to be the home of long period comets. Some notable examples include C/1999 F1 (Catalina), C/2006 P1 (...
  • 3,242
4 votes
Accepted

If sun steals comets from other stars, then what is the primary source of comets?

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-...
  • 1,261
4 votes
Accepted

Lack of objects between heliopause and Oort cloud?

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 ...
  • 34.2k
4 votes
Accepted

Can we measure comets in a similar way to exoplanets?

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 ...
  • 971
3 votes

Why do comets come from our local Oort cloud instead of from interstellar sources?

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, ...
  • 1,988
3 votes

What is the word for space that is in the solar system, but outside the heliopause?

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 ...
3 votes
Accepted

Is there Kuiper belt/Oort cloud like structure in gas giants?

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 ...
  • 22.9k
3 votes

If sun steals comets from other stars, then what is the primary source of comets?

It is likely that during the formation of most stars, comets are formed from the same gas and dust that the star and any planets it hosts were formed from. Extrapolating what we know and strongly ...
3 votes

How many observations does it take to determine the orbit of a TNO

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 ...
  • 176
3 votes
Accepted

Is the Oort Cloud actually opaque, or is the "cloud" used euphemistically because minor planets inside of it are too dim to be seen?

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 ...
  • 120k

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