How do Oort Cloud objects become short-period comets?

In summary, the Oort Cloud is a potential reservoir of short-period comets that may help replenish the Solar System. It is unknown how many objects are in the Oort Cloud, and it is an active area of research to learn more. If an object from the Oort Cloud enters the Solar System, it will likely be pulled into the Sun.
  • #1
O Great One
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Something I've thought about before but never asked anybody...The existence of short-period comets is a problem if one believes the solar system is 4 billion years old, because obviously after that length of time all of the short-period comets would have disintegrated. So, we need a way of replenishing them, hence the Oort cloud. So there's a dormant, potential comet floating out there in the Oort cloud. But what I am wondering is this...

If the object from the Oort cloud simply drifts into the solar system it seems that it will simply be pulled into the sun. In order to become a short-period comet orbiting the sun, it needs some kind of force directing it a point a distance away from the sun, so that when it approaches that point the sun's gravity will sling-shot the object and force it into an elliptical orbit around the sun.
Is my understanding of physics correct, that it needs something to force it towards a point a distance away from the sun?

But how does the object get that force, where does it come from?
 
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  • #2
It's true that an object a long way away will fall into the Sun, IF:
1) there are no other forces - than the mutual gravitation - acting on it
2) it's not moving away for the Sun at faster than escape velocity to begin with
3) the component of its initial motion at right angles to the line to the Sun is exactly zero.

(There are other IF's too, but we'll ignore them for now).

If there is initial transverse motion (3), the object will fall in towards the Sun, whip round it, and shoot back out, in a parabolic (or hyperbolic) orbit. Not a short-period comet.

There are other forces which will act on a body such as a comet. Perhaps the most important is the gravitational pull of Jupiter (Saturn, ...), which may provide just the right amount of change to the comet's orbit to 'capture' it for the Sun. Only a fairly narrow range of initial conditions are right for this to happen, so most incoming comets don't become short period ones.

Just to note a few other things:
- the origin of most short-period comets is still somewhat of a mystery; from what we know of the lifetime of such comets, and the Edgeworth-Kuiper Belt (EKB), mutual collisions of EKB bodies cannot create enough short-period comets
- there's very little known about the Oort Cloud, in the sense that we don't know how many objects there are, what sizes they are, their compositions, etc
- this is an active area of reseach in astronomy, with quite a few interesting discoveries in the last few years; binary EKB objects, Pluto-Charon as merely the largest of a whole class of EKB objects, evidence that many (most?) aren't likely to be pristine relics of the early days of the solar system, ...
 
  • #3
If the object from the Oort cloud simply drifts into the solar system it seems that it will simply be pulled into the sun.
If an object is in the Oort cloud, it must already have a tangential velocity. Else, the oort cloud would spontaneously fall back in towards the sun.
 
  • #4
EKB - interesting new hypothesis on its origin

Following the recent finding that EKB seems to have a sharp outer edge - at least the normal belt, the 'excited disk' has objects that go out beyond 1,000 au - along comes an idea to account for this.
http://skyandtelescope.com/news/article_1115_1.asp
 

1. What is the Oort Cloud?

The Oort Cloud is a theoretical spherical cloud of comets and other icy bodies that surrounds our solar system. It is believed to extend up to 100,000 astronomical units (AU) from the sun.

2. How do objects in the Oort Cloud become short-period comets?

Objects in the Oort Cloud can become short-period comets through gravitational interactions with other objects in the solar system. When a passing star or a disturbance from the outer planets disrupts the orbit of an Oort Cloud object, it can be sent on a trajectory towards the inner solar system, where it becomes a short-period comet.

3. Can Oort Cloud objects become long-period comets?

Yes, Oort Cloud objects can also become long-period comets. If the gravitational disturbance is not strong enough to send the object towards the inner solar system, it may still be pushed into a larger, more elongated orbit that brings it back to the inner solar system every few thousand or million years.

4. What is the difference between short-period and long-period comets?

The main difference between short-period and long-period comets is their orbital period. Short-period comets have orbital periods of less than 200 years, while long-period comets have orbital periods of hundreds or thousands of years. Short-period comets are believed to originate from the Kuiper Belt or the scattered disc, while long-period comets come from the Oort Cloud.

5. How do scientists study Oort Cloud objects and comets?

Scientists study Oort Cloud objects and comets through various methods, including telescopic observations, space missions, and studying debris from comet tails. They also use mathematical models and simulations to understand the dynamics of these objects and their interactions with the rest of the solar system.

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