# How far away is the Oort Cloud?

1. Sep 7, 2011

### cph

How far away is the Oort comet cloud? 1000 AU or 10,000 AU? c=10^10 cm/sec. for 10^8 sec/yr., gives 10^18 cm/lyr. Approximately then, is 1000 AU ~ .01 lyr? And 10,000 AU ~ .1 lyr? Would this be large enough to contain a multi-stellar system, since stars form in multiple? Hence a common Oort cloud for a center of mass for such system?

2. Sep 7, 2011

### Drakkith

Staff Emeritus
According to wikipedia the Oort cloud is theorized to exist roughly from 2,000-5,000 AU to 50,000 AU, or 1 light year from the sun. Some estimates put the outer edge at up to 100,000 - 200,000 AU. (1.58-3.16 ly)

Multi-star systems have been observed with the stars seperated by anywhere between a few AU up to hundreds or thousands of AU if not more, so the Oort cloud can easily be shared by two stars if it actually does form. Depending on the configuration of the system I could see having more than one star making conditions too unstable for the cloud to form.

3. Nov 18, 2011

### Jack Dash

I have seen several posts on the web that put the Oort cloud at anything up to 3 LY away.

What no one seems to consider is that the gravitational mid point between the sun and Alpha centaury is at 1.5LY from our sun. This means that any object in the Oort that is orbiting further out than this will be either be captured by Alpha Centaury or it must be orbiting both stars in a figure of eight orbit and the Oort cloud would have an hourglass shape with a lobe around each star and the waist of the hourglass at the gravitational mid point.

I have made a request for feedback on this point in a seaprate post, any input would be welcomed.

4. Nov 18, 2011

### Chronos

The best guess at the Oort cloud size is about 50,000 AU. The alpha centauri system is about 270,000 AU distant. It has probably been disrupted by near approaches from wandering stars, brown dwarfs or even ejection of planets from the primordial solar system. Such events number among those conjectured to explain the late heavy bombardment period.

5. Nov 26, 2011

### Aidyan

Nobody knows for sure because it is extremely hard to obtain observational data on this. The best what can be done actually is to resort to numerical simulations. From these it became clear that one can not set a precise boundary to the Oort cloud because the number of comets per unit volume decrease with the distance from the sun according to some law. However, from these simulations one can guess that most of the comets is contained in a radius of 30-50.000 AU. But theere is no cut-off and few comets may go much further, fading away with some having aphelions extending as far as 300.000 AU. That is about alpha centauri's distance and in fact it is speculated that several of our Oort cloud comets might have extra solar origin. However, these comets orbiting further away from the sun might be just those more relevant for planetary impacts (and therefore for the existence of life) since they are those which are most perturbed by stellar encounters and galactic tides.