The sun steals comets from other stars

November 24, 2010 By Dauna Coulter, Science@NASA
An artist's concept of the Oort cloud. Note that the distance scale is logarithmic. Compared to the size of planetary orbits, the Oort cloud is very far away. Indeed, the estimated size of the Oort cloud, 10^5 AU, is approximately 1 light year. If the Sun passed within 2 light years of another sun-like star, the stars' Oort clouds would overlap and their comets would intermingle. Image credit: ESO

The next time you thrill at the sight of a comet blazing across the night sky, consider this: it's a stolen pleasure. You're enjoying the spectacle at the expense of a distant star.

Sophisticated computer simulations run by researchers at the Southwest Research Institute (SWRI) have exposed the crime.

"If the results are right, our Sun snatched comets from neighboring stars' back yards," says SWRI scientist Hal Levison. And he believes this kind of thievery accounts for most of the comets in the Oort Cloud at the edge of our solar system.

"We know that form in clusters. The Sun was born within a huge community of other stars that formed in the same . In that birth cluster, the stars were close enough together to pull comets away from each other via . It's like neighborhood children playing in each others' back yards. It's hard to imagine it not happening."

According to this "thief" model, comets accompanied the nearest star when the birth cluster blew apart. The Sun made off with quite a treasure – the Oort Cloud, which was swarming with comets from all over the "neighborhood."

The Oort cloud is an immense cloud of comets orbiting the Sun far beyond Pluto. It is named after mid-20th century Dutch astronomer Jan Oort, who first proposed such a cloud to explain the origin of comets sometimes seen falling into the inner . Although no confirmed direct observations of the Oort cloud have been made, most astronomers believe that it is the source of all long-period and Halley-type comets.

The standard model of production asserts that our Sun came by these comets honestly.

"That model says the comets are dregs of our own solar system's planetary formation and that our planets gravitationally booted them to huge distances, populating the cloud. But we believe this kind of scenario happened in all the solar systems before the birth cluster dispersed."

A cluster of stars forming in the Orion nebula. According to Hal Levison's research, these stars could be swapping comets.

Otherwise, says Levison, the numbers just don't add up.

"The standard model can't produce anywhere near the number of comets we see [falling in from the Oort Cloud]. The Sun's sibling stars had to have contributed some comets to the mix."

Comets in the Oort Cloud are typically 1 or 2 miles across, and they're so far away that estimating their numbers is no easy task. But Levison and his team say that, based on observations, that there should be something like 400 billion comets there. The "domestic" model of comet formation can account for a population of only about 6 billion.

"That's a pretty anemic Oort Cloud, and a huge discrepancy – too huge to be explained by mistakes in the estimates. There's no way we could be that far off, so there has to be something wrong with the model itself."

He points to the cometary orbits as evidence.

"These comets are in very odd orbits – highly eccentric long-period orbits that take them far from our Sun, into remote regions of space. So they couldn't have been born in orbit around the Sun. They had to have formed close to other stars and then been hijacked here."

This means comets can tell us not only about the early history of the – but also about the history of other stars.

"We can study the orbits of comets and put their chemistry into the context of where and around which star they formed. It's intriguing to think we got some of our 'stuff' from distant stars. We're kin."

Explore further: Many famous comets originally formed in other solar systems

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5 / 5 (1) Nov 24, 2010
In a gravitational tug-of-war, each star should come out about even. Stealing or sharing?
not rated yet Nov 24, 2010
5 / 5 (4) Nov 24, 2010
In a gravitational tug-of-war, each star should come out about even. Stealing or sharing?

No, more massive stars would come away with more comets, probably proportional to the squares of the masses. We tend to think of the sun as an "average" star, but it probably outmasses most or all of the stars born in the same nursery.

Second, what blows apart stellar nurseries? The current theory says extremely luminous stars live fast and die young, and their explosion as supernovas blasts the remaining gas out of the nursery and destroys the gravitational cohesion. The supernova remnant is often a neutron star massing less than the sun.

So the brightest stars give their comets away, and the smaller stars are robbed.
not rated yet Nov 24, 2010
Has any truly extra-solar, hyperbolic comets ever been observed? I don't believe so.
not rated yet Nov 24, 2010
you know it actually amazing that we can see out of the oort cloud -- amazing we can see into others like it


well mark -- only the tradgetory of the comet would give us any information on it in the past. In the last 80 years I do not believe we have seen one but once again, there very classification suggest that we only get to see them once. So if we encounter one from now on we will know if its not coming back
1 / 5 (2) Nov 27, 2010
Other hypotheses claim islands of stability of transuranic elements. Now we do not have very much of this in our system, and other systems may have similar shortages. However if our Oort cloud is an aggregation of captures from many passing stars, some of them not from our galaxy even, and taken over many eons of time; then we stand a chance of finding just about any amount of any possible element and stable isotopes of them as well if we look long enough and hard enough. So we have a dab of this and a dab of that, and we took from systems that had dabs of that and this of other we have everybody's stuff around other words. Better start teachin my grandkids Chinese as they and maybe the Russians have the guts and perserverance to go get this stuff and whip it on us. We just aint got the grit anymore. Better teach 'em Russkye too...hedge our bets. Leastwise the Russians have the intelligence to build nuclear rockets.

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