Comets: Looks Like They May Not All be From Around Here.

"Wanted for Theft: Sun Stole Its Comets From Other Stars"
Nola Redd, Space.com (November 23, 2010)

"It turns out our sun may be a cosmic thief that's stolen most of its comets from other stars, a new study suggests.

"Comets are small icy bodies that flare up when they near the sun as solar radiation vaporizes their ice to create a glowing tail.

"New computer simulations of the billions of comets crisscrossing the solar system suggest that most of them originated beyond our local neighborhood, but got grabbed and pulled in by our sun's gravity later...."

Current models of how the Solar system formed give a pretty good explanation for where comets come from: There's good reason to think that they formed from the same cloud of gas and dust that our sun, Earth, and the other planets did.

Just one problem. Although the Oort cloud comets are too far away to detect - directly - so far - we've got a pretty good census for comets that swing in close to the sun. That's not the problem.

It's the numbers.

They don't add up.

Back to the article:

"...[Southwest Research Institute, Boulder, Colorado's Hal] Levison and his team say there seem to be around 400 billion comets hovering just beyond Pluto. In comparison, the conventional model predicts only 6 billion.

" 'That's...a huge discrepancy,' Levison said. '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.'..."

Assuming that comets - some of them, anyway - came from the neighborhood of other stars helps explain the number of comets we see. It also explains the orbits of quite a few long-period comets: which can go far into the depths of space.

That means that we may be able to get samples of material from other stars a whole lot sooner than however long it takes to build really fast starships.

"...Comets are generally regarded as excellent snapshots of the early solar system, because they spend much of their lives encased in ice. But if some of these comets come from outside our solar system, then they can tell us about their parent stars, as well.

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

Intriguing: and somewhat 'old news,' too. Our current models for how the universe works say that everything we're made of, apart from hydrogen, and maybe helium, was made in the cores of very old, very massive, stars.

And that's another topic.

Related posts:

• "A Serious Search for Other Worlds, Life, and - Maybe - Extra-Terrestrial Intelligence"