This is CBS, I On the World. I'm John Batchelor. I welcome Dr. Ken Croswell, an astronomer,

as well as of someone who teaches me the astronomy I did not learn in the 20th century.

Right now we're going to discuss something that has always been there, but in the 20th century, I don't believe we saw one.

Now we've seen more than one, and we can expect more.

Visitors from afar, and by that I mean another galaxy.

Ken, a very good evening to you.

You lay out a detective story that there are objects that we've recently ascertained,

passing through our solar system that come from outside the solar system.

Was this discovery news, or did they always expect to find it?

And it was just a matter of chance.

Good evening to you, Ken.

Good evening, John.

We have for many decades expected to find interstellar objects passing through our solar

system. These are objects, comets, asteroids that were flung out by other solar systems. And the

reason that we long expected such objects to be passing through

our solar system is because we know that our solar system has cast out comets and asteroids.

And in particular, the two largest and most massive planets in our solar system, Jupiter

and Saturn, if something swings close to one of those planets, their gravity will throw them clear out of the solar system.

And in fact, exactly the same thing happened with the two Voyager spacecraft.

They pass close to Jupiter, and Jupiter's gravity flung them outward on an interstellar trajectory.

So those two spacecraft are leaving the solar system.

And there's no reason that other solar systems shouldn't do the same.

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