h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Pieces following? Oh oh. I hadn't thought of that... (They are in a nearby suburb to us.) The hole in the roof was really something!

I remember a case last year, where an elderly couple had a massive block of ice come through their roof - and it was later determined to be *exactly* that - the product of a passing aeroplane! And they had put it in their freezer for investigators... Yeeccchhh!

John Campbell, on 3 News, said it had come from the asteroid belt between Mars and Jupiter, but there was a graphic implying something quite different! Confusing...

Oh?
What was the graphic implying?

I hope they didn't show a clip from "Deep Impact"

{from the backlog}

Reply to kea:

You have to think billiard balls.

Sometimes the asteroids collide, and get knocked out of their orbit. Then they're pulled towards Earth's gravity, but they've been given a knock, quite a knock, considering it was travelling at 30,000 mph when it hit our atmosphere.

There's no way to know how long it was in the asteroid belt, I reckon they can tell how old it is, they can even tell which ones come from like the one that was found in the Arctic something to do with the gas composition, it exactly matched Mars' atmosphere.
If you find one of those, you're gonna be quids in:
http://www.space.com/news/la001_sale_000430.html

So the asteroids are in orbit around the _sun_ not a planet?

Do they knock into each other?

And where is the force coming from that takes them in a certain direction until they get caught in the earth's gravitational field?

If the rock came from the asteroid belt and travelled in a straight line to here, they should be able to tell how long it took yeah? Or could it have been out there for much longer and if so what was it doing?


See what happens when you start answering questions

errr...

Without actually checking properly cos its half the fun, I read somewhere (torus II) that orbits actually degrade too?

So when a big lumpy bit is near the outside, then the orbit there would be weakish, and then get bumped out easier?

I sorta supposed that asteroids were bits of flotsam of stuff hanging out in space or orbits (fabulous!), and that ... meteorites were the asteroids, but called meteorites when they enter our atmosphere...

<>

I agree



Vix - not an astrologist, just read too much sci-fi

Hey, what do you wanna know about asteroids? http://www.solstation.com/stars/asteroid.htm

Pretty pictures & everthin.

I'm not sure being an astrologist would be much help here .

For objects to remain in orbit around the sun their orbital speed has to balance the pull of the sun's gravity - ie since gravity weakens with distance according to an inverse square law, the further out you are the more slowly you have to travel to stay in orbit. If a collision slows you down and/or pushes you slightly closer to the sun the force of gravity becomes stronger than that of inertia/momentum and you will gradually spiral inwards towards the sun. If that fall takes you close to another planet (in this case the earth) that planet's local gravity will pull you in.

Noggin

That makes sense

By spiral inwards do you mean there is both an orbit of sorts and a trajectory inwards because of the suns gravity?

Spot on, Kea.

I love learning new things.

but, but...what about decaying orbits....I said degrading didn't I?...'opps'

I thought that they might have something to do with stuff bouncing out too..

Energy has to be put in for an object to move out to a more distant orbit, so I don't expect that would be called either decaying or degrading.

Well, I can only make a guess (and hopefully inspire someone a bit more knowledgable to correct me if I'm wrong.)

As far as asteroids go I don't believe their orbits decay that much. Usually the term refers to satellites orbiting the Earth. (Natural and manmade) In Earth orbit, especially in Low Earth Orbit (LEO) orbits degrade rather quickly. For instance, the ISS needs regular boosts to retain its orbit. It used to get these from the shuttle. I'm assuming the Progress rockets are now performing this task. There are several factors that cause these satellites orbits to decay. The greatest of these is atmospheric drag. In LEO satellites are still within the fringes of the Earth's atmosphere. During sunspot activity the Earths atmosphere heats and expands increasing the drag effect.

Most asteroids are not normally within LEO and so orbital decay should not be associated with them.

Deep Impact - shudder! No, luckily not...

...interesting stuff,

check out :
http://www.meteorites.com

and click on 'meteorites for sale'

alec.