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Raz
2002-Jun-05, 03:45 PM
Hello fellow BA readers, thanks for for viewing my first post. Although I've been a visitor for a long while (I even remember what the BA's old homepage design looked like!), I've been only an interested lurker here on the forums. I've finally chosen the subject of a recent movie plot device as my first post, which may illustrate my current level of knowledge here /phpBB/images/smiles/icon_wink.gif

The film in question is the recent re-make of H.G.Wells' "The Time Machine". Anyone still planning to see this should be aware that this message contains Spoilers for a newly-introduced plot element. Those who've already seen the film might want to skip the following paragraph.

As the Traveller begins his journey into the future, he stops for a brief sojourn around the year 2030 or so. We learn that a corporation is planning to build tourist facilities on the Moon, and intends to begin hollowing out underground habitation using 20 megaton nuclear blasts. The Traveller moves on a handful of years, and arrives in a scene of chaos. The habitation plan has gone catastophically wrong - the Moon has been shattered and is raining down upon the Earth.

Many thousands of years later, the Traveller arrives on a Earth completed re-formed; the Moon fragments' impact devastated its surface. A sizeble Moon chunk, perhaps a quarter of its original mass, is still visible in the sky, surrounded by a close group of much smaller pieces.

As a side issue, I was quite dismayed when these events played out, because I've been planning for a number of years to incorporate this outcome into a story of my own... Now (if I ever do so) I'll simply be copying this film, despite a fervent desire for greater astronomical accuracy... but I digress.

I've a number of questions about the events portrayed, but perhaps I should just start by asking: how much Bad Astronomy was portrayed in these scenes? I'm already reasonably sure that something a lot more powerful than a few 20 Megaton blasts would be required to shatter the Moon. Also, if such an event occurred, wouldn't all the pieces of the Moon eventually head Earthwards, as our gravity increasingly affected their much smaller masses?

I'll leave this here for now, though, and see if anything develops =) Any insights will be greatfully received!

Raz

David Hall
2002-Jun-05, 03:55 PM
Hello Raz. Welcome aboard.

This was discussed a few months ago when it first came out. Needless to say, the moviemakers didn't do a very good job.

http://www.badastronomy.com/phpBB/viewtopic.php?topic=722&forum=4

Actually, I haven't yet gotten to see it. What do you think? Even if the astronomy/physics is off, is it worthwhile as a movie?

Silas
2002-Jun-05, 03:55 PM
I haven't seen the film... But...

You're right: the explosive force described isn't enough. I'd say it's insufficient by about 15 orders of magnitude, but that's just a back-of-the-envelope guesstimate.

Let's start with a mild version of the problem: say they set of an explosion that shatters a lunar mountain. A million tons of debris is sent up. Most of it would fall back to the moon. The small part that reached escape velocity would scatter into weird cislunar orbits, some of which would eventually wander back to the moon, and more of which would eventually wander to earth.

At the other extreme: suppose they entirely shatter the moon, dispersing all its parts away from its previous center of gravity. The vast bulk of the moon would smear out into a ring around the earth. A lot would fly off at escape velocity. A lot would hit the earth.

Somewhere in between is the scenario from the flick: there would be a ring, but it would be short-lived as the moon scooped most of it back again. A lot would hit the earth.

(Oh, and whatever is left of the moon would collapse back into the shape of a sphere again; it's too large to maintain an uneven shape.)

Silas

Kaptain K
2002-Jun-05, 06:29 PM
Welcome Raz.

As a side issue, I was quite dismayed when these events played out, because I've been planning for a number of years to incorporate this outcome into a story of my own... Now (if I ever do so) I'll simply be copying this film, despite a fervent desire for greater astronomical accuracy...
So???
There are very few truly original ideas in any branch of fiction, including science fiction. I wouldn't call it copying. More like: Similar idea...different perspective.

_________________
When all is said and done - sit down and shut up!

<font size=-1>[ This Message was edited by: Kaptain K on 2002-06-05 14:31 ]</font>

Raz
2002-Jun-06, 11:31 AM
Good point, Kaptain K. It's highly naive of me to imagine that the writer of this particular screenplay stumbled upon this idea too =)

David, thanks for the pointer to the earlier discussion. "The Time Machine" only opened here in the UK last weekend - there's irony in there somewhere, I'm sure /phpBB/images/smiles/icon_wink.gif - so I'd steered clear of any discussion of it until I got to see it. As a movie its a reasonably good watch; by no means a blockbuster, but interesting to see which elements remain true to the first film, and which receive the Hollywood makeover. I have to confess I haven't read the original story, so I can't compare it to that.

Silas, thanks for the info in your message. It sounds as though not only is it going to be problematic enough to actually break up the Moon, an equally large problem (at least for the story I eventually want to tell) would be the physics of getting most of it to land on Earth!

A couple of other thoughts - apologies if they've already been discussed:

Does the Moon have fault lines, or are these a peculiarity of Earth and/or other larger bodies? If it does, might these contribute to a break up given a suitably powerful catalyst?

Is it still thought that the Moon might have an ice core? If I don't have my wires crossed on that, then it seems that the pressure increase to be had from somehow vapourising all that ice might have, ah, 'interesting' results..?

Raz

David Hall
2002-Jun-06, 02:53 PM
On 2002-06-06 07:31, Raz wrote:

David, thanks for the pointer to the earlier discussion. "The Time Machine" only opened here in the UK last weekend - there's irony in there somewhere, I'm sure /phpBB/images/smiles/icon_wink.gif - so I'd steered clear of any discussion of it until I got to see it.



Tell me about it. Star Wars Episode 2 doesn't come out here until mid-July. There are now a couple of very long threads I haven't been able to touch for that reason. And I've got more than a month to go.

Aargh.

Come to think of it, I'm not too sure The Time Machine has opened up here either. I haven't seen anything of it.

Silas
2002-Jun-06, 04:16 PM
Does the Moon have fault lines, or are these a peculiarity of Earth and/or other larger bodies? If it does, might these contribute to a break up given a suitably powerful catalyst?


I believe that the moon is tectonically dead. So, no moonquakes, no lunar volcanoes, etc.

However, the moon's crust does have "fracture" lines from some of the larger impacts in its past.

Still, those are pretty minor, and wouldn't go very deep. As a really rough analogy, think of the chips and nicks you might find on a really old billiard ball. They wouldn't really make it all that much easier to shatter the entire ball.

Silas

Kaptain K
2002-Jun-06, 04:48 PM
...It sounds as though not only is it going to be problematic enough to actually break up the Moon, an equally large problem (at least for the story I eventually want to tell) would be the physics of getting most of it to land on Earth!
You're best bet to both pulverize the Moon and get most of it to impact the Earth would be a head-on collision with a sizable chunk (Ceres size or so) of interstellar debris or dislodged TNO (Trans-Neptunian Object).

Does the Moon have fault lines, or are these a peculiarity of Earth and/or other larger bodies? If it does, might these contribute to a break up given a suitably powerful catalyst?
Largely irrelevant. Fault lines are a feature of the crust and do not extend very deep into the interior.

Is it still thought that the Moon might have an ice core?
Nope! Iron.

Conrad
2002-Jun-07, 10:47 AM
From what I remember of the film and the rationale behind the shattered Moon (hasty exposition so I may have misheard) the nuclear detonations don't shatter the moon per se, but knock it out of it's orbit.
From what little I know about orbital mechanics (i.e. zero!) it would be extremely difficult to change the orbit of the Moon with squibs like 20MT devices. As mentioned above, the plot device would be better defined as a Big Thing Hitting The Moon Very Hard - but then that leads into Armageddon territory ...

Raz
2002-Jun-10, 09:37 AM
I think you're probably remembering the film better than me, yes. The film-makers problem is that they needed the catastrophe to be man-made... of course, they could have steered clear of the Moon entirely and stayed truer to the original film =) Unfortunately, I have a similar problem, but as well as needing a man-made cause, my story requires the Moon being brought down to Earth as well =) *sigh* Hmmm... an iron core, you say? Now how could we go vapourising *that*?? /phpBB/images/smiles/icon_wink.gif

Raz

<font size=-1>[ This Message was edited by: Raz on 2002-06-10 05:48 ]</font>