Film Deep Impact Discussion

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trims
Topic
01:30:39 AM Sep 18th 2016
edited by trims
Deleted the Artistic License Physics discussion of Gus being blown off the comet is actually not correctly represented.

The actual dialog is "he's at 1000 feet altitude and has reached escape velocity".

Escape velocity on something as small as the comet in question is less than 10m/s. Traveling 1000 feet (300 meters) in a couple of seconds (the time shown in the movie) requires an acceleration of only equivalent to a couple of "g". The section also severely over-estimates the amount of force applied to the astronaut's suit by the gas pulse.

The depiction is close enough to how it would actually happen to be reasonable. The primary error is the "1000 feet" one, which would more properly be 100m or so. But it's no so off of reality that this trope applies (since only a very, very technical reading would possibly consider this somewhat incorrect).

Also deleted the Imperial Stormtrooper Marksmanship Academy entry. The missiles didn't miss. They were simply stated to not succeed, which in this context, means that while at least some of them hit, the effects of surface-detonations of nukes on the comet wasn't enough to make any difference.

If anything, this would be No Sell.
Arivne
Topic
03:08:39 PM Jun 6th 2013
edited by 69.172.221.8
Deleted some Natter that violated Example Indentation from these trope listings.

Apathetic Citizens
  • Possibly justified — it's not like there's anywhere else to go.

Government Conspiracy

Outrun the Fireball
  • The force of the waves smacking off of the hills in the background should have shook the ground and made it difficult to run.

Deleted the following from trope entries because they have nothing to with the trope.

Made of Explodium
  • Not to mention that his phone somehow broke at a convenient moment, leading him to take a high-speed chase to deliver the information; since of course seconds counted in stopping the comet— and yet the crash delayed the discovery by over two months.
  • And the aforementioned space shuttle, which was more effective than all the nukes on earth at blowing the comet to pieces.

Suicide Mission
  • Surprisingly, no mention was made of the fact that, since their spacecraft uses an Orion Drive, its fuel supply is nuclear bombs.
Morgenthaler
Topic
04:04:58 AM Mar 4th 2013
This entry has some valid points, but it is long, rambling, and filled with Natter. Can someone more attuned with the science behind it clean this one up?

  • Hollywood Science: Deep Impact was lauded by critics and astronomers as more scientifically accurate than its rival, Armageddon. That's like saying Jurassic Park was more scientifically accurate than Godzilla.
    • You cannot determine the course and speed of a comet from one picture.
      • It is possible, sort of. Blue- and Redshifting occurs where the light from an interstellar object shifts slightly towards the blue end of the visible spectrum (implying that it is moving towards the observer, and therefore Earth) VS towards the red end of the visible spectrum (implying that the object is moving away from the observer, and therefore Earth), respectively. However, neither one is mentioned in the movie.
      • In real life astronomers would go and look back at older pictures to see if they can find the comet there, and then after getting several such images, calculate the trajectory.
    • The gas on a comet does not start igniting the second sunlight hits it. For that matter, why is a comet (made of dust, ICE and small rocks) creating gas that ignites in space?
    • The blast from the first nukes cause damage to the ship when it's several miles away, meaning those are not low yield bombs, but somehow all that energy at ground zero of the blast just cause a clean separation of the comet into two. Then ICMBs launched at the comets later on fail to divert them, even though those missiles are powerful enough to level cities, which neither comet is bigger than. The comets aren't even solid rock. They're made of bits of rock in a bunch of gas and ice, the latter of which would be vaporized by the heat of a nuke. Of course this is for the sake of the story, but worthy of praise of scientific accuracy?
      • One should also consider the very real possibility that many of the ICB Ms missed. ICB Ms are designed for suborbital trajectories, in which they fall back onto targets on the earth. That means that the missiles would not actually even have enough power to get into earth orbit, much less reliably hit something out in space. Since they were launched as a last ditch effort there would have been little time to recalculate their trajectories, or do anything to enhance the power of their rockets.
      • Consider that a city is gone when all its buildings are destroyed, not when there is a crate 500 feet deep and a few miles wide, which is something a nuke can't even come close to producing.
    • The tail of the comet is always shown trailing after it, because people think that's how comets look. Actually the so-called tail is always on the opposite side from the star the comet orbits.
    • Anyone close enough to see the comet's entry into the atmosphere would be pulverized from the soundwaves alone. Nobody on that Virginia highway would be alive to see the tsunami coming for them.
    • In reality, shattering the comet into many smaller pieces would make little difference. Would you rather get hit by a bowling ball thrown as fast as a car or the same bowling ball broken into chunks going as fast as a car? BOTH options HURT. Even if all those chunks burn up in the atmosphere, that's a lot of things burning up in the atmosphere in the same place at the same time. It still would be unpleasant for the planet.
    • Impact-induced waves don't travel like tsunamis do-they're a different type of wave, and they tend to peter out before they go more than a few dozen miles, a few hundred tops. Plus, waves have a hard time traveling very far inland because they're fighting gravity and friction with the ground along the way. This means that while Biederman would have doomed large swaths of Virgina, Maryland, North and South Carolina, and Delaware, the rest of the country and the world would have been fine.
      • The wave itself has a serious case of Hollywood Density. Water is heavy-a cubic meter weighs a metric ton, which is 2,205 lbs. At the bottom of the 3500-foot wave, the pressure would be 1,520 pounds per square inch. Every single skyscraper in Manhattan would have torn off its foundations and broken up into very, very small pieces.
trims
01:18:57 AM Sep 18th 2016
1. The gas on the comet isn't igniting. It's changing from a solid to a gas state, and obviously expanding rapidly. Technically, it's sublimating - moving from a solid to a gaseous state without first becoming liquid. The depiction is *entirely* scientifically correct as to what would happen

2. The nuclear bombs were quoted as 5,000 kilotons, or 5 Megatons. However, the ship is several DOZEN miles away (if not closer to 100 miles) when the detonation occurs, so, realistically, there should have been virtually no physical damage to the spacecraft except from very small debris of which very little should have hit the ship. The transmission interruption due to EMP is very correctly handled, though.

When it comes to the physics behind the separation of the comet into 2 chunks, it's a bit hard to evaluate. We're not told exactly how deep the "moles" went, and while 5MT sounds like a lot, a 7-mile-diameter comet has a *LOT* of mass. Presuming they got the fracture points right, the cleaving is entirely reasonable. When it comes to the ICB Ms, they're mostly useless, because merely detonating something on the surface (which is what the ICBM would do) absolutely wouldn't have much effect on a large solid mass. To use the analogy from another movie: put a firecracker in your open hand. When it goes off, it's likely to hurt but not severely damage your hand. Now, hold that firecracker in a closed fist. When it goes off, you're gonna need a whole new hand.

3. Phil's (mostly) incorrect about the effects of a pulverized comet. The main issue, of course, is how far away from the Earth the comet was when detonated - it's extremely hard to tell from the movie, but let's assume it was several minutes from impact (otherwise, flying the spacecraft into it is pretty much impossible). That puts the comet inside the lunar orbit, but still several tens of thousands of miles up. At that distance, a significant portion of the mass of the comet is going pushed AROUND the earthy due to the internal explosion. Even better, the total mass that does hit the earth is going to be: (1) made up of small fragments, and (2) spread out over a larger period of time (dozens of seconds) than the single comet.

While you're likely to have a "shotgun" effect on the earth - meaning that the footprint of actual strikes would be significantly greater - only a tiny portion of the mass would make it through the atmosphere to actually impact. So, rather than a huge billion-ton comet striking the surface, there'd be dozens of single-digit ton and below chunks hitting the surface. That's still bad - you'd end up with what looks like dozens of 1MT nuclear blasts covering a million square miles or so. But that's far, far, far better than the 20,000,000 MT explosion that intact comet would cause.

As to "dumping kinetic energy into the atmosphere" thing: the large portion of the fragmented comet does convert kinetic energy into heat while entering the atmosphere. But a significant portion is converted into light energy. It also matters a great deal that that energy is transmitted much more slowly and over a vastly larger volume than a solid impactor: so much so, that we're talking a dozen orders of magnitude difference. It's still a very significant effect, and yes, it would have major climate implications. But it's ludicrously better than a massive impactor.

4. Impact-produced waves are not any different than typical tsunamis. Here's a decent projection for a strike in the Eastern Atlantic: http://news.ucsc.edu/2003/05/355.html Note this was for a meteor about 1% of the volume of the comet in the movie. 1km+ height tsunamis across the Eastern Seaboard are entirely realistic.

And, no, waves aren't noticeably restricted by gravity or friction. The restriction is pretty prosaic: the total volume of water in the tsunami, and the height of the land being inundated. Due to the relatively flat nature of most of the Eastern Seaboard, particularly from Maryland southward, it's entirely likely that a 1km tall tsunami (which is likely a wave 25km or more deep) would travel up to the foothills of the Appalachian Mountains, or 200km+ inland.

Also, a major impact-caused tsunamis in the Atlantic Ocean would likely devastate pretty much all civilization within 100km of ANY place that had a coast with the Atlantic Ocean. That's the entire Eastern shores of North, Central and South America, the entire Caribbean island chain, Iceland, the British Isles, Western Europe, and the West Coast of Africa. In other words, roughly 10% of the world's population, and close to half of it's total wealth.
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