The asteroid -- or is it a comet? from Armageddon, as seen from its surface and from space.
Note: for purpose of this demo version of the website, images not shown to avoid copyright permission problems
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In all the comet-or-asteroid-crashes-into-Earth movies, and all the documentary shows about how an asteroid killed the dinosaurs and so on, they always want things to look as cool as possible -- and that means making the comet or asteroid look really scary or dangerous. They try, anyway. The problem is that when they try to be halfway realiistic, mostly what they come up looks like blobs of cookie dough sailing through space. Lots of times they don't try being realistic, and they just go for way cool. And they end up with asteroids that are big spiky jagged things with razor-sharp edges, and comets with skies full of clouand and thunder and lightning as jets of steam blasting up. And, almost always, the space rock has a conveniently strong gravity field that lets Our Heroes walk around on it without being forced to blow too much of the special-effects budget on zero-gee stuff. (And, of course, every movie space rock comes complete with its very own soundtrack -- usually scary music that appears whenever it is on-screen.)
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The asteroid -- or is it a comet? from Armageddon, as seen from its surface and from space.
Note: for purpose of this demo version of the website, images not shown to avoid copyright permission problems |
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In real life, your average asteroid resembles a giant grey potato. They tend to have rounded-off shapes, with very few sharp edges. Some are covered with craters -- the result of impacts with other, smaller bodies. Several asteroids (and smaller moons) have craters so big it's surprising that the impact didn't smash the asteroid or moon into bits. There are three main types of asteroid, each with a different basic composistion -- carbonaceous, stony, and metallic, with a small number that don't seem to fit into any of those categories. Asteroids are also classified by the type of orbit they are in, by size, and in various other ways. By no means are they all the same. Scientists are learning more and more about how various asteroids are different from each other.
Here are some images of REAL asteroids.
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| Here are two shots to give some idea of scale. (Click on images for larger views.) Ceres is compared to Earth and the Moon on the left, and to Mars, Vesta, and three more average-sized asteroids. The smallest of thes, Gaspra, is probably bigger than the rock that hit Earth and killed the dinosaurs. Ceres is big enough that its own gravity has shaped into a sphere (see below). | |
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| This is a shot of the asteroid Ida with its teeny-tiny satellite Dactyl (Another view of Ida is shown in the inset image) Click on image for larger view. | This image of the asteroid Itokawa, made by Japan's Haybusa probe. Scientists think this 535-meter long body might be what they call a "contact binary" -- two rocks that hit each other and stuck together, with smaller rocks gradually accumulatinig over time.The images clearly shows what appear to be little rocks that have stuck to the big one. All this suggests that Itokawa is a "rubble pile" asteroid. |
Your average comet looks like a big, blackened blob of dirty ice most of the time -- because it is a blob of blackened dirty ice, with various other molecules of one sort or another mixed in. (There is still a lot of uncertainty about the precise chemical makeup of comets. )This blob of dust, dirt, and ice is often called the comet nucleus, because it is the central structure that can produce the rest of the comet --sometimes.
It is only once a comet gets close enough to the Sun for the surface to be heated enough, the surface releases dust and vapor, and what you can then see of the comet looks like a patch of fog, or a cloud of dust -- which make sense, because that's mostly what the visible part of the comet is. The classic image of a comet -- a bright rounded head with a long, swooshy dramatic tail -- is actually pretty rare. The tail is really just dust and vapor that have come off the surface of the comet. This material is released when the Sun heats the comet, and than only happens when the comet gets fairly close to the Sun. Most comets never get that near the Sun. The rare ones that do are in orbits than take them out into the cold of the outer Solar System beyond Jupiter for years, decades, or even centuries -- and then swing them in toward the inner system for a few short months. On every close pass, the comet boils off more material -- and the vast majority of the dust and gas it releases is gone forever, never to be reabsorbed by the comet. The cloud of gas that forms around the nucleus is called the coma. (Some people call it the head of the comet._ Solar radiation and the solar wind push the gas and dust out away from the Sun, forming the comet tail.
A comet has to get very close to the Sun, and Earth has to be pretty close to the comet, and the comet has to be throwing off a lot of volatile material, in order to generate a naked-eye visible tail. I've seen a few blobby things through telescopes or binoculars, but never in my life have I gotten to see the dramatic, tail-sweeping-across-the-sky spectacle that we all think about when we hear the word "comet." None of the comets I have gotten to see have eer developed a classic tail that have come across the sky in my lifetime. (In 2007, Comet West became the brightest object (aside from the Sun) in the Solar System for a few days -- but Mother Nature saw to it that it was cloudy every night around here. Comet West must have formed a tail during that period, but it was more or or less directly behind the comet as seen from Earth.)
As for walking around on the surface, so as to save on the special effects budget: In real life, even Ceres, the largest asteroid of all (big enough that it is now considered a dwarf planet) is variously estimated to have somewhere between .028 (2.8%) and .07 (7%) of Earth gravity. If you weigh 50 kilos on Earth, you'd weigh somewhere betwee 1.4 and 3.5 kilos on Ceres. (And Ceres is thousands of times larger than the asteroids and comets that are likely to get near Earth.
Here are some REAL images of comets.
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| Comet Tempel-1 imaged by NASA's Deep Impact Space Probe | Comet Borelley, in a image captured by the Deep Space 1 spacecraft | The nucleus of Comet Halley in 1986, taken by the European Giotto probe during Halley's most recent close approach to the sun. Jets of gas and the cloud of dust and gas have formed around the nucleus. |
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Click on any image for a larger view.
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The short form is that asteroid and comet just don't look that scary. However, looks have nothing to do with how dangerous they are. If a spacerock is moving five times faster than a rifle bullet and weighs as much as Mount Everest, if it hits the Earth, that's bad news. Even if it doesn't have scary theme music following it around through space.
At one point in the movie Argmageddon, we are told the comet or asteroid or whatever it is "is the size of Texas." My best guess is that means the diameter of the space rock is about the same as the length of Texas, about 1200 kilometers. There are a few teeny problems with that, which we can best explore by paying a quick visit to reality (a place the screenwriters never visited). The largest known asteroid is Ceres, now generally considered a dwarf planet. It is all of 975 kilometers in diameter. The current best estimate is that has a surface gravity less that 3% of what we get here on Earth. Not very big.
Except, by the standards of a space rock, it's gigantic. It's estimated that the rock that killed the dinosaurs was about 15 kilometers across -- and maybe under 10 kilometers across. Let's be good sports and call it 15 km, and be even better sports, and assume it was a sphere, and give it the density of the densest stony asteroid. Unless I dropped a few decimal places along the way, Ceres has at least 250,000 times the volume of the dino-killer. But it's not the size of the iimpacto that matters -- it's how much mass, or just plain stuff, it contains. Taking the current estimate of Cere's density of 2.1 grams per cubic centimeter, and being super-good sports and giving the dino-killer the density of the densest known asteroid type, 7.9 grams per cc, Ceres is still 67,000 times more massive (heavier) than the dino-killer. A "Texas-sized" asteroid, 1200 km across, would be 136,000 times more massive than the real-life dino-killer. It would be one-third the diameter of the Moon. I don't care how many nuclear bombs you stick into something that size, or how deep you drill before you drop them in. You're not going to break it up into teeny-tiny pieces. And, by the way, if it is 136,000 times heavier, that means it's 136,000 times hard to divert from whatever orbit it was following into a new orbit that theatens Earth. Aside from all THAT -- if it's one third the size of the Moon, we'd have spotted it by now. There are literally thousands of bodies in the Solar System smaller than this imaginaryt object, many of the them cataloged a hundred years ago.
But, of course, the space-rock seen in the movie couldn't possibly be anywhere near that size -- because it isn't the right shape. Why? Anything that big would have been shaped into a sphere by the size of its own gravity. (This effect, of being a big enough body that gravity forces you into a spherical shape, is called hydrostatic equilibrium. If you ever notice yourself approaching that point, it's time to cut down on the fried food.) Ceres seems to be just teetering at the edge of hydrostatic equilibrium. Anything much smaller might not form into a sphere-- but any body bigger that would almost certainly do so. The asteroid Vesta is not that much smaller than Ceres, and it isn't spherical.
In other words, the movie makers who spent nine zillion dollars on the costumes and the special effects and the high-tech toupees for the lead actor could be bothered to spend five minutes looking stuff up or doing three minutes of grade-school math.
There is such a mish-mash of errors in all of this that , for me at least, it's like the boy who cried wolf, except it's mistakes instead of lies. If the movie makers were that lazy and sloppy I just find it impossible to believe anything else that the movie-makers tell me. If they cared that little about the details of their story, why should I care?
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