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comet
Couldn't a large comet or asteroid go right through one of our lage gaseous
planets (perhaps not right through the middle, to avoid an eventual hard, inner core), and come out the other side? br |
#2
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comet
"br" writes:
Couldn't a large comet or asteroid go right through one of our lage gaseous planets (perhaps not right through the middle, to avoid an eventual hard, inner core), and come out the other side? Some years ago, a comet made an attempt of this, at Jupiter. The pictures were spectacular. See http://seds.lpl.arizona.edu/sl9/sl9.html Given the speed a comet or asteroid is likely to have, I don't think it matters whether it hits gas (an atmosphere), or a hard surface. Hmm. From another perspective, I'd want to find out at what depth of a typical gas planet does the gas density surpass the density of the earth crust. best regards Patrick |
#3
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comet
br wrote:
Couldn't a large comet or asteroid go right through one of our lage gaseous planets (perhaps not right through the middle, to avoid an eventual hard, inner core), and come out the other side? Several points: 1) You know how when asteroids reach Earth's atmosphere, they're moving so fast that air friction generates a "fireball" of superheated gases around them? All the heat energy for that "fireball" is coming from one source: the asteroid's motion. It trades speed for heat, just like the brakes on your car or bike. 2) Further, aerodynamic drag increases dramatically the faster you go. Twice as fast means four times as much drag; three times as fast means nine times as much drag. In other words, the faster an asteroid is moving when it enters air, the harder it will "hit the brakes." You can see this in the difference between heat shields used for Earth-orbiting capsules (which hit the air at 17500mph), space capsules returning from the moon (25000mph), and the capsule dropped into Jupiter's atmosphere (106,000mph). The orbital capsules had the thinnest heat shields; the Apollo capsules had thicker and heavier heat shields; the Galileo probe's heat shield was about half shielding by weight. 3) Denser air means more drag, just like more speed. 4) When an asteroid or comet hits the atmosphere of a gas giant, it ends up falling longer and faster than an asteroid that will hit Earth. The gas giants are bigger and more massive than Earth, so their gravity field is stronger. Rocks falling toward them will move faster. 5) Earth's atmosphere gets thicker toward sea level. It starts out at a near-vacuum on the edge of space (~100 miles up) and compacts quite a bit by the bottom. In fact, about 95% of the atmosphere is in the first 20 miles. As you've noted, gas giants have even more atmosphere than Earth. A lot more. Their atmospheres just keeps getting denser and thicker and deeper until the gases liquify under their own weight, and then even turn solid. Let's put all those ideas together. When an asteroid or comet hits the atmosphere of a gas giant, it turns into a meteor, just like it would on Earth. Just like an meteor in Earth's atmosphere, the meteor in a gas giant's atmosphere "hits the brakes" as it plows through the gas giant's atmosphere. But an asteroid or comet hitting a gas giant's atmosphere will be moving faster than a meteor in Earth's atmosphere (see point 4), so it'll experience harder braking (point 2). Further, gas giants' atmospheres get thicker than Earth's (point 5), so the asteroid or comet will experience even harder braking (point 3). The end result is that if the asteroid or comet goes deeper into the gas giant's atmosphere than the uppermost fringes, the asteroid or comet will come to a complete halt, almost as if it hit solid ground. The braking will be so hard that G-forces and heat will pulverize even solid asteroids, let alone comets. For example, Comet Shoemaker-Levy-9 hit Jupiter some years ago. You can see the huge fireballs its separate parts made: they're just like asteroid impacts on Earth. http://www.mso.anu.edu.au/albums/sho...y/Impact_G.gif http://antwrp.gsfc.nasa.gov/apod/ima...ol_hst_big.jpg http://astro.uchicago.edu/cara/resea...irex/comet.gif http://jumk.de/astronomie/img/shoemaker.jpg Incidentally, when the Galileo spacecraft dropped a probe into Jupiter, the probe went from 106,000mph to a halt in 4 minutes. That's about 20Gs just due to air friction. The probe was much more streamlined than a comet or asteroid. However, if the asteroid does just skim through the upper, thinnest fringes of the atmosphere, it can avoid coming to a halt. This (probably) happened on Earth in 1972: http://comets.amsmeteors.org/meteors/1972.html http://gep.alien.de/ifo/images/ifo_meteor01.jpg Mike Miller |
#4
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comet
br wrote:
Couldn't a large comet or asteroid go right through one of our lage gaseous planets (perhaps not right through the middle, to avoid an eventual hard, inner core), and come out the other side? No. Basically, once you get to where the mass of the planets atmosphere that the comet/asteroid intersects exceeds the mass of the asteroid - at orbital speeds, it's stopped. In practice, this means that any but grazing encounters plow in. |
#5
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comet
br wrote:
Couldn't a large comet or asteroid go right through one of our lage gaseous planets (perhaps not right through the middle, to avoid an eventual hard, inner core), and come out the other side? br No. The atmosphere gets dense quite quickly with depth in relation to the planet's size, so it's really more liquid than gas. |
#6
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comet
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