Wikipedia:Reference desk/Archives/Science/2011 October 5

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October 5

Why are impact craters on Moon all circular?

This came up at a Science Meet where an exponent of non-Standard Model of the Universe (to wit: Electric Universe) declared that these formations were volcanic in origin, and were not impact craters. He cited in evidence that if they were impact craters, then many would be like skid marks, from asteroids which came in obliquely. There were other criticisms of the asteroid theory, but they were quite technical. Otoh, the objection to craters in that they are all too circular and neat caused me to raise my monobrow like a big hairy boomerang. What do you think? Myles325a (talk) 01:14, 5 October 2011 (UTC)

What's important is the amount of energy released, not the direction of the impact. Dauto (talk) 01:35, 5 October 2011 (UTC)

The energy released at the point of impact converts to heat, causing debris to expand in all directions from that point. There will also be a few skid mark craters that are elliptical in shape due to glancing blows. Did you read Impact crater? Graeme Bartlett (talk) 01:41, 5 October 2011 (UTC)

I believe the maria are ancient lava flows, so volcanism did occur early on. Here's an example that looks like a skipping meteor blow to me, in the lower left corner: [1]. Also, if the meteor skips enough, it may make a shallow impact over a wide area rather than a single deep crater. That type of shallow crater is likely to be obscured more quickly by volcanism, dust, and later meteor impacts. StuRat (talk) 01:50, 5 October 2011 (UTC)

Reaching back into the inventory of everything I ever read, some fictional work about space exploration asserted that if you spread a layer of flour on a countertop, then throw little round dense objects (lead shot? peas?) at it vertically or at any conceivable angle, every crater is observed to be circular. Intuitively, I would have expected a vertical drop to produce a circle, but a 45 degree angle to produce an ellipse. Edison (talk) 04:53, 5 October 2011 (UTC)

There are young craters with asymmetric ray systems such as Proclus (crater) suggesting an oblique impact. I don't understand how the person who is suggesting a volcanic origin proposes to explain the extensive shock deformations you can see in lunar samples. Sean.hoyland - talk 05:49, 5 October 2011 (UTC)

Apparently the answer is most, but not all are circular. Please see Impact crater#Crater formation, "Since craters are caused by explosions, they are nearly always circular – only very low-angle impacts cause significantly elliptical craters." Ref. Melosh, H.J., 1989, Impact cratering: A geologic process. New York, Oxford University Press, 245 p.' The same section of the article also has a video of "a laboratory simulation of an impact event and crater formation" (apologies to Graeme Bartlett, who I now see has referred you to the same article.)
• Here is an Australian Broadcasting Corporation (ABC) webpage on the question, Are impact craters always circular? - 220.101 talk^\Contribs 08:44, 5 October 2011 (UTC),

Here's a link to a Scientific American article: Why are impact craters always round? .... This also supports most, but not all, impact craters are circular. - 220.101 talk^\Contribs 08:57, 5 October 2011 (UTC)

Visibility of 1-atom-thick Materials

If I were to have a sheet of say, aluminum that was a 2-inch square and 1 atom thick, would I be able to see it by looking at it from the "square" side? If so, would it look any different from the kind of aluminum foil that comes on a roll? (other than the fact that it appears much thinner) Assume that variables that could damage the foil (oxidation, corrosion, wind, etc.) are nonexistent. Hmmwhatsthisdo (talk) 06:34, 5 October 2011 (UTC)

It would be completely transparent at optical wavelengths (except for a few sharp faint frequency harmonic bands that you would be completely unable to discern.) The atomic radius of aluminum, 1.4 angstroms, is less than 1/2,500th the wavelength of visible light. Also it would spontaneously disintegrate due to unavoidable Brownian motion of the air, which isn't wind. 69.171.160.19 (talk) 07:03, 5 October 2011 (UTC)

It spontaneously disintegrates in a vacuum too, just as fast, due to inherent mechanical strain of the vibration of room temperature heat. There is essentially no cohesion of metals an atom thick. They might as well be molten as far as they act. 69.171.160.19 (talk) 07:28, 5 October 2011 (UTC)

Graphene is an interesting material. It attenuates light of any wavelength by πα = pi times the fine structure constant (~1/137). Wnt (talk) 11:07, 5 October 2011 (UTC)

Yes it is; it's 200 times stronger than steel! Graphene#Mechanical properties 64.134.156.47 (talk) 18:34, 5 October 2011 (UTC)

That's because graphene is held together by the stabilising force of resonance. elle _{vécut heureuse} ^{à jamais} (be free) 05:10, 6 October 2011 (UTC)

I've made a <5 nm (50 angstroms) bismuth nanofilm in the lab before. It's very translucent, and has infinite resistance (whereas a 20 nm nanofilm conducts a decent amount of electricity -- a small piece would have had a resistance of about 500-1000 ohms). elle _{vécut heureuse} ^{à jamais} (be free) 05:08, 6 October 2011 (UTC)

Height Increase

I have heard that height of a human being can be increased artificially by a painful surgery. Is it possible? Please give the name of it. — Preceding unsigned comment added by 119.235.51.130 (talk) 14:16, 5 October 2011 (UTC)

You're looking for distraction osteogenesis. TenOfAllTrades(talk) 14:48, 5 October 2011 (UTC)

Specially take a look at Distraction_osteogenesis#Cosmetic_lengthening_of_limbs if you intend to increase your height just because you wish you were a little bit taller. Quest09 (talk) 14:52, 5 October 2011 (UTC)

Definitely painful, and a risk of it going horribly wrong and maiming you for life. Some patients are wheelchair bound as an unfortunate result. Plasmic Physics (talk) 22:32, 5 October 2011 (UTC)

Do you have a reference for that claim PP. Richard Avery (talk) 07:33, 6 October 2011 (UTC)

I looked into this a while back and that is what I've read, I'd be hard pressed to find the reference now. You don't have to believe me. Plasmic Physics (talk) 10:00, 6 October 2011 (UTC)

I can't get to the meat of this article, which was referenced in distraction osteogenesis, but the abstract says that 100% of the cases in the study had complications, some severe. Comet Tuttle (talk) 18:37, 6 October 2011 (UTC)

Yes, that's a good reference CT. It seems that having your legs, specifically your femurs, surgically lengthened is a very risky business. Richard Avery (talk) 21:48, 6 October 2011 (UTC)

It's worth interpreting that number cautiously. It looks like the publication there may be the abstract of a conference poster or talk, so I don't know if it's possible to readily get hold of the full data, but the abstract has some relevant information. Of the 151 'complications' captured in their study, 78 (52%) fell into their Grade I: Benign complication without any unexpected surgery or anaesthesia. Only 14 (9%) fell into the highest Grade III: Severe complication category. Still not what I would call a safe or worry-free procedure by any means, but not quite the unmitigated disaster that one might infer from a 100% complication rate. TenOfAllTrades(talk) 14:15, 7 October 2011 (UTC)