Wikipedia:Reference desk/Archives/Science/2012 August 6

= August 6 =

Question about the plutonium in the curiosity rover
On the talk page for the Mars Science Laboratory, I posted a question about the plutonium generator in the Curiosity rover. Please take a look, thanks. 67.182.25.41 (talk) 08:03, 6 August 2012 (UTC)


 * It was an easy mistake to make. The figure given for the beginning of the mission is the total thermal energy produced by the fuel, whereas the figure given for the end of the mission specifically refers to the electrical output. It should also be noted that the relationship between remaining fuel and electrical output is not linear but is defined by the Seebeck effect, which is itself dependent on the temperature of the two nodes of the thermocouples used. So you actually expect a greater-than-exponential loss of power as the mission goes on. But anyway, the actual figures are 125 watts at the start of the mission, and 100 at the end. Although the RTG is actually designed to output 285. Someguy1221 (talk) 08:27, 6 August 2012 (UTC)
 * Oh, I take that back. I see simply read the passage too fast, and the distinction is made clear. Someguy1221 (talk) 08:28, 6 August 2012 (UTC)

Landing on Mars and coming back
Did some rover, or anything similar, ever landed on Mars and came back? Or is the Curiosity rover and its predecessors just meant to land, perform their work there and report the data to Earth? — Preceding unsigned comment added by 79.155.237.76 (talk) 11:34, 6 August 2012 (UTC)


 * No, no spacecraft has yet landed on Mars and returned, but there are plans for such a mission, see Mars sample return mission. - Lindert (talk) 12:08, 6 August 2012 (UTC)


 * I'm surprised they would even consider a return mission. For much less extra fuel and rocket size I'd expect they would be able to just include more analysis equipment.  The one advantage I could see is that it might be preparation for a human mission, in which case they should send an exact replica of the human capsule, with either empty seats or maybe a monkey or two (hopefully trained to use the toilet facilities). StuRat (talk) 19:15, 6 August 2012 (UTC)


 * One advantage of doing the analysis on Earth is that you can analyse things you didn't think of before you started. With in-situ analysis, you only have the equipment you thought of in advance. You can't spot something interesting and then come up with a new experiement to analyse it further. There are also things you can learn that would be useful for a human mission without the return capsule accurating simulating a manned one. --Tango (talk) 11:27, 7 August 2012 (UTC)


 * "Accurating" ? StuRat (talk) 06:20, 8 August 2012 (UTC)


 * And why wasn't it done yet? Why is it easier to transport the scientific equipment to Mars than to enhance the rover with a return device? 79.155.237.76 (talk) 12:31, 6 August 2012 (UTC)


 * Seems pretty obvious, doesn't it? A two-way trip would mean equipping the rover to somehow blast off of Mars. That means shipping a lot of fuel, an extra rocket, etc. Make no mistake: sending something on a rocket to Mars from Earth is hard. Sending something to Earth from Mars is no easier. --Mr.98 (talk) 13:05, 6 August 2012 (UTC)


 * But, the escape velocity of Mars is smaller than of the Earth, and the way Earth-Mars-Earth is almost for 'free' (I believe).
 * It's still obviously a lot more work to make a lander that can autonomously blast off again than it is to make one that just stays there. --Mr.98 (talk) 15:05, 6 August 2012 (UTC)


 * The escape velocity of Mars is indeed lower, but the latter bit is entirely wrong -- you don't subtract the energy load when making the return trip; rather, you add further requirements. And while comparatively less fuel is needed for Mars -> Earth than Earth -> Mars, you have to use a lot more fuel on the (less efficient) Earth -> Mars leg to get your return rocket to Mars in the first place.  Also consider: Curiosity (mass approx 1000 kg) was delivered to Mars by an Atlas V rocket, and we'll assume that 1000 kg is functionally the most mass that could have been so delivered by that platform.  1000 kg probably isn't enough to return anything from Mars to Earth.  The Atlas itself weighs 340000 kg, so that's a 340:1 mass-to-payload ratio for the Earth -> Mars trip.  You'd have (even granting the lesser escape velocity from Mars) less than 10 kg of total science package plus Earth-return package plus payload to play with, and that has to include all the stuff you need to survive re-entry at Earth.  So why not use a bigger rocket?  Because the Atlas is functionally the heaviest operational rocket available currently (+/- 10% or so). &mdash; Lomn 15:06, 6 August 2012 (UTC)


 * On the other hand, there was also the (failed) Russian Phobos-grunt probe, which would have attempted to return about 200 g of soil from Mars' moon Phobos. You get around the problem of getting off Mars, though the fuel then required for the return trip is similar.  It was launched on a Zenit-2M, a somewhat less-powerful rocket than the Atlas 541 that launched the MSL.  It's unclear how big the actual return-rocket of the Phobos-grunt probe was. Buddy431 (talk) 18:22, 6 August 2012 (UTC)

Updates To Darwin's Theory of Evolution by Natural Selection
Sorry if this is a somewhat common question; when you search the web and the reference desk archives, there's a lot of junk to filter through.

Does anyone know of a reasonably comprehensive list (for the layman) of modifications which have been made to Darwin's theory since he first proposed it? By this, I don't mean updated knowledge of the details of the events that occurred or the underlying chemical processes; I only mean modifications in the understanding of the principle. I'm no biologist, and the only example of an update that I'm familiar with is the selfish gene theory, but I'm sure there are many others.

Thanks. --75.102.79.215 (talk) 16:47, 6 August 2012 (UTC)


 * Have you seen the modern evolutionary synthesis article ? There's the history of evolutionary thought article too.  Sean.hoyland  - talk 17:05, 6 August 2012 (UTC)


 * History of evolutionary thought onwards gives an overview with links to more detailed articles, if you want a book then (or the more recent edition) gives pretty good coverage. . `dave souza, talk


 * The most significant modification seems to be that evolution doesn't happen at a slow, steady pace, but in jumps and starts, like growth spurts in a teenager. The causes are complex, such as a changing environment (or introduction to a new one), or the addition, loss or change of an interacting species (a predator, prey/food, competitor, or symbiont).  We have also discovered the mechanisms of inheritance (DNA) and mutation, but that doesn't modify Darwin so much as add detail. StuRat (talk) 19:03, 6 August 2012 (UTC)


 * See Punctuated equilibrium. I think your explaination is misleading. Both the PE and Phyletic gradualism models appear to be legitimate models for understanding historic evolutionary patterns . The question of the frequency of each model is an unresolved issue and besides, looking at it as a dichotomy is usually seen as flawed anyway. I also suspect you will find that many evolutionary biologists do not agree with your view that it's the most significant modification, in fact I think many would even question whether it's really a significant modification at all, see our article or   . Nil Einne (talk) 21:16, 6 August 2012 (UTC)


 * I am a fan of Gould's but Nil is correct here. μηδείς (talk) 23:16, 6 August 2012 (UTC)


 * And he's entirely wrong that the mechanisms of inheritance don't modify Darwin — they have profound effects on making sense of evolution. --Mr.98 (talk) 22:31, 6 August 2012 (UTC)


 * No, if it modified Darwin it would prove that something he said was wrong. It just adds detail. StuRat (talk) 22:58, 6 August 2012 (UTC)


 * Have you actually read Darwin, much less his discussion of heredity in his theory? Much of it is not correct. --Mr.98 (talk) 16:49, 7 August 2012 (UTC)


 * What portion of Darwin was proven wrong by "the mechanisms of inheritance (DNA) and mutation" ? StuRat (talk) 22:39, 7 August 2012 (UTC)
 * Anything related to Pangenesis, for one thing. --Mr.98 (talk) 23:01, 7 August 2012 (UTC)
 * Pangenesis is one of these things which is 99.9% unadulterated bull, but there's just enough to it that you can argue that he foresaw something if you want. Namely, we now know from modern epigenetics that there are some characteristics which can be influenced by environment.  And this influence might involve circulating hormones, growth factors, cytokines, and other molecules that transmit information from the somatic cells to the gonads.  Obviously, that is not what happened in the rabbit experiment mentioned in the article, but I would think it is possible, with just the right situation, to transfer blood, observe an effect on the next generation, and call the responsible factor a "gemmule" if you want. Wnt (talk) 13:35, 10 August 2012 (UTC)


 * The most important modification is known as the modern evolutionary synthesis. Basically what this means, in lay terms, is the merging of Darwinian natural selection with modern understandings of population genetics. This took a lot of work and happened relatively recently (the 1930s or so) — before then was a sea of competing theories torn between the neo-Darwinians (like August Weismann) and the biometricians (like Karl Pearson). (It is amazing to many in retrospect that Darwin was not seen as particularly correct in the period between his death and the creation of the MES.) The MES is basically a version of evolutionary theory that takes the best of both of those worlds and makes them into one coherent theory. Aspects of it would be recognizable to Darwin but much would be new to him, as he had by modern standards a quite poor understanding of how heredity worked and that has big implications for making sense of the theory. As for other sub-theories (like selfish gene), there are tons... Category:Selection is a nice place to start for much "smaller" topics. --Mr.98 (talk) 22:31, 6 August 2012 (UTC)

The answer, given twice above, is the modern evolutionary synthesis. Part of that, and the most important, is Mendelian genetics followed by the elucidation of the nature and function of DNA by Watson and Crick. There is also the mathematicalization of population genetics by Dobzhansky, et al., and the biological species concept of Ernst Mayr. Most importantly, these are all elucidations. Nothing contradicts Darwin's theory of evolution by natural and sexual selection. μηδείς (talk) 23:14, 6 August 2012 (UTC)


 * Well, unless you count all of the other modes of selection Darwin never thought about, and ignore all of the parts of Darwin that are, err, contradicted by later research (like Darwin's own theory of how heredity worked in evolution). --Mr.98 (talk) 16:50, 7 August 2012 (UTC)

Thomson jumping ring
In a Thomson jumping ring experiment, how do you derive the relationship between the mass/current/temperature of the ring and its jump height?--150.203.114.14 (talk) 17:44, 6 August 2012 (UTC)
 * It is worked out in an article from The Physics Teacher, available at http://physicsed.buffalostate.edu/wnypta/meetings/2004-05/02-05-05/Hall1997TPT35p80-83.pdf. Looie496 (talk) 18:30, 6 August 2012 (UTC)


 * WP:WHAAOE has failed! Thomson jumping ring is a redlink... Roger (talk) 16:33, 7 August 2012 (UTC)
 * Point it to Electrodynamic suspension? DMacks (talk) 16:39, 7 August 2012 (UTC)

Sci Fi Movie Another Earth
In the movie Another Earth, a second Earth appears in our horizon, which looks as far away as our moon. Due to it's proxmity, what would be the physical consequences of earth in the movie Another Earth? Reticuli88 (talk) 18:09, 6 August 2012 (UTC)
 * Greater magnitude of (due to more mass in close proximity) and variability of (due to varying orbital periods) tidal effects, nighttime reflected sunlight, and solar eclipses. &mdash; Lomn 18:28, 6 August 2012 (UTC)
 * Specifically, I ballpark the tidal influence of Earth2 as being about 5 times that of the moon: Earth2 sits at 4x lunar orbital radius (as Earth is about 4x the radius of the moon), and is 81 times as massive. 81/42 = 5. &mdash; Lomn 18:33, 6 August 2012 (UTC)
 * More importantly, if I recall correctly that's an unstable configuration. In a short period of time the moon would either hit one of the planets or (more likely) be ejected from the system.  The two planets would then either drift together or drift apart. Looie496 (talk) 18:37, 6 August 2012 (UTC)


 * Tide is proportional to the inverse cube of distance; 81/4³≈5/4 —Tamfang (talk) 20:05, 6 August 2012 (UTC)


 * The second Earth doesn't looks as far as the moon. It looks as big as out moon. Since the earth is bigger, it would be much far away than the moon. Comploose (talk) 18:52, 6 August 2012 (UTC)
 * I based my numbers on "Earth2 has the same angular size (looks as big) as the moon". However, looking at the pictures in our article, Earth2 is in fact pictured by the film as being far closer than the moon's orbit, which would easily result in immediately catastrophic consequences. &mdash; Lomn 19:16, 6 August 2012 (UTC)

In the productions notes in the wiki article:
 * "The DVD/Blu-ray deleted scenes feature reveals that the filmmakers did intend to illustrate some of the consequences to gravity by filming a scene in which Rhoda encounters flowers floating in mid-air, but the scene was cut from the final film."

...would floating flowers really be possible? What other things would we observe happening if such a thing occured? Reticuli88 (talk) 19:42, 6 August 2012 (UTC)


 * No. The change in gravity even on the near-Earth2 side of the Earth would be undetectable over small scales. Someguy1221 (talk) 20:05, 6 August 2012 (UTC)


 * Changes of gravity don't only affect light things. Consider that gravity, besides holding flowers down, holds the ground down. —Tamfang (talk) 20:08, 6 August 2012 (UTC)
 * Yeah that would have been a terrible gaff. Vespine (talk) 22:21, 6 August 2012 (UTC)


 * Actually, I'd argue that there might be no consequences at all. Consider what this looks like from the orbit of Jupiter.  If the new Earth has its own extra mass, then conservation of mass goes completely out the window, with an enormous amount of mass-energy appearing out of nowhere, and you have a discontinuity in the gravity experienced from the region of Earth.  Note that this is very different from if the mass is secretly flown in on shuttle drones, because then there are gravity waves and such to make all the paperwork line up - the extra Earth out of nowhere would throw off all the calculations in the cosmos, at least in principle.  The "likelier" explanation for such an absurd event is that some kind of mirror has appeared - if as the article says, events diverge on the two Earths, call it a "quantum mirror".  You'd have to come up with some sort of rule - probably not a 50/50 split of mass, because there are no half-weight particles, rather some physics that says that copy 1 particles don't attract copy 2 particles, and responses of individual particles that are from neither copy will be 50% probability to either at any given moment.  So if you travelled to the other Earth you'd be weightless.  Indeed, I suppose electromagnetic forces would probably work the same way, so your ship would simply pass through the ground like a ghost (oh, so that's where they come from...)  But then again, the light interacts, so your ship would be roasted when it sunk through the core.  But isn't light an electromagnetic force.  Hmmm...  bottom line: you'd have a lot of experiments to try before you get a consistent theory. ;) Wnt (talk) 14:14, 10 August 2012 (UTC)

Silviring Analogues for other Metals
I know that you can coat something with a thin layer of silver just by putting it in a hot mixture of Tollens' reagent and sugar, but are there other similar reactions that can be used on non-metallic surfaces but using other metals? I am specifically thinking about possible use for coating something to make it conductive enough to electroplate, so the metal doesn't matter as long as it is cheaper than silver. Bakmoon (talk) 22:21, 6 August 2012 (UTC)


 * In the electronics industry, there is a need for ceap arbitarily or odd shaped "shield boxes", Over the years, a number of processes for giving molded plastic boxes a conductive surfacehave been developed. A common one is the Pearlstein process:  First, "sensitising" is done with a bath of SnCl2 solution. Next, it is "activated" in a bath of PdCl2 solution.  The result is a reliable but thin conductive surface that can be built up by electroplating.  Electonic parts are mounted in printed circuit boards.  These boards comprise an insulator substrate, eg fibreglas or phenolic, about 1.6 mm thick, on which copper tracks are manufactured.  Often, tracks are on both sides, and plated through holes (PTH) connect from one side to the other, and provide places where the wire end of the parts are soldered.  At first the Pearstein process was used to make PTH's conductive after drilling the substrate.  Since then better methods have been developed - you might like to research the Atkinson & Wein process and CU-EDTA.  You could do a patent search on PTH.  You could also consider "aquadag", which is a "paint" comprising fine carbon particles mixed in a water soluble binder.  Once somthing has been "dagged" it can be electroplated.  This may be acceptable for hobby use or one off's - it is a bit too slow and fussy for production use. Keit121.221.208.142 (talk) 23:05, 6 August 2012 (UTC)


 * One can chrome plate plastics. There are many ways to make a mirror on various non-metallic substrates, for example using elemental mercury (not sure the process for depositing it) or aluminium (vacuum deposition probably the most common). I've made some really cool-looking metal-film mirrors on various glass objects by precipitation of metallic lithium or sodium, but obviously those are a bit hard to handle (and probably not suitable for most electrochemical cells). DMacks (talk) 23:10, 6 August 2012 (UTC)
 * Such methods are either difficult, or use hazardous materials though. The advantage of electronics industry methods such as Pearlstein, Cu-EDTA, and aquadag is that they don't require exotic methods, are easy to use (though cleanliness is key) and the chemicals are not particularly hazardous.  Keit120.145.61.75 (talk) 02:06, 7 August 2012 (UTC)

What makes Curiosity so special?
Hi all, What makes the Curiosity rover so special compared to previous Mars rovers? There seems to be more excitement over this one than previous landings (if I recall correctly). - Akamad (talk) 22:45, 6 August 2012 (UTC)
 * It's the most advanced to date. Shadowjams (talk) 22:51, 6 August 2012 (UTC)


 * The Curiosity rover has an incredibly complex landing system, so people might just be amazed that anything that complex can actually work. StuRat (talk) 22:54, 6 August 2012 (UTC)


 * True. Also, that complex landing system allowed it to get to a really neat place, where it can examine ground seemingly shaped by flowing water, and look at layers of rock exposed in canyons going back two billion years. Wnt (talk) 14:18, 10 August 2012 (UTC)


 * It's a tremendous boost for ailurophobes. Clarityfiend (talk) 23:03, 6 August 2012 (UTC)
 * Thanks. I also ended up finding some information here. - Akamad (talk) 23:05, 6 August 2012 (UTC)


 * I'll also add that the previous rovers were pretty much limited to looking at things, although in addition to regular cameras they could look with spectrometers, microscopes, X-rays, and even the result of blasting a rock with gamma rays. But the Curiosity can do real chemistry on Martian rocks and soil, and let us learn a lot more than we could in the past. Someguy1221 (talk) 23:10, 6 August 2012 (UTC)

The Curiosity is a huge advancement in the Planetory Exploration process that is so very vital to the Success to the human race and maybe the discovery of new life forms even if it is the dead ancester of some Microbe. -concerned Life form
 * For mac cultists or UK fans, its computing power as supplied by BAE is essentially the G3 as used in the original iMac G3, with the same operating system as the AirPort Extreme. . . So that makes it kinda special! . . dave souza, talk 22:52, 7 August 2012 (UTC)

How close would an alien species have to be to detect us if they had our current level of technology?
If an alien species had our current level of technology and they were to focus detection efforts on our portion of their celestial view looking for alien (to them) signals, how close would they need to be to detect us given our output of signals--light, television, radio—whatever we broadcast that they might detect)? One premise: let's ignore time delay. What I mean is that a species forty light years away, if they could detect our electromagnetic output, would only be able to detect what was put out forty years ago. I don't want to limit it in this way. So at any time. Signals spread out and get weaker over distance so I assume it's pretty limited. To state it backwards, if there were aliens on a planet orbiting proxima centauri with our current level of technology, would they be able to detect us given what we output? Barnard's star? and so on, growing more distant.--108.54.25.10 (talk) 23:12, 6 August 2012 (UTC)


 * I suspect that the answer very much depends on directional transmissions and receivers. If we put all our technology to work to send a powerful signal to a specific planet, and they happened to have put all their technology to aiming a powerful directional telescope right at Earth (or where Earth was) when the signal comes in, then they could be far more distant than if they just try to detect signals when only random radio and TV signals arrive.  In the later case, I'd think they would need to be within our own solar system.  Of course, the aliens would also need to avoid looking toward Earth when we are behind the Sun or in front of it, as interference from the Sun would make our signals hard to pick out.  So, the answer might come down to how close they would need to be to detect Earth, since that's a prereq for them to point a powerful antenna at Earth. StuRat (talk) 23:23, 6 August 2012 (UTC)


 * This is discussed on our article on the Fermi paradox. Dominus Vobisdu (talk) 23:27, 6 August 2012 (UTC)

I'm just gonna copy my comment from last time this was asked, since I was the only one to respond:

In the best case scenario, the Arecibo message is received at another planet while that planet has its own Arecibo-sized dish pointed directly at Earth. In this case, even a pessimistic estimate gives the Arecibo a detectable range of 10,000 light years. In that same page, it is noted that Frank Drake claims the technology exists to boost this range ten-fold. It's hard to imagine, however, that we'd manage to land the message right on an equivalent detector. I recall seeing a calculation (but I can't recall where), that a modern radio receiver without a directional dish like Arecibo would detect the message from ~400 light years at most. A non-directional emitter and a non-directional detector would have a drastically reduced range, and with modern equipment (I'm told), you may have trouble communicating with Alpha Centauri. Someguy1221 (talk) 04:09, 19 March 2012 (UTC)

If Aliens were pointing their version of the Arecibo Observatory at us, they should be able to detect us easily from a few hundred light years away. All of this is answering based on what has already been built. We have the technology to build, if we so desired but it would be very expensive, intergalactic radio transmitters. Not that we would get any use out of them in our lifetime. But as mentioned in the article linked by Dominus, if the aliens aren't listening to the stars, they won't hear us, unless we happen to nail them directly with Arecibo, and from relatively nearby. Someguy1221 (talk) 23:33, 6 August 2012 (UTC)


 * Given that the speed of light is a limitation, they'd have to be no more than about a light century away to detect our radio broadcasts, likely much closer. The fact that we have an oxygen-rich atmosphere almost mandates the presence of photosynthetic, if not intelligent life.  Detecting oxygen from other planets' atmospheres is at just about our level of skill now; although we have not done it yet, we do know how. μηδείς (talk) 23:41, 6 August 2012 (UTC)


 * The OP specifically asked us to ignore the speed of light delay. StuRat (talk) 23:45, 6 August 2012 (UTC)
 * In that case my points are false. μηδείς (talk) 02:46, 7 August 2012 (UTC)


 * If you mean our technological ability, we could build space VLBI telescopes which could detect city lights and radar signals tens of thousands of light years away, and campfires on an Earth-like planet hundreds of light years away, given the necessary budget and clearances. However, only the military uses the formation flight technology enabling large synthetic apertures, and they keep it secret and actively dissuade astronomers from using it. So our actual passive detection capabilities of city lights are presently limited to the few earth like planets within a few dozen light years. Write your congresspeople. 70.59.11.32 (talk) 03:07, 7 August 2012 (UTC)


 * Synthetic aperture imaging is good for improving the angular resolution of your telescope (increase the distance at which you can tell one city light from another), but to see fainter (or more distant) objects, you need an increase in true aperture. --Carnildo (talk) 01:41, 9 August 2012 (UTC)

If you simplify the problem to that of being able to detect some transmitter that transmit some signal at some power at some frequency using a given receiver with some given antenna, then the distance at which you can detect that signal depends on the noise and the integration time. Now, you can estimate the noise, but the integration time is arbitrary, it is bounded by the time the transmitter is going to transmit the signal.

Then if there are a large number of transmitters that transmit on various frequencies for different time periods, you could still extract this fact without being able to resolve the individual transmitters, if the (unknown) formal description of the set of the transmitters is simple enough compared to the number of transmitters. Count Iblis (talk) 16:19, 7 August 2012 (UTC)


 * There is no way to shield a planet's atmosphere from being analyzed spectroscopically. Given that the presence of advanced life on a planet is likely to drive its atmosphere away from equilibrium, one should search for planets withg oxygen-rich or other non-stable atmospheres.  Such planets having been identified, one can scan them intensively for radio or other unexpected transmissions.  I apologize for repeating myself. μηδείς (talk) 22:23, 7 August 2012 (UTC)


 * That assumes that a spectroscopic analysis can be done easier than scanning for transmissions. While it's easy to analyze the spectrum of stars, planets reflect far less light, and it's difficult to separate that tiny amount of light from the huge amount coming off the nearby star(s). StuRat (talk) 06:16, 8 August 2012 (UTC)


 * Yes, but there does seem to be a large number of planets the Kepler Telescope is able to find by occultation. μηδείς (talk) 06:32, 8 August 2012 (UTC)