Wikipedia:Reference desk/Archives/Science/2015 January 22

= January 22 =

Reviving the Beagle
Now that the location of the Beagle 2 is known, is it conceivable to "shake" the spacecraft and possibly free a stuck part by aiming a powerful laser at it to heat it up and/or move it with light pressure? (A big part of this is how precisely you can focus a laser; I assume it must be better now than during the 1962 Lunar Laser Ranging experiment but Mars is a looong way off) Wnt (talk) 02:43, 22 January 2015 (UTC)
 * No, only very tiny things can be moved. The amount of energy required would easily vapourize the thing, rather than just move it. And it cannot be so accurately focused. It will be easier to send a robot there to move it, and even easier to send another working machine! Graeme Bartlett (talk) 08:41, 22 January 2015 (UTC)
 * see Optical tweezers, forces are on the order of pico Newtons. Graeme Bartlett (talk) 11:48, 22 January 2015 (UTC)
 * Nichols radiometer and solar sail illustrate that (small) macroscopic pressure can be applied, but yes, mostly I was thinking to nudge the spacecraft by heating it up substantially then letting it cool. I doubt it's easier to send a robot and it's definitely not faster! :)  The focusing issue is indeed the main problem I don't know about.  Sometimes I've heard noises about self-focusing in interstellar medium  but I don't know if there's any practical way to apply that -- nor what other clever things might be accomplished with perfect lenses and such, perhaps using metamaterials and IR/terahertz/microwaves.  So I dropped this hook in the water... Wnt (talk) 15:13, 22 January 2015 (UTC)


 * Given that we have no clue as to WHY the solar panel 'petals' failed to open - why would anyone invest any significant amount of money in it?  It would be fairly unlikely that a thermal trick would nudge open a stuck panel unless the thing was very *VERY* close to being able to open by itself.   It's far more likely that one of the half dozen causes of failure listed in the report would have resulted in a broken motor/gearbox/hinge/wiring or a bent panel or that it's stuck by just a little bit more than a thermal nudge would fix.  Add to that the problem that without adequate solar power and YEARS beyond it's anticipated mission life, it's batteries will be quite utterly dead - and even if it were still alive, would it really still be running software that would repeatedly try to move that same stuck panel over and over again for 10 years?  These spacecraft do not generally survive martian winters without actively heating their electronics - and it's unlikely that Beagle would have been able to do that without fully operational solar panels and good batteries.  Then there is the issue that cooking parts of the craft that weren't designed to be cooked would be highly likely to break something else.   Then there is the problem that the team who were prepared to do science with this craft have long ago been disbanded.  Also, just how much power do you think a "powerful laser" fired from here on Earth would have on Mars?   For sure not enough to make a measurable difference to the temperature of anything there!  There are far, far, FAR too many obvious flaws here before we even start to consider the not-so-obvious ones.
 * Sorry but this is just a ridiculous proposal - it doesn't even have a one in a million chance of working...and since the entire mission only cost $66,000,000 - a cost-benefit analysis would say that spending more than $66 on trying to fix it would likely be a bad idea!
 * SteveBaker (talk) 21:55, 22 January 2015 (UTC)

Just use a laser to power the deployed solar panels. Laser divergence angle is in the ideal case 2.44 lambda/D where lambda is the wavelength of the laserlight and D is the diameter of the laserbeam as it exists the laser. So, the laser will radiate into a solid angle of approximately pi (2.44 lambda/D)^2. The flux of a laser of power P a distance r away will therefore be P D^2/(5.95 pi lambda^2 r^2), the power intercepted by a solar panel of area A will thus be P_received = P A D^2/(5.95 pi lambda^2 r^2). To deliver 30 Watt of power to a solar panel of 1 m^2 at a distance of 100 million kilometers requires a laser with a power of 17 Gigawatt and an aperture of 10 meters, which is possible to realize with existing technology. Count Iblis (talk) 22:23, 22 January 2015 (UTC)


 * That laser would have to run continuously...I don't think that combination of power, aperture and duration are possible with existing technology...and in any case, the problem with Beagle is nothing to do with not having enough power - it's because the antenna it was suppose to use to talk to earth is folded up and covered by one of the solar panel petals.  At the moment it landed, it had plenty of battery power to talk to us - and it didn't.   So giving it more power won't help in the slightest.  So, no, this is still a hopelessly stupid idea that doesn't stand up to the smallest amount of critical thinking!  Furthermore, it presumes that the spacecraft will have survived a decade with no heat applied to the electronics or the batteries - and that's simply not possible throughout martian winters.  Consider the final fate of Spirit (rover) which had a fully functioning solar panel, good batteries, etc going into Martian winter.   Without the ability to align all of it's solar panels to the sun, it cooled below the minimum storage temperature of batteries and electronics and died.  When martian summer returned, and it should have had plenty of power to revive, it never transmitted again.  Beagle 2 was in an even worse situation - immobile *and* with only a fraction of it's solar panels it stood no chance.  SteveBaker (talk) 16:40, 23 January 2015 (UTC)


 * Count, have you allowed for the two atmospheric attenuations involved? I suspect you'd have to get your laser into LEO to eliminate the larger of the two. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:42, 23 January 2015 (UTC)
 * Well... that's a good question. The U.S. Air Force has been talking about having lasers and reflectors in orbit since (at least) the 1990s, and there must be all sorts of powerful lasers in existence as part of Strategic Defense Initiative research and the like.  If it can vaporize a missile near Earth maybe it can heat up or modestly jiggle a probe on Mars.  I was thinking someone could just aim one of those things at Mars and do a weapons check with the Beagle, and if they happened to knock it loose, super.  Even if a solar panel simply fell, with nothing else happening, it would be an interesting proof-of-concept for other space situations where something gets stuck a long way away. Wnt (talk) 16:04, 23 January 2015 (UTC)


 * Oh good grief...again? No!  You've evidently read far too much science fiction!


 * The only SDI lasers used in the way you describe (to shoot things down) were either:


 * Nuclear-bomb powered...sure, you get a hell of a lot of light for a few milliseconds, but then your entire laser (and everything for half a mile around it!) is vaporized.


 * Chemical lasers that never achieved more than a megawatt or so did manage to destroy a missile - but only because it had been especially prepared by over-pressurizing the interior.  The missile wasn't "vaporized" - it had a tiny hole punched in its outer skin that caused the over-pressurized interior to pop like a balloon.


 * The only other high energy (terawatt and petawatt range) lasers out there have to charge up for hours in order to generate incredibly short pulses, right now, they are capable of running for a few picoseconds just twice per day. So, you might (maybe) get a tiny amount of light to the lander - but it would be over long before enough energy could be used to do anything useful.


 * You may be thinking of the newly added laser weapon on USS Ponce -- LaWS. Sadly this is just a 30kW laser...but it doesn't vaporize things...it relies on heating up key parts of the target for several seconds to the point where they fail.   The most powerful military laser that's even in the earliest planning stages is only 300 kWatt.


 * This idea you have that there exist GigaWatt power continuous wave lasers with 10 meter diameter beams is complete and utter nonsense.


 * So, please, stop talking about things you clearly know nothing about - and listen to what we're telling you.  THIS WON'T WORK.   Not by a very, very large factor - and for at least a dozen very good reasons that I've painstakingly explained to you.


 * SteveBaker (talk) 21:22, 23 January 2015 (UTC)


 * Well, not knowing was why I asked the question. I see the megawatt laser you were talking about (MIRACL) mentioned in the SDI article (they need a cite for the part about the pressurization, and I'm afraid I never really grasped the degree of the deception needed to get a positive result).  We have a variety of articles about weaker lasers like Boeing YAL-1, Advanced Tactical Laser, High Energy Liquid Laser Area Defense System ... it never dawned on me that the one built in 1980 would be the be-all and end-all of all powerful lasers, or that there would be any limit to how powerful you could make lasers simply by duplicating them as modules to work side by side or to be aimed together from around the planet.  In the YAL-1 article Gates is quoted, "I don't know anybody at the Department of Defense, Mr. Tiahrt, who thinks that this program should, or would, ever be operationally deployed. The reality is that you would need a laser something like 20 to 30 times more powerful than the chemical laser in the plane right now to be able to get any distance from the launch site to fire".  My assumption from that time was that surely they would actually build one at least 30 times more powerful, using a satellite reflector to reach the target rather than putting it all on board a plane.  If the military never did that I'm surprisingly unimpressed. Wnt (talk) 23:06, 25 January 2015 (UTC)


 * What you're completely missing is that even though these lasers are less powerful than you imagined, that's only scratching the surface of the problem. All of these lasers are designed to fire a very brief pulse - typically in the picosecond range - perhaps up to a second or two - and then spend a very long time recharging.  To heat up something on Mars, you'd need a continuous beam laser - and the power you can get from one of those is orders of magnitude less than with a pulsed laser.  You can (perhaps, just) kill an aircraft or missile a few miles away with a pulse - but without a continuous beam, you're not going to be heating anything up for very long.    SteveBaker (talk) 23:26, 25 January 2015 (UTC)


 * Everything else aside, a pulse is really what I had in mind from the beginning. I just want to give the thing a jiggle, not cook it for lunch.  To illustrate, you described a petawatt laser (1018 J/s) for 1 picosecond (10-12 s) delivers 106 J of energy; at 4184 J/kcal that's over 200 dietary calories, like throwing a decent-sized shot of burning vegetable oil on something.  In light pressure alone it carries 1 000 000 J / 299 792 458 m/s is over 3 g m / s of momentum, which is, well, like tossing a few raisins at the target.  The instantaneous aspect of the heating is what I'd think is desirable if you want one part to expand relative to another to perhaps make something stuck come loose; I'd think continuous heating isn't going to work well on Mars because it will keep radiating away in the cold surroundings (though continuous light for solar panels to be more powerful as suggested above would make sense).  Of course, you'd have to get it there, which is very possibly an insurmountable challenge. Wnt (talk) 23:44, 25 January 2015 (UTC)
 * An exawatt laser is 1018 J/s. Petawatt is only 1015 J/s. For certain values of "only."
 * Main point's still valid. - ¡Ouch! (hurt me / more pain) 10:40, 26 January 2015 (UTC)
 * Erm, ouch!. Actually it kind of blows it away, unless I can spange an extra three decimal points from a secret government laser lab.  Thanks for reminding me of SI units!  Ouch. Wnt (talk) 14:08, 26 January 2015 (UTC)

Electronic cigarettes and devices
The use of electronic cigarettes have become very popular and I would like to know if electronic smoking devices create Formaldehyde. If so, is the formaldehyde in a high concentration or low?

Thank you — Preceding unsigned comment added by 50.58.210.13 (talk) 19:33, 22 January 2015 (UTC)


 * We have a section Electronic_cigarette. Some companies tell you the ingredients in their liquids, like this one -. Formaldehyde is not listed as an ingredient in either place. The main ingredients tend to be water, either propylene glycol or glycerine, some flavors. Nicotine is optional. This NPR story says that somehow formaldehyde can turn up in some vapors . But there is some controversy as to how these laboratory tests at high voltage compare to real-world experience. The original research paper is here, the abstract is freely available but the full article requires access . You can ask at WP:REX if you want a copy and don't have another way to get it. There are some known risks and unknown risks to using electronic cigarettes. No reputable source says there are no risks. Most sources seem to indicate that it is less dangerous than smoking cigarettes.  SemanticMantis (talk) 21:51, 22 January 2015 (UTC)

Urinating while sitting vs. standing up
A judge has ruled that men should be allowed to urinate while standing up, but he did say that it's mostly a cultural matter. However, I cannot urinate well while sitting, my bladder then doesn't empty well. So, it seems to me that there is also a biological reason why men should be allowed to urinate while standing. Count Iblis (talk) 21:28, 22 January 2015 (UTC)
 * I'm skeptical of a biological reason why men should be "allowed" to urinate while standing. I'd wager that most men don't have a problem either way. A lot of men urinate while defecating in a seated or squatting position (seated in the West, squatting in Asia, Africa, and Eastern Europe).


 * Perhaps being overweight may be a factor in the ability to urinate while sitting, in which case gender wouldn't make any difference.


 * If a man doesn't enjoy cleaning bathroom floors, there's an advantage to urinating while seated. ~Amatulić (talk) 21:42, 22 January 2015 (UTC)
 * What's the question? Vespine (talk) 22:31, 22 January 2015 (UTC)


 * Whether or not the judge should have invoked biology as well to motivate why men should be allowed to stand up in the toilet. Count Iblis (talk) 22:34, 22 January 2015 (UTC)


 * Only in Germany. μηδείς (talk) 22:35, 22 January 2015 (UTC)

Snark is not helpful.50.43.56.168 (talk) 13:22, 24 January 2015 (UTC)

Slope or relief maps?
There was a c. 2001 map of Antarctica with average slope angle and maybe relief color coded on the back. That was a great National Geographic map. What's the best way to get maps like that for places that aren't Antarctica? Preferably the US? I see something you have to pay for on Google.

Most maps color code elevation of the pixel or roughly shade the relief, National Geographic's idea is much better at giving you an idea of how hilly a place is. It should be relatively easy to calculate with free elevation datasets and simple software. It'd be cool if you could set it to "non-continuous" and make the color bands really narrow to see what 10 different levels of "Florida Peninsula flat" look like. Sagittarian Milky Way (talk) 22:09, 22 January 2015 (UTC)


 * Or maybe National Geographic made one for the US and you could buy it on eBay or something. Sagittarian Milky Way (talk) 22:12, 22 January 2015 (UTC)


 * I think a standard elevation map does a good job. Where the elevation lines are close together, that's a steep hill.  Where they are far apart, that's a flat area.  And you can also read elevation directly off the map, which is always a plus. StuRat (talk) 04:41, 23 January 2015 (UTC)


 * Topo maps generally are of small areas, aren't they? Wouldn't it be better for violet to mean flat, blue to mean as steep as these parts of my hometown, teal to always mean "steepest neighborhood I ever lived in steep", green to always mean "Upper Manhattan steep" and yellow Palisades steep everywhere? Or something like that? You can always look up the elevations in a topo map, like you said. This would not be a good general purpose hiking map as you've now used up all the colors which could show a lot of information like what's a state forest, what's built-up, and so on. But it'd be good to look at I'd you already have the topo map. A staircase-steep slope that's only 20 feet tall isn't really that impressive though (maybe cause I half-grew up near one). A 2.6 mile high view down a 50 mile slope to the sea would be impressive though (that's Mauna Kea) but the slope is mild like a Greek shield so another color coded map that tells the height of the hills (relief) at a glance would be good, too. Sagittarian Milky Way (talk) 05:58, 23 January 2015 (UTC)

Minimum photons to see something
I'm not really sure how to phrase this question so I'll do my best. Let's say you have an apple floating out in outerspace. If there are no photons being reflected off of it, it should be totally black. How many photons would need to be reflected off of it in order for it to be "seen" so to speak. I know that's a very poor way of putting it, but to put it another way, let's say just 1 photon of light is reflected off of that apple, and enters some photon sensor. Would that single photon be sufficient in letting an observer know that it's an apple? Would you be able to "see" an apple if it reflects 1 mere photon. 69.121.131.137 (talk) 23:37, 22 January 2015 (UTC)


 * In pitch black, about 90 photons of green (510nm) light will produce a visible response in 60% of the trials. Interestingly, humans can also see infrared light from a laser, if two infrared photons strike the same receptor pigment at once, and this happens enough times to reach the above threshold. This has been dealt with in the archives, so you can search their for previous commentery.


 * μηδείς (talk) 00:07, 23 January 2015 (UTC)


 * See Elitzur–Vaidman bomb tester for how to detect something without any photons hitting it, one can even tell the color of something with near 100% chance of never hitting it with any photons! Anyway as to the question many animals which live in low light see single photons at a time, describes how even human rod cells detect single photons at a time. Dmcq (talk) 01:28, 23 January 2015 (UTC)


 * If you have a photon sensor at hand, then one single photon can be detected, since there is such a thing as Photon counting devices which can detect individual photons. However, a human eye needs a higher number of photons to register it as a stimulus. The absolute threshold article has all the details. Notice that even if you reach the minimum perceptual threshold, and you are able to perceive the presence of something, you'll still need more light to recognize it as an apple. After all, reaching the minimum threshold (slightly higher above 50 photons to be detected 60% of the times) would still provide less information than seeing a pixel of a picture. --Pathnew (talk) 01:36, 23 January 2015 (UTC)