Wikipedia:Reference desk/Archives/Science/2016 July 5

= July 5 =

Smelly hot water
I recently stayed in a private home in Vilnius, Lithuania. The home appeared to be recent construction (< 5 years old, is my guess, but I didn't ask). The cold water appeared normal, but the hot water carried a strong odor that resembled bad eggs. We were told that this had something to do with the builder using the wrong type of pipes to carry hot water. Being Lithuania, we weren't drinking the water at all (bottled water only), though we did use the water for showering / cleaning, as the people who lived there recommended. Can anyone make an educated guess of what kind of pipes react with hot water to give a strong odor? Is this likely to be H2S, or something else? Both the hot and cold water appeared clear. Dragons flight (talk) 07:42, 5 July 2016 (UTC)


 * It is doubtful that the metal or plastic of the pipes is caused the smell. Look at this and this, they both seem to think it is something to do with some sort of (?harmless) anaerobic bacteria that react with the anodes in the heating system and make hydrogen sulphide which causes the odour. Richard Avery (talk) 11:04, 5 July 2016 (UTC)


 * It's usually a combination of several things. Gypsum in the local geology leads to sulphur in the supply water, then a steel water heater is used, which requires a magnesium sacrificial anode. These encourage anaerobic bacteria to develop which produce hydrogen sulphide you can smell.
 * It's hard to eradicate this, especially in showers. Hydrogen sulphide can be smelled at very low concentrations (1 or 2 parts per million) and standing in an aerosol of water droplets gives a large surface area to release the dissolved gas from the water. Chlorinated water supplies tend to stop it - but you might then smell the chlorine.  A regular drain, clean and bleach treatment for the water heater can be useful in bad cases. This is often needed for properties only used intermittently. Controlling the water heater temperature can help too, and also helps against Legionella. Some makers sell non-bacteriogenic anodes. The traditional British alternative was copper water heaters which didn't need anodes. Germany uses modern stainless or plastic water heaters.  A modern solution is to avoid a large-volume stored water heater in favour of low-volume, high-power on-demand "instant" water heating. That's usually the simplest option, if the electricity supply permits it. Andy Dingley (talk) 11:26, 5 July 2016 (UTC)


 * We have a garden hose, that when left in the sunlight, produces what smells like swamp water, even though we started with nice chlorinated water. So, you're not alone. StuRat (talk) 00:52, 8 July 2016 (UTC)

Artist renditions of spacecraft instead of photos
I noticed that many, if not the majority of our articles on spacecraft, most recently Juno uses artist renditions of them rather than actual photos. Isn't it easy for NASA or ESA to make a photo and release it under the same free license they publish artist renditions? Brandmeistertalk  09:07, 5 July 2016 (UTC)
 * I don't think anyone would see it with all panels attached and unfurled like that. -- Q Chris (talk) 10:35, 5 July 2016 (UTC)
 * The drawings usually show them in space with a planet, moon, asteroid or at least stars in the background. That was also the case in your example where the transparent version was made at Commons. I have displayed both versions here. PrimeHunter (talk) 10:47, 5 July 2016 (UTC)


 * In June of this year, I received a ticket to explore JPL, and we got to tour High Bay 1 (the clean-room where Juno was assembled and packed for transport to its launch facility). The clean-room is one of the largest in its class, world-wide - and even still, it would be very difficult to fully assemble the Juno orbiter in its deployed, space-flight configuration.  Furthermore, the space-craft is structurally designed for operation in microgravity - it surely is not sturdy enough to hold its own weight with its solar panels deployed in Earth gravity.  For demonstration-purposes, an engineering mechanical mock-up of one of Juno's solar panel arrays was fully extended and mounted on a display platform - and the panels are very large compared to the room.
 * I'll try to find a good photograph from that tour and upload it to an appropriate article. It helps demonstrate why it is difficult to photograph a fully-assembled spacecraft.  It may also help to remember that the clean-room is not a photo studio: it is a shared resource for all of NASA JPL.  As a one-of-a-kind, world-class, operational engineering facility, its special capabilities must be in continual use to prepare other missions in the multi-year pipeline that is the work of building spacecraft!  There's not a lot of "free space" to put together a photo-shoot.
 * Once in orbit - the spacecraft is usually far away from any person or robot who might take a photograph of it! Sometimes, cameras can be mounted on launch vehicles, or on separated stages, and so forth - but for the most part, the only available cameras are the scientific experiment packages mounted on the spacecraft, pointing away from the spacecraft!  Except in very rare cases - like a few of the recent Mars landers - those kinds of science payload cameras can't be pointed or moved at all, so they're totally unable to "take a selfie" of the orbiter platform.  For a good conceptual exercise, the next time you ride on a commercial airline flight, think about trying to photograph the airplane, from the outside, while it's flying - and you'll have a greater understanding of how very difficult it would be to get that photo!  You can't simply pop open the door and walk onto the wing - and even if you could, you still wouldn't be able to frame the wing in your picture!
 * Nimur (talk) 14:28, 5 July 2016 (UTC)
 * Sure you could. Just wait a couple tenths of a second... Wnt (talk) 15:41, 5 July 2016 (UTC)
 * Launch of the Hubble Space Telescope was delayed from 1986 to 1990 due to the Challenger disaster. During that time, it was stored in a nitrogen atmosphere clean room in Silicon Valley. I had the chance to see it during that time through a window. It was impressive but seeing it operational in orbit is another thing entirely. Many in orbit photos are available since it has been serviced four times by astronauts, and it looks much more impressive in orbit than in a crowded clean room. On the other hand, there is no opportunity to take photos of operational deep space probes. Cullen328  Let's discuss it  07:39, 6 July 2016 (UTC)


 * The only recognisable photos of probes in deep space that I'm aware of are the pictures that Philae and Rosetta took of each other as they separated: photo 1, photo 2. These show another problem with trying to get pictures in space: you're not going to get anywhere near the quality you do on Earth (If you think those are bad, here's how Huygens looked pictured by Cassini). The cameras aren't designed for tracking a fast-moving, nearby object, especially one that's not well lit by sun. Plus, a spacecraft being a few metres across means that you need to be relatively close to it to get a decent photo (even the Lunar Reconnaissance Orbiter, our best Moon spacecraft, can barely make out the Apollo landing craft). Smurrayinchester 07:45, 7 July 2016 (UTC)

Bats eating mosquitoes
A headline in today's NYTimes reads: "Devouring 1,000 Mosquitoes an Hour, Bats Are Now Welcome Guests as Zika Fears Rise". A quick google search indeed suggests that this 1000/hr rate is widely quoted. That would be one mosquito every 2.7 seconds for an hour straight... I'm skeptical. It just doesn't pass the common sense test. I would like to be pointed to a credible scientific source confirming or repudiating such a claim. I reckon the NYTimes should be better than this, and maybe also the local officials in towns hoping to impact Zika by housing bats. It isn't hard to find seemingly authoritative sources suggesting that controlling mozzies with bats has not been proven as effective...thanks if you can shed any echolocation on this claim. — Preceding unsigned comment added by 94.210.130.103 (talk) 12:40, 5 July 2016 (UTC)


 * Wouldn't that be one every 3.6 seconds ? Also note that they could consume at the rate of 1000 per hour without actually eating for an hour.  (If they eat 250 in 15 minutes, that's still the rate of 1000 per hour, even if they then stop.) StuRat (talk) 20:35, 5 July 2016 (UTC)


 * Note that the star-nosed mole can eat worms in less than a quarter second: . In the case of bats, that speed may be based on the assumption that the mosquitoes are tightly packed, say near a swamp. StuRat (talk) 20:43, 5 July 2016 (UTC)


 * Yeah I strongly suspect this would be "when there's a swarm of mosquitos", I doubt they "chase and hunt" each mosquito one by one. Vespine (talk) 23:30, 5 July 2016 (UTC)

Yes, your math is way better to get to the one every 3.6 seconds. Thanks for that. But I think my question remains ... the headline and the story, and the many repetitions of the number and the claim - don't talk about 'at a rate of 1000 hour', over a short time - I can also kill one mosquito in 3.6 seconds - but my point, and my curiosity about finding any real research, is that even though I can kill a mosquito in 3.6 seconds by a method of slapping it with my hands, and maybe another in another 3.6 seconds in the right circumstances - I'm sure I wouldn't sustain the rate and be able to kill 1000 mosquitoes in an hour, and I'll be surprised if a bat can. The headline, story and other sources really talk about a bat eating as many as 1000 mosquitoes in an hour. The only time I don't like the ref desk is when a query specifies trying to find actual academic, scientific, or other referenced sources. In this case, speculating that in a swarm of mosquitoes, in a swamp, a bat might eat some mosquitoes at a rate pf one every 3.6 seconds for a while, which when you multiply that out means that they eat at a rate of 1000 an hour...and therefore local officials are encouraging bat boxes in urban neighborhoods to fight the Zika virus...the logic breaks down which is the point of my original question. — Preceding unsigned comment added by 94.210.130.103 (talk) 02:52, 6 July 2016 (UTC)


 * I would also be skeptical of the 1000 per hour claim, but that doesn't invalidate the argument that bats eat a lot of skeeters and that they are therefore a welcome addition to the battle against mosquito-borne diseases. OR here, but my Mom's house has bats, and mosquitoes are rare there, while my house does not, and I have lots of the buzzing bastards around.  Also, bats are amazingly stealthy.  All I ever see is the slightest flicker out of the corner of my eye in a shadow.  No sound I can detect, and they stay hidden when I am around.  They were a problem when they were living in my Mom's attic (and pooping there), but the bat houses would solve that. StuRat (talk) 03:33, 6 July 2016 (UTC)
 * Well.... I found ONE relevant study which actually states that most insectivorous bats DON'T eat a lot of mozzies. Of course saying that most don't does not exclude that a few DO. I've seen some interesting reading if you search for "bat diet mosquito" in google scholar, if you spent a couple of hours going through the results you could possibly find your answer. I suspect, but have not found where, the answer was derived from studying bat droppings which extrapolated or determined that in a 2 hour "feeding" period, a colony of 1000 bats ate 10kg of insects (10g each), of which 50% was mosquitoes. 5kg makes 2 million mosquitoes (at 2.5 milligrams each), that's 2000 mosquitoes per bat, or 1000 per bat per hour. It would ALSO not surprise me if one step had been left out or left to assumption, like someone came up with total numbers and someone ELSE decided to count mosquitoes but forgot to count the moths out of the equation for example. So I do not consider this settled..  Vespine (talk) 05:31, 6 July 2016 (UTC)
 * This probably isn't an unbiased source but some of the details could be followed up on. Interestingly they mention a fairly artificial study which estimated a consumption rate of 600 mosquitos per hour. While searching for info on the person (who I thought) did the study I found  which is mostly looking at the potential effect of mosquito control on bat populations. More interesting was  which quotes a 500-1000 per hour figure with  and . Looking at the sources, the first one could be a decent study although it was in 1960, however as with the Tuttle study, it seems fairly artificial. The second one is interesting, but I'm not sure "With a bat detector and a stop watch, I have recorded as many as 20 catches per minute, which means that one bat may eat more than 1,000 mosquitoes in an hour!" should be counted as a particularly reliable measure. Going back to the PLOS study, it sounds like the 600 per hour figure from Tuttle wasn't actually from their own study but was simply mentioned in their book   and was based on the 1960 Griffin, et al. study. (Re-reading the first source, it doesn't actually say the experiment was conducted by Tuttle.) So the actual sourcing for consumption figures I could find don't seem particularly robust. Nil Einne (talk) 20:26, 7 July 2016 (UTC)

"Sparkler bomb"
I'm seeing some crazy stories about a kid who supposedly taped 180 sparklers together and ended up blinding himself and a friend with metal fragments, blowing off the fingers of one hand, having part of a leg amputated, surgery on both arms, and leaving a "4 foot hole in the ground". Reading the article, apparently sparkler bomb really is a thing, with rare injuries of this type. But why do ordinary sparklers burn slowly and to all appearances safely, even when kids hold them clumped together in their hands, yet bump the number up an order of magnitude and they become an apparent high explosive? Or were these not ordinary sparklers? Wnt (talk) 15:39, 5 July 2016 (UTC)


 * From what the sparkler article says, a sparkler bomb is when you bundle a bunch of sparklers together and light them on fire. This will cause all the fuel in the sparklers to combust extremely rapidly. Combustion is a chemical reaction. The rate at which the reaction proceeds is affected by surface area. Light a single sparkler normally, and the reaction only proceeds at the tip. But if you ignite the whole thing, a lot more energy is released. This kind of thing is how you get dust explosions. See for instance what happens when you ignite a bunch of match heads all at once. Turns out explosives can be dangerous! This is why you have a bunch of people blowing their fingers off every Fourth of July here in the good old USA; they don't have a healthy respect for fire and explosives, and think fireworks are magic devices that just make cool lights and sounds, and can't possibly harm people or start fires. --71.110.8.102 (talk) 17:01, 5 July 2016 (UTC)


 * Hmmm, match heads are a weird case also. A safety match being struck, as far as I know, is essentially an application of Armstrong's mixture, one of the most notoriously user-hostile compositions in all of pyrotechnics.  But it's true that without the striker they're just an oxidizer and fuel mixture, just as sparklers are.  So I guess the mystery comes down to when sometimes fuel with oxidizer burns slowly, why some "combusts rapidly" and why some (like the Unabomber's aluminum powder fuel) is AFAIK truly a high explosive.  It doesn't even depend on the chemical, come to think of it - charcoal in oxygen is a nice little fire, charcoal soaked in liquid oxygen is like dynamite.  I guess a big part of it also is that we (or at least I) lack an intuitive sense for how much motion is hidden in a bit of heat - you work through calculations in joules and it just seems crazy.  I guess nobody expects this, especially not kids playing with a big bundle of sparklers. Wnt (talk) 19:19, 5 July 2016 (UTC)


 * I suspect what you see in a sparkler bomb is chain reaction. Of course, a single sparkler also is a chain reaction, of a sort, in that the bit currently burning lights to next bit, etc.  But the big difference is that with a single sparkler, most of the energy is dissipated into the air, while, if there are adjacent sparklers, the energy instead goes into lighting them, then their energy goes into lighting others, etc.  Once they are all lit, the energy has no place to go other than further up the already lit sparklers, forcing them to burn faster. StuRat (talk) 20:30, 5 July 2016 (UTC)
 * I learned this lesson the hard way myself. I used to make home made blackpowder smoke bombs when I was a kid, you wrapped some of the black powder in a tissue and light it and it fizzles and spits and makes an enormous amount of smoke. One day I wrapped one up a bit too tightly with a bit too much tissue and instead of fizzling, it exploded. Fortunately it was only about a tablespoon worth and all I suffered from was a start and some burned eyebrows and a good helping of embarrassment because all my friends who were watching were rolling around on the floor laughing at me. Vespine (talk) 23:27, 5 July 2016 (UTC)
 * Pressure can accelerate burning rate, even to the extent of a deflagration to detonation transition. And partially constraining something that releases energy can increase the amount of energy directed in a certain direction (increasing the general acceleration of reaction due to pressure and/or the destructive power at a certain area). Constraining or putting many devices close together prevents energy loss to the surrounding air, which can cause temperature to increase more than usual, which acclerates reactions (and possibly leads to other reactions that don't occur at expected temperatures). DMacks (talk) 03:22, 8 July 2016 (UTC)

Attempting to identify this insect
Found a mile or so inland on the Sonoma Coast in California.

http://imgur.com/a/VFK9P

Thanks in advance! Waggie (talk) 16:31, 5 July 2016 (UTC)


 * Beautiful photos - worth uploading to Commons. You are in the top 5% of people asking for insect IDs around here.
 * Looking at them, I'd say that this insect has wing covers (elytra) instead of forewings, which puts it into the "sheath-winged" category of Coleoptera. It has filiform antennae with, oh, by counting I'd guess 11 segments but I'm likely to be off by one.  (See ) for terminology.  It has overall a fairly primitive appearance; this is not a scarab beetle, say, but seems like a fairly generic insect.


 * Now given that the antennae are longer than the body, I'm tempted to call this a longhorn beetle of some sort. There is such ridiculous variety among beetles that this doesn't come with a guarantee, but it's a place to start.  Before we get too paranoid, note this doesn't look at all like an Asian longhorn beetle, so don't worry about that.  Anyway, it's possible to start there and navigate taxonomy at sites like this, but I wouldn't expect this to be as easy as the usual case because we're dealing with beetles here.  I can see some boring beetles with the same number of antenna segments (give or take one) as I counted in your photo, a few with antennae that long... not nearly enough.  We're not getting through this gate with a pick gun; we're gonna need a key.  Going to, I fooled around and got a list of five possibles based almost entirely on saying yes to "head distinctly elongate, forming a muzzle".  I think that is true, but this isn't something I've done.  The five are Compsocerini Rhagiomorphini Rhinotragini Stenoderini Uracanthini.  The catch is that sample photos don't really make one look any better than the others; they all seem too graceful of wing, so to speak.  And the suck is that that's just the first of five options from .  Their higher level key may allow me to narrow things down to Lamiinae and Cerambycinae (the one I used as an example above), based largely on my perception that there's a really short second antennomere (antennal segment).  So it might be one of those five, but I don't know; even in those there is digging to do.  So far, haven't struck gold yet.  (That's a wonderful site and I should have gotten to an answer, but I'm not sure how to answer many of the questions)  Wnt (talk) 21:00, 5 July 2016 (UTC)


 * I just went back and did a little random browsing of Compsocerini and initially got excited by an intriguing photo but without annotation (the page linked to by bing images was blank, but it said it was a "eucalypt ringbarker longicorn", which is unfortunately just as vague.  Phoracantha is an imported pest in California and so it is tempting, but the examples I see have spines on many antennomeres and too recognizable a pattern on the elytra.  For all I know the image was mislabeled in the first place anyway.  But I don't think this is very far phylogenetically.  Unfortunately the key used above doesn't resolve down to species.  Searching compsocerini on PubMed gets no results; searching compsocerini key on Google Scholar got me to this dissertation.  This is absolutely stunning, one of the most gorgeous taxonomic works, richly illustrated, that I have come across (if only because I look so infrequently, and haven't done so much lately).  Alas, many of the characters they look at are hard to assess even with your excellent photos; and worse, looking through the pictures makes me realize that some of the aspects of body shape that I was looking for in a search by eye really vary widely within many different groups and in any one of them there are beetles that look a little bit like this one.  (Homoplasy)  There is still an answer here, but it requires a more careful approach. Wnt (talk) 13:25, 6 July 2016 (UTC)

Equation of plane
moved to mathematics reference desk

Juno orbiter
I've read that the Juno orbiter will be deliberately crashed into Jupiter once it has completed its 37 orbits, because it might contain minute traces of Earth life, and if it happens that some of Jupiter's moons harbour life of their own, the Earth life might contaminate or even eradicate it. Does this mean we cannot ever send a lander, let alone a manned mission, to Jupiter's moons?

And also, I'm quite sure I've asked this before, but I noted that the spacecraft carries three special Lego minifigures, which are made of aluminum instead of plastic to withstand the harsh conditions of space. What's the point of this, given that no one will ever see them in space? But anyway, it was Lego, not NASA, who paid for them, and it's not like the money ever actually left Earth. J I P &#124; Talk 22:09, 5 July 2016 (UTC)


 * I would imagine that landers would be held to an even higher level of scrutiny than satellites to make sure they don't leave Earth carrying contaminants, but I'm not sure if there's a way to be completely sure a lander wouldn't cause contamination. As for the second question, it's really just a symbolic thing, as the minifigures represent Galileo, who discovered the moons orbiting Jupiter, and the Roman gods Juno (namesake of the orbiter) and Jupiter (namesake of the planet). clpo13(talk) 22:15, 5 July 2016 (UTC)


 * Actually, to take this contamination thing even further, strictly speaking, we cannot ever send anything to any heavenly body we are not completely certain is lifeless. The common sci-fi scenario of meeting extraterrestrial life is never going to happen, as we are actively trying to prevent it. Might it be possible if we first find evidence of existence of extraterrestrial life without risking contaminating it? J I P  &#124; Talk 22:22, 5 July 2016 (UTC)


 * COSPAR (Committee on Space Research) have rules for how deeply sterilized a spacecraft has to be, and these vary depending on the target. Where there is a chance of contamination (Mars is the obvious example), cleanroom assembly, extensive disinfecting and constant monitoring is required to ensure the spacecraft is clean. Where contamination is unlikely to cause problems, there only needs to be risk assessment and reporting in the event of the spacecraft impacting a body. An orbiter around Jupiter is Category II, so it doesn't need extensive cleaning, but a lander on Europa (the only moon of Jupiter so far assessed) would be in the much more rigorous Category IV. So we certainly can send a spacecraft to Europa, it'll just cost more and take longer to build. Smurrayinchester 14:42, 6 July 2016 (UTC)
 * (Edit: Ganymede has also been investigated. It is provisionally Category II) Smurrayinchester 15:03, 6 July 2016 (UTC)
 * Our article: Planetary protection. -- ToE 12:21, 6 July 2016 (UTC)