Wikipedia:Reference desk/Archives/Science/2012 April 20

= April 20 =

Bleach and chlorine
So what happens if you mix Clorox bleach with chlorine? Albacore (talk) 02:21, 20 April 2012 (UTC)
 * Chlorine + water + high pH = Clorox bleach. If you add more chlorine, your just going to get more concentrated bleach.  See Hypochlorous acid.  -- Jayron  32  02:28, 20 April 2012 (UTC)
 * Correction: If you add more chlorine, you're just going to get more concentrated bleach. See Hypochlorous acid. 84.209.89.214 (talk) 03:17, 25 April 2012 (UTC)
 * Thanks. I have this smell coming from my laundry room, smells like chlorine and bleach but stronger; I'm trying to find out what this is. Albacore (talk) 02:37, 20 April 2012 (UTC)
 * Please note that sodium hypochlorite and chlorine are two different chemicals - chlorine gas is an authentic chemical weapon from the bad old days. Hopefully you have not mixed your bleach with chlorine, but that leaves open the question of whether you mixed it with something else, and if so what.
 * Also note that Wikipedia cannot give medical advice, in particular, advice about whether your laundry room is dangerous to you or not. Wnt (talk) 18:52, 20 April 2012 (UTC)
 * They're different, but they're found in equilibrium in solution, as per Jayron. Mixing bleach with chlorine would just give stronger bleach.  The smell from bleach is mostly chlorine gas.  Chlorine gas is an irritant, but it's not particularily dangerous at low concentrations in well ventilated areas.  See Chlorine bombings in Iraq: most of the deaths came from the blasts, the actual chemical is readily dispersed, and really doesn't make a good weapon. Buddy431 (talk) 18:03, 22 April 2012 (UTC)
 * My grandmother sometimes combined chlorine bleach with other products such as Drano to clean toilets or unclog drains, liberating large amounts of chlorine (I do not recommend this). The exact chemical equation is left as an exercise for others. Liquid bleach seems always poised to liberate chlorine, given the slightest provocation. Edison (talk) 03:36, 23 April 2012 (UTC)
 * Actually, Drano is a lye-containing (basic) drain cleaner, which should not produce chlorine gas with bleach, but other drain cleaners are indeed acids and could do so. Wnt (talk) 00:35, 24 April 2012 (UTC)

Mechanics problem
I tried this problem and I couldn't get the answer at the back of the book. I use 0.31 as the x in F=kx, but the solution manual uses 1.31. I don't know how they do that. Can anyone explain this to me? Thanks. Problem: http://i41.tinypic.com/i384f6.png --116.71.13.116 (talk) 04:45, 20 April 2012 (UTC)


 * The springs are intially stretched 1 foot therefore side rope intial tension = 30 Lb.
 * When centre rope pulled down 1 foot, by pythagorus the additional spring stretch is 5^0.5 - 2.
 * Therefore final side rope tension is 30 + 30(5^0.5 - 2) = 30(5^0.5 - 1).
 * Tension on centre rope is then 2 x 30(5^0.5 - 1) / 5^0.5 = 33.167 Lb.
 * Wickwack60.228.237.42 (talk) 05:28, 20 April 2012 (UTC)


 * Why would the center rope be pulled down 1 foot? The ropes BA and DA increase in length by 0.3 feet when θ=30 (after solving triangle). So by this, I deduced that the springs would extend by 0.3 feet as well. --119.155.36.194 (talk) 08:11, 20 April 2012 (UTC)
 * You are told that the spring is already tensioned by stretching 1 foot so you have to add this to x. I agree the rope is not pulled down one foot, it is pulled down √2 feet, but you don't need to calculate this.  Wickwack is also mistaken in calculation of final tension on the rope.  The forces form a 60° triangle so the magnitude of the downward force is going to equal the tension in the spring.   Spinning  Spark  10:28, 20 April 2012 (UTC)


 * Poster 119.155.36.194 has indeed spotted my mistake (I was just seeing if you all are awake, as the saying goes...). The springs get stretched from the initial 1 foot to 1 + (2/sin(30))-2. so the final tension is 30(4/√3 - 1) = 30 x 1.3094...  close to the 1.31 that the IP said was in the answer.  So it appears that the IP's error was that he/she ignored the initial tension.  The tension in the centre rope is twice 30(4/√3 -1) x sin(30), i.e., 30(4/√3 - 1).  Spinningspark is correct in saying the tension in the centre rope is equal to that of the springs, but this isn't a 60-60-60 triangle. You don't indeed need to claculate the how much the centre rope is pulled down, but it is 2/√3 Wickwack60.228.237.42 (talk) 10:48, 20 April 2012 (UTC)
 * No..., the forces do form an equilateral triangle (if they are all going to be equal they have to). The angle made by the centre of the rope is 120° and the force from the springs must act along them.  The weight produces a force straight down so the angle to both ropes must be 120° as well.  Translating the forces to a balanced triangle (do they still ue parallelograms in colleges) cannot fail to form an equilateral triangle.  Spinning  Spark  12:59, 20 April 2012 (UTC)

Ah, yes, I see now that I forgot to consider the 1 foot that the spring was already stretched. Thanks! --119.155.49.170 (talk) 11:02, 20 April 2012 (UTC)

Hail
I came across this sentence in the hail article. Seems to be some sort of vandalism but I can determine what the original would have been; graupel perhaps? I thought folk here would be more likely to know than on the Help desk. "Hail is most frequently formed in the interior of continents within the mid-latitudes of Earth, with hail [sic] generally confined to higher elevations within the tropics."--Shantavira|feed me 12:04, 20 April 2012 (UTC)
 * I don't think it is vandalism, it was inserted way back in 2009 with this edit. What exactly do you think is wrong with it?  Spinning  Spark  12:34, 20 April 2012 (UTC)
 * I suspect that it's the second use of 'hail', which is in my view a little clumsy - it could be rewritten as "Hail is most frequently formed in the interior of continents within the mid-latitudes of Earth, but is generally confined to higher elevations within the tropics." Mikenorton (talk) 12:38, 20 April 2012 (UTC)
 * That's still pretty unclear. I'd hate to be answering an exam question based on that. I reckon it could be interpreted in several ways. Not sure what the "but" is really doing there. HiLo48 (talk) 12:43, 20 April 2012 (UTC)
 * Actually 'mid-latitudes' is a problem, I was interpreting that to be anywhere from about 60°N to 60°S, so the reference to the tropics being confined to higher altitudes would be a special case, hence the 'but'. If however it means the zone from 60° to 30° N or S as in our article, then it should be 'and' rather than 'but' - my mistake I think. In which case "Hail is most frequently formed in the interior of continents within the mid-latitudes of Earth and within the tropics, where it is generally confined to higher elevations." Any clearer? Mikenorton (talk) 13:00, 20 April 2012 (UTC)
 * I don't see how anyone can say that hail is "generally confined to higher elevations within the tropics". We've just had hail showers on two consecutive days in Birmingham (UK), which is a long way from any tropics.--Shantavira|feed me 13:05, 20 April 2012 (UTC)
 * Try this: "In the mid-latitudes, hail forms near the interiors of continents, while in the tropics, it tends to be confined to high elevations." Does that work? Better use of parallel construction helps aid comprehension. -- Jayron  32  13:08, 20 April 2012 (UTC)
 * I was about to say something similar myself, so instead I have boldly pu it in the article.  Spinning Spark  13:12, 20 April 2012 (UTC)
 * I'm with Shantavira and still a bit puzzled; here in London, there was a light hail shower about 10 minutes ago. The wind direction is South West, which means that it's coming from the Atlantic, not the "interiors of continents". So demonstrably untrue I'd say, even if it is OR. Alansplodge (talk) 17:32, 20 April 2012 (UTC)
 * I think that the key phrase in the original text was 'most frequently', not excluding the type of weather we're experiencing in our temperate maritime climate at the moment - unfortunately the source that backs up this statement in the article is currently a deadlink. Mikenorton (talk) 17:42, 20 April 2012 (UTC)
 * Ok, "most frequently" helps. Alansplodge (talk) 19:46, 20 April 2012 (UTC)

As a meteorologist, I believe I can clear this up: The sentence is trying to say that "Hail is most frequent towards the center of mid-latitude continents, and at high elevations in the tropics." However I do not believe this is correct, and I will look to improve the wording of the article. I suspect (and will look for references to back up) that smaller hail (0.25 in to 1 in diameter) is most common in the mid-latitudes regardless of proximity to water. However, very large hail (2 in or greater diameter) occurs almost exclusively over Bangladesh/eastern India and in the Central United States, which are (not coincidently) the same areas where the most violent tornadoes typically form. This link has a good US map of very large hail occurrences. - Running On Brains (talk) 20:02, 20 April 2012 (UTC)
 * Thanks RunningOnBrains, it could certainly do with some help. I'm in Melbourne, Australia, latitude around 38⁰, and at sea level. In any year we get several instances of small hail, and occasional events with golfball size. HiLo48 (talk) 21:30, 20 April 2012 (UTC)
 * South Africa also gets large haistones as can be seen in this video. It must happen frequently enough for there to be specialist hail damage repair businesses for cars.  Spinning  Spark  22:27, 20 April 2012 (UTC)
 * , Yes, RunningOnBrains needs to check his stats. In Perth, Western Australia, a long way from USA or India, we occaisonally get hail over 2 cm, sometimes well over 2 cm.  You sometimes see cars with small dents all over them, because they were left outside when a large hail hailstorm occurred and the owners hadn't got them repaired.  My house (as with hundreds of others) was damaged last year from hail about 10 to 15 cm.  Keit121.215.149.247 (talk) 00:57, 21 April 2012 (UTC)
 * Note that I said 2 inches, not centimeters. 2 cm hail is fairly common. And I'll agree, maybe I should say 2+ inch (5+cm) hail is extremely uncommon outside of these areas, but not unheard of. Unfortunately there is no complete worldwide climatology, but I've found various sources for various areas. Southwest Germany had only 9 such events from 1900–2009, and New South Wales has had a few such events, most notably the 1947 and 1999 Sydney hailstorms. But some areas in the central US can expect hail of such sizes at any given location once every year or two.- Running On Brains (talk) 01:13, 21 April 2012 (UTC)

regrading r-e model of a BJT
In the input portion of a simple r-e model of a transistor, there is essentially a diode. During AC analysis, an AC signal source, if considered, will alternate the direction of current flow. This means that current will flow in one direction for one half cycle and in another for the second half cycle. But a diode will allow current flow in one direction only. So how does an AC signal work with an r-e model? — Preceding unsigned comment added by 210.4.65.52 (talk) 12:51, 20 April 2012 (UTC)


 * What do you mean by r-e model? It does not seem to be this which is what I would have assumed if you had not mentioned diodes. Transistors in amplifler circuits are usually modelled with linear components only.  Spinning  Spark  13:06, 20 April 2012 (UTC)


 * The IP does mean the re model this. The reason why the base emittor diode is not considered to be rectifying, is because this is a small signal model - the DC bias is of far larger magnitude than the AC signal and thus can hold the base-emittor diode biased on at all times.  The signal will of course modulate the input resistance (modelled as re x beta) to a degree - the model assumes this modulation is negligible. This question is essentially a re-written version of the IP's last question about AC signal & DC bias in the same BJT circuit. The IP needs to go back and study basic loop & mesh circuits, & superposition of voltages & currents until he thoroughly understands them, as I previously recommended. Keit58.169.237.250 (talk) 14:21, 20 April 2012 (UTC)

Environmental effects of a plastic bag ban
Last time I asked this, my question was not answered properly so I'll try to clarify some things first. The question remains: What are the possible long-term positive and negative effects of a plastic bag ban? This time, I'll clarify what my definition of a "plastic bag" ban is, partially based on the ban currently in place in my hometown. In a "plastic bag ban", at first, the use of plastic bags and styrofoam will be prohibited for dry goods, and instead people will be encouraged to bring their own bags, in addition to the use of paper bags. A total ban on plastic bags (and presumably styrofoams) for wet goods follows after 6 months. So my question now is, what will be the long-term environmental effects of such a ban? In the long term, will it be for the better or for the worse? Obviously, it will encourage the use of more environmentally-friendly containers, but I read somewhere that more paper bags means more trees are cut, and more water is used, which would in the long-term actually harm the environment. Is this true? Narutolovehinata5 tccsdnew 14:28, 20 April 2012 (UTC)
 * Paper is heavier than plastic, so there would also be a significant increase in carbon emissions via transportation of bags. That is, it takes more trucks to move the same amount of bags, which is a significant environmental disadvantage to using paper.  The "cutting down of trees" is usually a red herring as paper production depends on tree farming, that is companies that own large tracts of land have a strong financial incentive to not just clear trees and leave barren land; it devalues the land.  Instead, land owners who are involved in growing trees for lumber and paper production want to maintain the value of their land, no less so than any other farmer, and thus will plant trees to continue to keep the land productive.  In simpler terms, just as a cabbage farmer doesn't grow a single crop of cabbage and leave his land fallow for eternity after that, a tree farmer doesn't just produce one crop of trees and leave the land fallow forever.  In terms of number of trees, paper production in a properly managed economy will be roughly "tree neutral".  -- Jayron  32  14:51, 20 April 2012 (UTC)
 * Except that increased use of paper bags mean more land has to be put into wood pulp production reducing the amount of natural forest or food crop farmland. Rmhermen (talk) 15:13, 20 April 2012 (UTC)
 * From http://www.dcnr.state.pa.us/forestry/farmbill/pdfs/assessment.pdf : "The certified public forest base provides a sound foundation for certified product production and marketing; without it, Pennsylvania’s solid wood products would be only a niche market and certified paper production would likely become infeasible."  And if you've ever seen what these orcs do to your favorite wilderness getaway, the lack of degradation of plastic bags in a landfill no longer seems such a high priority. Wnt (talk) 16:32, 20 April 2012 (UTC)
 * I live in Taiwan and it's been probably a decade since the island-wide ban of free plastic bags. If you want one, pay about US$0.07 for it. Since probably also ten years ago, the county government decided to get rid of ALL STREET-SIDE TRASH CANS so people are forced to bring their garbage home or reduce their garbage productions. In my county, the per-bag garbage collection fees are in their 4th year, I guess. These draconian rules really work well. I have to say.
 * My city enforces a US$0.05 charge per plastic bag, but that's not what OP is talking about at all. Philippine is banning all plastic bags, not just free plastic bags. It's a ~$200 USD fine for the first offense, not just a couple of cents. 142.150.237.18 (talk) 18:34, 20 April 2012 (UTC)


 * Long before the plastic bag ban, I carry my back pack almost every day. I put everything in my XXL back pack each time I go shopping for food. This is not the end of the world. As a result, the plastic bag ban does not change my lifestyle too much. Anyway, most of the people now carry their bags. Paper bags are supposedly expensive here. We have to import paper from Scandinavian countries. -- Toytoy (talk) 18:02, 20 April 2012 (UTC)


 * I'm amazed that eliminating trash cans would work. In the U.S. it is a challenge to get people to not litter even if a trash can is ten steps away... Wnt (talk) 18:11, 20 April 2012 (UTC)


 * The question presupposes that the only options are disposable plastic bags and disposable paper bags. As Toytoy mentions, there are other options.  Back in my undergrad days, I always took a backpack to the grocery store&mdash;not to save the planet, but because it was the only way I had to carry stuff on my bicycle.  Today I live in a jurisdiction that charges for plastic bags, so I bring reusable bags with me when I go shopping.  (I also have a couple of compact, lightweight bags that I can stuff in my pocket or bag when I'm out and about, so I'm never without some sort of bag.)  I note that the reusable bags generally have much more comfortable handles than the disposable plastic bags (and may also include shoulder loops as well as regular handles), which makes the walk home from the store much more pleasant. TenOfAllTrades(talk) 18:51, 20 April 2012 (UTC)
 * Backpacks ARE a good alternative. What's not good are those other seemingly woven bags sold by supermarkets for repeat usage. I don't believe they're made from natural fibres anyway. They wear out and get thrown away too straight to landfill. And we have to pay for them! In my household the older style plastic bags always have at least one more life, if only for cleaning up dog poo, although I note that supermarkets are happy to sell me plastic bags for that purpose too. I'm very cynical about all these "improvements". HiLo48 (talk) 21:23, 20 April 2012 (UTC)
 * The other issue is that the plastic bags should go straight back to a recycling bin at the market, so it's really just an issue that people spend the energy to remelt and recast them for aesthetics and ease of dispensing. Wnt (talk) 02:14, 21 April 2012 (UTC)

How many people alive today were born before the year 1900?
If we don't look at official birth records, but instead estimate this from statistics about population sizes and life expectancies of all the countries of the World, what is the approximate figure for this number? Also, what is the probability for zero people being alive who were born before 1900, as a function of time? So, e.g. when can we be 99% sure that no one is alive who was born before the year 1900? Count Iblis (talk) 17:28, 20 April 2012 (UTC)


 * For your second question, Wikipedia has decided that someone is likely to have died by their 115th birthday (see WP:BDP). Therefore, under this assumption, 2015 would be the answer. We also have the list of Oldest people, which shows that no-one has ever (verifiably) lived past 123. Therefore, 2023 is another potential answer. - Cucumber Mike (talk) 18:00, 20 April 2012 (UTC)


 * If you don't mind stats on people born in or before 1902, SUPERCENTENARIANS is the website for you. Apparently there are 67 people known, who can be proved to be 110 or older. The distribution map shows that they all seem to live in North America, Europe or Japan. Alansplodge (talk) 20:00, 20 April 2012 (UTC)


 * Note: This may be a record-keeping-related bias: I'm sure that reliable birth records are not available outside the west prior to the mid-20th century, and in some parts of Africa and southeast Asia are likely still not available. - Running On Brains (talk) 20:07, 20 April 2012 (UTC)


 * According to our List of living supercentenarians, there are currently 25 living people verified as having been born before 1900. If the youngest of them, Grace Jones (no, not that one), were to live as long as the oldest ever verified person, Jeanne Calment, she would, by my reckoning, die on 20 May 2022.  Ghmyrtle (talk) 20:19, 20 April 2012 (UTC)

If there are a few dozen such people in the US, Europe and Japan, could there be a few hundred in total? Count Iblis (talk) 15:13, 21 April 2012 (UTC)

Inside of a hen it's too ... whatever ... to breathe

 * http://www.bbc.co.uk/news/17769677
 *  the egg was incubated in the hen for 21 days and then hatched inside the hen.

Now, how does the egg get its own air inside the hen's body? -- Toytoy (talk) 17:48, 20 April 2012 (UTC)


 * Unfortunately, we don't know where exactly it stopped - the answer could be something trivial, like one end exposed to the air. Also, remember the oxygen requirements of eggs are relatively small; indeed, some birds even bury their eggs.   The episode just goes to show how evolutionarily labile live birth really is - though archaic textbooks made it sound like it was some kind of advance toward humanity, really, going back to live birth is more of a degeneration that can readily take hold in almost any lineage. Wnt (talk) 18:09, 20 April 2012 (UTC)
 * There is a big difference between ovoviviparity, which is what unintentionally happened here, and live births in placental mammals. The placenta is the result of a long line of evolutionary advances. Ovoviviparity is a relatively simple step from the regular laying of eggs (and was, I think, one of the first steps towards the placenta). --Tango (talk) 13:18, 21 April 2012 (UTC)
 * True. Wnt (talk) 23:31, 23 April 2012 (UTC)

Does water ice get colder or is it temperature static?
I've been wondering about the coldness of water ice. Of course I know it freezes at 32°F/0°C but can it get colder than that or is it stuck at that temperature? For example, could you make ice much colder, maybe by letting it sit in some liquid nitrogen, and then because it was much colder, you could pour hot coffee over it and only a little would melt while cooling it down quickly, so you wouldn't get watery ice coffee (as they do at my local bodega when you order ice coffee (yuck).--108.54.17.230 (talk) 22:34, 20 April 2012 (UTC)


 * Yes, you can make ice as cold as your equipment allows. However, if it's too cold, it make actually freeze the coffee, and also becomes dangerous to handle. StuRat (talk) 22:40, 20 April 2012 (UTC)


 * A mixture of ice and water will, after a time, equilibrate at 0C. There are conditions where you can supercool liquid water.  See supercooling.  -- Jayron  32  22:53, 20 April 2012 (UTC)


 * That would depend on the mixture, and the temperature of the surrounding environment. StuRat (talk) 00:06, 21 April 2012 (UTC)


 * You can make ice as cold as your freezer will get, but the cooling it produces does not change as much as you might think. The latent heat of melting for water is high -- if I have my numbers straight, it takes as much energy to change a quantity of water from 0°C (frozen) to 0°C (liquid) as it does to raise the temperature of the same quantity of water by 90°C without changing its state. Looie496 (talk) 23:00, 20 April 2012 (UTC)


 * You can cool ice to any arbitrary temperature above absolute zero. However, at very low temperatures, or very high pressures there are a number of further phase (matter) changes.  Spinning  Spark  00:28, 21 April 2012 (UTC)


 * At reasonable pressures, this is how it works: At temperatures not too much lower than 0 C, the specific heat of ice is approx 2.1 Joules per gram per centigrade. In other words, from 0 C (freeze point) for every 2.1 J /g heat you remove from ice by refigeration, you lower it's temperature by 1 degree C. You can, if you have good enough refrigeration keep on doing this until you get to absolute zero, -273 C, and by then you will have removed 5.2 kJ/mol.  However, as you get it colder and colder, the specific heat reduces, tending to zero at absolute zero.  Kiet121.215.149.247 (talk) 00:40, 21 April 2012 (UTC)


 * If you've got liquid nitrogen, why not cool the coffee directly with that? Then you won't dilute it at all. --Trovatore (talk) 00:45, 21 April 2012 (UTC)


 * Because you'd shatter the cup. Also, you may want continuous cooling, so you have iced coffee for an hour, rather than frozen coffee at first, and room temp coffee later. StuRat (talk) 00:49, 21 April 2012 (UTC)
 * Bubble it through the coffee before you put it in the cup. Then you can add ice if you want for later cooling, but the dilution effect will be much less because the coffee is already cold.  --Trovatore (talk) 00:55, 21 April 2012 (UTC)

I think the question asks if you can have ice and water co-existing at temperatures different from 0°C. Of course, you can consider water not in thermal equilibrium with the ice or even supercooled water. But when they are in thermal equilibrium with each other, then you can change the temperature of the ice-water mixture by changing the pressure. Count Iblis (talk) 01:36, 21 April 2012 (UTC)


 * This would be moving along the melt line in the pressure-temperature phase diagram. However, this is of no practical significance, as the temperature change over a pressure range of from the triple point (612 Pa) to 10 Mpa (ie from 0.006 atmospheres to ~100 atmospheres) the temperature change is only a fraction of a degree. Keit60.230.226.13 (talk) 03:02, 21 April 2012 (UTC)
 * Still, note that triple point with ice and ice III at 251 K - there's a narrow range of high pressures where pure water is liquid at under -20 C. This might be relevant for finding deep oceans in places like Enceladus (moon), though of course dissolved salts may affect this even more. Wnt (talk) 19:41, 21 April 2012 (UTC)

How can Mars acquire to more substantial atmosphere over sun's brightening
This article said when Mars gets warmed up by sun's brightening by 10 to 20 percent it can actually create a greenhouse effect which creates a more substantial atmosphere. That is quite weird because Mars have lost so much atmosphere over billion years by solar wind, I don't know how can it get its atmosphere back. I heard is because of frozen gases beneath the soil and at the poles is acts like a thick ice sheet. Mars don't have magnetic field or magnetosphere, then what makes Mars get its atmosphere back? --69.228.132.91 (talk) 23:35, 20 April 2012 (UTC)


 * I can see how warming would temporarily increase the thickness of Mar's atmosphere, but I agree that, over the long term, the solar wind would blow it away in the absence of a strong magnetic field. However, that "long term" might be millions of years, so not something we humans need be much concerned with. StuRat (talk) 23:43, 20 April 2012 (UTC)


 * Indeed, if you converted all the frozen CO2 in the Martian ice caps to a gas, you would achieve a significant fraction of Earth's atmospheric pressure (I'm away from my work papers so I couldn't tell you how much, but I'd conservatively say at least 10% of Earth's atmospheric pressure, up from its current 0.6%). This is not counting the suspected underground reserves of CO2 and water vapor. The loss of atmosphere would occur due to thermal escape, but I believe StuRat is correct to say that it would occur over a process of millions to tens of millions of years. This leaves more than enough time for a sufficiently advanced civilization to import atmosphere from other sources, like comets and such. - Running On Brains (talk) 02:09, 21 April 2012 (UTC)


 * Much of Mars's former atmosphere (and hydrosphere) is still contained in its rocks and soil, not as separate ices, but chemically combined with other elements to form solid minerals, such as carbonates and oxides. These combinatory processes occur all the time on Earth, but Earth's active tectonics cause the minerals to be subducted and decomposed, and the gasses are recycled back into our atmosphere via volcanic processes.
 * Because Mars is smaller than Earth, it (supposedly) cooled quicker and its tectonics (if it ever had any) and volcanism (which it most certainly had), shut down a few billion years ago, so the gasses remain locked up. If one could release enough of them to form an atmosphere comparable in density (if not composition) to Earth's, it has been estimated – by, for example, Martyn J. Fogg – that it would last for at least tens of thousands of years before requiring further renewal.
 * Fogg has suggested using thermonuclear devices buried in major carbonate deposits to achieve this ("in one go", to quote the film), with the drawback that their installation would be difficult to achieve before significant colonisation, but their use disruptive to existing colonists. Another suggestion is to steer a sizeable comet so as to impact the planet and contribute (much of) its frozen gasses and liquids: again, one would not want to be on the planet when this occurred. {The poster formerly known as 87.81.230.195} 90.197.66.64 (talk) 08:35, 21 April 2012 (UTC)

Europa's atmosphere
how can Europa, Jupiter's moon get an atmosphere? It have a weak scale heights which isn't even sufficient. Does Jupiter have a magnetic fields or is it the volatiles can hang on to keep Europa an atmosphere.--69.228.132.91 (talk) 23:35, 20 April 2012 (UTC)


 * I broke this question off as it's own section. StuRat (talk) 23:40, 20 April 2012 (UTC)


 * Have you read Europa_(moon)? SmartSE (talk) 00:12, 21 April 2012 (UTC)
 * Because all solids have a vapour pressure, meaning that they sublime and reverse-sublime into an equilibrium state; and gravity limits the rate at which a tenuous atmosphere can escape; gravity captures solar wind and any other interplanetary gasses permeating space; tidal forces experienced by the moon increases the production of vapours. Every astronomical body has an atmosphere, however thin. Mercury has an atmosphere of sodium vapour. Plasmic Physics (talk) 06:04, 21 April 2012 (UTC)
 * Planets are always losing or gaining atmosphere from external sources, this produces a net effect. If the vacuum around the planet is high enough, the planet may eventually evaporate away into a diffuse cloud, which may take longer than the age of the universe. If the vaccuum is low enough, the planet may grow. This does not take into account contributions from collisions with foreign bodies. Gravity does not stop the evaporation of a planet, it can only alter its rate. This is the same process by which a black hole evaporates, only difference is that the atmosphere of a black hole is composed of Hawking radiation. Plasmic Physics (talk) 06:22, 21 April 2012 (UTC)
 * To answer the original question: Europa can obtain an atmosphere by gravitationally collecting volatiles evaporating from Jupiter, the other moons, from solar wind, and other volatiles permiating space. Plasmic Physics (talk) 06:28, 21 April 2012 (UTC)
 * In the heat death scenario of the universe, it is expected that eventually everything will diffuse completely into a ever thining cloud of something with very high entropy. Plasmic Physics (talk) 06:32, 21 April 2012 (UTC)
 * Solar wind also has the potential to remove atmosphere. Plasmic Physics (talk) 09:15, 21 April 2012 (UTC)

Why Earth dies Mars survives
Dr. Smith's calculation shows when sun hits RGB, once it reaches Earth's orbit at 1 AU, when sun loses one-fifth of its mass, then Earth's orbit gets sucked it to sun. My astronomy teacher told me once sun passes Earth's orbit, then Earth is gone completely. if Earth gets sucked in once sun crosses Earth's orbit, how can Mars and the outer planets escape to higher orbit. Where will Mars and the outer planets expand to a higher orbit, at the tip of RGB, or when sun expands at gradual degree between 5 and 7.5 billion years Mars and outer planets will escape. And about astroengineer to nudge Earth's orbit so it may be saved, does nudging Earth's orbit by flying asteroids work for Earth only, or it can also work with Mercury and Venus along with it together. If we move Earth orbit further by astroengineer asteroid nudging can we also move Mercury and Venus along with it together?--69.228.132.91 (talk) 23:58, 20 April 2012 (UTC)
 * Formation and evolution of the Solar System has information about the future of the solar system. Speculation about what fantastical astroengineering magic may save the earth is outside of the scope of this Reference desk.  -- Jayron  32  00:22, 21 April 2012 (UTC)
 * Oh, just because the technology is unknown doesn't mean we can't say anything scientific about it. Consider that the potential energy is -GMm/r, where G is 6.67E-11 m3kg-1s-2,  M is the mass of the Sun (1.99E30 kg) and m is the mass of the Earth (5.98E24 kg) and r is 1.50E11 m at Earth orbit, 2.28E11 m at Mars orbit.  So the difference in potential energy is (79.4E43 kg m3s-2)(1/1.50E11 m - 1/2.28E11 m = 0.228E-11m-1) = 18.1E32 kg m2s-2 or 1.81 x 1033 joules.  This is about 4 trillion times the Annual global energy consumption of 0.5 x 1021 joules, which for today does seem beyond the reach of humanity, except perhaps in its government deficits.  Still, given a significant fraction of a billion years, with an energy budget that might be thousands if not millions of times larger?  Only the future can tell. Wnt (talk) 02:09, 21 April 2012 (UTC)  Note: I have been thoroughly leeted by Gr8xoz below, who points out half this energy comes from the orbital speed and much of the energy could be stolen from some other planet (Jupiter) with clever orbital mechanics. Wnt (talk) 19:19, 21 April 2012 (UTC)
 * Who's to say that anything resembling a human will even exist. That's a long time for evolution to just quit working... -- Jayron  32  03:25, 21 April 2012 (UTC)
 * My guess would be the penal system. Life means life, you know. Wnt (talk) 15:12, 21 April 2012 (UTC)
 * I can't see why anyone would want to keep Earth out of the Sun when by that time we probably will have hundreds of thousands of self-sufficient space stations with artificial gravity and asteroid fragment hull shielding, will have colonized the entire galaxy, and maybe even other galaxies. Mars and multiple moons of Jupiter and Saturn will likely be terraformed by then, too. 71.212.237.20 (talk) 03:45, 21 April 2012 (UTC)
 * Sentimental value? 203.27.72.5 (talk) 06:36, 21 April 2012 (UTC)
 * Conservation Areas?--Shantavira|feed me 08:40, 21 April 2012 (UTC)
 * This is such a long time into the future that there will probably be no-one who even remembers or wants to conserve the origin of humans from time immemorial, but, if "we" (our descendants) are still in existence and remember our origin, then technology might have advanced so far that we could encase the Earth in a radiation and meteor shield, provide a temporary artificial energy source, and move it to a new sun that would be stable for millions of years more.   D b f i r s   13:25, 21 April 2012 (UTC)
 * Actually it is a loot easier to move the Earth than the potential energy difference indicates. (Given that you have a few million of our current years available.) Half the energy comes from the decreases of orbital speed but even 1.81 x 1033/2 joules is rather much energy. In order to do this we will need to use different mechanisms that amplifies our actions. Let say we put 16 Psyche in a cycler orbit between Earth and Jupiter so that it exchanges momentum between Earth and Jupiter. Psyche is about 4 x 10-6 earth masses so it needs in the order of magnitude about 250 000 orbits to change the orbit of the Earth a significant part of the distance to Jupiter. Each orbit takes about 10 years so the operation will take a few million years, given that the expansion of the Sun are process over billions (1e9) of years this is very fast. The next question is how to move  Psyche in to the cycler orbit, the energy  needed are on the the scale of  1.81 x 1033 x 4 x 10-6  Joules, around 1 x 10 28  Joules. This is still to much to just use ordinary rockets but we can move other smaller objects in to colliding orbits and in order to do that we can use even smaller objects.
 * It seems that the way to do this depends more on good telescopes and computers than on massive rockets. If we know about more objects to chose from and can plan the collisions for longer times then we can use smaller rockets. To me it seems like we could build the equipment needed to get started within our lifetime.
 * I see no reason the same could not be done with the other planets in the inner solar system.
 * According to Stability_of_the_Solar_System it is not clear that dramatic changes in the orbit of Earth will not happen without intervention. The development of the solar system seems to bee very sensitive, they tried 2500 simulations that each differed by a meter in the initial position of Mercury. In one of them Mars collided with Earth. Gr8xoz (talk) 16:25, 21 April 2012 (UTC)