Wikipedia:Reference desk/Archives/Science/2020 July 14

= July 14 =

Earthquakes can be predicted?
See https://phys.org/news/2020-07-math-formulas-earthquakes.html --83.73.199.185 (talk) 15:29, 14 July 2020 (UTC)
 * I will believe it when they predict their second earthquake. --Guy Macon (talk) 18:19, 14 July 2020 (UTC)
 * They still have to (successfully) predict their first. The scientific article reported on does not even hint at the possibility of using their new models for earthquake prediction.  --Lambiam 14:23, 17 July 2020 (UTC)


 * Earthquakes have been occasionally scientifically predicted. For example the 1975 Haicheng earthquake was preceded by a successful mass evacuation 12 hours before the event. The problem is of course finding a prediction method that works on more than a few freak cases. To make an analogy, we have a radar already, but it only happens to work on a tiny sliver of the sky. 93.136.16.89 (talk) 17:53, 16 July 2020 (UTC)


 * From the Phys.org article linked to by the OP: "A lot of time and effort has been spent over the past several decades trying to figure out a way to predict when a major earthquake will strike, but to date, such efforts have come up short. In this new effort, the researchers have taken another approach to the problem: using math." Who would've thunk that math could be useful in developing a predictive formula? --Lambiam 14:23, 17 July 2020 (UTC)

Enthalpies of carbonate precipitation from brine
How can one obtain a list of the known precipitates of carbonate from brine, and their enthalpies, including electrochemical processing of seawater?

This is related to a question from a few weeks ago. EllenCT (talk) 19:13, 14 July 2020 (UTC)
 * This question must be https://en.wikipedia.org/w/index.php?title=Wikipedia:Reference_desk/Science&oldid=964496927#Fixing_ocean_carbonate
 * Naturally calcium carbonate is precipitated from sea water, and also when it is concentrated by evaporation. Magnesium carbonate or dolomite are also possible solids. But you would have to add calcium or magnesium ions to make much more of this precipitate. This might come about from rock weathering. But none of this is answering your question. The easiest way as per original question would be for some natural process to do it. Perhaps this can be encouraged by making a favourable place for reefs (coral, shell, bacterial) to grow. But it will likely be limited by calcium in the water. Graeme Bartlett (talk) 00:06, 15 July 2020 (UTC)
 * If you can tell what they are talking about discusses it. The NaCl makes CaCO3 harder to crystallise.
 * And it is even more complex as the solids can be vaterite, aragonite calcite or amorphous calcium carbonate (which also contains water). Different energy is involved in seeding a crystal compared to growing one. Note enzymes can assist in crystallisation in organisms eg you probably have otoconin to make your ear dust. Graeme Bartlett (talk) 00:55, 15 July 2020 (UTC)
 * you lost me on that last sentence, but I will study those sources. Have you heard of Mango Materials Co.? Here is a sequestration-constrained citation search on one of the CEO's recent publications. I can't imagine why there wouldn't be more efficient biotic precipitations in aqueous phase, since presumably that is where life arose and all. EllenCT (talk) 03:43, 17 July 2020 (UTC)
 * That last sentence is saying that it takes more energy to start off a crystal, than to deposit on it. If the energy was lower than crystals would not grow, and instead you would just get a proliferation of seeds. Graeme Bartlett (talk) 07:45, 17 July 2020 (UTC)
 * Thank you! When you electrolyze seawater with different (possibly catalytic) platings on the electrodes, does that change how the carbonate does or does not precipitate? Are enzymes a path to the greater time efficiencies of abiotic processes? EllenCT (talk) 21:38, 20 July 2020 (UTC)
 * I don't know about that topic, but one reference is https://doi.org/10.11457/swsj1965.57.103 where aragonite and brucite are precipitated at the cathode with H2. Graeme Bartlett (talk) 06:07, 21 July 2020 (UTC)

Gravity pulling apart moons
I understand that the moons of planets can be torn apart by gravity if they get too close to the planet about which they orbit. How's that work? Wouldn't gravity pull the moon down into the planet as one large solid rock? † dismas †|(talk) 22:24, 14 July 2020 (UTC)
 * see tidal force, Mars’ Moon Phobos is Slowly Falling Apart. fiveby(zero) 22:30, 14 July 2020 (UTC)
 * Also see Roche limit. 85.76.78.180 (talk) 01:14, 15 July 2020 (UTC)
 * The key point is that "solid rock" is a description that only applies to small bodies, on which the tidal forces are small. Something the size of a moon is not solid enough to resist the forces. --174.89.49.204 (talk) 02:33, 15 July 2020 (UTC)
 * Imagine two rocks, on in a lower orbit and one in a higher orbit. Would they spend the same amount of time competing an orbit? No. Now hook them together with a rope. That will force them to spend the same amount of time competing an orbit but they would pull the rope tight trying. If the rope was too weak it would break. This is known as "tidal force" because it is the same thing that causes tides.


 * Now imagine the same two rocks sitting on the surface of the moon, one on the side facing earth and the other on the far side. Instead of the rope you have the moon's gravity that stops them from taking separate paths.


 * In the case of the moon, gravity is stronger than the tidal force. Same thing with the earth, otherwise the tides would be so high that the water would escape the earth and orbit the sun independently. --Guy Macon (talk) 06:14, 15 July 2020 (UTC)
 * "Moon" is used for any astronomical body that orbits a planet regardless of size. Lots of moons in our solar system are small captured asteroids. --47.146.63.87 (talk) 08:26, 15 July 2020 (UTC)
 * It happens gradually, rather like slowly dismantling a building. Large moons aren't solid; they have liquid interiors, just as rocky planets do. Moons that are below the size necessary for planetary differentiation (or I guess technically uh, lunar differentiation?) generally are only loosely held-together "rubble piles", since gravity of course scales with mass. So, it only takes a small force continually applied to gradually pull the moon apart into a ring system, which will then continue to inspiral. According to the favored hypothesis, our Moon basically formed through this process in reverse: a planetary collision created a debris ring around Earth that then coalesced into the Moon, which has continued gradually moving further away from Earth due to Earth's tidal force. --47.146.63.87 (talk) 08:26, 15 July 2020 (UTC)
 * Even more to the point, a moon does not suddenly appear out of nowhere as a solid object. (Rare asteroid capture notwithstanding).  Close moons are not torn apart, but rather they are prevented from coalescing into solid objects in the first place.  Again, Roche limit is key.  Close moons are not dismantled by anything because physics prevents them from existing.  85.76.78.136 (talk) 20:05, 15 July 2020 (UTC)
 * Nice theory, but it ignores the fact that many close moons used to be far moons. See [ https://www.nasa.gov/feature/goddard/phobos-is-falling-apart ] for details. --Guy Macon (talk) 20:29, 15 July 2020 (UTC)
 * Thank you, all! † dismas †|(talk) 18:19, 16 July 2020 (UTC)
 * Annoyingly, that article says nothing (beyond "gravity") about why Phobos and Triton are falling. —Tamfang (talk) 01:36, 19 July 2020 (UTC)
 * I can clear that one up. On any planet or moon that is not tidally locked there are tides. Sometimes there are liquid oceans and the tides are easy to see. Sometimes the body is solid and it is hard to detect the periodic squeezing and stretching but it is there.
 * The tides use up energy. The moving water or stretching rock generates a certain amount of heat. Now ask yourself; where does that energy come from? Nothing is being burned. No isotopes are decaying. It happens even where there is no sunlight.
 * The answer is that the energy is "stolen" from the orbit. Every tide moves the body into a slightly lower, slightly lower-energy orbit, and that energy goes into the creating the tides. --Guy Macon (talk) 02:20, 19 July 2020 (UTC)