Wikipedia:Reference desk/Archives/Science/2022 December 5

= December 5 =

Why is IC engine exhaust blue if it is burning oil?
I was having a debate with a guy over a truck engine that was emitting smoke. It was white, so I said it was unburnt fuel. If it was lube oil it would be blue, which he said was not necessarily so. Any book on engine repair will say blue indicates oil, but they don't say why - so it was kind of a she-said-he-said unprovable argument. Why does the presence of burnt lube oil in exhaust have a blue colour? Dionne Court (talk) 03:36, 5 December 2022 (UTC)


 * What matters is the size of the particles. Very small particles (smaller than the wavelength of light) scatter light following Rayleigh scattering. This mostly scatters blue light, so when viewing the smoke in sunlight against a dark background, it appears blue. When viewing it in transmission against a bright background, it appears brown. Larger particles cause scattering of light following Mie scattering, which has no preference for short wavelengths and therefore makes white smoke. Unless the particles in the smoke absorb certain wavelengths, which can lead to coloured smoke. Soot in particular leads to black smoke.
 * My suspicion (but nothing more than a suspicion) is that lubricant oil may pass through the engine without burning at all, making very small oil droplets and blue smoke. Fuel would partially burn, giving soot and black smoke. Water vapour or ash would give white or grey smoke. Funny chemicals may give smoke in funny colours, like orange or purple. PiusImpavidus (talk) 11:02, 5 December 2022 (UTC)
 * Those of us who work in the diesel engine industry generally associate blue exhaust with oil (burning lube oil).  But there are some engine faults, such as damaged valves, and worn out injectors that cause white smoke, which is fuel mist.   In some large engines (eg railway traction - see YouTube videos on locomotive cold starting), white "smoke" is emitted upon cold start cranking, until a cylinder fires, whereupon the exhaust turns black, until the engine warms up and fully burns its fuel and the exhaust becomes clear.
 * So, fully unburnt fuel gives a white exhaust. There may be other causes of white exhaust.
 * Now, lube oil has a vastly larger viscosity than diesel fuel. Wouldn't that mean that expelled oil droplets would be larger, and thus not be blue due to Rayleigh scattering?  Dionne Court (talk) 01:11, 6 December 2022 (UTC)

Could humans somehow adapt to new planets / satellites (like Titan)?
Could humans somehow adapt to new planets / satellites (like Titan) with genetic functions like adaption to consume it's metan, plants, or maybe animals?

149.0.135.107 (talk) 19:25, 5 December 2022 (UTC)


 * I searched the archives of the journal Icarus - I mean, where else would we look, if we wanted a speculative but scientifically-informed viewpoint?
 * I used the search-query: human adaptation —
 * In lieu of a long-winded answer, let's go with "NO." Not even the optimistic scientists think that; if you're looking for an optimistic non-scientist, those people are a lot easier to find!
 * Nimur (talk) 20:11, 5 December 2022 (UTC)


 * The main way in which living organisms adapt to non-trivial changes in their environment is through the process of evolution. This will only work across several generations, and requires that (on the timescale of a generation) the changes are not too drastic. For example, the peoples living high up in the Andes mountains or the Himalayas are genetically adapted to the low oxygen levels there. It seems a sure bet that in the not too far future far-reaching adaptations will become technically possible through genetic engineering, and for example adaptation to life under water is a stock theme in science fiction. However, the conditions elsewhere in our solar system, as soon as you leave Earth's biosphere, are so radically different in almost all respects from what is needed for human metabolic homeostasis that even extensive genetic engineering offers no plausible path. Human life outside the protection of Mother Earth will require maintaining a bubble with Earth-like conditions at all times. --Lambiam 01:20, 6 December 2022 (UTC)
 * For interest, if not real-world relevance, the term traditionally used in science fiction for physically adapting humans to non-terrestrial conditions is Pantropy. {The poster formerly known as 87.81.230.195} 176.249.29.80 (talk) 03:46, 6 December 2022 (UTC)
 * Just for completeness, the main way that humans adapt to their environment is technology, the evolution of which occurs on much shorter time scales than biological evolution. -- Jayron 32 19:26, 6 December 2022 (UTC)
 * Pedantic nitpick: technology is when we humans adapt the environment to us. Adapting humans to an environment would be a non-existent sci-fi level genetic engineering technology. Bumptump (talk) 01:21, 7 December 2022 (UTC)
 * Not necessarily. Humans alter the environment with technology, but they also use technology in ways that does not alter the environment.  A space suit, for example, does basically nothing to the space around the astronaut, but still uses technology to allow the human to adapt to the environment of space.  Humans do also adapt the environment (see, for example, Anthropocene), but that is not what I was referring to.  -- Jayron 32 14:15, 7 December 2022 (UTC)
 * metan? oh, methane. —Tamfang (talk) 05:33, 8 December 2022 (UTC)
 * And what plants and animals? Double sharp (talk) 15:01, 12 December 2022 (UTC)

How big was Ardynia praecox?
I really want to know how big was Ardynia praecox. CuddleKing1993 (talk) 21:00, 5 December 2022 (UTC)
 * That's nice. This paper has a picture of a lower jaw of Ardynia praecox, length is some 10 cm. Nothing other than jaw and skull bones seem to be extant (but what do I know...), so you'll have to take it from there. --Wrongfilter (talk) 21:16, 5 December 2022 (UTC)
 * I wanted to know if Ardynia praecox was the same size as Hyracodon nebraskensis, was the lower jaw of Hyracodon nebraskensis 10 cm? CuddleKing1993 (talk) 21:28, 5 December 2022 (UTC)
 * You figure it out from this picture, which says the piece of Hyracodon is 2.67 in. --jpgordon&#x1d122;&#x1d106;&#x1D110;&#x1d107; 23:45, 6 December 2022 (UTC)