Wikipedia:Reference desk/Archives/Science/2023 May 10

= May 10 =

Why is there meteorites from Mars on Earth bt none from Venus?
why — Preceding unsigned comment added by 115.188.152.213 (talk) 10:19, 10 May 2023 (UTC)
 * Two reasons I can think of are firstly that Venus has an atmosphere that would stop most things getting in or out, and secondly Venus is in a gravity well compared to Earth, I think a deflection by a close pass to Venus or Mars would be needed in either case but probably the deflection by Mars to go into an orbit near earth would be easier. NadVolum (talk) 10:57, 10 May 2023 (UTC)
 * Just looking up about this and it seems some people think there may be meteorites which came from Mercury being struck by another large body when it was new and some of the bits could have been pushed out to join the asteroid belt by the solar wind. So solar wind could get bits of Vewnus here too if they could get through its thick atmosphere. NadVolum (talk) 11:08, 10 May 2023 (UTC)


 * No such meteorites have so far been found (on Earth), but some astronomers have proposed that they could theoretically exist: see for example https://ui.adsabs.harvard.edu/abs/2018DDA....4910202D/abstract.
 * Of course, most meteorites that have reached the Earth's surface from any source have not been found, since the majority fall into the sea, and on land they can become buried by normal geological processes, and are in any case very rare and difficult to spot amongst all the non-meteoritic rocks; some ice-fields in Antarctica are searched for meteorites because their flow concentrates objects in accessible (if remote and cold) areas and dark rocks are easier to spot on/in white ice.
 * It has been proposed that Venusian/Cytherian meteorites may be findable on the surface of the Moon (once you're there), which has not had appreciable surface processing for a very long time: see for example https://www.futurity.org/venus-meteorites-moon-2453822/. {The poster formerly known as 87.81.230.195} — Preceding unsigned comment added by 90.199.210.77 (talk) 11:25, 10 May 2023 (UTC)
 * How would we know if a rock is from Venus? It's not like we have independent samples to match. —Tamfang (talk) 03:17, 16 May 2023 (UTC)

How exactly does the Law of Conservation of Mass apply to expansion?
I heard that pouring hydrogen peroxide on a tick stuck to a leg would cause the tick to swell up as a result of the blood mixing with the hydrogen peroxide. I know that this is a strange series of statements, but how exactly does the Law of Conservation of Mass apply to these two substances, or any two substances that "swell" something? It is to my understanding that there is something that I am, well, misunderstanding. I can't make sense of the reasoning because I have been struggling to find it. Parameci (talk) 19:27, 10 May 2023 (UTC)
 * Maybe it would be useful for you to articulate more precisely what exactly you think is in tension with conservation of mass in this particular scenario. The only thing I can see is that the tick gets bigger, but you've both added stuff to the tick and the stuff itself is becoming less dense, so I don't see any conflict there.  If you could help us understand your thought process better we might be able to help more. --Trovatore (talk) 19:37, 10 May 2023 (UTC)
 * If it helps, the weight of the tick remains the same, from just before it starts swelling up until is all swollen up. Foam takes up a lot of space but does not weigh much. --Lambiam 20:18, 10 May 2023 (UTC)


 * I suspect this relates to density, for example, heating a balloon will cause it to expand, while not changing its mass. In the tick's case,  hydrogen peroxide produces O2 bubbles when in contact with blood (specifically, the enzyme catalase); these bubbles might form in the tick causing it to expand (?). --136.56.52.157 (talk) 20:29, 10 May 2023 (UTC)
 * Yes, I believe it is density I am thinking of. To clarify knowing this is about density now (thank you!), what allows the dioxygen produced to rapidly exceed the tick's limits? Is this a matter of scale and volume? Parameci (talk) 21:52, 10 May 2023 (UTC)
 * I haven't tried this, but I suppose the H2O2 permeates the blood sac membrane (alloscutum), and if the tick has already gorged to near max capacity, then the reaction (as described here) produces oxygen gas which expands, thus causing the critter to burst (not a pleasant image to imagine, tbh), 136.56.52.157 (talk) 05:58, 11 May 2023 (UTC) ... To more directly answer your question, the chemical reaction sort of rearranges the atoms to form different molecules, one of which is a gas. The result has the same mass because the same atoms are there, but the O2 molecule, being a gas, expands since gas is less dense than liquid or solid, therefore the overall density decreases as the volume increases.
 * One mol of hydrogen peroxide (H2O2) produces one mol of dioxygen (O2). The molar mass of hydrogen peroxide is 34&thinsp;g/mol and the density at 20&thinsp;°C is about 1.45&thinsp;g/cm3, so the volume of one mol is 34&thinsp;g / (1.45&thinsp;g/cm3) ≈ 23.5&thinsp;cm3. The molar mass of dioxygen is 32&thinsp;g/mol and the density at STP is about 1.43&thinsp;g/L, which means that it is about 1.33&thinsp;g/L at 20&thinsp;°C. So the volume of one mol of dioxygen is about 32&thinsp;g / (1.33&thinsp;g/L) ≈ 24&thinsp;L = 24,000&thinsp;cm3. The expansion in volume is thousandfold. --Lambiam 11:30, 11 May 2023 (UTC)