Phosphine and Life on Venus - Periodic Table of Videos

well that gas might come out so when you poke the mud at the bottom bubbles of gas come out in principle this contains a trace of phosphine but you won't be able to see any phosphine but watch it's not often the professor does an experiment very recently papers been published that has caused huge excitements astronomers have detected the gas phosphine ph3 on the planet venus but what's really caused excitement is that they've said this could be the sign of life on the planet which is really surprising because up till now people have thought venus is really hot and unpleasant so life couldn't possibly exist phosphine molecule ph3 is as brady likes to say the older brother of ammonia nh3 because phosphorus is underneath nitrogen on the periodic table so i'm at home i don't have all my molecular models you've got to imagine this black bit is a pair of electrons and the molecule has phosphorus with three hydrogen atoms around it in the actual molecule these hydrogen atoms are a bit further down there are two ways of making phosphene you can make it by reacting a metal phosphide that's a compound of a metal say zinc or aluminium and phosphorus and if you react it with this with acid phosphine bubbles out usually it comes out slightly impure mixed with a molecule p2h4 and this p2h4 has a strong smell of garlic it also has the property that if it's exposed to oxygen in the air it immediately bursts into flames but ph3 itself does not catch fire and can exist for quite a long time in the atmosphere until i read the paper about venus i didn't realize that phosphine is also present in the earth's atmosphere phosphine is really quite poisonous but it's at such low concentrations in the atmosphere it can't possibly harm you phosphine is at a very very low level phosphine on earth comes largely from decomposition of plant matter in the mud at the bottom of ponds the bacteria turn the phosphorus which is found for example in the dna of the plant material dna contains a lot of phosphate this is turned into phosphine phosphine is not very soluble in water so it can bubble out together with the marsh gas the methane that is the major product of these bacteria there is actually a story which i'm not sure is true but is sounds fun which is that in the old days by old days i mean seven 800 900 years ago when there was no street lighting and people were walking through marshy areas they sometimes saw strange lights which in english are called willow the wisp these strange lights they thought were houses and therefore they walked into the marsh and were drowned and the suggestion is that perhaps it was phosphine coming out with its impurity with the marsh gas and setting the methane on fire but this may be complete rubbish industrially phosphine is made by reacting white phosphorus you will have seen our video on white phosphorus with peat burning it to produce huge amount of light white phosphorus can react with alkali and produce phosphine phosphine is used industrially for two major applications one in the electronics industry the other use is fumigating clothes to kill parasites let's get back to venus the first point which was a real surprise to me that venus is not the first planet that ph3 phosphine has been discovered on there's very good data for phosphine being discovered on jupiter and saturn where the cassini space probe used the absorption of infrared light to detect phosphine in the atmosphere how did they discover it on venus because they weren't using a space probe they were using telescopes here on earth and the way that they discovered it was due to the absorption of light when the molecules rotate now a molecule like phosphine can rotate round and round and when it rotates it can absorb energy and rotate faster and the absorptions due to the rotation give rise to many many lines in the spectrum at very long wave light almost in the microwave region millimeter wavelength there are a lot of these absorptions and they are very sharp which means that even if you have all sorts of absorptions due to other molecules there will be a gap where you can see the absorption of phosphine if it's there i should say this model is difficult to rotate because it squeaks the earth's atmosphere absorbs a lot of this radiation so you can only record the spectra using a telescope that is very high in altitude so there isn't much air above it between you and venus and one of the key pieces of evidence was they got the same result from different telescopes which meant there wasn't a factory nearby releasing phosphine into the air if phosphine's already been observed on saturn and jupiter why aren't people saying there's life on saturn and jupiter but there might be on venus and the reason is using modeling of atmospheric chemistry you can produce a good mechanism how phosphine could arise in saturn and jupiter the problem with venus which has a very dense atmosphere with a lot of carbon dioxide not very much hydrogen it's difficult if not impossible for the authors to construct a model that would explain why the phosphine was there the problem is that once the phosphine is formed it will drift up in the atmosphere and venus you ought to know is close to the sun so there is a lot of uv light from the sun that can quickly destroy the phosphine so there must be something that is generating this phosphine continuously to match the rate at which it's being destroyed the authors write in their paper that they can't think of another mechanism and it could be due to some form of life in their favor the bacteria in the bottom of ponds are anaerobic bacteria that they operate in the absence of oxygen and there's no or very little free oxygen on venus we don't really understand entirely how the bacteria make this material on earth so one would have to go into considerable speculation to work out what might make it on venus they may be right but it's important to be quite skeptical and think there could be some different explanation i'm not an atmospheric chemist so i'm not going to tell you now some brilliant explanation because i don't know one but i know enough about chemistry to reserve my judgment and say that i wouldn't be surprised if quite soon somebody comes up with an alternative explanation of course it would be thrilling if they were right and there is life on venus but be really strange life because it will be floating in the atmosphere some considerable distance above ground level perhaps 30 kilometers up chemists as opposed to people who are trying to fumigate clothes don't use phosphine very much i've only done one reaction in my career with a phosphine derivative that's a compound between phosphine and iron ph3 itself is a slightly strange compound all chemists know about it if you ask them about the use they would probably have to look it up phosphine is used to kill rodents like rats now you don't gas them with phosphine but instead you give them food that contains metal phosphides the food smells a bit of garlic but this doesn't seem to put the rats off from eating it and when they eat it the phosphides in the food zinc phosphide aluminium phosphide reacts with the acid in the right stomach and generates phosphine which then poisons the rats how do you stop it poisoning other animals and there's quite a cunning twist the commercial rat poison usually contains an antimony compound which makes people violently sick and most animals and you mix this in with the rat poison so you might ask why doesn't the rat get sick as well because if i ate the rat poison or you did you'd immediately vomit and it would all come out again and it turns out that rats cannot vomit they don't have the physiological mechanism to be sick so if you learn nothing else from the phosphine on venus is the fact that rats cannot be sick

Channel: Periodic Videos

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Rating: 4.9746332 out of 5

Keywords: periodic, videos, chemistry

Id: NKWiOwt7eCo

Length: 10min 55sec (655 seconds)

Published: Sun Sep 20 2020

Reddit Comments

[u/demagogue-Ad-7644]

how does organic life decay in a gaseous atmosphere? how would decomposition occur in venus's atmosphere? wouldn't their decomposition require other living organisms? I think that the presence of phosphine may not be because of living organisms.