11 ms·
Supersonic plasma jets discovered
- dahart 10y agoSomething I somehow missed in school and only found out recently is that temperatures in the upper atmosphere are super high. The thermosphere is often reported as going up to ~2k degrees Celsius. (And you wouldn't even know it if you were there, due to the low density.) I'm curious what supersonic means in this case - what is the speed of these plasma jets; what is supersonic speed in the ionosphere?
- djaychela 10y agoThere's a nice graph on Wikipedia about this, and what I didn't realise is that the pressure doesn't have a lot of influence on the speed, it's nearly all temperature-based. I would never have looked had you not made the comment above. https://en.wikipedia.org/wiki/Speed_of_sound#Altitude_variation_and_implications_for_atmospheric_acoustics https://en.wikipedia.org/wiki/Speed_of_sound#Altitude_variat...
- colechristensen 10y agoFor practical engineering purposes, it is only dependent on temperature, proportional to the square root of the temp. A mediocre intuition is that the speed of sound is governed by the speed of the individual gas molecules. Higher pressure and density mean there are more molecules hitting each other more often, but the speed of any individual molecule is the same and defined by temperature only. (it's only a mediocre intuition because the statistical dynamics that relate bulk properties to individual molecule interactions are complicated)
- dahart 10y agoI'm curious if the practical approximation still roughly holds in the thermosphere at very high temps and very low densities, do you know? So according to the above graph, supersonic speed in the ionosphere is ~280-300 m/s, lower than at sea level. Temps are lower on average too. But a plasma jet punching through the ionosphere at 10k C would mean the plasma itself is creating the condition for supersonic speeds on the order of 2000 m/s. (Not sure if the research is saying this, or saying the jets are moving at supersonic relative to the surrounding atmosphere...) Just found this super-helpful link: http://www.sengpielaudio.com/calculator-speedsound.htm http://www.sengpielaudio.com/calculator-speedsound.htm I had forgotten about speed of sound being primarily governed by temperature until @djaychela reminded me. But I still find it completely unintuitive, even with your explanation... which is really interesting!
- colechristensen 10y agoDepends on what you're trying to do with it. Hot near-vacuum gases often need molecular approaches to make models. "Sound" itself needs careful definition in such atmospheres. They're talking about jets of air pushed around by huge electric fields. "Speed of sound" is just a good way to indicate scale, it probably doesn't have much other useful meaning.
- dahart 10y ago> "Speed of sound" is just a good way to indicate scale, it probably doesn't have much other useful meaning. Yeah, that's pretty much what I'm getting out of the article... the problem is I still have no idea what that scale is, do you? I'm sure the term 'supersonic' was meant to impress and sound fast, but there's at least an order of magnitude uncertainty. > "Sound" itself needs careful definition in such atmospheres. Nothing to say here except I love that sentence.
- colechristensen 10y agoI could hazard a guess, but I doubt the scientists have particularly precise measurements (and if they did they'd be better found in a paper rather than my guessing). Having a number and concentrating on it misses the forest for the trees, it's a big number, but not the most interesting part by far.
- greglindahl 10y agoSupersonic means there are shock waves; subsonic means there are no shocks.
- randomtest 10y agoWell. In layman terms, 1) Gas's thermal energy is: E=kT, k -some constant, T is a temperature in Kelvins 2) that thermal energy is roughly a kinetic energy at molecular level, i assume :), hence it is something like E = (mv^2)/2, m - molecule mass, v - its speed 3) so we have kT = (mv^2)/2 ==> ==> v = sqrt(2kT/m) this way it maybe more intuitive
- TeMPOraL 10y agoWow, I completely forgot the ranges of different atmosphere regions since I was in secondary school. This picture here makes me wonder: https://upload.wikimedia.org/wikipedia/commons/8/8c/Earth%27s_atmosphere.svg https://upload.wikimedia.org/wikipedia/commons/8/8c/Earth%27... Did any spacecraft manage to fly through an aurora? Wouldn't it be cool if someone did that and shoot photos from within?
- ygra 10y agoUsually spacecraft are launched near the equator if possible, so aurorae aren't particularly prevalent there. Furthermore, since the atmosphere is ionized there, I'd guess spacecraft would avoid launching if it meant passing through it. Since atmospheric charges due to thunderstorms and clouds are already a concern I wouldn't expect an ionized part of the atmosphere to be any different.
- greglindahl 10y agoMany spacecraft are launched into polar orbits. For the rest, it takes less fuel if you launch to the inclination of the launch pad. The ISS is inclined midway between the main US and Russian launch sites. Antares cargo rockets launch from a mid-Atlantic launch site because it's closer to the ISS' inclination. SpaceX's new Texas launch site is as far south as you can get in the continental US, and will be mainly used for GEO satellites that want to be on the Equator.
- dahart 10y agoCheck this out https://www.nasa.gov/content/flying-through-an-aurora https://www.nasa.gov/content/flying-through-an-aurora Also google image search for "space shuttle aurora"... spectacular pictures!
- ygra 10y agoAh, good point, I forgot that the ISS effectively passes through that region anyway.
- danesparza 10y agoThe article points out temperatures rise "up to almost 10,000°C" I had no idea!
- colechristensen 10y agoAnd if you were floating in it shaded from the sun you'd freeze to death. It's something like talking about the temperature of the air in a vacuum chamber. There is _always_ air in a vacuum chamber and it'll have a temperature, and that temperature will mean different things than normal intuition gives.
- jamiek88 10y agoSimilar to wind speeds on Mars, you read about hurricane speeds of 200mph+ then remember with the low density that would feel like a fairly strong breeze to a human standing there. The problem with the storms is dust and blocking of the sun. Planet wide storms have been recorded, that bodes poorly for solar powered installations without significant battery backup.
- daveguy 10y agoConsidering how well the mars rovers have done with just a few panels the dust issue is definitely surmountable.
- odonnellryan 10y agoWell, there's always alternative power sources, like on Curiosity.
- greglindahl 10y agoBut that's partly luck: the panels get somewhat cleaned by passing dust devils. Didn't Spirit end up freezing to death, after it got bogged down? Edit: https://en.wikipedia.org/wiki/Spirit_(rover)#Mars_winter_at_Troy https://en.wikipedia.org/wiki/Spirit_(rover)#Mars_winter_at_... yes: normally they'd park it on a south-facing slope to maximize insolation during the winter, but it was stuck on flat ground.
- unityByFreedom 10y agoT-minus 10 minutes until Musk explains there is a way to easily harness the electrical energy from these jets, and it'll only take Tesla a year to do it.
- TECHGUYOC 10y ago.....or it's free!
- jlebrech 10y agoor he could aim his rockets so they can ride the jets
- cat199 10y agoTesla probably already did it in a year - too bad his notebooks were 'lost' ...
- michaelcampbell 10y agoIs there a history behind this quote? Would love to hear it.
- McKayDavis 10y agoNikola Tesla was supposedly working on the production and wireless transmission of power -- including a "death beam". After his death, many of his papers were claimed to be missing: http://www.pbs.org/tesla/ll/ll_mispapers.html http://www.pbs.org/tesla/ll/ll_mispapers.html Interestingly, one of the main investigators into the incident was Dr. John G. Trump (uncle of President Trump).
- macawfish 10y agoI came to the comments because I'm worried about just that kind of attitude. It strikes me that messing with this kind of thing could have some major impacts on the functioning of the atmosphere and magnetosphere, so I'd want to see very careful studies done by numerous independent organizations before we even remotely considered collectively giving Elon Musk a chance at something like that.
- SjuulJanssen 10y agoAnyone else who clicked on the link and expected airplanes?
- officelineback 10y agoYeah I kind of thought that, but "discovered" gave pause to that thought, since it's not "invented."
- greglindahl 10y agoI was wondering why they were announcing that they'd found an astrophysical jet, when there are a zillion of them known already. 'Jet' is an overloaded term in science.
- jlebrech 10y agoso here's our space elevator, nature already created it for us. problem it only takes us up from the 2nd floor.
- deleted 10y ago[deleted]
- eternalban 10y agoSo what's the best way to harvest this energy?