[HN Gopher] NASA's Voyager Found a 30k-50k Kelvin "Wall" at the ...
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NASA's Voyager Found a 30k-50k Kelvin "Wall" at the Edge of Solar
System
Author : world2vec
Score : 164 points
Date : 2025-06-23 16:24 UTC (6 hours ago)
(HTM) web link (www.iflscience.com)
(TXT) w3m dump (www.iflscience.com)
| bbarnett wrote:
| https://en.wikipedia.org/wiki/The_Crystal_Spheres
|
| Made me think of this Brin book. The first ship to try to leave
| the solar system, crashes into an invisible crystal barrier. It's
| unbreakable.
| CamperBob2 wrote:
| I'm confused. The plot summary talks about an impenetrable
| sphere around our solar system, but also says, "The main
| character takes part in an expedition to a newly discovered
| habitable solar system with a shattered sphere." How'd the
| character escape from our own system?
| graemep wrote:
| Unbreakable from outside.
| cosmicgadget wrote:
| Says it right here:
|
| > From studying the Nataral's artifacts and writings, they
| learn that the only way to break the crystal spheres is from
| the inside.
|
| He just had to go to the other solar system to learn how to
| go to the other solar system.
| throwawayffffas wrote:
| > It is also discovered that the Nataral chose to go into a
| kind of suspended animation around a black hole, joining
| two even earlier species, to wait for the other
| civilizations of the universe to develop interstellar
| flight capabilities.
|
| They used their interstellar flight capabilities to go wait
| for someone in the universe to develop interstellar flight
| capabilities. Checks out.
| clort wrote:
| If I recall (its been 25+ years and my copy is in
| storage), they went there to wait for other civilisations
| to _develop_. They were truly early life and there was
| literally nobody else and they determined that they would
| be waiting for millions of years, if not billions.
|
| I don't know if it was this book, but the 'suspended
| animation' was basically pushing several large stars and
| neutron stars close enough together that the flat space
| between them was inside an encompassing event horizon,
| and there they waited, living their lives at an extremely
| slow (compared to the outside universe) pace.
| pulvinar wrote:
| It crashes into the sphere, but must have also broken it:
| "the only way to break the crystal spheres is from the
| inside".
| throwawayffffas wrote:
| Yeah found it online, the ship that crashed on it broke it.
| IAmBroom wrote:
| While in the very-much-breakable sphere around Earth category,
| there's Unsong (https://unsongbook.com) by Scott Alexander.
| oconnore wrote:
| Perhaps change the link to the original NASA JPL post:
| https://www.jpl.nasa.gov/news/voyager-2-illuminates-boundary...
| world2vec wrote:
| Seems I no longer can edit it but that link doesn't directly
| reference the high temperature environment, unless I misread
| it?
| mlhpdx wrote:
| It's very odd to think of something extremely hot but with almost
| no density, and therefore very little heat transfer.
| jordanb wrote:
| That's actually most of space. Space is a very hot environment,
| especially where we are so close to the sun. Think about it.
| When you stand outside in the sun you heat up. All that heat is
| coming from the sun. But a lot of it was filtered by the
| atmosphere, so if you're in space near earth it will be hotter
| than standing at the equator on a sunny day, in terms of
| radiation.
|
| Then there's the fact that heat is very difficult to get rid of
| when in space. The ISS's radiators are much bigger than its
| solar panels. If you wanted to have a very-long eva spacesuit
| you'd have to have radiators much bigger than your body hanging
| off of it. Short evas are handled by starting the eva with cold
| liquids in the suit and letting them heat up.
|
| All of the mockups of starships going to Mars mostly fail to
| represent where they're going to put the radiators to get rid
| of all the excess heat.
| cma wrote:
| But boiling water is just a few hundred Kelvin, this is tens
| of thousands. Would EVA spacesuits be able to radiate that
| much away if it was really that hot but for the atmosphere
| absorbing some?
|
| I know it is much hotter, but that's way way hotter and they
| only find it at a "wall" way farther out.
|
| This is more the temperature of the solar wind, dwarfing the
| steady state temperature you'd reach from the photonic solar
| radiation at any distance. The Sun's blackbody varies from
| like 5000K to 7000K, you won't see objects heated in the
| solar system heated higher than that even with full
| reflectors covering the field of view of the rear with more
| sun and being near the surface of the sun, other than a tiny
| amount higher from stellar wind, tidal friction, or nuclear
| radiation from the object's own material I don't think.
| foxyv wrote:
| > Would EVA spacesuits be able to radiate that much away if
| it was really that hot but for the atmosphere absorbing
| some?
|
| Yes! The tiny number of particles are moving really fast,
| but there are very few of them. We are talking about vacuum
| that is less than 10^-17 torr. A thermos is about 10^-4
| torr. The LHC only gets down to 10^-10 torr. At those
| pressures you can lower the temperature of a kilometer cube
| by 10 thousand kelvin by raising the temperature of a cubic
| centimeter of water by 1 kelvin. There is very little
| thermal mass in such a vacuum which is why temperature can
| swing to such wild levels.
|
| This is also why spacecraft have to reject heat purely
| using radiation. Typically you heat up a panel with a lot
| of surface area using a heat pump and dump the energy into
| space as infrared. Some cooling paints on roofing do this
| at night which is kind of neat.
| jamiek88 wrote:
| To add to this: Most of the heat the EVA suits deal with
| is generated by the human inside not the giant ball of
| nuclear fusion 8 light minutes away.
| rtkwe wrote:
| Absorbed light too but that's a bit easier to deal with
| and is why most things are white or reflective on the
| outside of anything in space that's not intentionally
| trying to absorb heat.
| semi-extrinsic wrote:
| At this low density, temperature is very different from
| what you are used to experiencing. You have to work through
| a heat flux balance to really get a grasp of it.
|
| Temperature is just the heat of particles moving. In the
| extreme case of a handful of N2 molecules moving at 1% the
| speed of light, it has a temperature of something like 9
| billion Kelvin. But it's not going to heat you up if it
| hits you.
| im3w1l wrote:
| Okay this may sound silly but what about a solar powered ac
| for cooling? Like solar radiation is 6000K right, so if you
| used that to pump your waste heat into say a 1000K radiator
| (aimed away from the sun obviously) I'm thinking it might
| give you plenty of negentropy but also radiate away heat at a
| decent pace.
| thatguy0900 wrote:
| Acs don't get rid of heat, they just move it around. At
| some point you need to put the heat somewhere and then your
| just back to giant radiators
| eesmith wrote:
| https://en.wikipedia.org/wiki/Absorption_refrigerator
|
| > An absorption refrigerator is a refrigerator that uses
| a heat source to provide the energy needed to drive the
| cooling process. Solar energy, burning a fossil fuel,
| waste heat from factories, and district heating systems
| are examples of heat sources that can be used. An
| absorption refrigerator uses two coolants: the first
| coolant performs evaporative cooling and then is absorbed
| into the second coolant; heat is needed to reset the two
| coolants to their initial states.
|
| https://www.scientificamerican.com/article/solar-
| refrigerati...
|
| > Fishermen in the village of Maruata, which is located
| on the Mexican Pacific coast 18 degrees north of the
| equator, have no electricity. But for the past 16 years
| they have been able to store their fish on ice: Seven ice
| makers, powered by nothing but the scorching sun, churn
| out a half ton of ice every day.
| mrguyorama wrote:
| It literally doesn't matter what your refrigeration
| process is. You have to "reject" the heat energy at some
| point. In space, you can only do that with large
| radiators.
|
| There is no physical process that turns energy into cold.
| All "cooling" processes are just a way of extracting heat
| from a closed space and rejecting it to a different
| space. You cannot destroy heat, only move it. That's
| fundamental to the universe. You cannot destroy energy,
| only transform it.
|
| Neither link is a rebuttal of that. An absorption
| refrigerator still has to reject the pumped heat
| somewhere else. Those people making ice with solar energy
| are still rejecting at minimum the ~334kj/kg to the
| environment.
|
| An absorption refrigerator does not absorb heat, it's
| called that because you are taking advantage of some
| energy configurations that occur when one fluid absorbs
| another. The action of pumping heat is the same.
| eesmith wrote:
| The question was 'what about a solar powered ac for
| cooling?', yes?
|
| Giant radiators don't make ice.
|
| The proposed method of pumping heat into someplace hot to
| make it hotter doesn't work. But there area definitely
| ways to do solar powered ac for cooling.
| Sharlin wrote:
| Yes? That's in the atmosphere where heat rejection is a
| vastly easier problem than in vacuum, thanks to
| convection.
| hwillis wrote:
| Radiative heat transfer is proportional to T^4. If your
| suit is 300 K(80F), bumping the temperature up by 100 C
| lets you radiate 3.16x as much heat from the same area.
| itishappy wrote:
| Skip the Sun! There's an "atmospheric window" in the IR. If
| you make a material that emits/absorbs (they're reversible)
| only in that region, and don't expose it to the Sun, then
| it will cool down to the temperature of space, roughly 3K
| or -270degC. In practice, it won't cool down anywhere near
| that much. It'll steal energy from it's surroundings due to
| conduction/convection, and the amount of energy that's
| actually radiated in this band by a slightly below room
| temperature material is pretty minimal. Still neat,
| entirely passive cooling by radiating to space!
|
| https://en.wikipedia.org/wiki/Atmospheric_window
|
| https://en.wikipedia.org/wiki/Passive_daytime_radiative_coo
| l...
| energ8 wrote:
| It's a thing in from thousands of years ago
| https://en.m.wikipedia.org/wiki/Yakhch%C4%81l and today htt
| ps://en.m.wikipedia.org/wiki/Passive_daytime_radiative_co..
| .
|
| for PDRC there are a couple good videos about it from
| NightHawkInLight https://youtu.be/N3bJnKmeNJY?t=19s,
| https://youtu.be/KDRnEm-B3AI and Tech Ingredients
| https://www.youtube.com/watch?v=5zW9_ztTiw8
| https://www.youtube.com/watch?v=dNs_kNilSjk
| thom wrote:
| See also: "let's build data centres in space, it's cold up
| there!"
| hwillis wrote:
| Per wiki: radiators reject 100-350 watts per m^2 and weigh
| ~12 kg per m^2. Not unlikely you would need 10x as much
| radiator as server. You need about as much area for
| radiators as you do for solar panels, but radiators are
| much heavier.
|
| That also makes nuclear totally infeasible- since turbines
| are inefficient you'd need 2.5x as many radiators to reject
| waste heat. Solar would be much lighter.
|
| https://en.wikipedia.org/wiki/Spacecraft_thermal_control#Ra
| d...
| perihelions wrote:
| Nuclear power is _very_ feasible in space. Perhaps you
| 're overlooking that radiated power scales with the
| quartic of absolute temperature (T4); it's not difficult
| at all to radiate heat from a hot object, as it is for a
| room-temperature one.
|
| (How hot? I won't quote a number, but space nuclear
| reactors are generally engineered around molten metals).
| hwillis wrote:
| Yeah, fair to say its feasible. ROSA on the ISS produces
| 240 W/m^2 and weighs 4 kg/m^2.
|
| The S6W reactor in the seawolf submarines run at ~300 C
| and produce 177 MW waste heat for 43 MWe. If the
| radiators are 12 kg/m^2 and reject 16x as much heat (call
| it 3600 W/m^2) then you can produce 875 watts of
| electricity per m^2 and 290 watts at the same weight as
| the solar panels. Water coolant at 300 C also needs to be
| pressurized to 2000+ PSI, which would require a _much_
| heavier radiator, and the weight of the reactor,
| shielding, turbines and coolant makes it very hard to
| believe it could ever be better than solar panels, but it
| isn 't infeasible.
|
| Plus, liquid metal reactors can run at ~600 C and reject
| 5x as much heat per unit area. They have their own
| problems: it would be extremely difficult to re-liquify a
| lead-bismuth mix if the reactor is ever shut off. I'm
| also not particularly convinced that radiators running at
| higher temperatures wouldn't be far heavier, but for a
| sufficiently large station it would be an obvious choice.
| perihelions wrote:
| It goes up to 1,344 degC with Li, I think--it's a very
| different engineering space from the stuff on Earth.
|
| The Soviet ones used K (or maybe NaK eutectic); there's a
| ring of potassium metal dust around the Earth people
| track by radar (highly reflective)--a remnant from one of
| them exploding.
| pomian wrote:
| Reminds me of the book Saturn Run, by John Sanford - which
| has a lot of effort put into the technology and radiation of
| heat in their space ship. Fun science fiction book.
| seekup wrote:
| I recall a good treatment of this issue in the early part
| of Joe Haldeman's classic The Forever War. Highly
| recommended.
| hwillis wrote:
| > If you wanted to have a very-long eva spacesuit you'd have
| to have radiators much bigger than your body hanging off of
| it.
|
| I was curious about this! The Extravehicular Mobility Units
| on the ISS have 8 hours of life support running on 1.42 kg of
| LiOH. That releases ~2 kJ per gram used, so .092 watts.
|
| The 390 Wh battery puts out an average of 50 watts.
|
| And the human is putting out at minimum 100 watts with bursts
| of 200+.
|
| Long term it's probably reasonable to need at least 200 watts
| of heat rejection. That's about a square meter of most
| radiator, but it needs to be facing away from the station.
| You could put zones on the front/back and swap them depending
| on direction, as long as you aren't inside an enclosed but
| evacuated area, like between the Hubble and the Shuttle. The
| human body has a surface area of roughly 2 m^2 so its
| definitely not enough to handle it- half of that area is on
| your arms or between your legs and will just be radiating
| onto itself.
|
| It's also not very feasible to have a sail-sized radiator
| floating around you. You'd definitely need a more effective
| radiator- something that absorbs all your heat and glows red
| hot to dump all that energy.
| HPsquared wrote:
| Or, evaporative cooling for spacewalks. Water heat of
| evaporation at 25degC is 678 Wh/kg, so 200W of heat is
| about 0.3 kg per hour. Quite manageable!
|
| EDIT: Apparently the Apollo suits did this. An interesting
| detail is that they used sublimation (evaporating ice
| directly to vapor), because I suppose that's a lot more
| practical to exchange the heat.
| arscan wrote:
| What is the temperature on either side of this "wall"? My
| mental model here, which is probably incorrect, is that the
| "temperature" on the outside of the wall could be higher but
| the density is much lower, thus even less heat transfer going
| on (but, still, high energy particles that can hit you,
| registering a high temperature). I get all kinds of mixed up
| regarding the difference between heat transfer and measured
| temperature.
| kadoban wrote:
| Closer to home you can get similar things when you grind metals
| for instance. The sparks are at extremely high temperatures,
| but won't typically start fires or cause burns (it depends)
| because they're just too small to impart much actual energy to
| anything they touch.
|
| You only get fire risks when the things they touch are
| themselves tiny (like dust), so they're unable to absorb and
| spread the heat.
|
| A similar thing happens when you bake with tinfoil. The foil
| will be at like 350 F, but you can still touch it basically
| immediately if you're willing to gamble that nothing with
| thermal mass is stuck to it where you can't see. It just
| doesn't have enough thermal mass on its own to burn you, but if
| there's a good-sized glob of cheese or water or something on
| the other side you can really be in for a nasty surprise.
| chasil wrote:
| I wonder if actual tin foil would behave differently from the
| aluminum foil that we are all now using.
|
| https://en.wikipedia.org/wiki/Tin_foil
| toast0 wrote:
| Tin foil and aluminum foil do have generally different
| properties. For instance, tin foil can disrupt mind control
| and aluminum foil can't, and corrosion effects are likely
| at least different. But any thin metal foil isn't going to
| be able to hold much heat, because there's just not that
| much material.
| chasil wrote:
| I do not think that you are correct.
|
| "The thermal conductivity of aluminum is 237 W/mK, and
| that of tin is only 66.6 W/mK, so the thermal
| conductivity of aluminum foil is much better than that of
| tin foil. Due to its high thermal conductivity, aluminum
| foil is often used in cooking, for example, to wrap food
| to promote even heating and grilling, and to make heat
| sinks to facilitate rapid heat conduction and cooling."
|
| https://www.chalcoaluminum.com/blog/aluminum-foil-tin-
| foil/
| piker wrote:
| If it rounds to zero, then perhaps 4x'ing it won't make a
| difference?
| kardos wrote:
| Well, heat capacity and thermal conductivity are not the
| same thing
| haneul wrote:
| > tin foil can disrupt mind control
|
| You're not weaponizing Gell-Mann amnesia against us are
| you?
| toast0 wrote:
| Not at all. Just doing my part to point out, whenever
| it's topical, that tin foil hats work and aluminum foil
| hats don't. There's a reason _they_ want you to call
| aluminum foil by the wrong name.
| aydyn wrote:
| Mind control waves are pure magnetic fields as opposed to
| traditional EM waves. So although aluminum can act as a
| Faraday cage, its not a magnetic shield and hence not
| capable of stopping mind control.
| kosievdmerwe wrote:
| The other thing that helps you is that you're made mostly of
| water, which is one of the substances with the highest heat
| capacity. So it's hard to heat up or cool.
| HPsquared wrote:
| I think similar of radiant heaters. The heating elements are
| clearly very hot, glowing even, but you never reach
| equilibrium with it: your leg will not get that hot. This is
| because your leg is cooled by conduction and convection
| (which is basically conduction again) and possibly a little
| evaporation.
| DrBazza wrote:
| Temperature is a totally valid measurement. For physicists. Not
| really for clickbait articles. High energy particles wouldn't
| attract as many views.
|
| If it were really that hot we'd never observe the CMB at a
| balmy 2.7K.
| pseudosavant wrote:
| I thought the same thing too. It is very hot, without having
| very much heat - in a way.
|
| The Parker Solar probe encounters a similar situation where it
| has to handle high amounts of direct radiation, but the
| latent/ambient environment is full of incredibly hot particles
| at very low density (because they are so hot) which means it
| isn't _that_ hard to make the probe survive it.
| HPsquared wrote:
| The plasma inside arc lamps (e.g. xenon headlights) are
| somewhere around 6,000-10,000 K.
|
| Then there are things like fusion reactors where the
| temperature is in the millions of degrees and the whole point
| of the design is to keep the heat in.
|
| Edit: although interestingly in an electric arc, often the
| electrons have a higher kinetic energy (temperature) than the
| heavier ions and atoms in the plasma. It's a highly non-
| equilibrium situation. That plays into your "high temperature,
| slow transfer" thing quite nicely: even the atoms within the
| plasma don't reach the full temperature of the electrons.
| kurthr wrote:
| Came to say this about fluorescents, but even the tungsten
| filament in an old style bulb could easily be 5000K which is
| ~8500F.
| kibwen wrote:
| What sensor is Voyager using to measure "temperature" here?
| ynac wrote:
| https://science.nasa.gov/mission/voyager/spacecraft/
|
| It seems they use several tools - inferring from the
| descriptions, they can measure and compare the data when it
| gets back here to determine simple things like temps.
| dotancohen wrote:
| Is it possible that one of the sensors failed, thus giving
| the impression of a sudden change in value?
| PaulDavisThe1st wrote:
| TFA states that Voyager 1 _and_ Voyager 2 found the same
| thing and that the data aligns in space too.
| acc_297 wrote:
| In both Edge and Firefox I'm blocked for using Adblock but from
| what I can tell I do not have adblock on either browser.
| danjc wrote:
| Which side of the wall were you on?
| redundantly wrote:
| This made me giggle
| righthand wrote:
| Firefox has enhanced tracking protection and I got through fine
| with it set to "strict". Are you on a vpn?
| acc_297 wrote:
| Ah yes, I turned off a bunch of Kaspersky internet security
| settings and I'm through. This is my work computer I forget
| what's running in the background sometimes.
| jlarocco wrote:
| That's funny... I'm using Firefox, _definitely_ have an ad-
| blocker, and had no problem.
| righthand wrote:
| Very cool, our solar system has an atmosphere, which seems
| obvious but isn't discussed or taught at least when I was in high
| school.
| IAmBroom wrote:
| Basically, the Oort cloud. Except for the high temps, which are
| the surprise.
| hotpocket777 wrote:
| Well, not a surprise. They predicted it before measuring it.
| righthand wrote:
| From my understanding the wall is not the Oort cloud but
| instead the solar winds bouncing off the exterior winds more
| like how the Pacific and Atlantic oceans don't mix.
| knappe wrote:
| One of my favorite quotes from one of my Astro professors is
| "Everything has an atmosphere, it is a matter of how tenuous".
|
| I think the article shows how relevant this still is today.
| pndy wrote:
| You may find this article on wikipedia interesting:
| https://en.wikipedia.org/wiki/Heliosphere?useskin=vector
| cooper_ganglia wrote:
| I remember being in school in 2006 and being told that outside of
| our solar system is a "wall of fire" that we would never be able
| to cross.
|
| I don't know if any of this info was speculated at that point in
| time, but it turns out that teacher was at least partially
| correct!
| jordanb wrote:
| Probably true, in that if you try to travel interstellar
| distances you'll going to have to deal with very hot particles
| hitting your ship on occasion. If you travel slowly the more
| time you're going to be spend getting hit by high energy
| particles. If you try to travel quickly you're going to have to
| deal with more _relatively_ high energy particles. It 's
| potentially enough to make interstellar travel impossible.
| SoftTalker wrote:
| It's impossible for many reasons unless there are physics we
| haven't discovered yet. To me that's the simple answer for
| the Fermi paradox.
| andrewflnr wrote:
| The Fermi paradox doesn't require travel, though. The lack
| of any sign of life at all is still surprising (no radio
| signals, etc), even if we knew it couldn't physically come
| here.
| flatline wrote:
| It would take a lot of power to send even a radio signal
| that could be picked out from the noise at a few light
| years. Add a requirement for that signal to be more or
| less continuous over geologic timescales - we've only
| been able to emit and detect these for ~100 years - and
| my personal surprise diminishes rapidly. Huge distances
| in time and space with human-level technology make
| detection highly unlikely.
| strictnein wrote:
| Systems we built in the 1970s were able to easily pass
| through this though. Which doesn't seem to indicate that it
| would make interstellar travel impossible.
| andrewflnr wrote:
| Systems from the 1970s travel at, by interstellar
| standards, agonizingly slow speeds. The voyagers will be
| exposed to hard radiation for thousands of years before
| they get anywhere interesting. They will not survive.
| strictnein wrote:
| Not sure exactly why you're responding to me. The comment
| I was responding to was talking about the hot particles
| that would be encountered, and that their existence could
| preclude future interstellar missions.
|
| What level of "hard radiation" are they now getting
| bombarded by that we will be unable to shield systems
| from in far future interstellar space travel?
| andrewflnr wrote:
| I'm saying the Voyager probes don't make a counter
| example to interstellar travel being impossible. That's
| still very much an open question. We might be able to
| develop adequate shielding to protect spacecraft from
| radiation over mildly geologic timespans, but we might
| not. I'm certain it won't be as easy as you seem to think
| it is.
|
| (Unless you count slinging a dead pile of former
| computers through a distant star system as successful
| interstellar travel, but that's not what most people are
| interested in.)
| relaxing wrote:
| That's weird. What class was it and what was their motivation
| for telling you this?
| jakeydus wrote:
| Thought this was an interesting example of reading the headline
| vs reading the article.
|
| Headline: > NASA's Voyager found a 30k-50k Kelvin "Wall"...
| Article: > While not a hard edge, or a "wall" as it has sometimes
| been called...
| stuff4ben wrote:
| Fascinating that we're still getting useful science out of almost
| 50 year old tech. I think New Horizons is the only other probe
| that's expected to go interstellar.
| ElijahLynn wrote:
| "While not a hard edge, or a "wall" as it has sometimes been
| called, here both spacecraft measured temperatures of
| 30,000-50,000 kelvin (54,000-90,000 degrees Fahrenheit), which is
| why it is sometimes also referred to as a "wall of fire". The
| craft survived the wall as, though the particles they measured
| were extremely energetic, the chances of collision in this
| particle-sparse region of space are so low that not enough heat
| could be transferred to the duo."
| dogma1138 wrote:
| Is there a chance this is an instrument error? Seems a strange
| phenomenon.
| echelon wrote:
| I'm just a layperson, but I'd suspect the research is sound.
|
| I hate the telephone tag, livescience.com-type journalism.
| Instead, I'd love to read an abstract and methods. The
| research must talk about this in detail and explain how the
| conclusions are reached. It probably isn't too inaccessible.
|
| I suspect that there may be many such measurements correlated
| between both probes taken against some other baseline signal
| or an observed return to the mean.
| gmueckl wrote:
| This isn't strange at all, but rather an artifact of the
| nature of heat energy in a medium. Heat is the uncorrelated
| movement of particles that evens out to zero effective
| velocity. Temperature is the measure of the velocity
| magnitude of these individual particles. This is independent
| of the medium's density.
| koolala wrote:
| That's the best part of them sending two of them. It can't be
| a random error.
| archermarks wrote:
| Also, worth noting that these temperatures are not that high as
| far as plasmas go. This is 3-5 eV, which is firmly in the "low
| temperature" regime (like a fluorescent bulb).
| LeratoAustini wrote:
| I often think about how cold our lifeforms on earth are, relative
| to temperatures of things in the universe. 0 Kelvin is
| theoretical lowest possible temp, quasars are apparently > 10
| trillion Kelvin (10,000,000,000,000K), yet all life we know of is
| between what, 250K and 400K?
| steve_adams_86 wrote:
| I was aware of this, but you putting it into numerical terms
| rather than an intuitive understanding is really cool. Even a
| small fire is dramatically hotter than life, yet nothing in
| comparison to what happens outside of our relatively frozen
| little bubble here on Earth
| robin_reala wrote:
| _0 Kelvin is theoretical lowest possible temp_
|
| Let me introduce you to negative temperature systems!
|
| https://en.wikipedia.org/wiki/Negative_temperature
| Sniffnoy wrote:
| Negative temperatures are hotter than positive temperatures,
| though, so this isn't really relevant to the parent comment.
| Sniffnoy wrote:
| Basically it's because the relevant structures are somewhat
| fragile. Matt Strassler has a good post about "why does
| everything we care about move so slowly compared to the cosmic
| speed limit?" (https://profmattstrassler.com/2024/10/03/why-is-
| the-speed-of...), and the answer is, it's because we're made of
| atoms, atoms are held together by the electromagenetic force,
| and that's only so strong, if things moved way faster then
| collisions would tear atoms apart. But of course life is
| dependent not only on atoms, but also on electromagnetic bonds
| much weaker than the ones that hold atoms together. So this
| limits how hot it can get.
| httpz wrote:
| Well unless there's some ghost-like life form in a gas state,
| we sort of need the molecules to stay together to form life.
| OisinMoran wrote:
| We're also interestingly enough at around the geometric mean
| between atoms and stars! (as in the scale of humans)
| tpurves wrote:
| Well, lifeforms on earth are all pretty dependent on being
| water based, and water in the liquid state specifically. Maybe
| there is a possibility of exotic life based on some other types
| of chemistry and/or phases of matter. But the fact that earth
| happened to form in this particular goldilocks zone for water-
| based life is probably why that's the only life we can see for
| now.
| onestay42 wrote:
| I have to mention Robert L. Forward's Dragon Egg--it explores
| life on a white dwarf with nuclear reactions instead of
| chemical ones. Not the best book, IMHO, but a fun thought to
| entertain.
| hanche wrote:
| If you'll excuse a bit of trivia: SI units named after people
| are not capitalized. So we have newton, joule, weber, kelvin,
| named after Newton, Joule, Weber, and Kelvin. (But their
| abbreviations are capitalized: N, J, Wb, K.)
| TheBigSalad wrote:
| Can someone explain to me why this isn't melting Voyager?
| Terr_ wrote:
| The average _stuff_ is very hot, but there 's also basically no
| stuff out there anyway, so you won't run into enough of it to
| care.
|
| Imagine that there is one venomous and aggressive snake (in a
| cute little survival-suit) in some random spot in Antarctica.
| This means "the average snake in Antarctica" is ultra-
| dangerous.
|
| But there's only one, and it's almost impossible for you ever
| to meet, so in practical terms it's still safer than Australia.
| :p
| robin_reala wrote:
| _The craft survived the wall as, though the particles they
| measured were extremely energetic, the chances of collision in
| this particle-sparse region of space are so low that not enough
| heat could be transferred to the duo._
|
| Temperature is a measure of the kinetic energy of a particle,
| so they can be both extremely hot and extremely diffuse.
| threeducks wrote:
| > why this isn't melting Voyager?
|
| Same reason why you can sit in a sauna with very hot air or
| pass your hand through a flame quickly without severe burns.
| Low density matter does not transfer heat very well. And space
| is especially devoid of matter.
| spiritplumber wrote:
| High temperature, almost no actual heat because there are very
| few particles.
| mystified5016 wrote:
| Because very few hot particles ever touched the craft. The gas
| is so incredibly thin that Voyager largely sailed straight
| through the space in between molecules.
| jandrese wrote:
| There is no thermal mass. It's almost pure vacuum but the
| handful of particles that are out there are whizzing around at
| high energies that make them very hot.
|
| Interesting to think that while it's not a concern to Voyager
| at its pokey 17km/second, a true interstellar ship traveling at
| some respectable fraction of C would compress the diffuse
| interstellar gasses enough to make them a potential hazard. You
| frequently see people saying stuff like "if we could accelerate
| to a high fraction of C you could get anywhere in the galaxy in
| a single lifetime", but it may not be so simple.
| mvdtnz wrote:
| This is explained in the article.
| TheBigSalad wrote:
| It did, but I still didn't understand it. Sorry, not a
| physics major. And I understand that heat radiates through
| empty space. Sounds like it's not actually that hot where
| voyager is, but instead filled with random particles that are
| that hot.
| everforward wrote:
| You're mixing together temperature and heat transfer. That
| region is very hot, but it transfers very little heat. It's
| like getting hit with a blast of hot air when you open the
| oven. The air is hot enough to harm you, but it can't carry
| enough heat to actually harm you unless you stay there for
| a long time.
|
| Except where Voyager is, the "air" is so thin there are
| like a dozens zeroes on the percentage thinner it is, so
| the amount of heat it carries is also divided by a similar
| amount.
|
| Each particle is carrying a huge amount of heat, but it
| gets hit by very few particles. Earth is the inverse; each
| particle carries a very moderate amount of heat, but you
| get hit by a lot of them.
| flippyhead wrote:
| This is obviously the thing aliens have setup to obscure
| themselves from us. Obviously.
| anigbrowl wrote:
| It's great that we're still getting data from these two probes 50
| years later but it absolutely sucks that these are the only 2
| probes we have out there. How long can they keep running, another
| 5 or 10 years max? It's already considered an engineering miracle
| that they are still going.
|
| What of people growing up 10, 20, 30 years from now? They'll be
| taught in school about stuff from Voyager and then told 'and that
| was what we learned in the golden age of space exploration, which
| ended long before you were born because we couldn't be bothered
| to keep at it.' Having grown up in the 70s, I feel somewhat
| betrayed that we just just gave up on doing moon stuff, rendering
| a whole generation's aspirations on space exploration into a lie.
| The claims that 'there is nothing more to discover up/out there'
| is nonsense, much like the claims that 'chips can't be made any
| smaller' that I would hear back in the 32nm period.
|
| The lack of long-term commitment to exploratory space is a
| terrible waste. To be sure we have been doing some stuff in
| system, but if he had kept putting out deep space probes every
| few years with more advanced instruments we would have learned a
| lot of other things by now, and we would have a long-term stream
| of new data coming in for the future. Now arguments for launching
| more deep space probes are dismissed with 'it'll take decades
| before we get anything useful back.' Yeah, because we stopped
| iterating! Meantime allowing that sort of exploration to become
| anachronistic is one reason we are overrun with flat-earthers and
| other science woo even at the highest levels of government.
| JKCalhoun wrote:
| Voyager of course took advantage of an alignment of the planets
| in order to perform the Grand Tour. Apparently it's 175 years
| before it happens again, FWIW.
|
| I suppose an extra-solar-system probe though would simply need
| some gravitational slingshotting and not necessarily visit many
| of the outer planets. I suppose that changes the time scale.
| floxy wrote:
| Solar sails for the near term:
|
| https://youtu.be/NQFqDKRAROI?si=AzuL-NZ6JYJ71Rpj&t=883
|
| ...which might get up to 22 AU per year. And then in the
| future: laser-pushed light sails:
|
| https://ia800108.us.archive.org/view_archive.php?archive=/24.
| ..
| JSteph22 wrote:
| New Horizons is being sent into the interstellar medium.
|
| More and more deep space missions are orbiters or landers now,
| so there are fewer flyby missions that can double as
| interstellar medium missions like Voyager/Pioneer, but New
| Horizons is one of them.
| imchillyb wrote:
| Exploration, especially space exploration, has only ever come
| with military advantages. If one could interest military
| agencies that the exploration was in their best interests we
| could see a space-revival of sorts. That would only last for as
| long as the military advantage lasts.
|
| This is an unfortunate reality of our society. We've only ever
| spent dollars in space when it was advantageous to our
| Department of Defense, and the military in general.
|
| People and companies who have succeeded in space have tied
| their goals to overarching military objectives. It's the best
| way to win the space race. Make the military understand they
| need to do the thing you want to do.
| 1970-01-01 wrote:
| What happens when an object enters a solar orbit inside this
| wall? Theoretically, it could be heated to life-sustaining
| temperatures?
| whycome wrote:
| 30K to 50K K? K. It's not clear what the range represents. Were
| they polling and those are max and min values they got? Was that
| their range of uncertainty because it's hard to accurately
| measure there?
|
| Also, I hate the ambiguity of a title that references "Voyager
| Spacecraft" so it's unclear if it was one or both.
| Y_Y wrote:
| Small k for kilo-, big K for kelvin.
|
| I skimmed the links that TFA provided and couldn't find the
| source of that figure. With rare space plasmas near shocks it's
| typical to have non-thermal distributions where the temperature
| isn't well defined. I don't think it's anything to get to
| excited about without having a proper article from NASA instead
| of IFL slop.
| whycome wrote:
| So it's more the temperature range uncertainty? is that a
| product of the environment (and with few particles one can
| actually measure) or a product of the measurement apparatus?
| Karawebnetwork wrote:
| First paragraph of the article:
|
| "In 1977, NASA launched the Voyager probes to study the Solar
| System's edge, and the interstellar medium between the stars.
| One by one, they both hit the "wall of fire" at the boundaries
| of our home system, measuring temperatures of 30,000-50,000
| kelvin (54,000-90,000 degrees Fahrenheit) on their passage
| through it."
| whycome wrote:
| That paragraph is the problem. It doesn't actually explain
| it. Were they continuously polling temps and reached as low
| as 30K and as high as 50K? If the 'wall of fire' is based on
| temps, did they have a continuous rise? what was the temp
| just outside the 'wall'?
| floxy wrote:
| Are the particle velocities that are being measure correlated at
| all? As in, flowing away from the sun or similar? I'd think that
| something with a well-defined "temperature" would be composed of
| randomly moving particles with a mean velocity of zero. I'd also
| be interested in the distribution of particle speeds. Would
| anyone one consider a collimated beam of neutrons to have a
| temperature?
|
| And I wonder what the distance mean free path length is. I
| suppose that must be pretty large. So that the T^4 Boltzmann
| radiation law doesn't really apply to these ~40,000 Kelvin
| temperatures? Or maybe the emissivity of hard vacuum is really
| low? I guess I've never thought about it before.
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