NASA's Voyager Found a 30k-50k Kelvin "Wall" at the Edge of Solar System
107 comments
·June 23, 2025mlhpdx
kadoban
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
I wonder if actual tin foil would behave differently from the aluminum foil that we are all now using.
toast0
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.
kosievdmerwe
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.
jordanb
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.
hwillis
> 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.
pomian
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
I recall a good treatment of this issue in the early part of Joe Haldeman's classic The Forever War. Highly recommended.
thom
See also: "let's build data centres in space, it's cold up there!"
hwillis
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#Rad...
cma
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
> 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.
semi-extrinsic
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
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.
itishappy
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 -270°C. 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_cool...
energ8
It's a thing in from thousands of years ago https://en.m.wikipedia.org/wiki/Yakhch%C4%81l and today https://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
thatguy0900
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
arscan
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.
pseudosavant
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.
DrBazza
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.
whycome
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
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.
LeratoAustini
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?
Sniffnoy
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.
tpurves
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.
robin_reala
0 Kelvin is theoretical lowest possible temp
Let me introduce you to negative temperature systems!
Sniffnoy
Negative temperatures are hotter than positive temperatures, though, so this isn't really relevant to the parent comment.
OisinMoran
We're also interestingly enough at around the geometric mean between atoms and stars! (as in the scale of humans)
httpz
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.
steve_adams_86
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
oconnore
Perhaps change the link to the original NASA JPL post: https://www.jpl.nasa.gov/news/voyager-2-illuminates-boundary...
world2vec
Seems I no longer can edit it but that link doesn't directly reference the high temperature environment, unless I misread it?
kibwen
What sensor is Voyager using to measure "temperature" here?
ynac
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
Is it possible that one of the sensors failed, thus giving the impression of a sudden change in value?
null
cooper_ganglia
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
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.
strictnein
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
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.
SoftTalker
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
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.
relaxing
That’s weird. What class was it and what was their motivation for telling you this?
anigbrowl
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
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
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...
jakeydus
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...
1970-01-01
What happens when an object enters a solar orbit inside this wall? Theoretically, it could be heated to life-sustaining temperatures?
stuff4ben
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
"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."
archermarks
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).
dogma1138
Is there a chance this is an instrument error? Seems a strange phenomenon.
gmueckl
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
That's the best part of them sending two of them. It can't be a random error.
echelon
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.
flippyhead
This is obviously the thing aliens have setup to obscure themselves from us. Obviously.
It’s very odd to think of something extremely hot but with almost no density, and therefore very little heat transfer.