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TheBigSalad parent
Can someone explain to me why this isn't melting Voyager?
threeducks
> 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.

jandrese
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.

IAmBroom
> but [a true interstellar ship traveling at some respectable fraction of C] may not be so simple.

And that is the champion understatement of this thread!

shmeeed
I suppose an interstellar ship that could accelerate to a notable fraction of c would also be powerful enough to leave the ecliptic and avoid this heat cloud.
meatmanek
Most replies are talking about the low density of the matter in that area, which is one part of the equation. The other part of the equation is radiative heat transfer. Without radiation pulling heat away, the spacecraft would asymptotically heat up to the temperature of the surrounding matter.

Radiative heat transfer, roughly speaking, tries to bring the temperature of the probe to the average temperature of all the matter that it has line of sight to -- somewhere between the temperature of the sun and the temperature of the cosmic background radiation. Since the probes are far away from the sun, this average temperature is very low.

Both effects are present everywhere. On Earth, with our dense atmosphere, conductive transfer is usually the stronger effect. In space, with extremely low density, radiative heat transfer is stronger.

spiritplumber
High temperature, almost no actual heat because there are very few particles.
Terr_
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

mystified5016
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.
robin_reala
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.

mvdtnz
This is explained in the article.
TheBigSalad OP
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
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.

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