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I am off to go find the coldest thing that I can get my hands on.

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And I cannot think of a more fitting 

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place than this. 

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Speaking of cold things, we all know that canned air

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can get things cold. But why? This can has 

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pressurized liquid difluoroethane.

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Now difluoroethane has a really low boiling point. That means, when I

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push the nozzle, it escapes really quickly because it is boiling away.

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Now we use something else with a really low boiling point. In fact, it is 

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the lowest of all the boiling points, to cool things

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on the James Webb Space Telescope. And that element is helium. 

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How does helium make stuff cold?

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Helium's low boiling point has come

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in handy in a number of ways on this mission. The Webb Telescope traveled

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from Goddard Space Flight Center to John Space Center to be tested 

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in Chamber A. now this is the only thermal vacuum chamber

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chamber large enough to fit Webb. Chamber A even got an upgrade 

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so it can use helium to get even colder. 

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We also use helium in a special refrigerator called a cryocooler on the telescope itself. 

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Now one of the reasons that Webb has a cryocooler 

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is because it has to operate at very cold temperatures. This is because it detects

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in the infrared spectrum of light. Infrared is something we experience

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as heat. And so the telescope needs to be as cold to avoid any sources of heat

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that do not come from the cosmos. 

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Webb in fact is so sensitive to any infrared light, that the science instruments 

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need to be cooled to avoid detecting heat it creates by just operating!

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Three of the instruments are cooled passively by sitting 

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on the cool side of the sunshield. The last instrument, MIRI

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needs to be cooled more than the other instruments

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to 7 degrees Kelvin using the cryocooler.

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Now 7 degrees is unimaginably cold. 

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I have here the coldest thing that I could get my hands on

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music

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music

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It is dry ice. 

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And this is still 194 

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degrees Kelvin. Much warmer than Webb will be at its

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coldest point. Alright, we know that Webb has to 

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get cool using the cryocooler, but how does helium make it cool?

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It's because the atoms are really small and can move really fast

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Helium only has 2 protons and 2 electrons.

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That means it is super light and it means the gasses move really quickly. 

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That’s why it tends to float away. And because 

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the gases expand so quickly, it also means that it cools

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things really quickly. So when things go from a pressurized liquid

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liquid to a gas they tend to cool. You see that same effect if you use a

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pressurized pot. When its liquid and boiling it is very 

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very hot. The steam escaping it actually cools really rapidly. 

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If you were to put your hand above, right above where that steam is coming out

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its gonna be hot. But even just one foot

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above that, and that air is touchable.

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This is called the Joule-Thompson effect. If you blow on your hand

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with an open mouth, the air is going to be hot, but if you purse your lips, 

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the air has to expand more rapidly and it has a cooling effect. 

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The cryocooler’s liquid helium expands 

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and contracts and expands again in a chamber similar to this

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And because it needs to get even colder, it has

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has two chambers. And this is going to allow us to see

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the developing Universe!