Popular Science tackles your toughest (and most obscure) science questions

Popcorn in Space Gary C. Knapp/AP Photo
There’s a little bit of water inside each kernel of popcorn, and if you can heat the kernel above 212°F, that water should boil, turn into high-pressure steam, and pop the kernel. But in orbit, things aren’t so simple. First off, the cold vacuum of space would suck all the water out of the kernel before it could pop the corn. So any ordinary kernels would drop, not pop. But let’s say we figured out a way to keep the kernel watertight. In that case, it all depends. Anything falling through the atmosphere has what’s called a terminal velocity. This is the speed at which the upward force, or drag, from air resistance equals the downward force of gravity. Typically, a falling object, like a skydiver, speeds up until it reaches terminal velocity. If something like the space shuttle starts out in the airless vacuum of space, it can reach a speed higher than its terminal velocity. But as soon as it starts passing through the atmosphere, friction will slow it down. This friction generates heat—about 3,000° for the space shuttle. Just how much heat depends on how fast the object is going, as well as its size, shape and mass. If an astronaut were to throw a watertight kernel out of that space shuttle moving at 17,000 mph, would the kernel reach hot enough temperatures to pop as it flew through the atmosphere? It’s possible, says Kenneth Libbrecht, a physics professor at the California Institute of Technology, but he can’t run the numbers to say for sure, because no one has measured how much friction a kernel generates when it moves through the air. “Of course, the other possibility is that it will heat too quickly and the outer husk will burn off before the kernel has a chance to pop,” Libbrecht says. And so, for now at least, there’s no way to know. Note to the guys on the ISS: Let loose a pan of Jiffy Pop.
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21 Comments

Wouldnt the water inside the kernel boil when the kernel was exposed to the vacuum of space? Prior to entry into our atmosphere?

One way to test the theory might be to put some kernels in an arc jet furnace set to simulate the type of heating an object of that size and density would experience during reentry or just fire some out the high speed gun use to test MMOD shielding.

Wrongest ever!!!
Friction of air would nothing to heat corn. Heating might occur if the compression waves in front of the falling object formed. I doubt corn would even compress air at its terminal velocity. Same for feathers.

Kinsman, anything with volume will produce compression waves in front of it (you learn this in college). What you're failing to realize is that if the kernel already has a high velocity upon entering the atmosphere, those first few seconds during impact of the atmosphere will have a high velocity. Yes there will be a negative acceleration immediately but there could possibly be enough momentum to indeed cause friction and high heat.

Methinks the heating comes from the compression of the air in front of the object (PV=nRT). Don't think friction has much to do with it.

It is my understanding that most of the fleeting meteors that we see at night are caused by little bits of comets and asteroids smaller than a kernel of corn. Why would the corn be any different and heat up and burn away?

Pet peeve - please don't say "cold vacuum of space". A vacuum is nothing, so neither cold nor warm

But isn't the question "If there was nobody there to see it, would it pop?"

Oops sorry, I thought this was a philosophical website.

Did anyone actually test that the kernel would lose it's water? Because the reason corn pops is because the kernel is able to retain steam inside until it explodes. At room temperature the vapor pressure is very low, so the vacuum itself won't pop it.

@DiscoJer:

Perhaps Stuart Fox should not have used the word "vacuum" because space is not a vacuum, particularly near Earth. Further out in space, say beyond the Ort Cloud, space does thin out considerably, to about an average density of one molecule per square meter, though it can get many thousands of times more dense in the dust clouds and nebulae that are characteristic of the Milky Way galaxy. Intergalactic space is thinner still, but there is enough stuff there to radiate in the microwave band -- about 3 degrees Kelvin, which is plenty cold. The "atmosphere" between the galaxies is pretty rarified, but not a vacuum.

To summarize: Outer space is not a perfect vacuum, it is generally very cold, and a vacuum is certainly not nothing.

beb
You stole part of my thunder, except I was wondering, if there isn't anyone there to HEAR the pop, would it actually pop?

How much of a government grant did the researcher get to do the study?

Smorgasbord,

I screwed up the joke, it should have been HEAR it pop.

It's such a hypothetical question to begin with. Lets change the premise slightly for humors sake. If you dropped a Air Force Colonel from space, would you hear him pop on re-entry? Yes unless he was a full bird Colonel, in which case he'd spread his wings and fly away at about twenty thousand feet. LOL.

water may boil at 212 F
but the pressure from the steam isn't great enough to overcome the husk until 350 F
which is why when I cook I use a kernel of popcorn as a temperature alarm when heating a pan of oil
when it pops I know the oil is somewhere near 350

It would be simple enough to test to theory that the vacuum itself would pop the kernel. Simply get a vacuum chamber and some popcorn and have at it.

I wonder if on the 4th of July. If the astronaunts dropped a bushel basket full of marbles out of the shuttle. Would we have an incredable shooting star display? Or would the cost to haul 30 puounds of marbles to the ISS or in orbit would be to costly? Or would marbles float in orbit and put holes in the ISS or shuttle?

Wow besides Beb most of you geeks are trying to trump one another. one guys says you learn it in college, another says friction has nothing to do with it, and a vacuum is not, not nothing, it's something. Maybe I should put said kernel between my butt cheeks, it may pop from all the hot air being blown up my @$$. hehehe

It is very interesting that this question is being asked here. I was asked the same question this past fall. If you are interested in the logic decision tree, take a look at my response from Sept 15, 2008.

http://www.dailyplanettv.net/2008/09/15/lucian-solutions-04/

skypatrol250

from Wilmington , DE

Space does have temperature... for space is not completely "space" it has about 1 molecule per square meter in deep space. but can get denser near earth. just as CPL punishment said, but he is wrong about space having no temperature. for space can get VERY cold or VERY hot

skypatrol250

from Wilmington , DE

Actually correction to my last comment... it wasnt CPL Punushment... it was discojer... sorry

Here's how scientists are bracing themselves for the moment aliens make...

http://www.hedefnakliyat.com



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