NASA researchers think they understand why comets have a hard, crispy outside and a cold but soft inside just like fried ice cream.

Two NASA spacecraft have interacted with a comet surface, and both found a crunchy exterior and somewhat softer, more porous interior. Scientists know thatcomets are made of a mixture of rock and ice, but up until now they could not fully explain this change in texture from the inside to the outside.

Now, researchers using a souped-up refrigerator (officially known as a cryostat instrument) have re-created the conditions on the surface of a comet. They think they can explain the process that makes a comet not unlike a flying hunk of fried ice cream. [AmazingCometPhotos from Europe's Rosetta Probe]

Scientists suspect that the very coldest comets and icy moons in the solar system contain a special kind of ice called amorphous, or porous, ice. To create amorphous ice, water vapor molecules must be flash-frozen at a temperature of about minus 405 degrees Fahrenheit (243 degrees Celsius).

According to astatement from NASA, this flash-freezing process is "sort of like Han Solo in the Star Wars movie 'The Empire Strikes Back,'" in the film, Solo is flash-frozen alive in a slab of carbonite.

Amorphous ice is extremely cold, but relatively soft, like cotton candy, according to Murthy Gudipati, a researcher at NASA's Jet Propulsion Laboratory and an author on the new study.

When the comet makes its way toward the sun, the temperatures on the outside become too hot for amorphous ice to survive. In the new study, the researchers re-created what happens on the comet's exterior when the temperature starts to rise.

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Comets Are Like Deep Fried Ice Cream, Scientists Say