NASA researchers think they understand why comets have a hard, crispy outside and a cold but soft inside — just like fried ice cream.
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In the experiment, the amorphous ice is mixed with an organic molecule called polycyclic aromatic hydrocarbons, or PAHs, which, according to the press release, are common in deep space. As the researchers turned up the temperature, surprising things started to happen.
"The PAHs stuck together and were expelled from the ice host as it crystallized," Antti Lignell, a postdoctoral scholar at the California Institute of Technology in Pasadena and lead author in the new study, said in the statement. "This may be the first observation of molecules clustering together due to a phase transition of ice, and this certainly has many important consequences for the chemistry and physics of ice."
With the PAHs expelled, the now-purified ice was free to form a dense, crispy outer shell around the body of the comet. Inside, the ultracold, somewhat fluffy amorphous ice remains.
"Deep fried ice cream is really the perfect analogy, because the interior of the comets should still be very cold and contain the more porous, amorphous ice," said Gudipati.
The PAHs, meanwhile, come together to form a final layer on top of the crunchy outer shell, Gudipati said. "The organics are like a final layer of chocolate on top."