NASA Explains Why Comets Are Like Deep Fried Ice Cream
Astronomers have known for some time that comets have a hard outer shell and a softer, porous interior. But now, NASA not only has more insight into the formation of this "crunchy" shell, but has also come up with an extremely appetizing metaphor for the phenomenon. In a new study, NASA researchers explain exactly how comets form to resemble deep fried ice cream.
For this study, the researchers simulated a comet's initial composition and subsequent journey towards the Sun. They found that porous, amorphous ice crystallizes on the outside as its temperature increases, causing organic molecules to be expelled towards the surface.
"A comet is like deep fried ice cream," said study author Murthy Gudipati of NASA's Jet Propulsion Laboratory. "The crust is made of crystalline ice, while the interior is colder and more porous. The organics are like a final layer of chocolate on top."
All ice on Earth is crystalline, or composed of tiny crystals, but the ice that composes a comet is amorphous. Amorphous ice is "fluffier" than the ice with which we are familiar, as it is freeze dried at 30 Kelvin (negative 405 degrees Fahrenheit), temperatures much lower than naturally occur on Earth. "[It's] sort of like Han Solo in the Star Wars movie 'The Empire Strikes Back,'" NASA said in a statement. "Disorderly states are preserved: Water molecules are haphazardly mixed with other molecules, such as the organics, and remain frozen in that state."
Gudipati, who is apparently really into food metaphors, further explicated, "Amorphous ice is like cotton candy, light and fluffy and filled with pockets of space."
For the simulation, Gudipati and his colleagues slowly heated amorphous ice from from 30 Kelvin to 150 Kelvin (negative 190 degrees Fahrenheit), which imitates the increase in temperature that would occur in a comet during its journey towards the Sun. They found that the carbon-based molecules formed clumps and exploded to the surface, forming the distinctive sprinkling of dust.
"What we saw in the lab — a crystalline comet crust with organics on top — matches what has been suggested from observations in space," said Gudipati. "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."