NEW DELHI: NASA researchers may have discovered why comets are encased in a hard, outer crust like ice cream that has been deep fried. Using an icebox-like instrument nicknamed Himalaya, they showed that fluffy ice on the surface of a comet would crystalize and harden as the comet heads toward the sun and warms up.
“A comet is like deep fried ice cream,” said Murthy Gudipati of Nasa’s Jet Propulsion Laboratory, corresponding author of a recent study appearing in The Journal of Physical Chemistry.
“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.”
The lead author of the study is Antti Lignell, a postdoctoral scholar at the California Institute of Technology in Pasadena, who formerly worked with Gudipati at JPL.
Researchers already knew that comets have soft interiors and seemingly hard crusts. Last November, Rosetta’s Philae probe bounced to a landing on the surface of 67P/Churyumov-Gerasimenko, confirming that comets have a hard surface. But the exact composition of comet crust, and how it forms, was unclear.
In the new study, researchers turned to labs on Earth to put together a model of crystallizing comet crust. The experiments began with amorphous, or porous, ice — the proposed composition of the chilliest of comets and icy moons. At these extremely cold temperatures of around minus 243 degrees Celsius (minus 405 degrees Fahrenheit) water vapor molecules are flash-frozen and haphazardly mixed with other molecules, such as the organics. Amorphous ice is like cotton candy, explains Gudipati: light and fluffy and filled with pockets of space.
