Glowing Comets And Deep Fried Ice Cream

Comet 67P/C-G taken on February 6 from a distance of 77 miles (124 km) to the comet center. We see the comet’s small lobe on the left and larger lobe to the right. The image has been processed to bring out the details of the comet’s jetting activity. Exposure time was 6 seconds. Credits: ESA/Rosetta/NAVCAM

Everything’s glowing! This new photo from the Rosetta spacecraft was taken on Feb. 6 and processed to show jets active all over comet 67P. They’re brightest and most effervescent in the Hapi region, the name given to the neck of the comet, but take a look around the nucleus. You can see that the entire comet is swathed in a soft, nebulous halo of vaporizing ices and dust motes.

Some of the grainy white spots around the comet’s nucleus are background noise brought to the fore as a consequence of processing the images to see the jets more clearly, but some is actual comet stuff jetted into 67P’s coma like dried leaves from a leafblower.

Rosetta’s moved out from the comet temporarily as part of an orbit change that will see it fly just 3.7 miles (6 km) of its surface this Saturday. Photos from the flyby will be downlinked to Earth Sunday and Monday.

In other comet news, a team of astronomers have simulated what happens to a comet’s ices when it nears the Sun. It’s not what you’d expect.

Familiar ice like that on ponds, lakes and clinking as ice cubes in a glass are made of neatly ordered arrangements of water molecules. Amorphous ice is also made of water but its structure is disordered. Credit: Wikipedia

“A comet is like deep fried ice cream,” said Murthy Gudipati of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., 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.”

Comets, which formed in the bitter cold of the outer solar system, are probably composed of amorphous ice, a form of water ice where the H20 molecules are randomly arranged instead of packed into neat lattices like those that make up the more familiar crystalline ice we use to chill our sodas.

Researchers at NASA’s Jet Propulsion Laboratory use a cryostat instrument, nicknamed “Himalaya,” to study the icy conditions under which comets form. Image credit: NASA/JPL-Caltech

First, the team flash-froze water vapor infused with carbon compounds called polycyclic aromatic hydrocarbons (PAHs) at -405° F to preserve the disorderly states of the water molecules and create amorphous ice. Then, using a cryostat instrument nicknamed “Himalaya”, they gradually raised the temperature of the mixture from -405° F to -190° F (-243° C to -123° C).

The PAHS stuck together and were expelled by the ice as it crystallized. With the carbon compounds now gone, the water molecules moved into the empty spaces linking up to form more compact crystalline ice.

That rings true when it comes to the Rosetta mission’s Philae lander which hit 67P/C-G with a big bounce proving it had a hard surface. Some of the dust seen around 67P might well have been “squeezed” out when amorphous ice transformed into the crystalline variety.

Similar to the fried ice cream pictured here, comets have cold, icy interiors surrounded by a crust of organics expelled when amorphous ice warms to become crystalline ice. Credit: Wikipedia

“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.”

5 Responses

  1. Richard Keen

    Does the low albedo of the comet – dark as chocolate – give a hint as to the flavor of this “baked alaska”? Or is it ammonia flavored?

  2. Edward M. Boll

    Mint flavored green Lovejoy? After a week of not seeing this one, I think that the sky is clear tonight to try it again. The best I can figure out now is that Lovejoy should be around magnitude 5.1-5.2.

  3. Edward M. Boll

    Sigh! It looks like another cloudy night. I did happen to catch the conjunction of Saturn and the Moon this morning.

    1. astrobob

      That’s excellent. Like you I had to get up early this morning for an early work assignment. Managed to sneak in a view of both in the telescope. Copernicus was just splendid.

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