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Top Comments: Complex Sulfur-Containing Compounds Found in Cometary Dust [1]
['This Content Is Not Subject To Review Daily Kos Staff Prior To Publication.']
Date: 2023-07-02
You’ll have to humor me tonight. There are much sexier scientific subjects I could write about, but this particular item captured my heart. First, a word from our sponsor:
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Professionally, I’m a (retired) chemist, but as NASA’s space program was in high gear throughout my childhood, I also have a deep love for space exploration and discovery. So a study that analyzes the previously unknown content of a comet “in the wild” is right up my alley.
Comets, of course, are what Carl Sagan called “dirty snowballs” (i. e. mostly water ice contaminated with other compounds) that, when they get close to the Sun, produce long, luminous tails. These tails consist of dust and ice particles blown off the comet by the solar wind, that steady stream of particles speeding away from the Sun. Ground-based remote spectroscopy and analysis by some fly-by probes have reveal the presence of common volatile compounds, such as water, ammonia, hydrogen sulfide, and other small molecules, but that doesn’t say anything about the content of the heavier, nonvolatile dust that is also a portion of the comet’s makeup. In addition to learning what sorts of compounds can be found in a comet, discovering what cometary dust consists of can also provide clues to what sort of chemistry has occurred on the comet to produce it.
A cometary probe called Rosetta, launched by the European Space Agency (ESA), made a close approach to a comet called 67P. The probe had an instrument (called a mis spectrometer) capable of identifying multiple different compounds by breaking them apart and weighing the pieces. During the probe’s closest approach tp 67P, it is suspected that a solid chunk of ice or dust kicked up from the comet hit the probe, as the mass spectrometer collected data for the much larger, nonvolatile molecules present in the comet’s dust flowed from the probe back top Earth. The molecules detected largely proved to be of many different sulfur containing complex organic substances. While sulfur is a fairly common element in the universe, it is nonetheless a surprise to me that so many sulfur compounds would be found in cometary dust.
Now knowing what sorts of compounds are found in comets (or at least this one), the next question that arises is: How were these compounds formed? It is assumed that when comets form, they consist of fairly simple molecules (water (H 2 O), ammonia (NH 3 ), methane (CH 4 ), hydrogen sulfide (H 2 S), methanol (CH 3 OH), and other small organic molecules), which all congeal together in the very cold environment of the outer Solar System. Under these conditions, it is assumed that the driver for chemical transformation is radiation, which can break apart the small molecules, thus allowing them to start making larger ones. In order to test this hypothesis, researchers attempted to replicate this process in the laboratory.
The experimental setup included a high-vacuum stainless-steel chamber, where the team deposited ices on a gold substrate attached to a cold finger of a helium cryostat through a gas, to prepare gas mixtures. The setup included an electron gain in the chamber and a Faraday cup to monitor the electron beam current. The team detected the evolving samples with a Fourier transform infrared spectrometer. Further experiments highlighted the rapid dissociation of hydrogen sulfide in the setup, compared to methanol and water samples used in similar experiments, to produce a high concentration of reactive sulfur bearing radicals to predominantly affect the chemistry in the ice films.
In chemistry, a radical is a molecule with an unpaired electron, which makes them extremely reactive and prone to form bonds with other molecules.
In this way, Ahmed Mahjoub and colleagues characterized organic heteropolymers in small interstellar icy grains and icy bodies. They assumed hydrogen sulfide ice chemistry to be likely for the observed species. They highlighted the presence of other pathways to form organosulfur compounds in the diffuse interstellar medium, and in the solar nebula. Using in-lab simulations, the scientists showed that sulfur-bearing organic compounds could be formed via sulfur ion bombardment of astrophysical ices containing carbon, oxygen, and nitrogen constituents.
So complex sulfur-containing compounds are fairly common in cometary dust, and they likely form within the comet over eons as the comet is irradiated by cosmic rays and other energetic particles. The fact that sulfur is so important in cometary chemistry was a surprise. For decades, it has been speculated that many organic compounds, including the compounds necessary for the development of life, were delivered to the early Earth through cometary bombardment. Now we have a clue of what else fell to Earth.
Comments are below the fold.
Top Comments (July 1-2, 2023):
From inkstainedwretch:
Matt Z reply to DoctorH in annieli’s recommended diary take them to the train station… Selfishness and hatred so depraved as to have an almost nihilistic lack of concern for people and civilization.
From Paul A:
In The Overlords post by This Carbon Based Life, the lead image was of a protestor carrying a sign reading "God Almighty Hates Book Lerners (sic) — Psalm 5:5 / Psalm 11:5 / Amos 5:15". The comment by bumpa deftly checks references.
From Denise Oliver Velez:
in my diary about Afrofuturism in music, WarrenS shares his experience, and photographs of his encounter with the Sun Ra Arkestra.
From blueoregon:
I would like to nominate G2geek's comment in danarheaelliot's diary (on the fact that the 303 Creative lawsuit was based on a fictional premise) and would like to urge everyone to send this comment to every Senator, D or R or I.
Highlighted by oslyn7:
This comment by AttorneyT in Joan McCarter’s front page post on how Biden needs to focus next on corporate greed.
Top Mojo (June 30, 2023):
Top Mojo is courtesy of mik! Click here for more on how Top Mojo works.
Running the top mojo script resulted in a null return. My apologies to readers.
Top Mojo (June 24, 2023):
Top Photos (June 30, 2023):
Thanks to jotter (RIP) for creating it and elfling for restoring it.
Top Photos (July 1, 2023):
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