"Astronauts say that space smells like gunpowder and burnt steak. It being a vacuum and all, space isn't often thought of as having a scent of its own. And while no one has directly smelled outer space, exposure without a helmet would be fatal. Many astronauts have reported that it smells like a mix of gunpowder and burnt steak. The odor is most noticeable after an astronaut returns to their spacecraft through the airlock and removes their helmet, at which point the lingering scent can be detected by both the astronaut who had been outside the ship and their crewmates who remained aboard.
It has been theorized that the source of space's scent is dying stars, which release molecules called polycyclic aromatic hydrocarbons, a chemical compound also found in coal, oil, and food as they near the end of their existence.
There's even a cologne named Eau de Space based on the smell, which was originally synthesized by biochemist Steve Pearce at NASA's behest to better prepare astronauts for every aspect of the job. Based on his interviews with astronauts who had been to space, Pearce described the aroma as hot metal, burnt meat, burnt cakes, spent gunpowder, and welding of metal."
PAHs (polycyclic aromatic compounds) look like a possible explanation. They are produced in burning and are often poisonous. So called Unidentified Infrared Bands (UIBs) of radiation arriving from interstellar space are proposed to be produced by PAHs. Luca Turin (see this) discovered that the absorption of infrared light produces odour perception. The earlier view was that the purely chemical mechanism involving the attachment of odorant molecules to the odour receptors is the mechanism of the smell. At the basic level the odour sensation would be however produced by infrared light. In particular, space odout might be produced by the infrared light emitted by PAHs.
Also solar light could cause the sensation. The odorant molecules could be present in the air inside the helmet. They would be excited by UIB light arriving from interstellar space and emit IR photons as they return to the ground state. This would generate the sensation of the scent of space. In the long run sensory adaptation would lead to the situation in which the scent of space is not perceived anymore. When the astronaut is outside the aircraft sensory adaptation takes care that the sensation is not felt. The sensation is most intense when the helmet is removed after the return to the spacecraft.
Whether the UIBs are produced by chemical transitions or whether they involve new physics suggested by TGD, is an interesting question to ponder. This relates interestingly to the Pollack effect which is most effectively induced by infrared light. Pollack effect is indeed central in the TGD inspired quantum biology and is a non-chemical transition in which photons provide the energy kicking protons to the "magnetic body" of the molecule. This would increase the value of effective Planck constant heff for the protons. This could make the Compton length of the radiation, emitted as a dark photon as the proton transforms to ordinary proton, very long.
Could the large value of heff make possible space odour even in absence of PAHs in the nearby environment? Smell is usually regarded as a sense restricted to rather short scales. Could this make it possible to smell over astrophysical distances?!
In fact, insects are known to be able to smell over distances measured in tens of kilometers. Could the real reason be that the smell sensation is also now mediated by (dark) infrared photons rather than by diffusing odorant molecules? I learned from my chemist friend that the odour of vanilla cannot be produced artificially. Could one understand this in terms of dark IR photons?
PAHs have also been proposed to be involved with the early forms of chemical life.
For a summary of earlier postings see Latest progress in TGD.
For the lists of articles (most of them published in journals founded by Huping Hu) and books about TGD see this.
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