The organizers of Jean-Luc Mélenchon’s meeting had promised an experience “immersive” and “olfactory” at the Nantes Exhibition Center (Loire-Atlantique). And during the painting dedicated to space, indeed, the audience was able to detect a slight perfume mixing smells of gunpowder, grilled steak, raspberry and rum. The service provider behind the space perfume has remained anonymous, but the episode calls out: what are the secrets of the chemical cocktail that could fill the bottle of the Universe? NASA certainly had some discussions with a chemist in 2008, but the project never saw the light of day.
Let’s start with the testimonials. Of course, it is impossible to breathe directly in space, but some astronauts have nevertheless delivered stories based on the smell of the suits, after a spacewalk. And the least we can say is that their descriptions remain quite elusive. “Space really does smell different from anything in existence”, said Dominic Antonelli, Discovery shuttle pilot. Contacted by Space.com (in English), NASA veteran Thomas Jones described a “ozone smell, a slight pungent smell” or a “smell of burnt gunpowder” ; another finally mentioned “a soft metallic feeling quite pleasant”.
However, these testimonies present a possible bias, notes Robin Isnard, doctor in astrochemistry and popularizer of science on the web. “Some metal surfaces may have been weathered outside the International Space Station, resulting in the production of certain organic matter. This smell reported by the astronauts could therefore be the product of oxidation, more than an intrinsic quality of space. This is what happens with certain coins: in the presence of metal and sweat, the fatty acids generated by the skin produce certain molecules. They are what produce that smell we associate with metal, not the coin.
To obtain answers, it is therefore necessary to identify potential odorous molecules in space, thanks to the work of astrochemists. Last month, on the NASA website (in English), the American researcher Louis Allamandola evoked two distinct playgrounds in this quest for smells. He first cites the neighborhood of stars at the end of their life, which have finished consuming their hydrogen. At this stage, they then emit heavier elements such as carbon, nitrogen and oxygen. Depending on the distribution of these elements, some stars will produce silica and others will produce soot rich in polycyclic aromatic hydrocarbons (PAHs) – the smell of which can make you think of diesel vehicles or “with burnt burgers”. Here is a first track, in the vicinity of stars at the end of their life.
A second track leads to the heart of the “molecular clouds” of the Milky Way, where we “can find dust composed of a silicate rock core and a mantle of water ice and other compounds (methanol, ammonia, carbon monoxide…)”, explains Robin Isnard. In summary, we must therefore imagine “a kind of weird ice cream shop, with a cool splash of ice water dominated by a suffocating whiff of ammonia”, jokes Louis Allamandola. Visibly inspired, it also evokes the sad scent of a morgue, due to the possible presence of formaldehyde (formaldehyde). Dismal.
What about the space raspberry? The birth of a star, which gives off heat and radiation, can “activate chemical reactions in this ice” molecular clouds, continues Robin Isnard. Until producing more complex molecules, with an increased number of atoms: ethanols, aldehydes, even certain odorous molecules. Thereby, “the dust cloud at the center of the Milky Way [nommé Sagittarius B2] contains large amounts of ethyl formate”, adds another researcher, Scott Sandford, in the NASA article. This compound plays a role in raspberry aroma. Moreover, it is the product “of a reaction between an acid and a type of alcohol”, what “gives it a smell similar to that of rum”.
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Be careful, however, before falling for the latest “flambéed red fruits” collection from space. “The flavors result from the mixture of several molecules, indeed recalls Robin Isnard. And I’m not sure that ethyl formate alone makes you think of raspberry.” Several other compounds (ketone, ionone, etc.) thus play an essential role in the flavor of the fruit. Furthermore, “these compounds tend to aggregate on the surface [des poussières] and are not very volatile”, adds Grégoire Danger, astrochemist and deputy director of the Origins Institute at the University of Aix-Marseille.
Ethyl formate, finally, is only one of dozens of molecules to have been identified in 2009 (in English) by the Max-Planck Institute, during work carried out on Sagittarius B2. “In this list, you will certainly find molecules that do not smell good!” wrote to franceinfo Arnaud Belloche, who had co-signed the study. Difficult, therefore, to attach to one of them in particular. More broadly, some 260 molecules have been identified (in English) in the interstellar medium.
“Knowing which odor dominates does not seem obvious to me because it depends on the composition of the medium, that is to say on the proportion of each molecule in the interstellar gas.”
Arnaud Belloche, astrochemist at the Max-Planck Instituteat franceinfo
The organic chemistry of space, on the other hand, is still in its infancy. “In reality, there are molecules all over the Universe, far more numerous and complex than those that have been identified to date., adds Grégoire Danger. Radio astronomy is simply limited by detection tools. Beyond a certain number of atoms, a dozen”, it is difficult to reconstruct these molecules from the different wavelengths emitted by each type of atom. The molecular portfolio is therefore undoubtedly much fuller than we imagine today, which multiplies the possible combinations.
But let’s not go any further, because unfortunately there remains a major obstacle in the quest for space perfume. Even by identifying molecules of interest, their concentration would still have to be sufficient for them to be detected by the human body. Is that the case ? “That’s a good question, to which I don’t have an answer.”, replies Arnaud Belloche. A great specialist in the chemistry of aromas, researcher Uwe Meierhenrich explains to franceinfo “that the olfactory receptors (which are proteins) will not be operational at all under such conditions”. So all you have to do is dream, and imagine what you want.