**What Is the Actual Aroma of Space? Insights from Scientists**
Space is an almost perfect vacuum, indicating that there is no air to transmit odors in the way we recognize on Earth. However, astronauts have described various scents upon their return from spacewalks. How can this happen? Furthermore, scientists can investigate celestial bodies and utilize this data to theorize about the potential odors of these celestial objects. The exploration of space aromas extends beyond mere fascination. It provides crucial insights into the universe’s chemistry. Each unique scent is derived from a particular molecule, and by pinpointing those molecules, researchers can gain a deeper understanding of the makeup of planets, moons, and interstellar gases, as well as the processes of planetary and stellar formation.
For example, sulfur compounds indicate volcanic activity, while hydrocarbons suggest processes possibly related to the fundamental elements of life. Odors also serve as indicators of the surface conditions on planets and moons, along with their atmospheric interactions. This aids scientists in refining models of distant worlds that we cannot directly experience. In summary, the scents of space offer not merely sensory details but serve as a lens into planetary science, astrochemistry, and the narrative of our solar system.
**What did astronauts detect?**
Astronauts consistently report a unique, often metallic or sour scent after completing their spacewalks and lunar missions. Upon returning to the International Space Station and taking off their helmets, many describe an odor reminiscent of charred steak, heated metal, or welding fumes. For instance, NASA astronaut Don Pettit characterized it as “a pleasant sweet-smelling welding fume” that reminded him of his arc welding experiences (according to the Australian Academy of Science). Other astronauts have reported similar sensory experiences, likening it to charred meat, burnt cookies, and used gunpowder.
During the Apollo missions, the lunar module cabins became saturated with the fragrance of spent gunpowder. This was frequently noted by Apollo 17 astronaut Harrison “Jack” Schmitt, who stated, as reported by Space Insider, “The smell of spent gunpowder was likely much more entrenched in our memories than other similar smells.” Other astronauts echoed this experience. Charles Duke from Apollo 16 noted, “Lunar dust has the scent of gunpowder.”
Scientists speculate that atomic oxygen in low Earth orbit may cling to spacesuit materials and, during repressurization, interact with the surrounding air, generating these odors. Ozone or oxidized substances that elicit metallic scents may form during this repressurization process. Concerning the fragrance of lunar dust, one theory links it to reactive chemical bonds created by meteoroid impacts. These bonds then react with the cabin air, resulting in the distinctive gunpowder scent reported by astronauts following moonwalks. However, this odor diminishes the longer lunar dust is exposed to oxygen and humidity.
**Foul-smelling comets**
Through the European Space Agency’s Rosetta mission, scientists acquired remarkable insights into the olfactory — or molecular — signature of comet 67P/Churyumov-Gerasimenko. Utilizing the Philae probe aboard the Rosetta spacecraft, Swiss scientists “sniffed” the comet’s coma and discovered an unexpectedly complex mixture of volatile compounds. Mission lead Kathrin Altwegg described the scent in the project blog, “The fragrance of 67P/C-G is quite powerful, featuring the smell of rotten eggs (hydrogen sulfide), horse stable (ammonia), and the sharp, overwhelming scent of formaldehyde. This is blended with the subtle, bitter almond-like fragrance of hydrogen cyanide. Mixing in some hints of alcohol (methanol) along with the vinegar-like scent of sulfur dioxide and a touch of the sweet aromatic whiff of carbon disulfide leads you to the ‘fragrance’ of our comet.”
Despite the strong individual scents characterized, it’s important to note that they do not exist in large quantities in the comet’s coma (the gaseous halo surrounding a comet’s solid core). Instead, the coma is primarily composed of water vapor, carbon dioxide, and carbon monoxide. These results highlight how cometary chemistry provides a sensory glimpse into the foundational elements of our solar system.
**Sulfur on Mars**
Mars, characterized by its thin, carbon dioxide-heavy atmosphere and mineral-rich surface, is believed to emit a unique scent, although we cannot directly experience it ourselves. The rovers on Mars and orbital instruments have identified chemical compositions suggesting Mars has a primary scent of sulfur gas coupled with a chalky sweetness. This correlates to the Martian soil’s high levels of sulfur, magnesium, iron, chlorine, and various acids, enabling researchers to imagine what Mars might smell like based on these individual components. Significant amounts of other strongly aromatic compounds have yet to be found in Martian soil analyses, making the sulfur interpretation the most plausible.
