While there is still some debate about the shape of the universe—whether it’s round or saddle-shaped—we do know that it is probably beige—perhaps a bit pinkish.[1] We also know that outer space smells like fried steak, hot metal, or burnt electrical wiring. At least, that’s how it smells near the earth since it’s what astronauts report smelling after their space walks.[2] We’re not sure why, but it might be from oxidation of their space suits, or it might be from oxygen (O1) in the upper reaches of the earth’s atmosphere reacting with dioxygen (O2) inside the spacecraft to make ozone (O3), or it could be polycyclic aromatic hydrocarbon molecules that were expelled from a supernova. These smell like burned food or a barbecue grill.
Dying stars also make compounds that smell like solvents, mothballs, and burned plastics that spread throughout the universe[3], but in deep space, all of these scents are probably too faint for us to detect. Star and planet forming clouds have all sorts of areas with different chemicals and smells, from sweet to unpleasant. Some smell like oil, coal, or food. Interstellar clouds, if they’re strong enough to smell, would be faintly like urine and pickles or cleaning products.[4]
Interstellar space also has molecules that are part soot, sand, and grease. Australian and Turkish researchers found that our galaxy alone has about 11 billion trillion trillion tons of it (10 billion trillion trillion tonnes), which would probably coat any spacecraft traveling through it, making it feel sticky. This space grease is probably also toxic.[5]
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The earth rises above the moon in this photograph taken from orbit by the Lunar Reconnaissance Orbiter. NASA/Goddard/Arizona State University. |
The moon smells more like spent gunpowder or wet fireplace ashes according to astronauts who could smell it on their suits after walking around on the moon.[6] Others say it’s like hot metal, but slightly sweet.
It’s thought Mars smells like sulfur and chalk, with a touch of sweetness.[7] Mercury probably doesn’t have a smell and Venus’s clouds of sulfuric acid would have the sour smell of rotting eggs. The upper atmosphere of Uranus would also smell like rotten eggs with some ammonia, if they weren’t frozen as ice crystals.[8]
So far, Jupiter is thought to be the worst smelling place in the universe. To start with, Jupiter’s highly volcanic moon, Io, ejects a lot of sulfur. Jupiter itself has layers of clouds, so entering its atmosphere would smell of ammonia. Then rotten eggs would be added. Then gasoline and then garlic.[9]
Jupiter’s moon, Titan, is a bit more hospitable. It has an atmosphere that four times denser than ours and the pressure there is a bit more like on earth, but it is extremely cold and you’d still need oxygen. But if you could breathe the air without freezing your lungs, the smell would be musky sweet, with a hint of bitter almond, gasoline, and rotten fish, along with perhaps the ammonia-smell of urine in some places.[10] It’s thought that dogs can separate smells like this, but we tend to just smell the blend. To us, pizza smells like pizza, not its ingredients, so we have to imagine what the blend would smell like.
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This is an image of the center of the Milky Way, combining X-ray emissions (purple, orange, and green) and radio emissions (gray and blue). NASA. |
On analyzing the components of one comet, European scientists found it smelled like rotten eggs, urine, almonds, burning matches, and pickles or cleaning products from its traces of hydrogen sulphide, ammonia, hydrogen cyanide, hydrogen dioxide, and formaldehyde.[11] When a bit of an asteroid that was older than the solar system was ground up, it smelled like rotten peanut butter.[12] The center of our galaxy smells more like rum and tastes faintly of raspberries because of a vast cloud of ethyl formate, which helps give raspberries their flavor.[13]
Moving on to color, when astronomers averaged out all of the colors of light in the universe, it turned out that the universe is light beige, similar to the color of a latte. But since there’s a lot more area without light, it looks black to us since our eyes aren’t that sensitive.
What does space sound like? It doesn’t sound like anything, it’s completely silent. This is because there’s no air there. You can see fine, but you can’t hear because sound needs a medium to travel through, such as air or water.
When we look out into the universe, it took the light we see a long time to get to us, so we’re looking back in time. That means we can’t see what the distant universe looks like now, but it appears galaxies are evenly distributed throughout the universe, which means the distant parts probably now look like the parts that are close to us.
At the moment we’re not sure what the majority of the universe is made of. The current popular theories indicate there is something unknown out there, but whether it’s really there or whether there are flaws in the theories, we just don’t know yet. If we take into account everything astronomers know is out there in the universe, there is not enough matter to explain the gravitational force holding the galaxies together or to explain how they interact. For example, we can calculate from observations that the Milky Way galaxy should have a mass of around one hundred billion suns, but if we calculate the mass based on how rapidly gravity is pulling our galaxy toward our neighboring galaxy Andromeda we find the Milky Way’s mass is ten times greater.[14] The difference between these calculations leads us to believe there’s a lot more matter out there than we can see.
This additional matter that we suspect is in the universe is referred to as Dark Matter. Some physicists think Dark Matter might be made up of invisible dark galaxies, planetary material, and brown dwarf stars—one of which might even be orbiting at the edge of our own solar system. Others think Dark Matter could be subatomic particles that have mass but don’t interact with anything, making them extremely difficult to detect.[15]
The Hubble orbiting telescope was supposed to clear all this up. Instead, it added an even bigger mystery by revealing that distant galaxies aren’t slowing down from the expansion of the universe as expected, they are actually speeding up. Something appears to be pushing them away. One explanation for this is something referred to as dark energy. No one is sure what dark matter or dark energy is, or if they even exist, but it looks like there’s an awful lot of it about. If the currently accepted theories are correct, then the universe is roughly made up of from 68.3% to 70% dark energy and 26.8% dark matter, while the remaining three to five percent is everything we know about—all the stars, nebula, black holes, interstellar dust; all the gases, atoms, and subatomic particles. Everything astronomers can see with our amazing new telescopes all the way to the furthest reaches of the visible universe—all those billions of galaxies—only account for about five percent of what we think is out there. The other 95 percent is unknown and has yet to be discovered. That’s pretty amazing.[16]
Still, there are other explanations, but so far they’re controversial and none of them have caught on. There are a lot of interesting ideas, but we just need more evidence, which is why experiments are so important.
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[1] Karl Glazebrook and Ivan Baldry, “The Cosmic Spectrum and the Color of the Universe”, Johns Hopkins University, https://web.archive.org/web/20160412230008/http://www.pha.jhu.edu/~kgb/cosspec/.
See also NASA, "Astronomy Picture of the Day", http://apod.nasa.gov/apod/ap020702.html.
[2] “Space ‘smells like fried steak’ ”, Telegraph (UK), October 16, 2008, www.telegraph.co.uk/news/worldnews/northamerica/usa/3210415/Space-smells-like-fried-steak.html.
[3] Katherine Latham, “From cat urine to gunpowder: Exploring the peculiar smells of outer space”, BBC Future, May 25, 2025, https://www.bbc.co.uk/future/article/20250522-what-does-outer-space-smell-like.
[4] “December 2021: What does space smell like?”, NASA Ames Laboratory Astrophysics and Astrochemistry, December 2021, https://www.nasa.gov/space-science-and-astrobiology-at-ames/interesting-fact-of-the-month-current/interesting-fact-of-the-month-2021/.
[5] Hannah Devlin, “Space is full of dirty, toxic grease, scientists reveal”, The Guardian, June 27, 2018, https://www.theguardian.com/science/2018/jun/27/space-is-full-of-dirty-toxic-grease-scientists-reveal, citing B. Günay, T.W. Schmidt, M.G. Burton, M. Afşar, O. Krechkivska, K. Nauta, S.H. Kable, and A. Rawal, “Aliphatic hydrocarbon content of interstellar dust”, Monthly Notices of the Royal Astronomical Society, vol. 479, no. 4, October 2018, pp. 4336–4344, https://academic.oup.com/mnras/article/479/4/4336/5039660, https://doi.org/10.1093/mnras/sty1582.
Also Brandon Specktor, “The Milky Way Is Full of Toxic, Sticky Grease”, Live Science, June 28, 2018, https://www.livescience.com/62941-milky-way-space-grease.html.
[6] Tony Phillips, “The Mysterious Smell of Moondust”, NASA Science, January 30, 2006, https://phys.org/news/2006-02-mysterious-moondust.html.
And Jillian Scudder, “The Moon Smells Like Gunpowder”, Nautilus, February 8, 2023, https://nautil.us/the-moon-smells-like-gunpowder-261483/.
[7] Leonard David, “What Does Mars Smell Like?”, Space.com, June 9, 2016, www.space.com/33115-what-does-mars-smell-like.html.
[8] Lisa Grossman, “Uranus smells like rotten eggs”, Science News, April 23, 2018, https://www.sciencenews.org/article/uranus-smells-rotten-eggs.
And Nathaniel Scharping, “Uranus Smells Exactly How You Think It Does”, Discover Magazine, April 23, 2018, https://www.discovermagazine.com/the-sciences/uranus-smells-exactly-how-you-think-it-does.
[9] Katherine Latham, “From cat urine to gunpowder: Exploring the peculiar smells of outer space”, BBC Future, May 25, 2025, https://www.bbc.co.uk/future/article/20250522-what-does-outer-space-smell-like.
[10] Morgan L. Cable, “What does Titan smell like?”, Astronomy, September 3, 2020, https://www.astronomy.com/science/what-does-titan-smell-like/.
[11] Alastair Gunn, “What does a comet smell like?”, BBC Science Focus, November 9, 2021, https://www.sciencefocus.com/space/what-does-a-comet-smell-like/.
[12] Paul Rincon, “Oldest material on Earth discovered”, BBC News, Jan. 13, 2020, https://www.bbc.com/news/science-environment-51099609.
[13] Ian Sample, “Galaxy’s centre tastes of raspberries and smells of rum, say astronomers”, The Guardian, April 21, 2009, www.guardian.co.uk/science/2009/apr/21/space-raspberries-amino-acids-astrobiology, citing research by Arnaud Belloche and Robin Garrod.
[14] NASA, “Building Blocks”, https://science.nasa.gov/universe/overview/building-blocks/.
And Mark Peplow, “Planck telescope peers into primordial Universe”, Nature, March 21, 2013, www.nature.com/news/planck-telescope-peers-into-primordial-universe-1.12658, https://doi.org/10.1038/nature.2013.12658.