What Does the Universe Smell Like?

 

The Pillars of Creation are clouds of cosmic dust and gas that are just a small area at the center of Messier 16, or the Eagle Nebula, where new stars are forming. This is 6,500 light-years away from us. Blue is oxygen and orange is sulfur, while hydrogen and nitrogen are green. NASA, ESA and the Hubble Heritage Team (STScI/AURA).

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]

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.

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.

 

Go to my index of posts to see more.

If you'd like to comment, please email me at John@AWondrousWorld.com.

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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.

You are Older than Dirt

We are stardust

We are golden

And we’ve got to get ourselves

Back to the garden

 —Joni Mitchell’s song “Woodstock”, which was popularized by Crosby, Stills, Nash & Young

 

We are actually much older than you think, since every bit of you was made long before you were born. Almost two-thirds of your weight is water and essentially none of it was created during your lifetime. Up to half of the earth’s surface water is older than our sun. Additional water formed in the crust and atmosphere of the early earth, meaning much of the water in you is likely to be two to five billion years old.

That’s at a molecular level. At an atomic level, many of your atoms were created in long-dead stars that could have been up to a thousand times the mass of the sun. While it’s thought the three lightest elements—hydrogen, helium, and about one fifth of today’s lithium, all of which make up 98% of the ordinary matter in the universe—were made in the first three minutes after the Big Bang, elements with 3 through 26 protons—much of the additional lithium through iron—were made inside stars, with the exception of beryllium and boron (elements 4 and 5), which, on Earth, are made in our atmosphere.

Most of these atoms are roughly five to eight billion years old, although some might even date back to around 13.2 billion years—just 550 million years after the Big Bang. These ancient stars exploded as supernovas, scattering dust that drifted for millennia through interstellar space becoming parts of new stars that also ended up going supernova—perhaps repeating this process several times.

Some of it even left our galaxy for long periods in currents known as the circumgalactic medium, travelling out up to four times the width of our galaxy away from the Milky Way, before being pulled back in. Astronomer Jessica Werk, with the University of Washington, who had studied this, noted, “The same carbon in our bodies most likely spent a significant amount of time outside of the galaxy!”[1] This applies to other elements as well, suggesting that most of what we’re made of was once intergalactic. That’s stuff from the Milky Way that left and came back. Researchers estimate that half the stuff in us came from another galaxy, possibly from before our galaxy even existed.[2]

As we eat and breathe, new material enters our body, while some leaves. We’re constantly exchanging bits of us with the universe in a process of renewal. Obviously most of us wasn’t part of us when we were born and a large part of us only became part of us recently, but all of us are made from non-us elements.

When you look at a photograph of yourself when you were young, you know it’s you, but much of what you were made of then has been replaced. You have a sense of continuity, but you’re not the same as you were. You also think and act differently, and many of your interests and preferences have changed as well. If the you of then stood next to the you of now and you talked about your likes and dislikes, people would probably have trouble realizing the two of you are the same person. There are even some minor changes to your DNA.

Supernovas leave behind dead stars called neutron stars. Neutron stars are so compact and dense, that the protons and neutrons form what’s called nuclear pasta, which is a hundred trillion times denser than anything on earth and more than 10 billion times stronger than steel.

It’s now believed that many of the 90-plus heavier elements, which include nickel, copper, zinc, silver, tin, iodine, platinum, gold, mercury, lead, uranium, and plutonium, were formed when two neutron stars crashed together generating temperatures up to 1.4 trillion degrees Fahrenheit (800 billion C), shooting out these higher elements. Some might even come from smashups of a neutron star with a black hole. While you may think these smash-ups are rare, they’re actually thought to be quite common. Scientists estimate that there are actually about 100 million black holes and about a billion neutron stars in our galaxy alone.

(Top) This artist’s impression compares the size of a 12-mile-wide (19 km) neutron star with that of Manhattan. Neutron stars are the densest objects in the universe that we can directly observe. It takes matter equal to half-a-million Earths, compressed down to a sphere a few miles wide to form a neutron star. It’s so dense that on Earth one teaspoonful would weight a billion tons. A neutron star can spin faster than 700 times a second and, compared to the Earth, its magnetic field is a trillion times stronger. Astrophysicists think neutron stars consist of various oddities—such as a neutron superfluid—with a crust of ions and electrons.[3] (Bottom) Formed in a supernova a million years ago, this 17-mile-wide (28 km) neutron star named RX J18563.5-3754 is only about 200 light years away from us and travelling at 4,000 miles (6,500 km) per second. It will reach its closest point to Earth, 170 light years away, about 300,000 years from now. (Top credit: NASA's Goddard Space Flight Center. Bottom: NASA and F.M. Walter of State University of New York at Stony Brook.)

An alternate idea is that some of the heavier elements came from collapsars. Collapsars are massive rapidly spinning stars that collapse before going supernova. Although rare, these might produce even more heavy elements than a neutron star collusion.[4]

There’s also evidence that up to 10% came from massive ejections of material from magnetars. Magnetars are neutron stars with extremely strong magnetic fields that are about a thousand times stronger than a normal neutron star. Their flairs could widely distribute these elements, without a collusion. Some magnetars are also pulsars.[5]

A minute amount, relatively speaking, of this dust from supernovas and neutron star collusions coalesced to form our solar system and, eventually, you. As author and astrophysicist Carl Sagan used to say, we are all made of star-stuff.

Moving from the origin of our atoms to the distribution of molecules, there’s an interesting exercise that professors present to their chemistry and physics students. On March 15th back in 44 b.c., Julius Caesar was stabbed to death at the Forum by sixty Roman senators. How likely is it that you have ever breathed in one of the molecules from Caesar’s final breath?

Assuming his dying exhalation was the average volume of a deep breath, which is a liter of air, then we can estimate that it consisted of something like 25 sextillion gas molecules. Making some assumptions about the lifetimes of molecules and how gases mix, we can calculate that on average, one of Caesar’s molecules is in every breath we have ever taken and every breath we will ever take.

There’s also a good chance that some of the water molecules in you right now once passed through a number of dinosaurs...along with many other interesting creatures—before getting into you. In fact, the same applies to all of the elements in your body. They too were once parts of dinosaurs, trilobites, trees, bot fly maggots, fungi, and rocks. The varied elements that came together to make us will eventually be dispersed back into the environment once again where they will become part of something else. In this way, everything on earth is related. Everything is made from the same stuff that’s continually recycled.

While the water in you is ancient, it only recently got into you. It comes from what you eat and drink. Most of it comes from tap water. Even if you don’t drink much water, it comes from the tap water used to make your soda or beer or reconstituted fruit juices. Within minutes of drinking it, water becomes part of your bloodstream, which is also mostly made of tap water (or well water or rain water or mountain-stream water, if that’s what you drink, but remember, filtered water is just tap water unless it comes directly from a well, stream, or rain and into a bottle). Your blood has some cells, salts and organic molecules in it, but it’s mostly water. If you think blood is thicker than water...well, not by much. From your blood, the water is distributed throughout your body, becoming a major part of all your organs.

Water passes through us like a stream. It’s unlikely that any of the molecules of water that are in you now will still be in you in two years’ time.

If all of this isn’t strange enough for you, your head is older than your feet are because of time dilation—a well-proven aspect of Einstein’s Special Theory of Relativity.

So on the day you turned 10 years old, next to none of you was actually 10. Most of you was much, much older, while some formations of those elements were much younger.

 

Go to my index of posts to see more. 

If you'd like to comment, please email me at John@AWondrousWorld.com.

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[1] James Urton, University of Washington press release, “The carbon in our bodies probably left the galaxy and came back on cosmic ‘conveyer belt’ ”, UW News, January 3, 2025, https://www.washington.edu/news/2025/01/03/galaxy-carbon-conveyer-belt/, citing Samantha L. Garza, Jessica K. Werk, Trystyn A. M. Berg, Yakov Faerman, Benjamin D. Oppenheimer, Rongmon Bordoloi, and Sara L. Ellison, “The CIViL* Survey: The Discovery of a C iv Dichotomy in the Circumgalactic Medium of L* Galaxies”, The Astrophysical Journal Letters, 2024; 978 (1): L12, https://doi.org/10.3847/2041-8213/ad9c69.

[2] Ziya Tong, The Reality Bubble, Toronto: Prentice Hall Press, 2019.

[3] Francis Reddy, “NASA’s Swift Reveals New Phenomenon in a Neutron Star”, NASA’s Goddard Space Flight Center, May 29, 2013, https://www.nasa.gov/mission_pages/swift/bursts/new-phenom.html.

[4] Caleb A. Scharf, “Moon Blobs, Collapsars, and Long Planets”, Scientific American, May 10, 2019, https://www.scientificamerican.com/blog/life-unbounded/moon-blobs-collapsars-and-long-planets/.

[5] Tatyana Woodall, Ohio State University press release, “Stellar collapse and explosions distribute gold throughout the universe”, ScienceDaily, May 7, 2025, https://www.sciencedaily.com/releases/2025/05/250507130338.htm, citing Anirudh Patel, Brian D. Metzger, Jakub Cehula, Eric Burns, Jared A. Goldberg, and Todd A. Thompson, “Direct Evidence for r-process Nucleosynthesis in Delayed MeV Emission from the SGR 1806–20 Magnetar Giant Flare”, The Astrophysical Journal Letters, 2025; 984 (1): L29, https://iopscience.iop.org/article/10.3847/2041-8213/adc9b0,
https://doi.org/10.3847/2041-8213/adc9b0.