If you think the smell of burnt toast or a subway station can be off-putting, brace yourself—because scientists have uncovered the truly awful scent of a comet.
And it’s not what you might expect.
Thanks to the European Space Agency’s Rosetta Spacecraft, we now know what Comet 67P/Churyumov-Gerasimenko smells like, and it’s a mix of rotten eggs, horse urine, and a splash of formaldehyde.
Yes, you read that right—this comet smells awful.
But it’s not just a quirky bit of space trivia.
This discovery offers us a glimpse into the chemical makeup of comets and how they might have shaped the early days of our solar system.
Let’s dig into the surprising science behind these smells, how they were detected, and what it all means for our understanding of the universe.
Comet 67P
The European Space Agency’s Rosetta mission has been one of the most ambitious space explorations of our time. Launched in 2004, the Rosetta spacecraft’s mission was to follow and land on Comet 67P/Churyumov-Gerasimenko, a large icy body zipping through space at breakneck speeds.
This mission has allowed scientists to study the comet up close and collect vital data about its composition—including its very distinctive smell.
In November 2014, Rosetta was on the verge of landing on the comet, but at the same time, the comet was becoming more “active” as it moved closer to the Sun.
When a comet gets close to the Sun, the heat causes gases and dust trapped inside the comet to escape through cracks and pores on its surface.
These escaping gases are the key to unlocking the chemical secrets of the comet—and, yes, it turns out that they’re not particularly pleasant.
The Rosetta Orbiter Sensor for Ion and Neutral Analysis (ROSINA), one of the instruments aboard the spacecraft, detected a wide range of chemicals in the comet’s gas emissions.
These chemicals paint a distinctive, albeit unpleasant, olfactory picture of what the comet smells like.
A Mix of Rotten Eggs and Horse Pee
Before we go deeper into the science, let’s talk about the smell itself.
What exactly does Comet 67P smell like?
According to Kathrin Altwegg, the principal investigator for the ROSINA instrument, the scent is a bizarre and foul mix of rotten eggs, horse stables, formaldehyde, and almonds.
Not exactly a fragrance you’d find at your local department store.
Here’s the breakdown of the smells detected on the comet:
- Rotten eggs (hydrogen sulfide)
- Horse stable (ammonia)
- Formaldehyde, which is pungent and suffocating
- A bitter, almond-like aroma (hydrogen cyanide)
- A whiff of alcohol (methanol)
- A vinegar-like smell (sulfur dioxide)
- A hint of sweetness (carbon disulfide)
Altwegg’s description of this chemical cocktail might make you think of a mad scientist’s laboratory, but instead, it’s the scent of a comet traveling through space at incredible speeds.
According to Altwegg, the overall “perfume” of Comet 67P is quite strong, and it is far from appealing.
What Did the Instruments Detect?
So, how did the scientists pinpoint these revolting aromas?
The Rosetta spacecraft’s instruments were equipped with mass spectrometers, devices capable of measuring the chemical composition of gases.
As the spacecraft flew through the cloud of gas escaping from Comet 67P, these instruments were able to capture and identify multiple volatile compounds that were being released.
Here’s a closer look at some of the key chemicals found:
- Water (H2O): Of course, water is a major component of comets, and it’s essential for understanding their structure.
- Carbon monoxide (CO): A common gas found in space, this is typically produced by the breakdown of carbon-based compounds.
- Carbon dioxide (CO2): Another simple molecule, carbon dioxide is released when organic matter is heated.
- Ammonia (NH3): This compound gives off a strong odor, similar to the scent of horse urine or cleaning products.
- Methane (CH4): A common volatile compound that is found throughout the universe, methane is often associated with energy and biological processes.
- Methanol (CH3OH): An alcohol that’s present in small quantities.
- Formaldehyde (CH2O): This highly pungent compound is commonly used as a preservative and disinfectant.
- Hydrogen sulfide (H2S): Known for its distinct rotten egg smell, this compound is produced by the breakdown of organic materials.
- Hydrogen cyanide (HCN): A highly toxic compound with a bitter, almond-like odor, hydrogen cyanide is notorious for being poisonous in large quantities.
- Sulfur dioxide (SO2): This gas is responsible for the vinegar-like aroma, and it’s often associated with volcanic activity.
- Carbon disulfide (CS2): This chemical compound has a faintly sweet scent, adding an oddly pleasant note to an otherwise pungent mix.
The array of compounds detected gives us a snapshot of the comet’s chemistry—but it also paints a vivid (and unpleasant) picture of what it would smell like if you could somehow get close enough to the comet without freezing or suffocating.
Challenging Assumptions: Do Comets Have a Pleasant Aroma?
When you think about comets, you probably picture icy, dusty objects speeding through the vacuum of space.
You might imagine something cold and distant, but not something that evokes any strong sensory images, particularly not smell.
After all, space is a near-perfect vacuum, so there’s no air for smells to travel through.
So why would the scent of a comet even matter?
Here’s where things get interesting: The discovery of the comet’s scent challenges our understanding of the relationship between smell and space.
While we can’t actually smell anything in space (due to the lack of air), the chemical composition of a comet can still give us an idea of its “olfactory profile.”
These volatile compounds are emitted by the comet as it moves closer to the Sun, and they provide a tangible connection to the history and evolution of the solar system.
This raises some intriguing questions about the formation of life: Could the chemicals in comets have played a role in the origins of life on Earth?
Some scientists speculate that comets and asteroids may have carried organic molecules to early Earth, contributing to the development of life as we know it.
So, while the smell of Comet 67P may be unpleasant, it may have once been part of the foundation for life on our planet.
The Role of Comets in Our Understanding of the Early Solar System
The scent of a comet may seem trivial, but its chemical makeup is actually incredibly important for understanding the early solar system.
Comets are thought to be some of the oldest and most primitive bodies in our solar system, acting as time capsules that preserve chemical remnants from the early days of the universe.
By studying the gases emitted by Comet 67P, scientists can learn more about the conditions that existed when the solar system was forming.
As the comet travels closer to the Sun, the heat causes the volatile compounds inside it to vaporize, creating a fascinating chemical signature.
These compounds can tell scientists about the pre-solar cloud—the material from which our solar system formed billions of years ago.
In this sense, the smell of Comet 67P is a reminder of the raw materials that were once scattered throughout the early solar system.
What’s Next for the Rosetta Mission?
While Comet 67P’s scent is certainly a fun discovery, it’s just one small part of the larger mission that the Rosetta spacecraft undertook.
The spacecraft successfully landed on the comet in November 2014, marking the first time in history that a spacecraft had touched down on a comet’s surface.
This historic achievement was a major milestone in space exploration and provided a wealth of data about the physical and chemical properties of the comet.
In the years since the Rosetta mission, scientists have continued to analyze the data gathered by Rosetta’s instruments, and new insights are still emerging.
As more missions explore comets, asteroids, and other celestial bodies, we can expect further revelations that help us understand how life on Earth might have begun and what role comets played in our planet’s history.
Smelly, But Essential
The stinky truth about Comet 67P is that it smells like something you’d rather not encounter—rotten eggs, horse pee, and formaldehyde are not exactly ingredients for a pleasant fragrance.
But beyond the unpleasant aromas, the data gathered from this comet is scientifically invaluable.
It provides a window into the early solar system and gives us a clearer understanding of the processes that may have shaped the Earth and the potential origins of life itself.
In the grand scheme of things, the “smell” of a comet is a small but intriguing clue in the puzzle of our solar system’s history.
And while we may never get a chance to smell the comet ourselves, we can rest easy knowing that the Rosetta spacecraft has done the dirty work for us.
It may smell bad, but it’s helping
