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3I/ATLAS: A Cosmic Messenger From The Beginning Of Time  

Article by Katherine Eliza

5-10 minutes

The ‘Interstellar Medium’ encompasses those vast, icy spaces between stars. These spaces are thought to hold uncountable interstellar entities, largely made up of comets. It’s currently theorised that these comets are birthed during the formation of star systems, flung onto an eternal journey through the Universe’ expanses. The discovery of three objects confirms this; 1I/’Oumuamua, 2I/Borisov and 3I/ATLAS. All on hyperbolic trajectories through our solar system, the chance to observe these cosmic messengers is like having an extraterrestrial time capsule hand-delivered to our Earthly doorstep. 

3I/ATLAS is a comet from far beyond our own solar system. Estimated to be roughly seven miles wide, it zooms across the night sky at over 130,000mph. It was first discovered in July 2025, emerging from just beyond the orbit of Jupiter. However the comet’s trajectory was unusually flat and straight, which revealed it likely did not originate from within our solar system, but from a much older, far away star system (Livescience, 2026). Using the powerful James Webb Telescope paired with advanced spectroscopy, which is the analysis of how matter interacts with light, scientists could discover what chemicals are present, how they formed and what kind of environment they came from (Pester, 2026). They also looked at isotopes. Similar to elements, they act as chemical fingerprints. The important ones here are Deuteurium (heavy hydrogen) and carbon ratios (normal vs heavy carbon). Comparing heavy and normal water quantities can reveal how cold the comet’s birthplace was and chemically, what was happening in that environment. Carbon ratios on the other hand are how scientists measure how evolved an object is. This helps to estimate age and place of origin within the galaxy. 

Around the comets’ nucleus, different gases glow an array of colours because they exist at different wavelengths. These colour signals are measured to determine which gases are present and in what quantities. Scientists detected huge amounts of H2O (water), CO2 (carbon dioxide) and CO (carbon monoxide). The comet is producing vast amounts of these gases and producing them quickly, with most gases coming directly from the nucleus and some coming from icy debris as it evaporates. When 3I/ATLAS was observed in early 2025, the dominant gas being produced was CO2. Now however, the comet is more CO rich, meaning its chemistry is evolving over time (Cordiner et al., 2026).

3I/ATLAS is estimated to be 10-12 billion years old. Almost as old as the theorised Universe itself. Scientists measured a high ratio of normal carbon compared with heavy carbon. Heavy carbon wasn’t being produced until later in our Galaxy’s lifetime, therefore it has been concluded that the comet formed very early in the galaxy. During the Milky Way’s early life, lots of massive stars formed rapidly, whereas later, smaller stars formed producing more heavy carbon and nitrogen as well. Since 3I/ATLAS has little of both and is high in CO, it was concluded that it formed early within the galaxy. It is difficult to estimate exactly where in the galaxy the comet formed, however given current data, it is likely the comet formed in the thick disk of the Milky Way. The Galactic Bulge (centre) fits the chemical makeup, however stars there are too fast moving and don’t fit with the comet’s motion. The Galactic Disk (where we are) somewhat fits the comets’ motion and chemistry, however the thick disk fits both the chemistry and motion more accurately. The thick disk is made up of older stars which sit above and below the main disk. This is the older part of the Milky Way. Another clue is that the comet also has far higher quantities of deuterium than normal comets; higher than most stars forming today and furthermore, higher than most objects in our solar system. Deuterium forms best in extremely cold temperatures and when the environment consists of high radiation and low metallicity (low dust). 

Deteurium is a fusion fuel. It acts as a huge source for nuclear fusion and is often used in fusion experiments. Combined with the tritium isotope, it ignites at extremely low temperatures, compared with other fusion fuels. Further research on 3I/ATLAS shows unusually high quantities of methane. Due to the abundance of deuterium and methane, it seems natural to conclude that formation was a result of extremely low temperatures, within a protoplanetary disk 10-12 billion years ago. However, the plot thickens. According to Loeb (2026), the population of these old, low-in-metal stars did not carry high enough quantities of heavy elements. He also points out that the protoplanetary disk in question could not have been cooler than the cosmic microwave background at that time, which would have been somewhere around 30 degrees Kelvin. He posits that the abundance of fusion-fuel deuterium, combined with the inconsistencies in the comet’s deduced origin, could signal a technological influence. 

Whether comet 3I/ATLAS is really an alien spacecraft, some form of traveling satellite or entirely of natural origin, remains to be seen. But one thing is for sure – it’s not everyday an interstellar visitor comes knocking on our door. We are incredibly lucky to be at the right place, at the right time to make these fascinating observations and, who knows? Perhaps we are one step closer to understanding how our own Milky Way galaxy was born. 

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