Interstellar comet 3I/Atlas is unusually enriched with antifreeze

Comet 3I/Atlas as seen by Hubble
in November 2025. Click for original.
While interstellar comet 3I/Atlas is remarkably like most comets from our own solar system, scientists have now found new evidence that it spalled off unusual amounts of methanol (CH3OH), the material we normally call antifreeze, when it made its close fly-by of the Sun in the fall of 2025.
You can read the paper here [pdf] . The research also detected large amounts of prussic acid (HCN). As the comet made its closest pass to the Sun, the numbers increased. From the paper’s abstract:
The CH3OH production rate increased sharply from August through October, including an uptick near the inner edge of the H2 O sublimation zone at r H = 2 au. Compared to comets measured to date at radio wavelengths, the derived CH3 OH/HCN ratios in 3I/ATLAS of 124+30 −34 and 79−14 +11 on September 12 and 15, respectively, are among the most enriched values measured in any comet, surpassed only by anomalous solar system comet C/2016 R2 (PanSTARRS).
Though the numbers are high, they aren’t outside the range of what has been found in comets from our own solar system. Instead, this data suggests — as has all data so far — that Comet 3I/Atlas is a normal comet, but unique in its own way, as are all comets and in fact every object in space.

Comet 3I/Atlas as seen by Hubble
in November 2025. Click for original.
While interstellar comet 3I/Atlas is remarkably like most comets from our own solar system, scientists have now found new evidence that it spalled off unusual amounts of methanol (CH3OH), the material we normally call antifreeze, when it made its close fly-by of the Sun in the fall of 2025.
You can read the paper here [pdf] . The research also detected large amounts of prussic acid (HCN). As the comet made its closest pass to the Sun, the numbers increased. From the paper’s abstract:
The CH3OH production rate increased sharply from August through October, including an uptick near the inner edge of the H2 O sublimation zone at r H = 2 au. Compared to comets measured to date at radio wavelengths, the derived CH3 OH/HCN ratios in 3I/ATLAS of 124+30 −34 and 79−14 +11 on September 12 and 15, respectively, are among the most enriched values measured in any comet, surpassed only by anomalous solar system comet C/2016 R2 (PanSTARRS).
Though the numbers are high, they aren’t outside the range of what has been found in comets from our own solar system. Instead, this data suggests — as has all data so far — that Comet 3I/Atlas is a normal comet, but unique in its own way, as are all comets and in fact every object in space.













