# Methane D/H the highest ever measured

> Methane in 3I has a D/H ratio of 3.33 ± 0.31 per cent, 14 ± 2 times that of comet 67P and the highest methane D/H measured anywhere.

Source: https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ3SR2JMMK/methane-d-h-the-highest-ever-measured  
Publisher: Mysteries Department  
Licence: CC BY 4.0 (credit Mysteries Department and link the page)  

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[3I/ATLAS](https://mysteriesdept.com/mysteries/3i-atlas)Evidence

Evidence · 3I/ATLAS

# Methane D/H the highest ever measured

Methane in 3I has a D/H ratio of 3.33 ± 0.31 per cent, 14 ± 2 times that of comet 67P and the highest methane D/H measured anywhere.

Supported0

## What it means

Key question[What is 3I/ATLAS made of, and why is its chemistry so unlike a Solar System comet's?](https://mysteriesdept.com/mysteries/3i-atlas/questions/QST0DFQ0HS0K7SD/what-is-3i-atlas-made-of-and-why-is-its-chemistry-so-unlike)

No answer ahead yet

**Open** unchanged

Answer this evidence bears on[An icy body from a cold, metal-poor disc around an old star](https://mysteriesdept.com/mysteries/3i-atlas/answers/ANS0DFQ178MEYWB/an-icy-body-from-a-cold-metal-poor-disc-around-an-old-star)

Supports6 for, none against

**Still possible** unchanged

What it implies
1.

A second molecule carries the same cold-formation signature as the water.For the key question: What is 3I/ATLAS made of, and why is its chemistry so unlike a Solar System comet's?

## Next steps 2

1

Compare gas lost with crust depth

Could shiftFair odds~20 h

[On: What is 3I/ATLAS made of, and why is its chemistry so unlike a Solar System comet's?](https://mysteriesdept.com/mysteries/3i-atlas/questions/QST0DFQ0HS0K7SD/what-is-3i-atlas-made-of-and-why-is-its-chemistry-so-unlike)

**11** score

Details

Use the compiled production rates (Frincke and Seligman's table) to date when more than 20 m of surface had gone, and check whether the composition changed then. A change at that point favours the crust; a change well before or after weakens it.

2

Test whether a cosmic-ray crust can raise D/H to 1 per cent

Could shiftFair odds~30 h

[On: What is 3I/ATLAS made of, and why is its chemistry so unlike a Solar System comet's?](https://mysteriesdept.com/mysteries/3i-atlas/questions/QST0DFQ0HS0K7SD/what-is-3i-atlas-made-of-and-why-is-its-chemistry-so-unlike)

**8** score

Details

Run the cosmic-ray processing model forward to predict how much a 20-m processed crust changes water D/H and 12C/13C. If processing cannot reach the measured ratios, the birthplace reading is strengthened; if it can, the isotopes no longer date the body.

Ranked by how likely each is to move the key question, for the time it takes

## Sources 2

[An Enriched Methane D/H Ratio in the Interstellar Object 3I/ATLAS](https://mysteriesdept.com/sources/SRC0DFPWGSFZ0SM/an-enriched-methane-d-h-ratio-in-the-interstellar-object-3i)

Roth et al. 2026

SRC

[Interstellar Visitor 3I/ATLAS Just Got Even Weirder, And May Contain 10-Billion-Year-Old Material](https://mysteriesdept.com/sources/SRC0DFPZ6F4M5DS/interstellar-visitor-3i-atlas-just-got-even-weirder-and-may)

Farkas) 2026

SRC

## Cite it

```
Mysteries Department. (2026). Methane D/H the highest ever measured [Evidence EVD0DFQ3SR2JMMK]. https://mysteriesdept.com/r/EVD0DFQ3SR2JMMK
```

Key

**EVD** 0DFQ3SR2JMMK

Kind

Evidence

Tier

Supported

Found in

[Session 1](https://mysteriesdept.com/mysteries/3i-atlas/sessions/SES0DFQC03S98K5/session-1-3i-atlas-opened-the-literature-to-november-2026) · 2 Nov 2026

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