# An icy body from a cold, metal-poor disc around an old star

> Still possible: 3I/ATLAS is an ordinary icy planetesimal that formed in a very cold, metal-poor disc around an old star, and its unusual chemistry is the…

Source: https://mysteriesdept.com/mysteries/3i-atlas/answers/ANS0DFQ178MEYWB/an-icy-body-from-a-cold-metal-poor-disc-around-an-old-star  
Publisher: Mysteries Department  
Licence: CC BY 4.0 (credit Mysteries Department and link the page)  

---

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

Answer · 3I/ATLAS

# An icy body from a cold, metal-poor disc around an old star

3I/ATLAS is an ordinary icy planetesimal that formed in a very cold, metal-poor disc around an old star, and its unusual chemistry is the record of that birthplace.

**Still possible** Answers **1** question0

## Where it stands

**Still possible** Six pieces of evidence for, none against. It needs two reviews to be accepted.

## What it predicts

- Deeper ices exposed after perihelion keep high D/H and high 12C/13C
- Its dust stays dominated by amorphous silicates at every epoch
- Composition models for other interstellar objects place their hosts by metallicity the same way

## What would rule it out

- Water or methane from deeper layers shows Solar-System-like D/H
- Crystalline silicates make up a large share of the dust after perihelion

## Evidence 6 for · none against

[ALMA confirms deuterium-rich water independently](https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ3Q9YB4XN/alma-confirms-deuterium-rich-water-independently)

Supported

FOR

[Amorphous silicates, closer to interstellar dust](https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ3TYE9F15/amorphous-silicates-closer-to-interstellar-dust)

Suggestive

FOR

[High carbon and nitrogen isotope ratios in CN](https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ3T4VZPQZ/high-carbon-and-nitrogen-isotope-ratios-in-cn)

Suggestive

FOR

[JWST: water D/H near 1 per cent and high carbon-13 ratios](https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ3PX0VGG4/jwst-water-d-h-near-1-per-cent-and-high-carbon-13-ratios)

Supported

FOR

[Methane D/H the highest ever measured](https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ3SR2JMMK/methane-d-h-the-highest-ever-measured)

Supported

FOR

[Models reproduce the water at low metallicity](https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ3TH6PKZY/models-reproduce-the-water-at-low-metallicity)

Suggestive

FOR

## The questions it answers

[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)

OpenNo answer ahead yet

## Cite it

```
Mysteries Department. (2026). An icy body from a cold, metal-poor disc around an old star [Answer ANS0DFQ178MEYWB]. https://mysteriesdept.com/r/ANS0DFQ178MEYWB
```

Key

**ANS** 0DFQ178MEYWB

Kind

Answer · theory

Proposed

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

Version

1

Added by

[apollo](https://mysteriesdept.com/u/apollo)

The record

Every record is open data. Take this one as JSON, with its links and its history.

[JSON](https://mysteriesdept.com/api/v1/records/ANS0DFQ178MEYWB)