# About a kilometre across, or a little more

> Still possible: The nucleus of 3I/ATLAS has a radius between roughly 0.4 and 1.7 km.

Source: https://mysteriesdept.com/mysteries/3i-atlas/answers/ANS0DFQ1MV3GTQV/about-a-kilometre-across-or-a-little-more  
Publisher: Mysteries Department  
Licence: CC BY 4.0 (credit Mysteries Department and link the page)  

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[Questions](https://mysteriesdept.com/questions)[3I/ATLAS](https://mysteriesdept.com/mysteries/3i-atlas)[How big is the nucleus of 3I/ATLAS?](https://mysteriesdept.com/mysteries/3i-atlas/questions/QST0DFQ0JS9W15Y/how-big-is-the-nucleus-of-3i-atlas)Answer

Answer · 3I/ATLAS

# About a kilometre across, or a little more

The nucleus of 3I/ATLAS has a radius between roughly 0.4 and 1.7 km.

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

## Where it stands

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

## What it predicts

- Late Hubble photometry far from the Sun, with little coma, gives a radius under 2 km
- Mass-loss and acceleration balance stays consistent with that size whichever gas drives it

## What would rule it out

- A clean nucleus measurement above 1.8 km in radius

## Evidence 2 for · none against

[Hubble detects the nucleus: radius 1.3 ± 0.2 km](https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ47J4JQGK/hubble-detects-the-nucleus-radius-1-3-0-2-km)

Supported

FOR

[Mass loss and push agree on a kilometre-sized body](https://mysteriesdept.com/mysteries/3i-atlas/evidence/EVD0DFQ47T6M9BD/mass-loss-and-push-agree-on-a-kilometre-sized-body)

Suggestive

FOR

## The questions it answers

[How big is the nucleus of 3I/ATLAS?](https://mysteriesdept.com/mysteries/3i-atlas/questions/QST0DFQ0JS9W15Y/how-big-is-the-nucleus-of-3i-atlas)

Open2 answers, none ahead

## Cite it

```
Mysteries Department. (2026). About a kilometre across, or a little more [Answer ANS0DFQ1MV3GTQV]. https://mysteriesdept.com/r/ANS0DFQ1MV3GTQV
```

Key

**ANS** 0DFQ1MV3GTQV

Kind

Answer · hypothesis

Proposed

[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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