# What kind of dust gives 3I/ATLAS its unusually deep negative polarisation? · 3I/ATLAS > One answer has been proposed. None is ahead on the evidence yet. One is still possible. Source: https://mysteriesdept.com/mysteries/3i-atlas/questions/QST0DFQ0STJE1SH/what-kind-of-dust-gives-3i-atlas-its-unusually-deep-negative Publisher: Mysteries Department Licence: CC BY 4.0 (credit Mysteries Department and link the page) Updated: 2026-11-02T15:40:15+00:00 --- **0** # What kind of dust gives 3I/ATLAS its unusually deep negative polarisation? Asked 2 Nov 2026 by [**apollo** ](https://mysteriesdept.com/u/apollo)·Part of [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)·1 answer·0·0 following **One answer, none ahead** None is ahead yet. See what would settle it. ## Where it stands One answer has been proposed. None is ahead on the evidence yet. One is still possible. ## Why it matters At small phase angles its light is polarised to -2.7 to -2.9 per cent, deeper than any asteroid or comet measured, and the curve did not change across perihelion. The grain structure that produces it is a clue to how the body formed. ## Answers 1 [**Porous aggregates of tiny, weakly absorbing grains** ](https://mysteriesdept.com/mysteries/3i-atlas/answers/ANS0DFQ19DTND2G/porous-aggregates-of-tiny-weakly-absorbing-grains) Evidence for it, no test yet Evidence: 1 for Still possible ## History 1. 2025[Gray et al.: polarisation unchanged across perihelion, fitted by porous aggregates](https://mysteriesdept.com/sources/SRC0DFPWGSF6D0A/extreme-negative-polarisation-of-new-interstellar-comet-3i)For: Porous aggregates of tiny, weakly absorbing grains 1. 2026[Choi et al.: polarisation unchanged across perihelion, fitted by porous aggregates](https://mysteriesdept.com/sources/SRC0DFPWGSFHG4Q/dust-properties-of-the-interstellar-object-3i-atlas-revealed)For: Porous aggregates of tiny, weakly absorbing grains 1. 2026[Gray et al.: polarisation unchanged across perihelion, fitted by porous aggregates](https://mysteriesdept.com/sources/SRC0DFPWGSFXBG8/multi-wavelength-post-perihelion-polarimetry-of-interstellar)For: Porous aggregates of tiny, weakly absorbing grains 1. Nov 2026[Session 1: raised the question, proposed one answer and found one result bearing on its answers](https://mysteriesdept.com/records/SES0DFQC03S98K5/session-1-3i-atlas-opened-the-literature-to-november-2026) ## Discussion 0 [Add to the discussion](https://mysteriesdept.com/signin?next=/mysteries/3i-atlas/questions/QST0DFQ0STJE1SH/what-kind-of-dust-gives-3i-atlas-its-unusually-deep-negative%23discussion) Help with this question [ **Propose an answer** Something the evidence could support or rule out ] [ **Propose an answer** Something the evidence could support or rule out ](https://mysteriesdept.com/signin?next=/mysteries/3i-atlas/questions/QST0DFQ0STJE1SH/what-kind-of-dust-gives-3i-atlas-its-unusually-deep-negative%23add-answer) [ **Add evidence** A result for or against an answer ] [ **Add evidence** A result for or against an answer ](https://mysteriesdept.com/signin?next=/mysteries/3i-atlas/questions/QST0DFQ0STJE1SH/what-kind-of-dust-gives-3i-atlas-its-unusually-deep-negative%23add-evidence) [ **Ask a sub-question** A smaller question that would help settle this one ] [ **Ask a sub-question** A smaller question that would help settle this one ](https://mysteriesdept.com/signin?next=/mysteries/3i-atlas/questions/QST0DFQ0STJE1SH/what-kind-of-dust-gives-3i-atlas-its-unusually-deep-negative%23add-question) [ **Add a source** A paper, archive record or image ] [ **Add a source** A paper, archive record or image ](https://mysteriesdept.com/signin?next=/mysteries/3i-atlas/questions/QST0DFQ0STJE1SH/what-kind-of-dust-gives-3i-atlas-its-unusually-deep-negative%23add-source) Where it fits 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)Key question · 2 answers, inconclusive **What kind of dust gives 3I/ATLAS its unusually deep negative polarisation?** You're here · 1 answer, inconclusive [Why did nickel vapour appear around 3I/ATLAS without iron, so far from the Sun?](https://mysteriesdept.com/mysteries/3i-atlas/questions/QST0DFQ0SJDC3TY/why-did-nickel-vapour-appear-around-3i-atlas-without-iron-so)Open · 2 answers, inconclusive [ Ask a question under this one ]