# What was 'Oumuamua made of? · 1I/'Oumuamua > Seven answers have been proposed. An ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without… leads… Source: https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKBZN458NQ/what-was-oumuamua-made-of Publisher: Mysteries Department Licence: CC BY 4.0 (credit Mysteries Department and link the page) Updated: 2026-10-26T11:58:22+00:00 --- **0** # What was 'Oumuamua made of? Asked 26 Oct 2026 by [**apollo** ](https://mysteriesdept.com/u/apollo)·7 answers·0·0 following **Most likely: an ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without…** Ahead on the evidence, not yet confirmed. It needs two reviews to be accepted. ## Where it stands Seven answers have been proposed. An ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without… leads, with evidence 3 for, 1 against: partly supported by its tests. Six are still possible. Of the two narrower questions under it, none is answered yet. ## Why it matters Its red, featureless surface and the absence of any coma left its bulk composition unknown, and each answer implies a different birth site and a different population of interstellar objects⁠[[1]](https://mysteriesdept.com/sources/SRC0CSKB2BM5AXE/spectroscopy-and-thermal-modelling-of-the-first-interstellar)⁠[[2]](https://mysteriesdept.com/sources/SRC0CSKBJYW06A8/constraints-on-the-occurrence-of-oumuamua-like-objects). No composition proposed so far is free of serious difficulty⁠[[3]](https://mysteriesdept.com/sources/SRC0CSKBAX23QG7/the-interstellar-interlopers). ## Answers 7 [**An ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without…** ](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKC95T4XTH/an-ordinary-comet-like-planetesimal-of-water-ice-and-dust) Partly supported by its tests Evidence: 3 for, 1 against Most likely [**A dense, dry rocky or metal-rich body with no significant ice.** ](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCCK66HF0/a-dense-dry-rocky-or-metal-rich-body-with-no-significant-ice) Failed a test; not refuted outright Evidence: 1 for, 1 against Disputed [**An ultra-porous fractal aggregate of icy dust.** ](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCBVR4ARH/an-ultra-porous-fractal-aggregate-of-icy-dust) Not tested enough to call either way Evidence: 1 for, 1 against Still possible [**Manufactured material, a thin artificial sheet.** ](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCDAM421B/manufactured-material-a-thin-artificial-sheet) Failed a test; not refuted outright Evidence: 1 for, 1 against Disputed [**Mostly molecular hydrogen ice, formed in a giant molecular cloud core.** ](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCACW5ZD5/mostly-molecular-hydrogen-ice-formed-in-a-giant-molecular) Failed a test; not refuted outright Evidence: 1 for, 1 against Disputed [**Nitrogen ice, a surface fragment of a Pluto-like body.** ](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCB4A3EJ7/nitrogen-ice-a-surface-fragment-of-a-pluto-like-body) Tested, but the results don't decide it Evidence: 1 for, 1 against Disputed [**None of these.** ](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCE2217VN/none-of-these) Not tested enough to call either way Evidence: none yet Still possible [Show 2 more answers] ## History 1. 2017[European Southern Observatory puts forward: a dense, dry rocky or metal-rich body with no significant ice.](https://mysteriesdept.com/sources/SRC0CSKBGGR5HD7/eso-observations-show-first-interstellar-asteroid-is-like) 1. 2017[European Southern Observatory: the discovery-era interpretation was a dense, possibly rocky or metal-rich body lacking water or ice.](https://mysteriesdept.com/sources/SRC0CSKBGGR5HD7/eso-observations-show-first-interstellar-asteroid-is-like)For: A dense, dry rocky or metal-rich body with no significant ice. 1. 2018[Fitzsimmons et al. puts forward: an ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without…](https://mysteriesdept.com/sources/SRC0CSKB2BM5AXE/spectroscopy-and-thermal-modelling-of-the-first-interstellar) 1. 2018[Bialy & Loeb puts forward: manufactured material, a thin artificial sheet.](https://mysteriesdept.com/sources/SRC0CSKB6R811G8/could-solar-radiation-pressure-explain-oumuamuas-peculiar) 1. 2018[Trilling et al.: no water outgassing was ever detected.](https://mysteriesdept.com/sources/SRC0CSKB4HY02PY/spitzer-observations-of-interstellar-object-1i-oumuamua)Against: An ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without… 1. 2018[Fitzsimmons et al.: the red featureless spectrum fits an organic-rich mantle half a metre thick that could have kept interior ice…](https://mysteriesdept.com/sources/SRC0CSKB2BM5AXE/spectroscopy-and-thermal-modelling-of-the-first-interstellar)For: An ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without… 1. 2021[Hsieh et al.: kinematics suggest an age of about 35 million years and a link to a young moving group.](https://mysteriesdept.com/sources/SRC0CSKBMDR3PMT/evidence-suggesting-that-oumuamua-is-the-30-myr-old-product)For: Mostly molecular hydrogen ice, formed in a giant molecular cloud core. 1. 2021[Jackson & Desch: satisfies the acceleration, size, albedo and the CO/CO2/dust limits at once.](https://mysteriesdept.com/sources/SRC0CSKB7QG4ZV2/1i-oumuamua-as-an-n2-ice-fragment-of-an-exo-pluto-surface-i)For: Nitrogen ice, a surface fragment of a Pluto-like body. 1. 2021[Levine et al.: formation and survival of an aggregate this size are not demonstrated.](https://mysteriesdept.com/sources/SRC0CSKBJYW06A8/constraints-on-the-occurrence-of-oumuamua-like-objects)Against: An ultra-porous fractal aggregate of icy dust. 1. 2022[Siraj & Loeb: the mass budget and fragment-size arguments weigh against it.](https://mysteriesdept.com/sources/SRC0CSKB8747BCC/the-mass-budget-necessary-to-explain-oumuamua-as-a-nitrogen)Against: Nitrogen ice, a surface fragment of a Pluto-like body. 1. 2023[Bergner & Seligman: the radiolytic-hydrogen model makes an ordinary water-ice body fit the acceleration.](https://mysteriesdept.com/sources/SRC0CSKB8EY4Z1T/acceleration-of-1i-oumuamua-from-radiolytically-produced-h2)For: An ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without… 1. 2025[Cordiner et al.: 2I/Borisov and 3I/ATLAS were both ordinary comets in composition, if unusually rich in CO or CO2.](https://mysteriesdept.com/sources/SRC0CSKBDB607EW/jwst-detection-of-a-carbon-dioxide-dominated-gas-coma)For: An ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without… 1. 26 Oct 2026Asked on this site ## Discussion 0 [Add to the discussion](https://mysteriesdept.com/signin?next=/mysteries/oumuamua/questions/QST0CSKBZN458NQ/what-was-oumuamua-made-of%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/oumuamua/questions/QST0CSKBZN458NQ/what-was-oumuamua-made-of%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/oumuamua/questions/QST0CSKBZN458NQ/what-was-oumuamua-made-of%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/oumuamua/questions/QST0CSKBZN458NQ/what-was-oumuamua-made-of%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/oumuamua/questions/QST0CSKBZN458NQ/what-was-oumuamua-made-of%23add-source) Where it fits 1I/'Oumuamua **What was 'Oumuamua made of?** Key question · you're here [What shape was 'Oumuamua, and how did it spin?](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKBZWY4KE5/what-shape-was-oumuamua-and-how-did-it-spin)Open · 3 answers, inconclusive [Where did 'Oumuamua come from?](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKC04R56X5/where-did-oumuamua-come-from)Most likely · ejected from another star's planetary system during planet formation, like most interstellar objects should… [ Ask a question under this one ]