# 1I/'Oumuamua

> 'Oumuamua was the first object seen passing through the Solar System from interstellar space, found on 19 October 2017 and followed for eleven weeks. It…

Source: https://mysteriesdept.com/mysteries/oumuamua  
Publisher: Mysteries Department  
Licence: CC BY 4.0 (credit Mysteries Department and link the page)  
Updated: 2026-10-27T17:47:58+00:00  

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**MYS** 0CSKBPVW6FBV·Mystery · object

# 1I/'Oumuamua

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1I/'Oumuamua

![Photograph: 1I/'Oumuamua](https://mysteriesdept.com/media/folio/oumuamua-lead)

Alan Fitzsimmons, Isaac Newton Group · Public domain

Designation

1I/2017 U1 ('Oumuamua); provisionally A/2017 U1⁠[[4]]

Discovered

19 October 2017, Pan-STARRS1, Haleakala, Hawaii⁠[[1]]

Observed

14 October 2017 (earliest image) to 2 January 2018 (last Hubble image)⁠[[5]]

Orbit

Hyperbolic, eccentricity 1.20; perihelion 0.256 au on 9 September 2017⁠[[3]]

Incoming speed

About 26 km/s relative to the Sun, from the direction of Lyra⁠[[1]]

Size

Mean radius about 100 m for a comet-like albedo of 0.04⁠[[2]]

Infrared limit

Not detected by Spitzer; effective diameter below 98, 140 or 440 m depending on the thermal model⁠[[8]]

Light curve

Brightness range about 2.5 magnitudes; tumbling, with no single period⁠[[7]]

Extra acceleration

About 5 millionths of a metre per second squared at 1 au, directed away from the Sun, detected at 30 sigma⁠[[5]]

Activity

None detected: no coma, dust, CO or CO2⁠[[8]]

Status

Partly explained

Questions

1 of 6 answered

People [**Abraham (Avi) Loeb** Harvard astrophysicist; proposed the lightsail reading](https://mysteriesdept.com/mysteries/oumuamua/people/FIG0CSKBRJJ6DGG/abraham-avi-loeb)[**Marco Micheli** ESA astronomer; led the measurement of the non-gravitational acceleration](https://mysteriesdept.com/mysteries/oumuamua/people/FIG0CSKBRAR05DH/marco-micheli)[**Darryl Z. Seligman** Proposed the hydrogen-ice and radiolytic-hydrogen readings; led the dark-comet work](https://mysteriesdept.com/mysteries/oumuamua/people/FIG0CSKBS261SH6/darryl-z-seligman)[**Alan P. Jackson** Proposed the nitrogen-ice reading](https://mysteriesdept.com/mysteries/oumuamua/people/FIG0CSKBSHT44T2/alan-p-jackson)[**Jennifer B. Bergner** Astrochemist; proposed hydrogen from irradiated water ice](https://mysteriesdept.com/mysteries/oumuamua/people/FIG0CSKBSA068BA/jennifer-b-bergner)

All 9 people ›

[**Shmuel Bialy** Co-author of the radiation-pressure paper](https://mysteriesdept.com/mysteries/oumuamua/people/FIG0CSKBRTC26ZZ/shmuel-bialy)[**Steven J. Desch** Proposed the nitrogen-ice reading](https://mysteriesdept.com/mysteries/oumuamua/people/FIG0CSKBSSM20RV/steven-j-desch)[**Karen J. Meech** University of Hawaii astronomer; led the discovery and characterisation papers](https://mysteriesdept.com/mysteries/oumuamua/people/FIG0CSKBR2Y7CP4/karen-j-meech)[**Robert Weryk** University of Hawaii astronomer who first identified the object in Pan-STARRS1 data](https://mysteriesdept.com/mysteries/oumuamua/people/FIG0CSKBQV4641P/robert-weryk)

Catalog key**MYS** 0CSKBPVW6FBV

On 19 October 2017 the Pan-STARRS1 survey telescope on Haleakala, Hawaii, recorded a faint object moving fast across the sky⁠[[1]]. Its orbit turned out to be strongly hyperbolic: it was not bound to the Sun and had come from interstellar space, arriving at about 26 km/s from the direction of the constellation Lyra⁠[[2]]⁠[[1]]. It had already passed closest to the Sun, at 0.26 au on 9 September, and closest to Earth, at about 24 million km on 14 October⁠[[3]]⁠[[1]]. The Minor Planet Center created a new class of designation for it, 1I, and the Pan-STARRS team named it 'Oumuamua, a Hawaiian word for a scout or messenger⁠[[4]].

Telescopes worldwide followed it until it faded beyond reach on 2 January 2018⁠[[5]]. Three properties made it hard to classify. It varied in brightness by a factor of about ten, which implies a body far more elongated or flattened than any known asteroid or comet, and it tumbled rather than spinning about one axis⁠[[2]]⁠[[6]]⁠[[7]]. It showed no coma, dust or gas, even in the deepest images and in a 30-hour Spitzer integration⁠[[2]]⁠[[8]]. And its path departed from a purely gravitational one: a small extra push directed away from the Sun, detected at 30 sigma, of the size outgassing gives a comet⁠[[5]].

No explanation fits all three without strain. The readings in the literature are an ordinary icy body whose gas escaped unseen, a body of an exotic ice (molecular hydrogen, nitrogen), water ice that held hydrogen made by cosmic rays, a very porous dust aggregate pushed by sunlight, and a thin artificial sail⁠[[9]]⁠[[10]]. The International Space Science Institute team concluded in 2019 that every observation is consistent with a natural origin⁠[[11]]. Two later interstellar objects, 2I/Borisov in 2019 and 3I/ATLAS in 2025, were plainly comets, which leaves 'Oumuamua the odd one of three⁠[[12]]⁠[[13]]. Of the 6 questions on this site, 1 are answered. The most likely answer to “What was 'Oumuamua made of?”, not yet confirmed: an ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without….

### Key questionsset by the editors

[**Does any observation of 'Oumuamua require a non-natural explanation?** ](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKC0CJ74DR/does-any-observation-of-oumuamua-require-a-non-natural)Answered: no. Every property has at least one natural explanation consistent with the data, though none is confirmed.

[**What pushed 'Oumuamua away from the Sun?** ](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKBZDA67JF/what-pushed-oumuamua-away-from-the-sun)No answer ahead yet

[**What was 'Oumuamua made of?** ](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKBZN458NQ/what-was-oumuamua-made-of)Most likely: an ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without…

 [All 6 questions ](https://mysteriesdept.com/questions/key-questions?mystery=oumuamua)

## The object

What was seen of 'Oumuamua was a point of light, never resolved. Everything known about its size and shape is inferred from its brightness and how it changed. For a comet-like albedo of 0.04 its mean radius was about 100 m⁠[[2]]. Spitzer's non-detection at 4.5 microns sets an effective spherical diameter below 98, 140 or 440 m depending on the thermal model, and an albedo above 0.2, 0.1 or 0.01 to match⁠[[8]]. The surface was red, with a featureless spectral slope like that of outer Solar System bodies and irradiated organic-rich crusts⁠[[14]]⁠[[15]].

[![1I/'Oumuamua](https://mysteriesdept.com/files/v/714c9c97ed948633d08b436d3c7d5ca2da9ea211914dd665931d9d5685dccb5d/w800)](https://mysteriesdept.com/mysteries/oumuamua/artifacts/ART0CSKCV7Y2C6C/1i-oumuamua)

1I/'OumuamuaESO/K. Meech et al., 2017. CC BY 4.0[Artifact ](https://mysteriesdept.com/mysteries/oumuamua/artifacts/ART0CSKCV7Y2C6C/1i-oumuamua)

Its incoming velocity was within a few km/s of the local standard of rest, the average motion of nearby stars, which is unusual for any one star and suggests a young object or one that has been little disturbed⁠[[16]]. Its orbit is published by JPL as solution 16, fitted to 207 observations with a non-gravitational term⁠[[3]].

**Map of the continent** [Open the full map](https://mysteriesdept.com/mysteries/oumuamua/map)

[+][−]

1

**Haleakala Observatory (Pan-STARRS1), Maui, Hawaii** Observatory

Within 100 m

2

**Green Bank Telescope, West Virginia** Radio telescope

Within 100 m

MappedNatural Earth

### Timeline

**Timeline**

Squeezed where little happened. Each mark is a published claim, by how it stands:AcceptedMost likelyStill possibleDisputedRuled out

## What is known

The light curve. Its brightness changed by about 2.5 magnitudes, a factor of ten⁠[[2]]. Gemini North photometry over 8 hours on two nights found a range of 2.6 ± 0.2 magnitudes and a light curve that did not repeat from cycle to cycle⁠[[7]]. Fraser and colleagues, using all photometry then published, showed that no single period fits: the body was in non-principal-axis rotation, or tumbling, with an axis ratio of at least 5:1, and the damping time for such motion is a billion years or more, so the tumble was probably set before it reached the Sun⁠[[6]]. Belton and colleagues, from 818 observations over 29 days, found two periodicities of 8.67 and 3.74 hours and showed that the data fit either a long cigar or a very flat disc, which photometry alone cannot separate⁠[[17]]. Physical light-curve models favour a thin disc of about 1:6 over a cigar of about 1:8, and need a torque of the size outgassing produces⁠[[18]]; a 2023 model with outgassing torques fits October but not November⁠[[19]]. Time-resolved colour photometry from Apache Point adds an independent period search and colours; it is the one light-curve set released under an open licence⁠[[20]]⁠[[21]].

[![1I/'Oumuamua](https://mysteriesdept.com/files/v/8a59db1dea679afcde5590850ebad0f9be54c2aca662f2d94cdae17deebc9e33/w800)](https://mysteriesdept.com/mysteries/oumuamua/artifacts/ART0CSKCV7Y2C6C/1i-oumuamua)

1I/'OumuamuaJudy Schmidt, 2017. CC BY 2.0[Artifact ](https://mysteriesdept.com/mysteries/oumuamua/artifacts/ART0CSKCV7Y2C6C/1i-oumuamua)

The acceleration. Micheli and colleagues fitted 177 ground-based and 30 Hubble positions from 14 October 2017 to 2 January 2018. Gravity alone does not fit. Adding a radial acceleration that falls off as the inverse square (or inverse) of distance from the Sun does, with a magnitude of (4.92 ± 0.16) × 10^-6 m s^-2 at 1 au⁠[[5]]. The Hubble positions were combined with CFHT, VLT and Gemini South data for the measurement, and no dust, coma or tail appeared in them⁠[[22]]. An independent re-fit confirmed the signal and found a strong preference for a purely radial direction⁠[[23]].

The absence of activity. No coma was seen in any image⁠[[2]]⁠[[15]]⁠[[7]]. Spitzer's limits are 9 kg/s of dust, 9 × 10^22 molecules/s of CO2 and about 9 × 10^21 molecules/s of CO, the last some ten thousand times below the CO rate Micheli's outgassing model would have needed⁠[[8]]. Spitzer could not constrain water.

## What has been tested

Micheli and colleagues tested and rejected, one by one, radiation pressure on an ordinary rocky body, the Yarkovsky effect, friction-like drag, forces from the solar wind on a magnetised body, a binary or split nucleus, and an offset between the centre of light and the centre of mass. They found outgassing the one physically viable mechanism if the body had comet-like thermal properties⁠[[5]].

Three radio searches looked for transmitters. The Green Bank Telescope observed on 13 December 2017 across 1.1-11.6 GHz and found no narrowband signal, a limit of 0.08 W for an omnidirectional transmitter on the object⁠[[24]]. The Allen Telescope Array found nothing between 1 and 10 GHz, with limits of about 10 to 100 W in clean bands⁠[[25]]. The Murchison Widefield Array, which happened to have the object in its field on 28 November, found nothing at 72-102 MHz⁠[[26]]. The Green Bank raw data are public⁠[[27]].

Two quantitative tests have been run on the lightsail reading. A tumbling sail would produce a light-curve amplitude like the observed one with probability below 1.5 per cent, and would have been visible in all 55 observations with probability of 0.4 per cent⁠[[28]]. A sail of the inferred mass and thickness could not have been driven to speeds that would bring it from a nearby star in less than about half a billion years⁠[[29]].

The origin has been tested by tracing the trajectory back through the Galaxy. Using Gaia DR2, Bailer-Jones and colleagues found four candidate encounters in the last few million years, the closest with the M dwarf HIP 3757 at 0.60 pc about a million years ago and a slower one with the G dwarf HD 292249 3.8 million years ago. The authors note that their sample was a small fraction of all stars and that finding the true home was unlikely from the start⁠[[30]]. Scattering by the Galactic disc limits such traces to about 15 pc accuracy at 10 million years and 400 pc at 100 million, so a single home star cannot be named; the Carina and Columba moving groups are the most plausible source regions⁠[[31]]⁠[[32]]. Kinematic ages from its small excursion above the Galactic plane point the same way, to a young population of about a billion years or less⁠[[33]].

## The readings

An ordinary icy planetesimal outgassing water below detection. This was the discovery team's preferred reading⁠[[5]]. Its difficulty is that water sublimation driven by sunlight does not fit the outbound acceleration for a body of this size, and CO and CO2 were excluded by Spitzer⁠[[34]]⁠[[8]]. Since 2023 a Solar System analogue has been found: small near-Earth asteroids with no visible activity that show accelerations too large for the Yarkovsky effect, called dark comets, of which more than a dozen are now known⁠[[35]]⁠[[36]].

Molecular hydrogen ice. Seligman and Laughlin showed that hydrogen sublimation, which needs little energy, reproduces the acceleration without a visible coma, and that mass loss would sharpen the shape⁠[[34]]. Hoang and Loeb replied that starlight and collisions in molecular clouds would destroy such a body long before it reached the Sun⁠[[37]]. Levine and colleagues, including the reading's authors, found the required formation temperatures implausible⁠[[10]].

Nitrogen ice from an exo-Pluto. Jackson and Desch found that a fragment of nitrogen ice, like the surface of Pluto, matches the acceleration, the size, a high albedo and the absence of CO, CO2 and dust, giving a body of about 45 by 44 by 7.5 m at the time it was seen⁠[[38]]⁠[[39]]. Siraj and Loeb argued that the mass of exo-Plutos needed to make such fragments common enough would exceed the heavy elements available in stars⁠[[40]]; cosmic-ray erosion in transit worsens the budget⁠[[41]]; and cratering simulations do not produce nitrogen fragments that large⁠[[10]].

Hydrogen made by cosmic rays in water ice. Bergner and Seligman proposed that cosmic rays produced molecular hydrogen inside an ordinary water-rich body over its journey, and that warming near the Sun released it from annealing amorphous ice, giving the push with no dust⁠[[42]]. It needs no exotic ice and is grounded in laboratory work. Hoang and Loeb argued that cooling by the escaping hydrogen would cut the gas budget by a factor of five to nine⁠[[43]]; the model's code is public, so the dispute can be rerun⁠[[44]].

A fractal dust aggregate. If the body were extremely porous, sunlight alone could give the push. Moro-Martín found the density would need to be about 10^-5 g per cubic centimetre⁠[[45]]; Flekkøy and colleagues showed such a body could survive and could explain an apparent spin change, and proposed a formation route in the coma of a comet in another system⁠[[46]]⁠[[47]]. Optical and infrared observations of a future object could tell such a body from a solid one⁠[[48]].

A tidal fragment. Zhang and Lin showed that bodies passing close to their star can be torn into elongated shards with baked surfaces and buried ice, which could outgas without visible activity⁠[[49]]. This is a formation route compatible with several of the readings above rather than a separate composition.

An artificial lightsail. Bialy and Loeb showed that radiation pressure explains the acceleration if the body has a mass-to-area ratio of about 0.1 g per square centimetre, a sheet 0.3-0.9 mm thick, and suggested it might be an artificial sail⁠[[50]]. Loeb has argued since that every natural reading invokes an object of a kind never seen before, so an artificial origin must be considered⁠[[51]]. The ISSI team found no observation that requires it⁠[[11]]; the radio searches found nothing⁠[[24]]; and the light-curve and travel-time tests weigh against it⁠[[28]]⁠[[29]]⁠[[52]]. Elvis set out what the reading would predict and how it could be tested⁠[[53]].

### Published claims

**Published claims and their status**

| Year | Who | Claimed | Status | Reason |
|---|---|---|---|---|
| 2017 | Karen J. Meech and colleagues⁠[2] | 'Oumuamua's brightness varied by 2.5 magnitudes as it turned, so it is about ten times longer than it is wide. | Still possible | The spin data fit a long cigar or a flat disc equally well, and light-curve modelling slightly favours the disc⁠[17]⁠[18]. |
| 2017 | European Southern Observatory⁠[81] | 'Oumuamua is a dense, probably rocky or metal-rich body with no significant water or ice. | Disputed | Radiation pressure on a rocky body is far too weak to give the non-gravitational push measured later, so a dry rock leaves the acceleration unexplained⁠[5]. |
| 2018 | Marco Micheli and colleagues⁠[5] | 'Oumuamua's path shows a non-gravitational acceleration away from the Sun, most plausibly from comet-like outgassing. | Still possible | Spitzer ruled out carbon monoxide and dioxide at the needed rates but could not measure water⁠[8], and inactive dark comets with similar pushes have since been found⁠[36]. |
| 2018 | Alan Fitzsimmons and colleagues⁠[14] | 'Oumuamua's red, featureless spectrum fits an icy body under an organic-rich crust thick enough to keep the ice from sublimating. | Most likely | The default reading for an icy planetesimal, and the other interstellar objects were ordinary comets⁠[56], but no outgassing from 'Oumuamua was ever detected⁠[8]. |
| 2018 | J. Emilio Enriquez and colleagues (Breakthrough Listen)⁠[24] | Green Bank found no narrowband radio signal from 'Oumuamua across 1.1 to 11.6 GHz, which limits any transmitter on it to 0.08 W. | Accepted | Searches at the Allen Telescope Array and the Murchison Widefield Array also found nothing⁠[25]⁠[26]. |
| 2018 | Coryn Bailer-Jones and colleagues⁠[30] | Four stars in Gaia DR2, among them HIP 3757 and HD 292249, passed close enough to 'Oumuamua's traced-back path to be possible homes. | Disputed | The authors call the candidates weak, and galactic scattering limits traceback to about 15 pc after 10 million years⁠[31]. |
| 2018 | Shmuel Bialy and Abraham Loeb⁠[50] | Solar radiation pressure on a thin sheet could explain the acceleration, so 'Oumuamua might be an artificial lightsail. | Disputed | A tumbling sail would rarely give the observed light curve, its sideways motion does not match, and it could not have arrived from a nearby star in time⁠[28]⁠[29]. |
| 2019 | The 'Oumuamua ISSI Team⁠[11] | Every observed property of 'Oumuamua is consistent with a natural origin, by analogy with how planetary systems form and evolve. | Accepted | Natural explanations exist for each observation⁠[35], though none of the composition readings is confirmed⁠[10]. |
| 2019 | Amaya Moro-Martín⁠[45] | 'Oumuamua could be an icy fractal aggregate of very low density, light enough for sunlight alone to push it. | Still possible | Taken up as the dust-bunny model⁠[46], but forming and keeping an aggregate this large is not demonstrated⁠[10]. |
| 2019 | Sergey Mashchenko⁠[18] | Light-curve modelling favours a thin disc about six times wider than thick over a cigar, and needs a torque of the size outgassing gives. | Still possible | The spin data cannot separate the two shapes⁠[17], and later fits find no spin-up of the kind outgassing comets show⁠[19]. |
| 2020 | Darryl Seligman and Gregory Laughlin⁠[34] | 'Oumuamua was made mostly of molecular hydrogen ice, whose sublimation pushed it without a visible coma. | Disputed | Starlight and collisions would destroy such a body before it arrived⁠[37], and the authors' own later review found the required formation temperatures implausible⁠[10]. |
| 2020 | Yun Zhang and Douglas N. C. Lin⁠[49] | 'Oumuamua is a shard torn from a larger body by its star's tides during a close pass, then ejected. | Still possible | Simulations give the right elongation and surface⁠[49], and such shards are a few per cent of what a giant-planet system ejects⁠[82], but nothing ties 'Oumuamua to the process. |
| 2021 | Alan P. Jackson and Steven J. Desch⁠[38] | 'Oumuamua is a fragment of nitrogen ice chipped from the surface of a Pluto-like planet in another system. | Disputed | It fits the acceleration, size and albedo, but the required mass of exo-Plutos and the size of the fragments are disputed⁠[40]⁠[10]. |
| 2021 | Cheng-Han Hsieh, Gregory Laughlin and Hector Arce⁠[32] | 'Oumuamua is about 35 million years old and came from a young stellar group such as Carina or Columba. | Still possible | The kinematics fit, but source regions can be named only statistically⁠[31]. |
| 2022 | Abraham Loeb⁠[51] | Every natural reading of 'Oumuamua needs a kind of object never seen before, so an artificial origin should be considered. | Disputed | The light curve, motion and travel time weigh against a sail⁠[28]⁠[29], and inactive natural bodies with similar pushes are now known⁠[35]. |
| 2023 | Jennifer B. Bergner and Darryl Z. Seligman⁠[42] | Hydrogen made by cosmic rays inside ordinary water ice, freed as the ice warmed near the Sun, pushed 'Oumuamua without any exotic ice. | Still possible | Backed by laboratory work, but cooling by the escaping gas may cut the hydrogen budget five to nine times⁠[43]; the code is public for testing⁠[44]. |
| 2023 | Darryl Z. Seligman and colleagues⁠[35] | Some small near-Earth objects with no visible activity show non-gravitational accelerations too large for the Yarkovsky effect: dark comets. | Accepted | The sample has grown to more than a dozen, in two populations⁠[36]. |
| 2023 | Federico Spada⁠[23] | An independent fit of the astrometry confirms 'Oumuamua's non-gravitational acceleration and prefers a purely radial push. | Accepted | It agrees with the discovery team's tests, which excluded a photocentre offset and a binary⁠[5]. |

## The other interstellar objects

2I/Borisov, found on 30 August 2019, was an active comet in every respect: a coma, a tail, a nucleus of a few hundred metres to a kilometre, and an unusually high ratio of carbon monoxide to water⁠[[12]]⁠[[54]]⁠[[55]].

3I/ATLAS was found by the ATLAS survey on 1 July 2025, on a steeply hyperbolic orbit (eccentricity about 6.1, excess speed 58 km/s), already showing a compact coma⁠[[13]]. JWST found a coma dominated by carbon dioxide, with a CO2-to-water ratio among the highest seen in any comet, and later the first methane detected on an interstellar object⁠[[56]]⁠[[57]]. Nickel vapour was found far from the Sun, as it has been in Solar System comets and in 2I⁠[[58]]⁠[[59]]⁠[[60]]. It passed perihelion on 29 October 2025 at 1.36 au⁠[[61]]. Early Hubble images limited the nucleus radius to between 0.22 and 2.8 km⁠[[62]]. Images after perihelion give about 1.3 km, which the authors find consistent with the size implied by the non-gravitational acceleration⁠[[63]]. That acceleration, measured from nearly 7,800 positions, is required by the data but its systematic errors exceed the formal ones⁠[[61]]. Mass-balance estimates from it give a diameter of about 0.8-1.05 km⁠[[64]] and, from Loeb's group, a radius of 0.42-1.15 km depending on the gas that drives it⁠[[65]], both with large uncertainties. Two radio searches found no signals⁠[[66]]⁠[[67]]. NASA treats it as a comet and lists more than a dozen of its spacecraft that observed it⁠[[68]].

Loeb and colleagues raised the possibility that 3I is alien technology, in a paper they described as largely a pedagogical exercise⁠[[69]], argued from early astrometry for a nucleus above 5 km⁠[[70]], and placed both 1I and 3I at level 4 of a ten-point scale of anomaly⁠[[71]]. Other astronomers answered the claims point by point, notably Jason Wright, who argued that the reported features are known in comets and that the size claim did not survive the Hubble measurement⁠[[72]]. A Galactic population model applied a week after discovery found that 3I's speed implies an age above 7.6 billion years and a high water fraction, and makes a shared origin with 1I or 2I very unlikely⁠[[73]].

## What would settle it

'Oumuamua itself is beyond reach of telescopes. It can be reached only by a spacecraft, and every study of a chase finds a flight of decades: the most developed Project Lyra trajectory launches in 2028 and arrives about 26 years later, passing the object at about 18 km/s⁠[[74]]⁠[[75]]. A refuelled Starship or an expendable Falcon Heavy could launch it⁠[[76]]. No agency has adopted it.

The practical route is another object like it. The Vera C. Rubin Observatory began its ten-year survey in mid-2026; one estimate puts the number of 'Oumuamua-like objects it will find in ten years at between less than one and about 84, a measure of how poorly the population is known⁠[[77]]⁠[[78]]. For such an object, the tests are known. Infrared photometry at several wavelengths would give its size and albedo and distinguish a porous aggregate from a solid⁠[[48]]. Spectra of the escaping gas would identify it: molecular hydrogen, nitrogen or water⁠[[10]]. A well-sampled light curve would fix its shape and spin, and astrometry would measure the push again. ESA's Comet Interceptor, due to launch in late 2028 or early 2029 and wait at the Sun-Earth L2 point, could fly past one if it is reachable⁠[[79]]⁠[[80]]. A close image would settle the shape, and a spectrum of the surface its composition.

For 'Oumuamua's own data, the open questions are computational: a joint fit of the light curve and the astrometry with one physical model of outgassing and torque, which no published model yet achieves⁠[[19]].

## Questions

1 of 6 questions are answered.

**Key questions** [All 6](https://mysteriesdept.com/questions/key-questions?mystery=oumuamua)

 **0**

[Does any observation of 'Oumuamua require a non-natural explanation?](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKC0CJ74DR/does-any-observation-of-oumuamua-require-a-non-natural)

0 of 0 sub-questions answered·0

Answered: No. Every property has at least one natural explanation consistent with the data, though none is confirmed.



 **0**

[What pushed 'Oumuamua away from the Sun?](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKBZDA67JF/what-pushed-oumuamua-away-from-the-sun)

0 of 0 sub-questions answered·0

Open: 8 answers, none ahead



 **0**

[What was 'Oumuamua made of?](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKBZN458NQ/what-was-oumuamua-made-of)

0 of 2 sub-questions answered·0

Most likely: an ordinary comet-like planetesimal of water ice and dust under an insulating organic crust (with or without…



## Evidence 68 findings

[What pushed 'Oumuamua away from the Sun?](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKBZDA67JF/what-pushed-oumuamua-away-from-the-sun)26 findings

[Outgassing of water or another undetected ordinary volatile from an icy body, below the limits of every…](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKC0W61KZV/outgassing-of-water-or-another-undetected-ordinary-volatile)Still possible

+[Outgassing was the only mechanism the discovery team found physically viable, if the body had comet-like thermal properties.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC1407J6K/outgassing-was-the-only-mechanism-the-discovery-team-found)Supported

+[Small near-Earth asteroids with no visible activity show non-gravitational accelerations too large for the Yarkovsky effect; more than a dozen dark comets are now known.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC1VE1VM1/small-near-earth-asteroids-with-no-visible-activity-show-non)Supported

+[Light-curve models need a torque of the size outgassing produces in comets.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC2385WCD/light-curve-models-need-a-torque-of-the-size-outgassing)Suggestive

−[Spitzer limits CO and CO2 to about ten thousand times below what the outgassing model needed; water was not constrained.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC1BT03JA/spitzer-limits-co-and-co2-to-about-ten-thousand-times-below)Established

−[Water sublimation driven by sunlight does not fit the outbound acceleration for a body of this size.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC1KM4693/water-sublimation-driven-by-sunlight-does-not-fit-the)Supported

−[The light curve shows no secular change in spin, which is in tension with how outgassing comets spin up.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC2B22PP3/the-light-curve-shows-no-secular-change-in-spin-which-is-in)Suggestive

[Sublimation of molecular hydrogen ice from a body made largely of it.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKC2JW01ZS/sublimation-of-molecular-hydrogen-ice-from-a-body-made)Disputed

+[Hydrogen sublimation reproduces the acceleration without a visible coma and sharpens the axis ratio over time.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC2TP7Z1X/hydrogen-sublimation-reproduces-the-acceleration-without-a)Supported

−[Starlight would sublimate such a body in under ten million years, and collisional heating would destroy it in its birth cloud.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC32G0KQN/starlight-would-sublimate-such-a-body-in-under-ten-million)Supported

−[The required formation temperatures are implausibly cold, by the authors' own later review.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC3AA5ZEC/the-required-formation-temperatures-are-implausibly-cold-by)Supported

[Sublimation of nitrogen ice from a fragment of an exo-Pluto's surface.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKC3J40JAH/sublimation-of-nitrogen-ice-from-a-fragment-of-an-exo-plutos)Disputed

+[Nitrogen ice matches the acceleration, the size, the albedo and the absence of CO, CO2 and dust.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC3SY5W9G/nitrogen-ice-matches-the-acceleration-the-size-the-albedo)Supported

+[Dynamical instabilities could eject about 10^14 fragments per system, half nitrogen ice.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC41R1BQ4/dynamical-instabilities-could-eject-about-10-14-fragments)Suggestive

−[The exo-Pluto mass required exceeds the heavy elements locked in stars, at 95 per cent confidence.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC49J6R7V/the-exo-pluto-mass-required-exceeds-the-heavy-elements)Suggestive

−[Cosmic-ray erosion means the fragment must have started at least 0.5 km across, worsening the budget.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC4HC3GAX/cosmic-ray-erosion-means-the-fragment-must-have-started-at)Suggestive

−[Cratering simulations do not produce nitrogen fragments as large as 'Oumuamua.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC4S67V87/cratering-simulations-do-not-produce-nitrogen-fragments-as)Suggestive

[Release of molecular hydrogen made by cosmic rays inside an ordinary water-ice body, freed as the ice warmed…](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKC5106PB2/release-of-molecular-hydrogen-made-by-cosmic-rays-inside-an)Still possible

+[Laboratory work shows hydrogen is produced in irradiated water ice and released over a range of temperatures; the model explains the push without exotic ice.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC58T2VP1/laboratory-work-shows-hydrogen-is-produced-in-irradiated)Supported

+[The model code and data are public, so the cooling objection can be tested directly.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC5RE13DK/the-model-code-and-data-are-public-so-the-cooling-objection)Speculative

−[Cooling by the escaping hydrogen would cut the volume of warm ice and the gas budget by a factor of five to nine.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC5GM545A/cooling-by-the-escaping-hydrogen-would-cut-the-volume-of)Suggestive

[Solar radiation pressure on a natural body with a very low mass-to-area ratio, such as a fractal dust…](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKC6087NHD/solar-radiation-pressure-on-a-natural-body-with-a-very-low)Still possible

+[A mass-fractal aggregate of the required density could arise from icy dust growth beyond a disc's snow line.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC68238C5/a-mass-fractal-aggregate-of-the-required-density-could-arise)Speculative

+[Such a body could survive rotation and tides and explain an apparent spin-period change through the YORP effect.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC6FW1R0H/such-a-body-could-survive-rotation-and-tides-and-explain-an)Speculative

−[Ultra-porous aggregates have their own formation and survival difficulties.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC6QP6E6Q/ultra-porous-aggregates-have-their-own-formation-and)Suggestive

[Solar radiation pressure on an artificial lightsail.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKC6ZG5G17/solar-radiation-pressure-on-an-artificial-lightsail)Disputed

+[Radiation pressure on a sheet of mass-to-area ratio about 0.1 g per square centimetre reproduces the push.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC77A20BG/radiation-pressure-on-a-sheet-of-mass-to-area-ratio-about-0)Supported

−[A tumbling sail would produce the observed light-curve amplitude with probability below 1.5 per cent and its sideways displacement differs from the observed motion by about 1.5 sigma.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC7F41EMY/a-tumbling-sail-would-produce-the-observed-light-curve)Suggestive

−[No narrowband radio emission was found from 72 MHz to 11.6 GHz, to 0.08 W at Green Bank.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC7PY7XYY/no-narrowband-radio-emission-was-found-from-72-mhz-to-11-6)Established

−[Such a sail could not have been accelerated fast enough to arrive from a nearby star in less than about half a billion years.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC7YR1WYV/such-a-sail-could-not-have-been-accelerated-fast-enough-to)Suggestive

[The acceleration is an artefact of the astrometry or the orbit fit, not a real force.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKC86J73W1/the-acceleration-is-an-artefact-of-the-astrometry-or-the)Disputed

−[The discovery team tested and excluded a photocentre offset and a binary.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC8EC6VY9/the-discovery-team-tested-and-excluded-a-photocentre-offset)Established

−[An independent re-fit confirms the acceleration and finds it radial.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC8P63JG6/an-independent-re-fit-confirms-the-acceleration-and-finds-it)Established

[What was 'Oumuamua made of?](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKBZN458NQ/what-was-oumuamua-made-of)14 findings

[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)Most likely

+[The red featureless spectrum fits an organic-rich mantle half a metre thick that could have kept interior ice from sublimating.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC9DM58PB/the-red-featureless-spectrum-fits-an-organic-rich-mantle)Supported

+[The radiolytic-hydrogen model makes an ordinary water-ice body fit the acceleration.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC9NE57F6/the-radiolytic-hydrogen-model-makes-an-ordinary-water-ice)Suggestive

+[2I/Borisov and 3I/ATLAS were both ordinary comets in composition, if unusually rich in CO or CO2.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKC9X84DNV/2i-borisov-and-3i-atlas-were-both-ordinary-comets-in)Supported

−[No water outgassing was ever detected.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCA527WAC/no-water-outgassing-was-ever-detected)Established

[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)Disputed

+[Kinematics suggest an age of about 35 million years and a link to a young moving group.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCAMP21FT/kinematics-suggest-an-age-of-about-35-million-years-and-a)Suggestive

−[Starlight and collisions would destroy such a body before it could arrive.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCAWG6K3Z/starlight-and-collisions-would-destroy-such-a-body-before-it)Supported

[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)Disputed

+[Satisfies the acceleration, size, albedo and the CO/CO2/dust limits at once.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCBC458NZ/satisfies-the-acceleration-size-albedo-and-the-co-co2-dust)Supported

−[The mass budget and fragment-size arguments weigh against it.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCBKY6D5K/the-mass-budget-and-fragment-size-arguments-weigh-against-it)Suggestive

[An ultra-porous fractal aggregate of icy dust.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCBVR4ARH/an-ultra-porous-fractal-aggregate-of-icy-dust)Still possible

+[Explains the push by radiation pressure and an apparent spin change by YORP.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCC3J488A/explains-the-push-by-radiation-pressure-and-an-apparent-spin)Speculative

−[Formation and survival of an aggregate this size are not demonstrated.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCCBC5W0Y/formation-and-survival-of-an-aggregate-this-size-are-not)Suggestive

[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)Disputed

+[The discovery-era interpretation was a dense, possibly rocky or metal-rich body lacking water or ice.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCCV03T2S/the-discovery-era-interpretation-was-a-dense-possibly-rocky)Speculative

−[Radiation pressure on an ordinary rocky body is far too weak to give the measured acceleration.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCD2T4S3Y/radiation-pressure-on-an-ordinary-rocky-body-is-far-too-weak)Established

[Manufactured material, a thin artificial sheet.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCDAM421B/manufactured-material-a-thin-artificial-sheet)Disputed

+[A thin sheet explains the push by radiation pressure alone.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCDJE453H/a-thin-sheet-explains-the-push-by-radiation-pressure-alone)Suggestive

−[The ISSI team found every observation consistent with a natural body.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCDT86RK1/the-issi-team-found-every-observation-consistent-with-a)Supported

[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)6 findings

[A long, thin cigar (axis ratio about 1:8 or more) tumbling near its lowest rotational energy state.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCE9W2G6M/a-long-thin-cigar-axis-ratio-about-1-8-or-more-tumbling-near)Still possible

+[A 2.5-magnitude range implies a body about ten times longer than wide.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCEHP55TH/a-2-5-magnitude-range-implies-a-body-about-ten-times-longer)Supported

+[The body tumbles, with an axis ratio of at least 5:1.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCESG32C9/the-body-tumbles-with-an-axis-ratio-of-at-least-5-1)Established

−[A cigar of about 1:8 fits but is less probable than a disc (16 against 91 per cent) from the depth of the minima.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCF1A2JMK/a-cigar-of-about-1-8-fits-but-is-less-probable-than-a-disc)Suggestive

[A thin flattened disc (about 1:6) tumbling near its highest rotational energy state.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCF9453KG/a-thin-flattened-disc-about-1-6-tumbling-near-its-highest)Still possible

+[The spin data fit either a cigar or a very flat spheroid and cannot separate them.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCFGY7MPV/the-spin-data-fit-either-a-cigar-or-a-very-flat-spheroid-and)Established

+[Physical light-curve modelling favours the disc.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCFRR0N78/physical-light-curve-modelling-favours-the-disc)Suggestive

+[Sublimation of a volatile ice drives the axis ratio to extreme values.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCG0J1CWD/sublimation-of-a-volatile-ice-drives-the-axis-ratio-to)Speculative

[Where did 'Oumuamua come from?](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKC04R56X5/where-did-oumuamua-come-from)8 findings

[Ejected from another star's planetary system during planet formation, like most interstellar objects should…](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCGG662S6/ejected-from-another-stars-planetary-system-during-planet)Most likely

+[The ISSI review explains every property by analogy with planetary-system evolution.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCGR04QRZ/the-issi-review-explains-every-property-by-analogy-with)Supported

−[The implied number of such bodies is in tension with ejection from protostellar discs in the candidate source region.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCGZT4M0Q/the-implied-number-of-such-bodies-is-in-tension-with)Suggestive

[Born in a young stellar association such as the Carina or Columba moving groups, tens of millions of years…](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCH7M4GPK/born-in-a-young-stellar-association-such-as-the-carina-or)Still possible

+[The orbit is consistent with Carina-group membership and a dynamical age of about 35 million years.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCHFE30HX/the-orbit-is-consistent-with-carina-group-membership-and-a)Suggestive

+[Carina and Columba are the most plausible source regions, though only statistically.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCHQ861CF/carina-and-columba-are-the-most-plausible-source-regions)Suggestive

[A shard torn from a larger body by tides during a close pass by its star, then ejected.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCHZ24RYG/a-shard-torn-from-a-larger-body-by-tides-during-a-close-pass)Still possible

+[Simulations produce axis ratios below 1:10 with baked surfaces and buried water.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCJ6W4VJS/simulations-produce-axis-ratios-below-1-10-with-baked)Suggestive

+[About 3 per cent of objects ejected from a single giant-planet system would be extremely elongated.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCJEP1SWJ/about-3-per-cent-of-objects-ejected-from-a-single-giant)Suggestive

[A specific nearby star is its home, such as HIP 3757 or HD 292249.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCJPG2VYY/a-specific-nearby-star-is-its-home-such-as-hip-3757-or-hd)Disputed

+[Four candidate encounters were found, the closest at 0.60 pc with HIP 3757 about a million years ago.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCJYA1PVB/four-candidate-encounters-were-found-the-closest-at-0-60-pc)Speculative

−[Galactic scattering limits traceback accuracy to about 15 pc at 10 million years.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCK640HNX/galactic-scattering-limits-traceback-accuracy-to-about-15-pc)Supported

[Does any observation of 'Oumuamua require a non-natural explanation?](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKC0CJ74DR/does-any-observation-of-oumuamua-require-a-non-natural)9 findings

[No. Every property has at least one natural explanation consistent with the data, though none is confirmed.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCKNR630W/no-every-property-has-at-least-one-natural-explanation)Most likely

+[The ISSI team found every observation consistent with a purely natural origin.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCKXJ4W3Q/the-issi-team-found-every-observation-consistent-with-a)Supported

+[Radio searches at Green Bank, the Allen Telescope Array and the MWA found no signals.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCM5C3J4K/radio-searches-at-green-bank-the-allen-telescope-array-and)Established

+[Dark comets show that accelerations without visible activity occur naturally.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCMD66SQC/dark-comets-show-that-accelerations-without-visible-activity)Supported

−[Each natural composition reading has quantitative shortcomings, and none is accepted.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCMN006B9/each-natural-composition-reading-has-quantitative)Supported

[Yes, or at least the anomalies together favour an artificial object, such as a lightsail.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCMWT3KCY/yes-or-at-least-the-anomalies-together-favour-an-artificial)Disputed

+[All natural readings invoke an object of a type never seen before.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCN4M5XQ0/all-natural-readings-invoke-an-object-of-a-type-never-seen)Speculative

+[Radiation pressure on a thin sheet fits the push.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCNCE6SWQ/radiation-pressure-on-a-thin-sheet-fits-the-push)Suggestive

−[The light curve and lateral motion are unlikely for a sail.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCNM832AG/the-light-curve-and-lateral-motion-are-unlikely-for-a-sail)Suggestive

−[A sail would need about half a billion years to arrive from its likeliest origin.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCNW251J9/a-sail-would-need-about-half-a-billion-years-to-arrive-from)Suggestive

−[The same group's claims for 3I/ATLAS, such as a nucleus above 5 km, were not borne out by Hubble.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCP3W25F8/the-same-groups-claims-for-3i-atlas-such-as-a-nucleus-above)Suggestive

[Is 'Oumuamua typical of interstellar objects, or a rare kind?](https://mysteriesdept.com/mysteries/oumuamua/questions/QST0CSKC0MC0R58/is-oumuamua-typical-of-interstellar-objects-or-a-rare-kind)5 findings

[Asteroid-like, inactive interstellar objects are common, and 'Oumuamua is one of many.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCPKG11DT/asteroid-like-inactive-interstellar-objects-are-common-and)Still possible

+[Size-distribution modelling with 1I and 3I suggests asteroid-like bodies are produced more often than comets.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCPVA74AH/size-distribution-modelling-with-1i-and-3i-suggests-asteroid)Speculative

+[The detection implies a number density of about 0.1 per cubic au.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCQ346G4M/the-detection-implies-a-number-density-of-about-0-1-per)Supported

['Oumuamua was an unusual member of a population dominated by comets like 2I and 3I.](https://mysteriesdept.com/mysteries/oumuamua/answers/ANS0CSKCQAY6VKE/oumuamua-was-an-unusual-member-of-a-population-dominated-by)Still possible

+[2I/Borisov was an ordinary active comet.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCQJR31NX/2i-borisov-was-an-ordinary-active-comet)Established

+[3I/ATLAS was an active comet rich in CO2.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCQTJ5RCB/3i-atlas-was-an-active-comet-rich-in-co2)Established

−[3I's age and composition make a common origin with 1I or 2I very unlikely, so three objects sample different populations.](https://mysteriesdept.com/mysteries/oumuamua/evidence/EVD0CSKCR2C417Q/3is-age-and-composition-make-a-common-origin-with-1i-or-2i)Suggestive

## Artifacts

The films, photos, papers and objects this mystery rests on, each with its own key and its distance from the original.

**Artifacts** [See all 11](https://mysteriesdept.com/mysteries/oumuamua/artifacts)

Photo1 step from object

[1I/'Oumuamua](https://mysteriesdept.com/mysteries/oumuamua/artifacts/ART0CSKCV7Y2C6C/1i-oumuamua)

ESO/K. Meech et al · CC BY 4.0

Document1 step from object

[MPEC 2017-V17, the circular that designated 1I and named 'Oumuamua](https://mysteriesdept.com/mysteries/oumuamua/artifacts/ART0CSKCWPT17G3/mpec-2017-v17-the-circular-that-designated-1i-and-named)

Minor Planet Center · publisher

 [See all 11 artifacts](https://mysteriesdept.com/mysteries/oumuamua/artifacts)

## See also

 [

**Tabby's star (KIC 8462852)** A star in Cygnus that dimmed by up to 20 per cent at irregular times in Kepler data.

](https://mysteriesdept.com/mysteries/tabbys-star) [

**Shroud of Turin** A linen cloth with the image of a crucified man, radiocarbon-dated to 1260 to 1390.

](https://mysteriesdept.com/mysteries/shroud-of-turin) [

**Homo floresiensis, the origin of the Flores "hobbits"** A metre-tall hominin that lived on Flores, Indonesia, until about 50,000 years ago.

](https://mysteriesdept.com/mysteries/homo-floresiensis) [

**Phosphine in the clouds of Venus** A 2020 report of phosphine gas in the clouds of Venus, not independently confirmed.

](https://mysteriesdept.com/mysteries/venus-phosphine)

## References

1. 1.[NASA Jet Propulsion Laboratory 2017. Small Asteroid or Comet 'Visits' from Beyond the Solar System. JPL News.](https://mysteriesdept.com/sources/SRC0CSKBJQ26Y2V/small-asteroid-or-comet-visits-from-beyond-the-solar-system)cited 5 times here**SRC** 0CSKBJQ26Y2V
1. 2.[Meech, K., Weryk, R., Micheli, M. et al. 2017. A brief visit from a red and extremely elongated interstellar asteroid. Nature.](https://mysteriesdept.com/sources/SRC0CSKB1W02ZW4/a-brief-visit-from-a-red-and-extremely-elongated)[doi](https://doi.org/10.1038/nature25020)cited 7 times here**SRC** 0CSKB1W02ZW4
1. 3.[Jet Propulsion Laboratory Solar System Dynamics 2018. JPL Small-Body Database: 'Oumuamua (A/2017 U1), orbit solution 16. NASA JPL Small-Body Database.](https://mysteriesdept.com/sources/SRC0CSKBHG07RNH/jpl-small-body-database-oumuamua-a-2017-u1-orbit-solution-16)cited 3 times here**SRC** 0CSKBHG07RNH
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Last edited 27 Oct 2026