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Cited by 76Astro and Planetary ScienceStellar, planetary, and galactic studiesAstrophysics and Star Formation Studies

Implications for Planetary System Formation from Interstellar Object 1I/2017 U1 (‘Oumuamua)

Open access
Trilling, David E., Robinson, Tyler, Roegge, Alissa, Chandler, Colin Orion, Smith, Nathan, Loeffler, Mark, Trujillo, Chad, Navarro-Meza, Samuel +1 more·2017·The Astrophysical Journal Letters
DOI 10.3847/2041-8213/aa9989
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Abstract

The recently discovered minor body 1I/2017 U1 (‘Oumuamua) is the first known object in our solar system that is not bound by the Sun’s gravity. Its hyperbolic orbit (eccentricity greater than unity) strongly suggests that it originated outside our solar system; its red color is consistent with substantial space weathering experienced over a long interstellar journey. We carry out a simple calculation of the probability of detecting such an object. We find that the observed detection rate of 1I-like objects can be satisfied if the average mass of ejected material from nearby stars during the process of planetary formation is ∼20 Earth masses, similar to the expected value for our solar system. The current detection rate of such interstellar interlopers is estimated to be 0.2 yr−1, and the expected number of detections over the past few years is almost exactly one. When the Large Synoptic Survey Telescope begins its wide, fast, deep all-sky survey, the detection rate will increase to 1 yr−1. Those expected detections will provide further constraints on nearby planetary system formation through a better estimate of the number and properties of interstellar objects.

AI snapshot

Written from the paper’s full text.

TL;DR

The paper uses the discovery of interstellar object 1I/2017 U1 (‘Oumuamua) to estimate the prevalence of ejected planetary-system material and finds that the observed detection rate is consistent with nearby stars ejecting about 20 Earth masses during planet formation. It predicts that LSST will increase the detection rate of such interstellar objects from about 0.2 yr⁻¹ to about 1 yr⁻¹.

Key findings

  • 1I is the first known solar-system object on an unbound orbit, with eccentricity e ≈ 1.2 and inclination i ≈ 123°; its red 520–950 nm spectrum with no absorption features is consistent with an interstellar origin and substantial space weathering.
  • A simple calculation shows the observed detection rate of 1I-like objects can be satisfied if the average mass ejected from nearby stars during planetary formation is ∼20 Earth masses (10²⁶ kg), similar to estimates for our solar system (1–5 M⊕ from the asteroid belt and 12–30 M⊕ from the Kuiper Belt).
  • The current detection rate is estimated at 0.2 yr⁻¹, with the expected number over the past few years almost exactly one; the inferred number density of ejectoids is around 0.1 au⁻³ (∼10¹⁵ pc⁻³), and the plausible ejection-mass range is roughly 1–100 M⊕.
  • LSST is expected to detect interstellar objects at around 1 yr⁻¹, because its survey will be about three magnitudes deeper than Pan-STARRS’ typical V ∼ 21.5 limit, corresponding to a factor of three smaller size and roughly a factor of five more objects.

Methods

  • The authors perform an analytic probability calculation: they assume planet formation ejects a mass m of “ejectoids” with characteristic radius r_e and density ρ_e, and that surveys sweep a cylindrical volume V = π r_obs² Δv_e Δt; the number of detections is N = n_e V, and setting N = 1 constrains the characteristic ejected mass.
  • Adopted parameters include 357 stars within 10 pc, average stellar spacing R = 1.4 pc, average discovery distance r_obs = 0.3 au, Sun’s relative velocity Δv_e = 25 km s⁻¹, survey interval Δt = 5 years, 1I radius r_e ≈ 100 m from absolute magnitude 22.1, and density 2000 kg m⁻³.
  • The calculation uses 1I’s observed properties: hyperbolic orbit, high inclination, red 520–950 nm reflectance spectrum with no absorption features, and no signs of activity.

Limitations

  • Stated: the radius and density of 1I are unknown, though the adopted values are unlikely to be in error by more than a factor of two; geometry arguments are likely within a factor of two; the time interval is approximately correct; gravitational focusing is ignored; the largest uncertainty is the unknown statistical likelihood of detecting this ejectoid and the extrapolation from a single object.
  • Stated: the true ejected population must follow a size distribution and will not consist only of 100 m objects; small objects are presumably more numerous, but larger objects are preferentially detected; the calculation assumes a steady-state population ejected from all planetary systems, whereas ejectoids could instead be produced in a single early pulse; not every system need eject mass, and if only 50% of nearby stars have gas giants, the average mass ejected by those systems must be about twice the nominal value.
  • Evident from the text: the conclusions rest on one detected object and order-of-magnitude assumptions; there is no direct way to constrain 1I’s density, and the lack of observed activity leaves the adopted asteroidal-versus-cometary assumption uncertain.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.3847/2041-8213/aa9989

Cites

36 of 36 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 18 cited sources checked · 0 supported · 0 flagged

  • Premisecitation

    1I/2017 U1 is the first known solar system body that is not gravitationally bound to the Sun.

    “The recently discovered minor body 1I/2017 U1 ('Oumuamua) is the first known object in our solar system that is not bound by the Sun's gravity.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Williams 2017

      Not checked in the free run.

  • Not yet classified. 19

  • Not yet classified.

    Finding

    The number density of ejectoids is around 0.1 per au^3, or around 10^15 per pc^3.

    “The number density of ejectoids is, from Equation (3), around 0.1/au 3 , which is around 10 15 /pc 3 .”
    Quote in the paperNot yet classified
    • The authors state this as an assumption: The population of interstellar ejectoids has zero mean velocity because source planetary systems and ejection trajectories are isotropic.
    • The authors state this as an assumption: 1I is an interstellar interloper that originated in a different planetary system.
    • The authors state this as an assumption: 1I is representative of the population of ejectoids.
    • The authors state this as an assumption: A steady-state population of 1I-like objects is ejected from all planetary systems.
    • The authors state this as an assumption: The formation of a typical planetary system results in a mass m of ejectoids with typical size r_e and density ρ_e.

  • Not yet classified.

    Finding

    The expected number of detections of 1I-like objects over the past few years is almost exactly one.

    “the expected number of detections over the past few years is almost exactly one”
    • Also stated in: § 2. Ejectoid Encounters and Ejected Mass Constraints
      “We find that N is very close to unity-exactly matching the observations.”
    Quote in the paperNot yet classified
    • The authors state this as an assumption: The population of interstellar ejectoids has zero mean velocity because source planetary systems and ejection trajectories are isotropic.
    • The authors state this as an assumption: 1I is an interstellar interloper that originated in a different planetary system.
    • The authors state this as an assumption: 1I is representative of the population of ejectoids.
    • The authors state this as an assumption: A steady-state population of 1I-like objects is ejected from all planetary systems.
    • The authors state this as an assumption: The formation of a typical planetary system results in a mass m of ejectoids with typical size r_e and density ρ_e.

  • Not yet classified.

    Premise

    Systems without gas giants rarely eject planetesimals because escape velocity cannot readily be achieved by planetesimals.

    “systems without gas giants rarely eject planetesimals because in that case escape velocity cannot readily be achieved by planetesimals”
    Quote in the paperNot yet classified

  • Not yet classified.

    Interpretation

    The derived ejection mass is in remarkably good agreement with values for mass loss during formation of the solar system.

    “This is in remarkably good agreement with values derived for mass loss during the formation of our solar system.”
    Quote in the paperNot yet classified

  • Not yet classified.

    Interpretation

    Expected LSST detections will provide further constraints on nearby planetary system formation through a better estimate of the number and properties of interstellar objects.

    “Those expected detections will provide further constraints on nearby planetary system formation through a better estimate of the number and properties of interstellar objects.”
    • Also stated in: § 4. Implications
      “The LSST discovery rate of ejectoids will help us constrain the frequency and properties of planetary system formation in our nearby galaxy.”
    Quote in the paperNot yet classified
    • The authors state this as an assumption: 1I is an interstellar interloper that originated in a different planetary system.

  • Not yet classified.

    Interpretation

    Given cosmic rays and ionizing radiation, 1I's red spectral slope is entirely consistent with formation elsewhere and a long journey to the solar system.

    “Given the presence of cosmic rays in the interstellar medium and other forms of ionizing radiation that would have been present in 1I's natal stellar environment, 1I's red spectral slope is entirely consistent with formation elsewhere and a long journey to our solar system.”
    Quote in the paperNot yet classified
    • The authors state this as an assumption: 1I is an interstellar interloper that originated in a different planetary system.

  • Not yet classified.

    Premise

    Systems with gas giants on stable orbits can eject planetesimals on longer timescales.

    “and while systems with gas giants on stable orbits can eject planetesimals on longer timescales (Raymond et al. 2011;Barclay et al. 2017)”
    Quote in the paperNot yet classified0 of 2 sources checked
    • cites Raymond et al. 2011 source

      Not checked in the free run.

    • cites Barclay et al. 2017 source

      Not checked in the free run.

  • Not yet classified.

    Premise

    The only measured size distribution in this size range in the solar system is for the near-Earth object population; a factor of three in size corresponds roughly to a factor of five in number of objects.

    “The only measured size distribution in this size range in our solar system is for the near-Earth object population; a factor of three in size corresponds roughly to a factor of five in number of objects (Trilling et al. 2017).”
    Quote in the paperNot yet classified0 of 1 sources checked
    • cites Trilling et al. 2017 source

      Not checked in the free run.

  • Not yet classified.

    Premise

    Planet-planet scattering among gas giant planets likely produces a pulse of ejected planetesimals.

    “while planet-planet scattering among gas giant planets is likely to produce a pulse of ejected planetesimals (Raymond et al. 2011;Marzari 2014)”
    Quote in the paperNot yet classified0 of 2 sources checked
    • cites Raymond et al. 2011 source

      Not checked in the free run.

    • cites Marzari 2014 source

      Not checked in the free run.

  • Not yet classified.

    Premise

    A red spectral slope over 520-950 nm is not unexpected and is characteristic of many primitive objects in the solar system.

    “However, we note that a red spectral slope over this range is not unexpected and is characteristic of many primitive objects in our solar system (Cruikshank et al. 1998;Jewitt & Luu 1998;Bus & Binzel 2002;Sheppard 2010;Carry et al. 2016).”
    Quote in the paperNot yet classified0 of 3 sources checked
    • cites Cruikshank et al. 1998 source

      Not checked in the free run.

    • cites Jewitt & Luu 1998

      Not checked in the free run.

    • cites Bus & Binzel 2002

      Not checked in the free run.

  • Not yet classified.

    Interpretation

    1I's red color is consistent with substantial space weathering over a long interstellar journey.

    “its red color is consistent with substantial space weathering experienced over a long interstellar journey”
    • Also stated in: § 4. Implications
      “1I's red spectral slope is entirely consistent with formation elsewhere and a long journey to our solar system.”
    Quote in the paperNot yet classified0 of 2 sources checked
    • cites Masiero 2017

      Not checked in the free run.

    • cites Ye et al. 2017

      Not checked in the free run.

    • The authors state this as an assumption: 1I is an interstellar interloper that originated in a different planetary system.

  • Not yet classified.

    Interpretation

    Planet formation is a near-universal process.

    “which implies that planet formation is a near-universal process”
    Quote in the paperNot yet classified

  • Not yet classified.

    Interpretation

    1I's trajectory makes it very unlikely that it experienced a gravitational encounter with proposed as-yet unknown planets in the outermost solar system.

    “1I's trajectory makes it very unlikely that it experienced a gravitational encounter with any of the proposed as-yet unknown planets in the outermost part of our solar system (Trujillo & Sheppard 2014;Brown & Batygin 2016;Volk & Malhotra 2017).”
    Quote in the paperNot yet classified0 of 3 sources checked
    • cites Trujillo & Sheppard 2014 source

      Not checked in the free run.

    • cites Brown & Batygin 2016 source

      Not checked in the free run.

    • cites Volk & Malhotra 2017

      Not checked in the free run.

    • The authors state this as an assumption: 1I is an interstellar interloper that originated in a different planetary system.

  • Not yet classified.

    Interpretation

    The surface of 1I may have different properties than its bulk material.

    “This implies that the surface of 1I may have different properties than its bulk material.”
    Quote in the paperNot yet classified
    • The authors state this as an assumption: 1I is an interstellar interloper that originated in a different planetary system.

  • Not yet classified.

    Premise

    Gravitational microlensing results show that on average every star in the Milky Way is accompanied by at least one bound planet.

    “Gravitational microlensing results have shown that, on average, every star in the Milky Way is accompanied by at least one bound planet (Cassan et al. 2012)”
    Quote in the paperNot yet classified0 of 1 sources checked
    • cites Cassan et al. 2012 source

      Not checked in the free run.

  • Not yet classified.

    Premise

    LSST will commence its 10-year all-sky survey in 2022.

    “The Large Synoptic Survey Telescope (LSST; Ivezić et al. 2008) will commence its 10-year all-sky survey in 2022.”
    Quote in the paperNot yet classified0 of 1 sources checked
    • cites Ivezić et al. 2008

      Not checked in the free run.

  • Not yet classified.

    Interpretation

    1I's hyperbolic orbit strongly suggests that it originated outside the solar system.

    “Its hyperbolic orbit (eccentricity greater than unity) strongly suggests that it originated outside our solar system”
    • Also stated in: § 1. Introduction
      “With no gravitational perturbations to explain its anomalously high eccentricity, the most likely explanation is that this object originated outside of our solar system and happened to pass close to the Earth during its journey through interstellar space.”
    Quote in the paperNot yet classified0 of 1 sources checked
    • cites Williams 2017

      Not checked in the free run.

  • Not yet classified.

    Premise

    The possibility of LSST detecting interstellar comets increases by an order of magnitude or more when considering cometary outbursting.

    “The possibility of LSST detecting interstellar comets increases by an order(s) of magnitude when considering cometary outbursting (Cook et al. 2016), which makes objects brighter, although 1I has shown no signs of activity so far in its observational record.”
    Quote in the paperNot yet classified0 of 1 sources checked
    • cites Cook et al. 2016 source

      Not checked in the free run.

  • Not yet classified.

    Interpretation

    LSST will be sensitive to fainter and therefore smaller and/or more distant objects, and is therefore likely to have a greater detection rate than the current rate.

    “LSST will be sensitive to fainter and therefore smaller and/or more distant objects, and is therefore likely to have a greater detection rate than the current rate.”
    Quote in the paperNot yet classified
    • The authors state this as an assumption: 1I is an interstellar interloper that originated in a different planetary system.
19 of 19

  • The authors state this as an assumption.

    The population of interstellar ejectoids has zero mean velocity because source planetary systems and ejection trajectories are isotropic.

    “The fact that the Sun's relative velocity is comparable to the velocity of 1I confirms our assumption that the population of interstellar ejectoids has zero mean velocity (due to the fact that both the source planetary systems and ejection trajectories are assumed to be isotropic).”

  • The authors state this as an assumption.

    1I is an interstellar interloper that originated in a different planetary system.

    “in this work, we have assumed that 1I is an interstellar interloper that originated in a different plantary system.”

  • The authors state this as an assumption.

    1I is representative of the population of ejectoids.

    “We must simply take 1I to be representative.”

  • The authors state this as an assumption.

    A steady-state population of 1I-like objects is ejected from all planetary systems.

    “In the above calculation, we have assumed that a steady-state population of 1I-like objects is ejected from all planetary systems.”

  • The authors state this as an assumption.

    The formation of a typical planetary system results in a mass m of ejectoids with typical size r_e and density ρ_e.

    “We assume here that the formation of a typical planetary system results in a mass m of ejectoids with a typical size of r e and mass density ρ e .”
5 of 5

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • Estimates suggest LSST will increase the number of rare interstellar objects by an order of magnitude, helping constrain planetary system formation frequency and properties in the solar neighborhood.

    “Estimates from Cook et al. ( 2016 ) , Engelhardt et al. ( 2017 ) , and Trilling et al. ( 2017 ) suggest that LSST will increase the number of such rare objects by an order of magnitude, which, among other outcomes, will help constrain the frequency and properties of planetary system formation in the solar neighborhood.”

    From LSST: From Science Drivers to Reference Design and Anticipated Data Products (2019) · cites this paper as Trilling et al. 2017

Cites

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Research works printed but not linked: 1

  1. Sen, 1993, A&A, 275, 298

Cited by

Sorted by citations

Authors
Trilling, D. E., Robinson, T., Roegge, A., Chandler, C. O., Smith, N., Loeffler, M., Trujillo, C., Navarro-Meza, S., & Glaspie, L. M.
Affiliations
Northern Arizona University (US)
Corresponding author
Trilling, David E.
ORCID
Venue
The Astrophysical Journal Letters
Publisher
American Astronomical Society
Published
2017-11-30
Volume
850
Issue
2
Pages
L38
ISSN
  • 2041-8205 (ISSN-L)
  • 2041-8213
DOI
10.3847/2041-8213/aa9989
OpenAlex
W2767706394
Semantic Scholar
c249b06b1988edd85263132b954c8cef94bfad41
Cited by
76
References
36
Citations by year
2026: 2 · 2025: 4 · 2024: 2 · 2023: 8 · 2022: 8 · 2021: 12 · 2020: 8 · 2019: 8 · 2018: 21 · 2016: 3
FWCI
5.53
Type
journal article
Language
en
Open access
Licence
Locations
  • The Astrophysical Journal Letters (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • arXiv (Cornell University)
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astro and Planetary Science
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Stellar, planetary, and galactic studies
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysics and Star Formation Studies
Keywords
Oumuamua, interstellar objects, planetary system formation, hyperbolic orbits, interstellar travel, space weathering, detection rate, LSST

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