Constraints on the Density and Internal Strength of 1I/’Oumuamua

McNeill, Andrew; Trilling, David E.; Mommert, Michael

doi:10.3847/2041-8213/aab9ab

Cited by 35 publications

(31 citation statements)

References 17 publications

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“…The aspect ratios that we have chosen are illustrative, and not the result of model optimization. Other values, such as the 6:1 suggested by Jewitt et al (2017) and McNeill et al (2018), are equally capable of explaining the data. In the right column of Figure 3, we show the Lomb-Scargle periodograms, for the real and simulated observations, during the same time period.…”

Section: -Dimensional Dynamicsmentioning

confidence: 62%

On the Anomalous Acceleration of 1I/2017 U1 ‘Oumuamua

Seligman

Laughlin

Batygin

2019

ApJL

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We show that the P ∼ 8 h photometric period and the astrometrically measured A ng ∼ 2.5 × 10 −4 cm s −2 non-gravitational acceleration (at r ∼ 1.4 AU) of the interstellar object 1I/2017 ('Oumuamua) can be explained by a nozzle-like venting of volatiles whose activity migrated to track the subsolar location on the object's surface. Adopting the assumption that 'Oumuamua was an elongated a × b × c ellipsoid, this model produces a pendulum-like rotation of the body and implies a long semiaxis a ∼ 5A ng P 2 /4π 2 ∼ 260 m. This scale agrees with the independent estimates of 'Oumuamua's size that stem from its measured brightness, assuming an albedo of p ∼ 0.1, appropriate to ices that have undergone long-duration exposure to the interstellar cosmic ray flux. Using ray-tracing, we generate light curves for ellipsoidal bodies that are subject to both physically consistent sub-solar torques and to the time-varying geometry of the Sun-Earth-'Oumuamua configuration. Our synthetic light curves display variations from chaotic tumbling and changing cross-sectional illumination that are consistent with the observations, while avoiding significant secular changes in the photometric periodicity. If our model is correct, 'Oumuamua experienced mass loss that wasted ∼ 10% of its total mass during the ∼ 100 d span of its encounter with the inner Solar System and had an icy composition with a very low [C/O] 0.003. Our interpretation of 'Oumuamua's behavior is consistent with the hypothesis that it was ejected from either the outer regions of a planetesimal disk after an encounter with an embedded M p ∼ M Nep planet or from an exo-Oort cloud.

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Section: -Dimensional Dynamicsmentioning

confidence: 62%

On the Anomalous Acceleration of 1I/2017 U1 ‘Oumuamua

Seligman

Laughlin

Batygin

2019

ApJL

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“…Mashchenko (2019) finds aspect ratio of 8 to be most probable by using Lommel-Seeliger reflection (Lumme & Bowell 1981). A somewhat lower aspect ratio of 6±1 is found by McNeill et al (2018) using the lightcurve inversion model of Durech et al (2010). This elongation is less than some other estimates, but still remarkable.…”

Section: Introductionmentioning

confidence: 93%

“…(3) We assume a constant phase angle, because the SOE location is nearly constant during one rotation period. During the overall observation period of 'Oumuamua , the phase angle changed between 19 • − 27 • , and up to 24 • for the mag ≥ 2.2 observation period (Jewitt et al 2017;Bolin et al 2018;McNeill et al 2018;Belton et al 2018). Therefore we calculate here for Θ = 2π/15 = 24 • , but also consider cases of Θ = π/9 = 20 • , to show the effect of phase angle on the results.…”

Section: Model Assumptionsmentioning

confidence: 99%

“…This variation is linked mainly to the shape of 'Oumuamua , namely the ratio between its longest axis and its shortest axis (aspect ratio) ('Oumuamua ISSI Team 2019). The 'Oumuamua aspect ratio was derived in several approaches (e.g., Meech et al 2017;Bolin et al 2018;McNeill et al 2018) and is found to be extreme and much higher than the aspect ratio of objects in the solar system. Naively, one can expect the lightcurve magnitude variation between the brightest and the dimmest states (lightcurve ratio) to be equal to the aspect ratio.…”

Section: Introductionmentioning

confidence: 99%

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On the aspect ratio of ’Oumuamua : less elongated shape for irregular surface properties

Vazan

Sari

2020

Monthly Notices of the Royal Astronomical Society

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The large brightness variation in the observed lightcurve of 'Oumuamua is probably related to its shape, i.e., to the ratio between its longest axis and its shortest axis (aspect ratio). Several approaches found the aspect ratio of 'Oumuamua to be unusually elongated. Moreover, the spin axis orientation has to be almost perpendicular to the observer in order to obtain such an extreme lightcurve, a configuration which is unlikely. However, interstellar 'Oumuamua may have different surface properties than we know in our solar system. Therefore, in this work we widen the parameter space for surface properties beyond the asteroid-like models and study its effect on 'Oumuamua's lightcurve. We calculate reflection from a rotating ellipsoidal object for four models: Lambertian reflection, specular reflection, single scattering diffusive and backscatter . We then calculate the probability to obtain a lightcurve ratio larger than the observed, as a function of the object's aspect ratio, assuming an isotopic spin orientation distribution. We find the elongation of 'Oumuamua to be less extreme for the Lambertian and specular reflection models. Consequently, the probability to observe the lightcurve ratio of 'Oumuamua given its unknown spin axis orientation is larger for those models. We conclude that different surface reflection properties may suggest alternatives to the extreme shape of 'Oumuamua , relieving the need for complicated formation scenario, extreme albedo variation, or unnatural origin. Although the models suggested here are for ideal ellipsoidal shape and ideal reflection method, the results emphasize the importance of surface properties for the derived aspect ratio.

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“…Other estimates from visible/near-infrared observations lead to an effective radius in the range of 55-130 m (Jewitt et al 2017, Banninster et al 2017, Meech et al 2017, Drahus et al 2018, Bolin et al 2018, Frasser et al 2018, the uncertainties arising from its unknown shape and albedo. Based on its 2-2.5 mag variability (reduced to 1.5-1.9 when correcting for the phase angle of the observations; McNeill et al 2018), it is estimated that 1I/'Oumuamua has an axis ratio ranging from 3 to 10, most likely in the 6±1:1 range (McNeill et al 2018). This would make it unusually elongated compared to solar system objects, while other authors suggest it could be unusually oblate (Belton et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Could 1I/’Oumuamua be an Icy Fractal Aggregate?

Moro‐Martín

2019

ApJL

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1I/'Oumuamua is the first interstellar interloper to be detected, and it shows a non-gravitational acceleration that cannot be accounted for by outgassing, given the strict upper limits of outgassing evident from Spitzer observations, unless the relative abundances of the common volatiles are very different to those in comets. As an alternative, it has been suggested that its peculiar acceleration is due to radiation pressure, requiring a planar-sheet geometry of an unknown natural or artificial origin. Here we assess whether or not the internal structure of 1I/'Oumuamua, rather than its geometry, could support a radiation-pressure-driven scenario. We adopt a mass fractal structure and find that the type of aggregate that could yield the required area-to-mass ratio would have to be extraordinarily porous, with a density ∼ 10 −5 g cm −3 . Such porous aggregates can naturally arise from the collisional grow of icy dust particles beyond the snowline of a protoplanetary disk, and we propose that 1I/'Oumuamua might be a member of this population. This is a hypothesis worth investigating because, if this were the case, 1I/'Oumuamua would have opened a new observation window on to the study of the building blocks of planets around other stars. This could set unprecedented constraints on planet formation models.

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Constraints on the Density and Internal Strength of 1I/’Oumuamua

Cited by 35 publications

References 17 publications

On the Anomalous Acceleration of 1I/2017 U1 ‘Oumuamua

On the Anomalous Acceleration of 1I/2017 U1 ‘Oumuamua

On the aspect ratio of ’Oumuamua : less elongated shape for irregular surface properties

Could 1I/’Oumuamua be an Icy Fractal Aggregate?

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