A Caltech Library Service

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

Seligman, Darryl and Laughlin, Gregory and Batygin, Konstantin (2019) On the Anomalous Acceleration of 1I/2017 U1 'Oumuamua. Astrophysical Journal Letters, 876 (2). Art. No. L26. ISSN 2041-8213. doi:10.3847/2041-8213/ab0bb5.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


We show that the P ~ 8 hr 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 semi-axis a ∼ 5 A_(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, which is appropriate for 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 subsolar 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 days 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Laughlin, Gregory0000-0002-3253-2621
Batygin, Konstantin0000-0002-7094-7908
Additional Information:© 2019 The American Astronomical Society. Received 2019 February 8; revised 2019 February 20; accepted 2019 February 28; published 2019 May 7. This work was supported by the NASA Astrobiology Institute under Cooperative Agreement Notice NNH13ZDA017C issued through the Science Mission Directorate. We acknowledge support from the NASA Astrobiology Institute through a cooperative agreement between NASA Ames Research Center and Yale University. We thank Hanno Rein and Karen Meech for useful conversations, and we thank Avi Loeb for finding a numerical error in an earlier draft of this manuscript.
Group:Astronomy Department
Funding AgencyGrant Number
Subject Keywords:celestial mechanics – ISM: individual objects (1I/2017 U1)
Issue or Number:2
Record Number:CaltechAUTHORS:20190508-093119865
Persistent URL:
Official Citation:Darryl Seligman et al 2019 ApJL 876 L26
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95342
Deposited By: Tony Diaz
Deposited On:08 May 2019 23:51
Last Modified:16 Nov 2021 17:12

Repository Staff Only: item control page