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COULD SOLAR RADIATION PRESSURE EXPLAIN ‘OUMUAMUA’S PECULIAR ACCELERATION?
SHMUEL BIALY AND ABRAHAM LOEB
Harvard Smithsonian Center for Astrophysics, 60 Garden st., Cambridge, MA, 02138
Draft version November 1, 2018
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We discuss the possible origins of such an object
including the possibility that it might be a lightsail of artificial origin.
Our general results apply to any light probes designed for interstellar travelcut
If radiation pressure is the accelerating force, then ‘Oumuamua represents a new class of thin
interstellar material, either produced naturally,through a yet unknown process in the ISM or in proto-planetary disks,
or of an artificial origin.
Considering an artificial origin, one possibility is that ‘Oumuamua is a lightsail, floating in interstellar space as a debris from an advanced technological equipment (Loeb 2018).
Lightsails with similar dimensions have been designed and constructed by our own civilization, including the IKAROS project and the Starshot Initiative
The lightsail technology might be abundantly used for transportation of cargos between planets (Guillochon & Loeb 2015) or between stars(Lingam & Loeb 2017).
In the former case, dynamical ejection from a planetary System could result in space debris of
equipment that is not operational any more (Loeb 2018), and is floating at the characteristic speed of stars relative to each other in the Solar neighborhood.
This would account for the various anomalies of ‘Oumuamua, such as
the unusual geometry inferred from its lightcurve (Meech et al.2017; Fraser et al. 2018; Drahus et al. 2018; Belton et al.2018),
its low thermal emission, suggesting high reflectivity(Trilling et al. 2018), and
its deviation from a Keplerian orbit (Micheli et al. 2018)
without any sign of a cometary tail(Meech et al. 2017; Knight et al. 2017; Jewitt et al. 2017;Ye et al. 2017; Fitzsimmons et al. 2017)
or spin-up torques (Rafikov 2018).
Although ‘Oumuamua has a red surface color, similar to organic-rich surfaces of Solar-System comets and D-type asteroids (Meech et al. 2017),
this does not contradict the artificial scenario, since irrespective of the object’s composition,
as it travels through the ISM its surface will be covered by a layer of interstellar dust, which is itself composed of organic-rich materials (Draine 2003).
Alternatively, a more exotic scenario is that ‘Oumuamua may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization. Based on the PAN-STARRS1 survey characteristics, and assuming natural origins following random trajectories, Do et al. (2018) derived that the interstellar number density of ‘Oumuamua-like objects should be extremely high, equivalent to∼10 15 ejected planetisimals per star, and a factor of 100 to 10 8 larger than predicted by theoretical models (Moro-Martin et al. 2009).
This discrepancy is readily solved if ‘Oumuamua does not follow a random trajectory but is rather a targeted probe. Interestingly, ‘Oumuamua’s entry velocity is found to be extremely close to the velocity of the Local Standard of Rest, in a kinematic region that is occupied by less than 1 to 500 stars COULD SOLAR RADIATION PRESSURE EXPLAIN ‘OUMUAMUA’S PECULIAR ACCELERATION?