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From The Stars: An Assessment of the Scientific Opportunities Provided by Interstellar Objects

Presentation #431.03D in the session The Sun and Solar System III.

Published onJun 29, 2022
From The Stars: An Assessment of the Scientific Opportunities Provided by Interstellar Objects

`Oumuamua (I1 2017) was the first macroscopic body observed to traverse the inner solar system on an unbound hyperbolic orbit. Its light curve displayed strong periodic variation, and it showed no hint of a coma or emission from molecular outgassing. In this thesis, I briefly outline the consequences that this first detection of an interstellar object implies for the planet and star formation processes, and I assess the near-term prospects for detecting and observing (both remotely and in situ) future Solar System visitors of this type. Astrometric measurements indicate that ‘Oumuamua experienced non-gravitational acceleration on its outbound trajectory, but energy balance arguments indicate this acceleration is inconsistent with a water ice sublimation-driven jet of the type exhibited by solar system comets. I show that the 8 hour photometric period and the non-gravitational acceleration of ‘Oumuamua can be explained by a nozzle-like venting of volatiles whose activity migrated to track the sub-solar location on the object’s surface. I show that all of ‘Oumaumua’s observed properties can be explained if it contained a significant fraction of molecular hydrogen H2 ice. I show that H2 rich bodies plausibly form in the coldest dense cores of Giant Molecular Cloud Cores. While carbon monoxide (CO) has been dismissed as a possible accelerant because of its non-detection in emission by Spitzer, I show that outgassing from a surface characterized by a modest covering fraction of CO ice can satisfy the non-ballistic dynamics for a plausible range of assumed bulk densities and surface albedos. Spitzer upper limits on CO emission are, however, inconsistent with the CO production necessary to provide the acceleration. Nonetheless, an ad hoc but physically plausible explanation is that the activity level varied greatly during the time that the trajectory was monitored. I reproduce the astrometric analysis presented in Micheli et al. (2018), and verify that the non-gravitational acceleration was consistent with stochastic changes in outgassing.


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