Evidence that 1I/2017 U1 (`Oumuamua) was composed of molecular hydrogen ice

Abstract

`Oumuamua (I1 2017) was the first macroscopic ($l\sim 100\mathrm{m}$) 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. 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. We show that all of `Oumaumua's observed properties can be explained if it contained a significant fraction of molecular hydrogen (H${}_2$) ice. H${}_2$ sublimation at a rate proportional to the incident solar flux generates a surface-covering jet that reproduces the observed acceleration. Mass wasting from sublimation leads to monotonic increase in the body axis ratio, explaining `Oumuamua's shape. Back-tracing `Oumuamua's trajectory through the Solar System permits calculation of its mass and aspect ratio prior to encountering the Sun. We show that H${}_2$-rich bodies plausibly form in the coldest dense cores of Giant Molecular Clouds, where number densities are of order $n\sim 10^5$, and temperatures approach the $T=3\mathrm{K}$ background. Post-formation exposure to galactic cosmic rays implies a $\tau \sim 100$ Myr age, explaining the kinematics of `Oumuamua's inbound trajectory.

arXiv commentAccepted for publication in ApJL, 8 pages, 2 figures. All software is available at https://github.com/DSeligman/Oumuamua_Hydrogen

References in corpus (20)

• Interstellar Dust Grains
• From Filamentary Networks to Dense Cores in Molecular Clouds: Toward a New Paradigm for Star Formation
• Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes
• Color Systematics of Comets and Related Bodies
• Could Solar Radiation Pressure Explain 'Oumuamua's Peculiar Acceleration?
• Interstellar Interlopers: Number Density and Origins of 'Oumuamua-like Objects
• Interstellar dust charging in dense molecular clouds: cosmic ray effects
• Spitzer Observations of Interstellar Object 1I/`Oumuamua
• The tumbling rotational state of 1I/`Oumuamua
• The Feasibility and Benefits of In Situ Exploration of `Oumuamua-like objects
• Modeling the light curve of `Oumuamua: evidence for torque and disc-like shape
• The Deuterium Fraction in Massive Starless Cores and Dynamical Implications
• Revealing H2D+ depletion and compact structure in starless and protostellar cores with ALMA
• Could 1I/'Oumuamua be an icy fractal aggregate?
• The Excited Spin State of 1I/2017 U1 `Oumuamua
• Plausible home stars of the interstellar object 'Oumuamua found in Gaia DR2
• On the Anomalous Acceleration of 1I/2017 U1 `Oumuamua
• A hypothesis for the rapid formation of planets
• Explaining the elongated shape of 'Oumuamua by the Eikonal abrasion model
• Solid H2 in the interstellar medium

Cited by in corpus (32)

• Exocomets from a Solar System Perspective
• 1I/'Oumuamua as an N2 ice fragment of an exo-Pluto surface: I. size and compositional constraints
• Close encounters of the primordial kind: a new observable for primordial black holes as dark matter
• Constraints on the Occurrence of 'Oumuamua-Like Objects
• Acceleration of 1I/`Oumuamua from radiolytically produced H${}_2$ in H${}_2$O ice
• Destruction of molecular hydrogen ice and Implications for 1I/2017 U1 (`Oumuamua)
• From a Different Star: 3I/ATLAS in the context of the Ōtautahi-Oxford interstellar object population model
• Evidence Suggesting that 'Oumuamua is the ~30 Myr-old product of a Molecular Cloud
• Constraints on the Spin-Pole Orientation, Jet Morphology and Rotation of Interstellar Comet 2I/Borisov with Deep HST Imaging
• Assessing the Formation of Solid Hydrogen Objects in Starless Molecular Cloud Cores
• Survivor bias: divergent fates of the Solar System's ejected vs. persisting planetesimals
• On the Possibility of an Artificial Origin for `Oumuamua
• The Galactic Interstellar Object Population: A Framework for Prediction and Inference
• Interstellar planetesimals: potential seeds for planet formation?
• Inferring Late Stage Enrichment of Exoplanet Atmospheres from Observed Interstellar Comets
• Interstellar Comet 3I/ATLAS: Evidence for Galactic Cosmic Ray Processing
• Misaligned circumbinary disks as efficient progenitors of interstellar asteroids
• Numerical Simulations of Tidal Deformation and Resulting Light Curves of Small Bodies: Material Constraints of 99942 Apophis and 1I/`Oumuamua
• Constraints on sub-terrestrial free-floating planets from Subaru microlensing observations
• The New Astronomical Frontier of Interstellar Objects
• Fitting the Light Curve of 1I/`Oumuamua with a Nonprincipal Axis Rotational Model and Outgassing Torques
• Constraining the orientation of the spin axes of extrasolar minor bodies 1I/2017 U1 (`Oumuamua) and 2I/Borisov
• Discerning between different 'Oumuamua models by optical and infrared observations
• Research Programs Arising from 'Oumuamua Considered as an Alien Craft
• Shape-Driven Selection Effects for Aspherical Near-Earth Objects in Systematic Surveys
• On The Spin Dynamics of Elongated Minor Bodies with Applications to a Possible Solar System Analogue Composition for `Oumuamua
• Absorption spectra of electrified hydrogen molecules
• Implications of evaporative cooling by H${}_2$ for 1I/`Oumuamua
• The Implications of 'Oumuamua on Panspermia
• CO mapping of Cygnus-X -- volume density distribution
• Close Encounters of the Interstellar Kind: Examining the Capture of Interstellar Objects in Near Earth Orbit
• Tidal disruption of "snow clouds" by unassociated stars