Year: 2020
Type: article
Abstract: The Galilean satellites exhibit a monotonic decrease in density (and increase in ice mass fraction) with distance from Jupiter (Pollack & Fanale 1982). Whether this is because of the background conditions when they formed (Lunine & Stevenson 1982; Canup & Ward 2002; Mosqueira & Estrada 2003a; Ronnet et al. 2017), the process of accretion itself (Dwyer et al. 2013), or later loss due to tidal heating (Canup & Ward 2009), has been in dispute for forty years. We find that a hitherto largely neglected process - vapor loss driven by accretional heating (Kuramoto & Matsui 1994) - can reproduce the observed density trend for accretion timescales ≳300 kyr, consistent with gas-starved satellite formation models (Canup & Ward 2002, 2006). In this model both Io and Europa develop an early surface liquid water ocean. Vapor escape from this ocean causes the water inventories of Io and Europa to be completely and mostly lost, respectively. Isotopic fractionation arising from vapor loss means that Europa will develop a higher D/H ratio compared with Ganymede and Callisto. We make predictions that can be tested with in situ measurements of D/H of potential Europa plumes (Roth et al. 2014) by the Europa Clipper spacecraft, or infrared spectroscopic determinations (Clark et al. 2019) of D/H at all three bodies.
Authors: Carver J. Bierson, Francis Nimmo
Institution: University of California, Santa Cruz
Language: English
Topic: Astro and Planetary Science
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Awards: THE PROCESSES OF EARLY VOLATILE RETENTION OR LOSS IN SMALL BODIES HAVE A DIRECT INFLUENCE ON THE FINAL VOLATILE BUDGETS OF OUTER SOLAR SYSTEM MOONS AND DWARF PLANETS. THE MAIN OBJECTIVE OF THIS PROPOSAL IS TO CARRY OUT THEORETICAL MODELS OF A NOVEL MASS-LOSS PATHWAY WHICH WAS LIKELY IMPORTANT: VAPOR OUTFLOW DRIVEN BY HIGH SURFACE TEMPERATURES. MODEL RESULTS WILL BE COMPARED WITH AVAILABLE OBSERVATIONAL CONSTRAINTS TO IDENTIFY BODIES IN WHICH THIS PARTICULAR PROCESS WAS IMPORTANT. THE MASS LOSS RATE DEPENDS ON THE VAPOR THERMAL VELOCITY COMPARED TO THE ESCAPE VELOCITY SO THAT SMALL WARM BODIES ARE MOST VULNERABLE. THE LOSS RATE ALSO DEPENDS ON THE POWER AVAILABLE. THE PRINCIPAL POWER SOURCE THAT WE WILL CONSIDER IS THAT FROM ACCRETION. THIS CAN BE SUBSTANTIAL IF FORMATION IS RAPID E.G. VIA PEBBLE ACCRETION (FOR KUIPER BELT OBJECTS). THE MASS LOSS HAPPENS EARLY (AS DEFINED BY THE EMERGING WORLDS CALL): IT HAPPENS WHILE ACCRETION IS STILL OCCURRING. MASS LOSS IS THUS POTENTIALLY EARLY ENOUGH THAT NEBULAR GAS IS STILL PRESENT - WHICH COULD SIGNIFICANTLY CHANGE THE OUTCOME. WE WILL CALCULATE THE MASS LOSS RATE AND THE ATTENDANT CHANGES IN BULK DENSITY AND ISOTOPIC FRACTIONATION - ALL OF WHICH ARE POTENTIALLY MEASURABLE EFFECTS - UNDER VARIOUS SCENARIOS FOR BOTH LARGE KUIPER BELT OBJECTS AND THE GALILEAN SATELLITES. THE CALCULATIONS WILL BE BASED ON SIMILAR APPROACHES WHICH HAVE BEEN APPLIED IN THE PAST TO TERRESTRIAL PLANETS AND TO EXOPLANETS. FOR KUIPER BELT OBJECTS OUR APPROACH WILL PROVIDE A TEST OF THE HYPOTHESIS THAT THEY FORMED VIA PEBBLE ACCRETION. RAPID ACCRETION DRIVES VOLATILE LOSS AND MAY HELP TO EXPLAIN THE DENSITY INCREASE FROM CHARON TO PLUTO TO TRITON. FOR THE GALILEAN SATELLITES OUR MECHANISM CAN EXPLAIN WHY THERE IS A REGULAR PROGRESSION IN DENSITY WITH SEMI-MAJOR AXIS AND ALSO EXPLAINS THE LACK OF SUCH PROGRESSION FOR THE SATURNIAN AND URANIAN SATELLITES. THERE ARE SEVERAL POTENTIALLY SIGNIFICANT OUTCOMES OF OUR WORK. FIRST WE ARE PROPOSING A NOVEL MASS LOSS MECHANISM. SECOND WE CAN TEST PARTICULAR ACCRETION SCENARIOS (E.G. PEBBLE ACCRETION FOR KUIPER BELT OBJECTS). THIRD WE CAN TEST OUR HYPOTHESIS BY INVESTIGATING WHETHER MORE VOLATILE SUBSTANCES (E.G. N2) CAN BE RETAINED DURING ACCRETION. OUR PROPOSAL INVESTIGATES THE EARLY VOLATILE EVOLUTION OF SMALL BODIES AND IS THUS HIGHLY RELEVANT TO THE EMERGING WORLDS THEME OF EARLY EVOLUTION AND THE OVERARCHING SCIENCE QUESTION OF HOW THE SOLAR SYSTEM FORMED AND EVOLVED., Gradute Research Fellowship Program (GRFP)
OpenAlex ID: W3042757767