Hubble Space Telescope Search for Activity in High Perihelion Objects

Abstract

Solar system objects with perihelia beyond the orbit of Jupiter ($q>$ 5 AU) are too cold for water ice to generate an appreciable coma via sublimation. Despite this, numerous high perihelion objects (HPOs) including many comets and recently escaped Kuiper belt objects (``Centaurs'') are observed to be active out at least to the orbit of Saturn ($q\sim$ 10 AU). Peak equilibrium temperatures at 10 AU ($\sim$125 K), while far too low to sublimate water ice, are sufficient to sublimate super-volatiles such as CO and CO${}_2$ ice. Temperatures at 10 AU are also high enough to trigger the rapid crystallization of exposed amorphous ice, thus constituting another possible driver of distant activity. While supervolatile ices can sublimate strongly (as $r_H^{-2}$) to at least Kuiper belt (30 AU) distances, crystallization is an exponential function of temperature that cannot be sustained much beyond $\sim$10 AU. The heliocentric dependence of the activity thus suggests an observational test. If activity in high perihelion objects is triggered by crystallization, then no examples of activity should be found with perihelia $q>>$ 10 AU. If, on the other hand, activity is due to free sublimation of exposed supervolatile ices, or another cause, then distant activity might be detected. We obtained sensitive, high resolution Hubble Space Telescope observations of HPOs to search for activity beyond the crystallization zone. No examples of activity were detected in 53 objects with $q>$ 15 AU, consistent with the crystallization trigger hypothesis. However, sensitivity limits are such that we cannot reject the alternative hypothesis that mass loss is driven by the sublimation of supervolatile ices. We also searched for binary companions in our sample, finding none and setting an empirical 3$\sigma$ limit to the binary fraction of $<8$\%.

arXiv comment30 pages, 11 figures, 4 tables. Accepted by AJ

References in corpus (16)

• The Active Centaurs
• Simulations of the Population of Centaurs I: The Bulk Statistics
• The Dynamics of Known Centaurs
• The Scattered Disk as the source of the Jupiter Family comets
• The Diverse Solar Phase Curves of Distant Icy Bodies. Part I: Photometric Observations of 18 Trans-Neptunian Objects, 7 Centaurs, and Nereid
• The albedo-color diversity of transneptunian objects
• Centaurs and Scattered Disk Objects in the Thermal Infrared: Analysis of WISE/NEOWISE Observations
• CO in distantly active comets
• The orbit, mass, size, albedo, and density of (65489) Ceto/Phorcys: A tidally-evolved binary Centaur
• Simulations of the Population of Centaurs II: Individual Objects
• On the State of Water Ice on Saturn's Moon Titan and Implications to Icy Bodies in the Outer Solar System
• Carbon monoxide in the distantly active Centaur (60558) 174P/Echeclus at 6 AU
• Discovery of a Binary Centaur
• Absolute magnitudes and phase coefficients of trans-Neptunian objects
• Absolute colors and phase coefficients of trans-Neptunian objects: HV-HR and relative phase coefficients
• OSSOS: XV. No active Centaurs in the Outer Solar System Origins Survey

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• The Discovery and Evolution of a Possible New Epoch of Cometary Activity by the Centaur (2060) Chiron
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• Planetary Exploration Horizon 2061 Report, Chapter 4: From planetary exploration goals to technology requirements