14 research outputs found
Laboratory Measurement of Volatile Ice Vapor Pressures with a Quartz Crystal Microbalance
Nitrogen, carbon monoxide, and methane are key materials in the far outer
Solar System where their high volatility enables them to sublimate, potentially
driving activity at very low temperatures. Knowledge of their vapor pressures
and latent heats of sublimation at relevant temperatures is needed to model the
processes involved. We describe a method for using a quartz crystal
microbalance to measure the sublimation flux of these volatile ices in the free
molecular flow regime, accounting for the simultaneous sublimation from and
condensation onto the quartz crystal to derive vapor pressures and latent heats
of sublimation. We find vapor pressures to be somewhat lower than previous
estimates in literature, with carbon monoxide being the most discrepant of the
three species, almost an order of magnitude lower than had been thought. These
results have important implications across a variety of astrophysical and
planetary environments
29P/Schwassmann-Wachmann: A Rosetta Stone for Amorphous Water Ice and CO <-> CO2 Conversion in Centaurs and Comets?
Centaur 29P/Schwassmann-Wachmann 1 (SW1) is a highly active object orbiting
in the transitional Gateway region (Sarid et al. 2019) between the Centaur and
Jupiter Family Comet regions. SW1 is unique among the Centaurs in that it
experiences quasi-regular major outbursts and produces CO emission
continuously; however, the source of the CO is unclear. We argue that due to
its very large size (approx. 32 km radius), SW1 is likely still responding, via
amorphous water ice (AWI) conversion to crystalline water ice (CWI), to the
rapid change in its external thermal environment produced by its dynamical
migration from the Kuiper belt to the Gateway Region at the inner edge of the
Centaur region at 6 au. It is this conversion process that is the source of the
abundant CO and dust released from the object during its quiescent and outburst
phases. If correct, these arguments have a number of important predictions
testable via remote sensing and in situ spacecraft characterization, including:
the quick release on Myr timescales of CO from AWI conversion for any few
km-scale scattered disk KBO transiting into the inner system; that to date SW1
has only converted between 50 to 65% of its nuclear AWI to CWI; that volume
changes upon AWI conversion could have caused subsidence and cave-ins, but not
significant mass wasting or crater loss on SW1; that SW1s coma should contain
abundant amounts of CWI CO2-rich icy dust particles; and that when SW1 transits
into the inner system within the next 10,000 years, it will be a very different
kind of JFC comet.Comment: 29 Pages, 3 Figures, 2 Tables, accepted 16-Sept-2022 by the Planetary
Science Journal Corrected proof version 26-Oct-202
The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets
This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics
Fast boulder fracturing by thermal fatigue detected on stony asteroids.
Spacecraft observations revealed that rocks on carbonaceous asteroids, which constitute the most numerous class by composition, can develop millimeter-to-meter-scale fractures due to thermal stresses. However, signatures of this process on the second-most populous group of asteroids, the S-complex, have been poorly constrained. Here, we report observations of boulders' fractures on Dimorphos, which is the moonlet of the S-complex asteroid (65803) Didymos, the target of NASA's Double Asteroid Redirection Test (DART) planetary defense mission. We show that the size-frequency distribution and orientation of the mapped fractures are consistent with formation through thermal fatigue. The fractures' preferential orientation supports that these have originated in situ on Dimorphos boulders and not on Didymos boulders later transferred to Dimorphos. Based on our model of the fracture propagation, we propose that thermal fatigue on rocks exposed on the surface of S-type asteroids can form shallow, horizontally propagating fractures in much shorter timescales (100 kyr) than in the direction normal to the boulder surface (order of Myrs). The presence of boulder fields affected by thermal fracturing on near-Earth asteroid surfaces may contribute to an enhancement in the ejected mass and momentum from kinetic impactors when deflecting asteroids
29P/Schwassmann–Wachmann 1, A Centaur in the Gateway to the Jupiter-family Comets
Jupiter-family comets (JFCs) are the evolutionary products of trans-Neptunian objects (TNOs) that evolve through the giant planet region as Centaurs and into the inner solar system. Through numerical orbital evolution calculations following a large number of TNO test particles that enter the Centaur population, we have identified a short-lived dynamical Gateway, a temporary low-eccentricity region exterior to Jupiter through which the majority of JFCs pass. We apply an observationally based size distribution function to the known Centaur population and obtain an estimated Gateway region population. We then apply an empirical fading law to the rate of incoming JFCs implied by the the Gateway region residence times. Our derived estimates are consistent with observed population numbers for the JFC and Gateway populations. Currently, the most notable occupant of the Gateway region is 29P/Schwassmann–Wachmann 1 (SW1), a highly active, regularly outbursting Centaur. SW1's present-day, very-low-eccentricity orbit was established after a 1975 Jupiter conjunction and will persist until a 2038 Jupiter conjunction doubles its eccentricity and pushes its semimajor axis out to its current aphelion. Subsequent evolution will likely drive SW1's orbit out of the Gateway region, perhaps becoming one of the largest JFCs in recorded history. The JFC Gateway region coincides with a heliocentric distance range where the activity of observed cometary bodies increases significantly. SW1's activity may be typical of the early evolutionary processing experienced by most JFCs. Thus, the Gateway region, and its most notable occupant SW1, are critical to both the dynamical and physical transition between Centaurs and JFCs.National Science Foundation (NSF) [1615917, AST-1824869, 1910275]; National Aeronautics & Space Administration (NASA) [NNX15AH59G, 80NSSC19K0785, 80NSSC18K0497]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
A Predicted Dearth of Majority Hypervolatile Ices in Oort Cloud Comets
We present new, ice species-specific New Horizons/Alice upper gas coma
production limits from the 01 Jan 2019 MU69/Arrokoth flyby of Gladstone et al.
(2021) and use them to make predictions about the rarity of majority
hypervolatile (CO, N, CH) ices in KBOs and Oort Cloud comets. These
predictions have a number of important implications for the study of the Oort
Cloud, including: determination of hypervolatile rich comets as the first
objects emplaced into the Oort Cloud; measurement of CO/N/CH abundance
ratios in the proto-planetary disk from hypervolatile rich comets; and
population statistical constraints on early (< 20 Myr) planetary aggregation
driven versus later (> 50 Myr) planetary migration driven emplacement of
objects into the Oort Cloud. They imply that the phenomenon of ultra-distant
active comets like C/2017K2 (Jewitt et al. 2017, Hui et al. 2018) should be
rare, and thus not a general characteristic of all comets. They also suggest
that interstellar object 2I/Borisov did not originate in a planetary system
that was inordinately CO rich (Bodewits et al. 2020), but rather could have
been ejected onto an interstellar trajectory very early in its natal system's
history.Comment: 16 Pages, 2 Figures, 1 Table; accepted for Publication in PSJ
14-Mar-202
A Predicted Dearth of Majority Hypervolatile Ices in Oort Cloud Comets
International audienceWe present new, ice species-specific New Horizons/Alice upper gas coma production limits from the 2019 January 1 MU69/Arrokoth flyby of Gladstone et al. and use them to make predictions about the rarity of majority hypervolatile (CO, N2, CH4) ices in Kuiper Belt objects and Oort Cloud comets. These predictions have a number of important implications for the study of the Oort Cloud, including the determination of hypervolatile-rich comets as the first objects emplaced into the Oort Cloud, the measurement of CO/N2/CH4 abundance ratios in the protoplanetary disk from hypervolatile-rich comets, and population statistical constraints on early (50 Myr) planetary migration driven emplacement of objects into the Oort Cloud. They imply that the phenomenon of ultradistant active comets like C/2017K2 should be rare, and thus not a general characteristic of all comets. They also suggest that interstellar object 2I/Borisov may not have originated in a planetary system that was inordinately CO rich, but rather could have been ejected onto an interstellar trajectory very early in its natal system's history