arXiv subjects

Gal Sarid

Publications and source records attributed to Gal Sarid.

12 recordsLinked to original sources

arXiv2023

Ejecta Evolution Following a Planned Impact into an Asteroid: The First Five Weeks

The impact of the DART spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos' orbit substantially, largely from the ejection of material. We present results from twelve Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ~1.4 magnitudes, we find consistent dimming rates of 0.11-0.12 magnitudes/day in the first week, and 0.08-0.09 magnitudes/day over the entire study period. The system returned to its pre-impact brightness 24.3-25.3 days after impact through the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, through movement of the primary ejecta through the aperture likely played a role.

astro-ph.EP↗

arXiv2022

The Effects of Early Collisional Evolution on Amorphous Water Ice Bodies

Conditions in the outer protoplanetary disk during Solar System formation were thought to be favorable for the formation of amorphous water ice (AWI),a glassy phase of water ice. However, subsequent collisional processing could have shock crystallized any AWI present. Here we use the iSALE shock physics hydrocode to simulate impacts between large icy bodies at impact velocities relevant to these collisional environments, and then feed these results into a custom-built AWI crystallization script, to compute how much AWI crystallizes/survives these impact events. We find that impact speeds between icy bodies post-planet migration (i.e., between trans-Neptunian Objects or TNOs) are too slow to crystallize any meaningful fraction of AWI. During planet migration, however, the amount of AWI that crystallizes is highly stochastic: relatively little AWI crystallizes at lower impact velocities (less than ~2 km/s), yet most AWI present in the bodies (if equal sized) or impactor and impact site (if different sizes) crystallizes at higher impact velocities (greater than ~4 km/s). Given that suspected impact speeds during planet migration were ~2-4 km/s, this suggests that primordial AWI's ability to survive planet migration is highly stochastic. However, if proto-EKB objects and their fragments experienced multiple impact events, nearly all primordial AWI could have crystallized; such a highly collisional proto-EKB during planet migration is consistent with the lack of any unambiguous direct detection of AWI on any icy body. Ultimately, primordial AWI's survival to the present day depends sensitively on the proto-EKB's size-frequency distribution, which is currently poorly understood.

astro-ph.EP↗

arXiv2021

An N-body approach to modeling debris and ejecta off small bodies: Implementation and application

We introduce here our new approach to modeling particle cloud evolution off surface of small bodies (asteroids and comets), following the evolution of ejected particles requires dealing with various time and spatial scales, in an efficient, accurate and modular way. In order to improve computational efficiency and accuracy of such calculations, we created an N-body modeling package as an extension to the increasingly popular orbital dynamics N-body integrator Rebound. Our code is currently a stand-alone variant of the Rebound code and is aimed at advancing a comprehensive understanding of individual particle trajectories, external forcing, and interactions, at the scale which is otherwise overlooked by other modeling approaches. The package we developed -- Rebound Ejecta Dynamics (RED) -- is a Python-based implementation with no additional dependencies. It incorporates several major mechanisms that affect the evolution of particles in low-gravity environments and enables a more straightforward simulation of combined effects. We include variable size and velocity distributions, solar radiation pressure, ellipsoidal gravitational potential, binary or triple asteroid systems, and particle-particle interactions. In this paper, we present a sample of the RED package capabilities. These are applied to a small asteroid binary system (characterized following the Didymos/Dimorphos system, which is the target for NASA's Double Asteroid Redirection Test mission)

astro-ph.EP↗

arXiv2021

Contemporaneous Multi-Wavelength and Precovery Observations of Active Centaur P/2019 LD2 (ATLAS

Gateway Centaur and Jupiter co-orbital P/2019 LD2 (ATLAS) (Sarid et al. 2019) provides the first opportunity to observe the migration of a Solar System small body from a Centaur orbit to a Jupiter Family Comet (JFC) four decades from now (Kareta et al., 2020; Hsieh et al. 2020). The Gateway transition region is beyond where water ice can power cometary activity, and coma production there is as poorly understood as in all Centaurs. We present contemporaneous multi-wavelength observations of LD2 from 2020 July 2-4: Gemini-North visible imaging, NASA IRTF near-infrared spectroscopy, and ARO SMT millimeter-wavelength spectroscopy. Precovery DECam images limit the nucleu's effective radius to <=1.2 km and no large outbursts were seen in archival Catalina Sky Survey observations. LD2's coma has g'-r'=0.70+/-0.07, r'-i'=0.26+/-0.07, a dust production rate of ~10-20 kg/s, and an outflow velocity between v~0.6-3.3 m/s. We did not detect CO towards LD2 on 2020 July 2-3, with a 3-sigma upper limit of Q(CO) < 4.4 * 10^27 mol/s (<200 kg/s). Near-infrared spectra show evidence for water ice at the 1-10% level depending on grain size. Spatial profiles and archival data are consistent with sustained activity. The evidence supports the hypothesis that LD2 is a typical small Centaur that will become a typical JFC, and thus it is critical to understanding the transition between these two populations. Finally, we discuss potential strategies for a community-wide, long baseline monitoring effort.

astro-ph.EP↗

arXiv2020

P/2019 LD2 (ATLAS): An Active Centaur in Imminent Transition to the Jupiter Family

The recently discovered object P/2019 LD2 (ATLAS) was initially thought to be a Jupiter Trojan asteroid, until dynamical studies and the appearance of persistent cometary activity revealed that this object is actually an active Centaur. However, the dynamical history, thermal environment, and impact of such environments on the activity of 2019 LD2 are poorly understood. Here we conduct dynamical simulations to constrain its orbital history and resulting thermal environment over the past 3000 years. We find that 2019 LD2 is currently in the vicinity of a dynamical "Gateway" that facilitates the majority of transitions from the Centaur population into the Jupiter Family of Comets (JFC population; Sarid et al. 2019). Our calculations show that it is unlikely to have spent significant amounts of time in the inner solar system, suggesting that its nucleus is relatively pristine in terms of physical, chemical, and thermal processing through its history. This could explain its relatively high level of distant activity as a recently activated primordial body. Finally, we find that the median frequency of transition from the Gateway population into the JFC population varies from once every ~3 years to less than once every 70 years, if 2019 LD2's nucleus is ~1 km in radius or greater than 3 km in radius. Forward modeling of 2019 LD2 shows that it will transition into the JFC population in 2063, representing the first known opportunity to observe the evolution of an active Centaur nucleus as it experiences this population-defining transition.

astro-ph.EP↗

arXiv2020

The Scientific Impact of the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) for Solar System Science

Vera C. Rubin Observatory will be a key facility for small body science in planetary astronomy over the next decade. It will carry out the Legacy Survey of Space and Time (LSST), observing the sky repeatedly in u, g, r, i, z, and y over the course of ten years using a 6.5 m effective diameter telescope with a 9.6 square degree field of view, reaching approximately r = 24.5 mag (5-σ depth) per visit. The resulting dataset will provide extraordinary opportunities for both discovery and characterization of large numbers (10--100 times more than currently known) of small solar system bodies, furthering studies of planetary formation and evolution. This white paper summarizes some of the expected science from the ten years of LSST, and emphasizes that the planetary astronomy community should remain invested in the path of Rubin Observatory once the LSST is complete.

astro-ph.IM↗

arXiv2020

Strength In Diversity: Small Bodies as the Most Important Objects in Planetary Sciences

Small bodies, the unaccreted leftovers of planetary formation, are often mistaken for the leftovers of planetary science in the sense that they are everything else after the planets and their satellites (or sometimes just their regular satellites) are accounted for. This mistaken view elides the great diversity of compositions, histories, and present-day conditions and processes found in the small bodies, and the interdisciplinary nature of their study. Understanding small bodies is critical to planetary science as a field, and we urge planetary scientists and our decision makers to continue to support science-based mission selections and to recognize that while small bodies have been grouped together for convenience, the diversity of these objects in terms of composition, mass, differentiation, evolution, activity, dynamical state, physical structure, thermal environment, thermal history, and formation vastly exceeds the observed variability in the major planets and their satellites. Treating them as a monolithic group with interchangeable members does a grave injustice to the range of fundamental questions they address. We advocate for a deep and ongoing program of missions, telescopic observations, R and A funding, and student support that respects this diversity.

astro-ph.IM↗

arXiv2020

The Sublimative Evolution of (486958) Arrokoth

We consider the history of New Horizons target (486958) Arrokoth in the context of its sublimative evolution. Shortly after the Sun's protoplanetary disk (PPD) cleared, the newly intense sunlight sparked a sublimative period in Arrokoth's early history that lasted for ~10-100 Myr. Although this sublimation was too weak to significantly alter Arrokoth's spin state, it could drive mass transport around the surface significant enough to erase topographic features on length scales of ~10-100 m. This includes craters up to ~50-500 m in diameter, which suggests that the majority of Arrokoth's craters may not be primordial (dating from the merger of Arrokoth's lobes), but rather could date from after the end of this sublimative period. Thereafter, Arrokoth entered a Quiescent Period (which lasts to the present day), in which volatile production rates are at least 13 orders of magnitude less than the ~10^24 molecules/s detection limit of the New Horizons spacecraft (Lisse et al. 2020). This is insufficient to drive either mass transport or sublimative torques. These results suggest that the observed surface of Arrokoth is not primordial, but rather dates from the Quiescent Period. By contrast, the inability of sublimative torques to meaningfully alter Arrokoth's rotation state suggests that its shape is indeed primordial, and its observed rotation is representative of its spin state after formation.

astro-ph.EP↗

arXiv2019

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 semi-major 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.

astro-ph.EP↗

arXiv2017

Carbon monoxide in the distantly active Centaur (60558) 174P/Echeclus at 6 AU

(60558) 174P/Echeclus is an unusual object that belongs to a class of minor planets called Centaurs, which may be intermediate between Kuiper Belt Objects and Jupiter Family comets. It is sporadically active throughout its orbit at distances too far for water ice to sublimate, the source of activity for most comets. Thus, its coma must be triggered by another mechanism. In 2005, Echeclus had a strong outburst with peculiar behavior that raised questions about the nucleus homogeneity. In order to test nucleus models, we performed the most sensitive search to date for the highly volatile CO molecule via its J=2-1 emission toward Echeclus during 2016 May-June (at 6.1 astronomical units from the Sun) using the Arizona Radio Observatory 10-m Submillimeter Telescope. We obtained a 3.6-sigma detection with a slightly blue-shifted (delta v = -0.55 +- 0.1 km/s) and narrow (FWHM = 0.53 +- 0.23 km/s) line. The data are consistent with emission from a cold gas from the sunward side of the nucleus, as seen in two other comets at 6 AU. We derive a production rate of Q(CO) = (7.7 +- 3.3)x10^26 mol/s, which is capable of driving the estimated dust production rates. Echeclus CO outgassing rate is ~40 times lower than what is typically seen for another Centaur at this distance, 29P/Schwassmann-Wachmann 1. We also used the IRAM 30-m telescope to search for the CO J=2-1 line, and derive an upper limit that is above the SMT detection. Compared to the relatively unprocessed comet C/1995 O1 (Hale-Bopp), Echeclus produces significantly less CO, as do Chiron and four other Centaurs.

astro-ph.EP↗

arXiv2017

CO in distantly active comets

Activity of most comets near the Sun is dominated by sublimation of frozen water, the most abundant ice in comets. Some comets, however, are active well beyond the water-ice sublimation limit of ~3 AU. Three bodies dominate the observational record and modeling efforts for distantly active comets: the long-period comet C/1995 O1 Hale-Bopp and the short-period comets (with Centaur orbits) 29P/Schwassmann Wachmann 1 and 2060 Chiron. We summarize what is known about these three objects emphasizing their gaseous comae. We calculate their CN/CO and CO2/CO production rate ratios from the literature and discuss implications. Using our own data we derive CO production rates for all three objects, in order to examine a correlation between gas production and different orbital histories and/or size. We find that orbital history does not appear to play a significant role in explaining 29P's CO production rates. 29P outproduces Hale-Bopp at the same heliocentric distance, even though it has been subjected to much more solar heating. Previous modeling work on such objects predicts that 29P should have been de-volatilized over a fresher comet like Hale-Bopp. This may point to 29P having a different orbital history than current models predict, with its current orbit acquired more recently. On the other hand, Chiron's CO measurements are consistent with it being significantly depleted over its original state, perhaps due to increased radiogenic heating made possible by its much larger size or its higher processing due to orbital history. Observed spectral line profiles are consistent with development and sublimation of icy grains at about 5-6 AU for 29P and Hale-Bopp, and this is probably a common feature in distantly active comets, and an important source of volatiles for all comets within 5 AU. In contrast, the narrow CO line profiles indicate a nuclear, and not extended, origin for CO beyond ~4 AU.

astro-ph.EP↗

arXiv2016

Erosive Hit-and-Run Impact Events: Debris Unbound

Erosive collisions among planetary embryos in the inner solar system can lead to multiple remnant bodies, varied in mass, composition and residual velocity. Some of the smaller, unbound debris may become available to seed the main asteroid belt. The makeup of these collisionally produced bodies is different from the canonical chondritic composition, in terms of rock/iron ratio and may contain further shock-processed material. Having some of the material in the asteroid belt owe its origin from collisions of larger planetary bodies may help in explaining some of the diversity and oddities in composition of different asteroid groups.

astro-ph.EP↗