Observations of Comet 2P/Encke During the Fall 2013 Apparition

We will present preliminary results from our observational campaign of Comet 2P/Encke during its 2013 perihelion passage. At optical wavelengths Encke is an extremely dust poor comet that has in past perihelion passages emitted a gas jet in the form a sunward fan. We expect to characterize both the morphology and lightcurve of the comet. The low optical dust means that even near perihelion the nuclear signature can be obtained in lightcurve data taken with narrowband continuum filters which cut out the gas emission. The campaign will consist of both narrowband and broadband imaging as well as infrared spectroscopy. Imaging will be obtained from 8 nights on the KPNO 2.1m between Sept. 7 and 14 UT. Additionally, the Murillo Family Observatory, a 0.5m telescope on the CSUSB campus which is equipped with both broadband filters and a narrowband Hale-Bopp set of filters will be used to observe the comet every clear night the moon allows between late August and early October to obtain extensive lightcurve data. These data will overlap both the Kitt Peak observations and the infrared spectroscopy which will be obtained with the SpeX instrument at the IRTF on four nights between September 26 UT and October 2 UT

The Distribution, Excitation and Formation of Cometary Molecules: Methanol, Methyl Cyanide and Ethylene Glycol

We present an interferometric and single dish study of small organic species toward Comets C/1995 O1 (Hale-Bopp) and C/2002 T7 (LINEAR) using the BIMA interferometer at 3 mm and the ARO 12m telescope at 2 mm. For Comet Hale-Bopp, both the single-dish and interferometer observations of CH3OH indicate an excitation temperature of 105+/-5 K and an average production rate ratio Q(CH3OH)/Q(H2O)~1.3% at ~1 AU. Additionally, the aperture synthesis observations of CH3OH suggest a distribution well described by a spherical outflow and no evidence of significant extended emission. Single-dish observations of CH3CN in Comet Hale-Bopp indicate an excitation temperature of 200+/-10 K and a production rate ratio of Q(CH3CN)/Q(H2O)~0.017% at ~1 AU. The non-detection of a previously claimed transition of cometary (CH2OH)2 toward Comet Hale-Bopp with the 12m telescope indicates a compact distribution of emission, D<9'' (<8500 km). For the single-dish observations of Comet T7 LINEAR, we find an excitation temperature of CH3OH of 35+/-5 K and a CH3OH production rate ratio of Q(CH3OH)/Q(H2O)~1.5% at ~0.3 AU. Our data support current chemical models that CH3OH, CH3CN and (CH2OH)2 are parent nuclear species distributed into the coma via direct sublimation off cometary ices from the nucleus with no evidence of significant production in the outer coma.Comment: accepted for publication in Ap

Combined BIMA and OVRO observations of comet C/1999 S4 (LINEAR)

We present results from an observing campaign of the molecular content of the coma of comet C/1999 S4 (LINEAR) carried out jointly with the millimeter-arrays of the Berkeley-Illinois-Maryland Association (BIMA) and the Owens Valley Radio Observatory (OVRO). Using the BIMA array in autocorrelation (`single-dish') mode, we detected weak HCN J=1-0 emission from comet C/1999 S4 (LINEAR) at 14 +- 4 mK km/s averaged over the 143" beam. The three days over which emission was detected, 2000 July 21.9-24.2, immediately precede the reported full breakup of the nucleus of this comet. During this same period, we find an upper limit for HCN 1-0 of 144 mJy/beam km/s (203 mK km/s) in the 9"x12" synthesized beam of combined observations of BIMA and OVRO in cross-correlation (`imaging') mode. Together with reported values of HCN 1-0 emission in the 28" IRAM 30-meter beam, our data probe the spatial distribution of the HCN emission from radii of 1300 to 19,000 km. Using literature results of HCN excitation in cometary comae, we find that the relative line fluxes in the 12"x9", 28" and 143" beams are consistent with expectations for a nuclear source of HCN and expansion of the volatile gases and evaporating icy grains following a Haser model.Comment: 18 pages, 3 figures. Uses aastex. AJ in pres

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

Far‐UV emissions from the SL9 impacts with Jupiter

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95348/1/grl8617.pd

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]

Asteroids And Comets

Asteroids and comets are remnants from the era of solar system formation over 4.5 billion years ago and therefore allow us to address two fundamental questions in astronomy: what was the nature of our protoplanetary disk, and how did the process of planetary accretion occur? The objects we see today have suffered many geophysically relevant processes in the intervening eons that have altered their surfaces, interiors, and compositions. In this chapter, we review our understanding of the origins and evolution of these bodies, discuss the wealth of science returned from spacecraft missions, and motivate important questions to be addressed in the future

Dust outburst dynamics and hazard assessment for close spacecraft-comet encounters

Using the gas drag by sublimating cometary surface ices for the acceleration of dust particles and deceleration by the gravity field of the nucleus combined with basic laws of mechanics, the sizes, velocities, and number densities of escaping particles are calculated and evaluated with respect to the hazard assessment of comet-spacecraft flybys and encounters. We find good agreement between our analytical method and the more elaborate and precise DSMC calculations, but, being simpler, our method can more easily be used to explore a wide range of cometary conditions and can be more easily scaled to specific comets with different nucleus sizes, masses, and gravity potentials and various gas and dust production rates. Our analytical method is applied to outbursts expanding into a cone of ∼60°, where the gas density falls off with height from the surface rather than radial distance from the center of a uniformly outgassing nucleus. In this scenario, larger dust particles can be ejected and attain ballistic trajectories, go into orbit, or escape from the nucleus, thus being potentially more hazardous to a spacecraft. Sample calculations are carried out for potential dust outbursts for the highly active Centaur/Comet 29P/ Schwassmann-Wachmann 1 for various assumed active areas and dust particle size distributions. Particle velocity ranges for ballistic trajectories, orbiting particles, and particles escaping into the coma are presented. These calculations are used to estimate the coma particle number densities during outbursts to get an assessment of the hazards and required mitigation for a flyby or orbiting space mission 2021. The Author(s). Published by the American Astronomical Society. © 2021. The Author(s). Published by the American Astronomical Society.Open access journalThis 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]

The Deep Impact Earth-Based Campaign

International audiencePrior to the selection of the comet 9P/Tempel 1 as the Deep Impact mission target, the comet was not well observed. From 1999 through the present there has been an intensive world-wide observing campaign designed to obtain mission critical information about the target nucleus, including the nucleus size, albedo, rotation rate, rotation state, phase function, and the development of the dust and gas coma. The specific observing schemes used to obtain this information and the resources needed are presented here. The Deep Impact mission is unique in that part of the mission observations will rely on an Earth-based (ground and orbital) suite of complementary observations of the comet just prior to impact and in the weeks following. While the impact should result in new cometary activity, the actual physical outcome is uncertain, and the Earth-based observations must allow for a wide range of post-impact phenomena. A world-wide coordinated effort for these observations is described