22 research outputs found
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
BIMA ARRAY MOLECULAR SEARCHES IN COMET HALE-BOPP(C/1995 O1)
W.J. Welch et. al., PASP, 108, 93 (1996)Author Institution: Department of Astronomy, University of Illinois; Department of Earth Sciences, National Taiwan Normal University, and IAA; Department of Astronomy, University of California; Department of Astronomy, University of Maryland; Department of Astronomy and Astrophysics, University of Chicago.Cometary molecules specifically targeted for observation with the BIMA Array during the 1997 apparition of comet Hale-Bopp included HCN, , and CS, but because the BIMA Array has a very flexible, wideband , many other species had transitions in the bandpass which could be observed simultaneously with the target molecules. We discuss the results of these ``search'' observations which included transitions of , and (here, a molecular formula with no mass number denotes the main isotopomer). This work was partially funded by: NASA NAG5-4292, NAG5-4080, and NGT5-0083; NSF AST 96-13998, AST96-13999, AST96-13716, and AST96-15608; Taiwanese grants NSC 86-2112-M-003-T and 87-2112-M-003-007; and the Universities of Illinois, Maryland, and California, Berkeley