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Title: Trajectory analysis for the nucleus and dust of comet C/2013 A1 (Siding Spring)

Abstract

Comet C/2013 A1 (Siding Spring) will experience a high velocity encounter with Mars on 2014 October 19 at a distance of 135,000 km ± 5000 km from the planet center. We present a comprehensive analysis of the trajectory of both the comet nucleus and the dust tail. The nucleus of C/2013 A1 cannot impact on Mars even in the case of unexpectedly large nongravitational perturbations. Furthermore, we compute the required ejection velocities for the dust grains of the tail to reach Mars as a function of particle radius and density and heliocentric distance of the ejection. A comparison between our results and the most current modeling of the ejection velocities suggests that impacts are possible only for millimeter to centimeter size particles released more than 13 AU from the Sun. However, this level of cometary activity that far from the Sun is considered extremely unlikely. The arrival time of these particles spans a 20-minute time interval centered at 2014 October 19 at 20:09 TDB, i.e., around the time that Mars crosses the orbital plane of C/2013 A1. Ejection velocities larger than currently estimated by a factor >2 would allow impacts for smaller particles ejected as close as 3 AU frommore » the Sun. These particles would reach Mars from 19:13 TDB to 20:40 TDB.« less

Authors:
; ;  [1];  [2]; ;  [3]
  1. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
  2. Planetary Science Institute, Tucson, AZ 85719 (United States)
  3. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
Publication Date:
OSTI Identifier:
22365519
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 790; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMETS; COMPARATIVE EVALUATIONS; DENSITY; DISTURBANCES; DUSTS; MARS PLANET; NUCLEI; PERTURBATION THEORY; SIMULATION; SUN; TRAJECTORIES; VELOCITY

Citation Formats

Farnocchia, Davide, Chesley, Steven R., Chodas, Paul W., Tricarico, Pasquale, Kelley, Michael S. P., and Farnham, Tony L., E-mail: Davide.Farnocchia@jpl.nasa.gov. Trajectory analysis for the nucleus and dust of comet C/2013 A1 (Siding Spring). United States: N. p., 2014. Web. doi:10.1088/0004-637X/790/2/114.
Farnocchia, Davide, Chesley, Steven R., Chodas, Paul W., Tricarico, Pasquale, Kelley, Michael S. P., & Farnham, Tony L., E-mail: Davide.Farnocchia@jpl.nasa.gov. Trajectory analysis for the nucleus and dust of comet C/2013 A1 (Siding Spring). United States. doi:10.1088/0004-637X/790/2/114.
Farnocchia, Davide, Chesley, Steven R., Chodas, Paul W., Tricarico, Pasquale, Kelley, Michael S. P., and Farnham, Tony L., E-mail: Davide.Farnocchia@jpl.nasa.gov. Fri . "Trajectory analysis for the nucleus and dust of comet C/2013 A1 (Siding Spring)". United States. doi:10.1088/0004-637X/790/2/114.
@article{osti_22365519,
title = {Trajectory analysis for the nucleus and dust of comet C/2013 A1 (Siding Spring)},
author = {Farnocchia, Davide and Chesley, Steven R. and Chodas, Paul W. and Tricarico, Pasquale and Kelley, Michael S. P. and Farnham, Tony L., E-mail: Davide.Farnocchia@jpl.nasa.gov},
abstractNote = {Comet C/2013 A1 (Siding Spring) will experience a high velocity encounter with Mars on 2014 October 19 at a distance of 135,000 km ± 5000 km from the planet center. We present a comprehensive analysis of the trajectory of both the comet nucleus and the dust tail. The nucleus of C/2013 A1 cannot impact on Mars even in the case of unexpectedly large nongravitational perturbations. Furthermore, we compute the required ejection velocities for the dust grains of the tail to reach Mars as a function of particle radius and density and heliocentric distance of the ejection. A comparison between our results and the most current modeling of the ejection velocities suggests that impacts are possible only for millimeter to centimeter size particles released more than 13 AU from the Sun. However, this level of cometary activity that far from the Sun is considered extremely unlikely. The arrival time of these particles spans a 20-minute time interval centered at 2014 October 19 at 20:09 TDB, i.e., around the time that Mars crosses the orbital plane of C/2013 A1. Ejection velocities larger than currently estimated by a factor >2 would allow impacts for smaller particles ejected as close as 3 AU from the Sun. These particles would reach Mars from 19:13 TDB to 20:40 TDB.},
doi = {10.1088/0004-637X/790/2/114},
journal = {Astrophysical Journal},
number = 2,
volume = 790,
place = {United States},
year = {Fri Aug 01 00:00:00 EDT 2014},
month = {Fri Aug 01 00:00:00 EDT 2014}
}
  • The close encounter of comet C/2013 A1 (Siding Spring) with Mars on 2014 October 19 presented an extremely rare opportunity to obtain the first flyby quality data of the nucleus and inner coma of a dynamically new comet. However, the comet's dust tail potentially posed an impact hazard to those spacecraft orbiting Mars. To characterize the comet at large heliocentric distances, study its long-term evolution, and provide critical inputs to hazard modeling, we imaged C/Siding Spring with the Hubble Space Telescope when the comet was at 4.58, 3.77, and 3.28 AU from the Sun. The dust production rate, parameterized bymore » the quantity Afρ, was 2500, 2100, and 1700 cm (5000 km radius aperture) for the three epochs, respectively. The color of the dust coma is (5.0 ± 0.3)%/100 nm for the first two epochs, and (9.0 ± 0.3)%/100 nm for the last epoch, and reddens with increasing cometocentric distance out to ∼3000 km from the nucleus. The spatial distribution and the temporal evolution of the dust color are most consistent with the existence of icy grains in the coma. Two jet-like dust features appear in the northwest and south-southeast directions projected in the sky plane. Within each epoch of 1-2 hr, no temporal variations were observed for either feature, but the position angle of the south-southeastern feature varied between the three epochs by ∼30°. The dust feature morphology suggests two possible orientations for the rotational pole of the nucleus, (R.A., decl.) = (295° ± 5°, +43° ± 2°) and (190° ± 10°, +50° ± 5°), or their diametrically opposite orientations.« less
  • Although the nucleus of comet C/2013 A1 (Siding Spring) will safely pass Mars in 2014 October, the dust in the coma and tail will more closely approach the planet. Using a dynamical model of comet dust, we estimate the impact fluence. Based on our nominal model no impacts are expected at Mars. Relaxing our nominal model's parameters, the fluence is no greater than ∼10{sup –7} grains m{sup –2} for grain radii larger than 10 μm. Mars-orbiting spacecraft are unlikely to be impacted by large dust grains, but Mars may receive as many as ∼10{sup 7} grains, or ∼100 kg of total dust.more » We also estimate the flux of impacting gas molecules commonly observed in comet comae.« less
  • Comet C/2013 A1 (Siding Spring) will have a close encounter with Mars on 2014 October 19. We model the dynamical evolution of dust grains from the time of their ejection from the comet nucleus to the close encounter with Mars, and determine the flux at Mars. Constraints on the ejection velocity from Hubble Space Telescope observations indicate that the bulk of the grains will likely miss Mars, although it is possible that a few percent of the grains with higher velocities will reach Mars, peaking approximately 90-100 minutes after the close approach of the nucleus, and consisting mostly of millimeter-radiusmore » grains ejected from the comet nucleus at a heliocentric distance of approximately 9 AU or larger. At higher velocities, younger grains from submillimeter to several millimeters can also reach Mars, although an even smaller fraction of grains is expected have these velocities, with negligible effect on the peak timing. Using NEOWISE observations of the comet, we can estimate that the maximum fluence will be of the order of 10{sup –7} grains m{sup –2}. We include a detailed analysis of how the expected fluence depends on the grain density, ejection velocity, and size-frequency distribution, to account for current model uncertainties and in preparation of possible refined model values in the near future.« less
  • The dynamically new comet, C/2013 A1 (Siding Spring), is to make a close approach to Mars on 2014 October 19 at 18:30 UT at a distance of 40 ± 1 Martian radii. Such an extremely rare event offers a precious opportunity for the spacecrafts on Mars to closely study a dynamically new comet itself as well as the planet-comet interaction. Meanwhile, the high-speed meteoroids released from C/Siding Spring also pose a threat to physically damage the spacecrafts. Here we present our observations and modeling results of C/Siding Spring to characterize the comet and assess the risk posed to the spacecraftsmore » on Mars. We find that the optical tail of C/Siding Spring is dominated by larger particles at the time of the observation. Synchrone simulation suggests that the comet was already active in late 2012 when it was more than 7 AU from the Sun. By parameterizing the dust activity with a semi-analytic model, we find that the ejection speed of C/Siding Spring is comparable to comets such as the target of the Rosetta mission, 67P/Churyumov-Gerasimenko. Under a nominal situation, the simulated dust cone will miss the planet by about 20 Martian radii. At the extreme ends of uncertainties, the simulated dust cone will engulf Mars, but the meteoric influx at Mars is still comparable to the nominal sporadic influx, seemly indicating that an intense and enduring meteoroid bombardment due to C/Siding Spring is unlikely. Further simulation also suggests that gravitational disruption of the dust tail may be significant enough to be observable at Earth.« less
  • The Near-Earth Object Wide-field Infrared Survey Explorer mission observed comet C/2013 A1 (Siding Spring) three times at 3.4 μm and 4.6 μm as the comet approached Mars in 2014. The comet is an extremely interesting target since its close approach to Mars in late 2014 will be observed by various spacecraft in situ. The observations were taken in 2014 January, July, and September when the comet was at heliocentric distances of 3.82 AU, 1.88 AU, and 1.48 AU. The level of activity increased significantly between the January and July visits but then decreased by the time of the observations in September, approximately four weeksmore » prior to its close approach to Mars. In this work, we calculate Afρ values and CO/CO{sub 2} production rates.« less