Seasonal Evolution on the Nucleus of Comet C/2013 A1 (Siding Spring) (original) (raw)
Related papers
The Astrophysical Journal, 2014
The close encounter of Comet C/2013 A1 (Siding Spring) with Mars on October 19, 2014 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. 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 by 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 north-northwest and southeast directions projected in the sky plane. Within each epoch of 1-2 hour duration, no temporal variations were observed for either feature, but the PA of the southeastern feature varied between the three epochs by ~30º. The dust feature morphology suggests two possible orientations for the rotational pole of the nucleus, (RA, Dec) = (295º±5º, +43º±2º) and (190º±10º, 50º±5º), or their diametrically opposite orientations.
Comet C/2013 A1 (Siding Spring) as seen with the Herschel Space Observatory
Astronomy & Astrophysics, 2015
The thermal emission of comet C/2013 A1 (Siding Spring) was observed on March 31, 2013, at a heliocentric distance of 6.48 au using the PACS photometer camera of the Herschel Space Observatory. The comet was clearly active, showing a coma that could be traced to a distance of ∼10 , i.e. ∼50000 km. Analysis of the radial intensity profiles of the coma provided dust mass and dust production rate; the derived grain size distribution characteristics indicate an overabundance of large grains in the thermal emission. We estimate that activity started about 6 months before these observations, at a heliocentric distance of ∼8 au.
Icarus, 2010
We present the study of dust environment of dynamically new Comet C/2003 WT42 (LINEAR) based on spectroscopic and photometric observations. The comet was observed before and after the perihelion passage at heliocentric distances from 5.2 to 9.5 AU. Although the comet moved beyond the zone where water ice sublimation could be significant, its bright coma and extended dust tail evidenced the high level of physical activity. Afq values exceeded 3000 cm likely reaching its maximum before the perihelion passage. At the same time, the spectrum of the comet did not reveal molecular emission features above the reflected continuum. Reddening of the continuum derived from the cometary spectrum is nonlinear along the dispersion with the steeper slop in the blue region. The pair of the blue and red continuum images was analyzed to estimate a color of the comet. The mean normalized reflectivity gradient derived from the innermost part of the cometary coma equals to 8% per 1000 Å that is typical for Oort cloud objects. However, the color map shows that the reddening of the cometary dust varies over the coma increasing to 15% per 1000 Å along the tail axis. The photometric images were fitted with a Monte Carlo model to construct the theoretical brightness distribution of the cometary coma and tail and to investigate the development of the cometary activity along the orbit. As the dust particles of distant comets are expected to be icy, we propose here the model, which describes the tail formation taking into account sublimation of grains along their orbits. The chemical composition and structure of these particles are assumed to correspond with Greenberg's interstellar dust model of comet dust. All images were fitted with the close values of the model parameters. According to the results of the modeling, the physical activity of the comet is mainly determined by two active areas with outflows into the wide cones. The obliquity of the rotation axis of the nucleus equals to 20°relative to the comet's orbital plane. The grains occupying the coma and tail are rather large amounting to 1 mm in size, with the exponential size distribution of a À4.5 . The outflow velocities of the dust particles vary from a few centimeters to tens of meters per second depending on their sizes. Our observations and the model findings evidence that the activity of the nucleus decreased sharply to a low-level phase at the end of April-beginning of May 2007. About 190 days later, in the first half of November 2007 the nucleus stopped any activity, however, the remnant tail did not disappear for more than 1.5 years at least.
Photometry of distant active comet C/2010 S1 (LINEAR)
We present results of the photometric observations of dynamically new comet C/2010 S1 (LINEAR) made on June 18, 2012. The comet demonstrated the considerable level of physical activity at a heliocentric distance of 6.3 AU. The brightness, measured under a phase angle of 8.9 degree, was equal to 14.55±0.06 and 14.21±0.04 in V-and R-band respectively. The brightness distribution over the coma was found to be inverse proportion to the projected in a sky plane nucleocentic distance with a slope of about -1. Therefore, calculated Af ρ parameter, about 8400 cm and 8200 cm for V and R filters respectively, was used to estimate the dust production rate. Assuming the steady outflow of dust particles from the nucleus, the dust production rate was estimated to be between 20-60 kg/s depending on the assumed value of grain's albedo. The V-R color index obtained from the near nucleus region of the coma is in agreement with solar one and does not point out significant reddening of the reflected solar radiation in the spectral region of 540-683 nm.
Icarus, 2014
Comet C/1995 O1 (Hale-Bopp) has provided an unprecedented opportunity to observe a bright comet over a wide range of heliocentric distances. We present here Spitzer Space Telescope observations of Hale-Bopp from 2005 and 2008 that show a distinct coma and tail, the presence of which is uncommon given its large heliocentric distance (21.6 AU and 27.2 AU, respectively). The morphology of the dust is compared to dynamical models to understand the activity of the comet. Our analysis shows that the shape of Hale-Bopp's dust tail in these images cannot be explained using the usual Finson-Probstein (solar gravity + solar radiation pressure) dynamical model. Several alternative explanations are explored. The analysis suggests that the most likely cause of the discrepancy is that the dust is being charged by the solar wind, then being affected by the interplanetary magnetic field via the Lorentz force. Though this effect has been explored previously, if correct, this seems to be the first time that the Lorentz force has been required to model a cometary dust tail. The analysis also suggests that Hale-Bopp was actively emitting particles when these images were taken, and the tail characteristics changed between observations.
Delivery of Dust Grains From Comet C/2013 A1 (Siding Spring) to Mars
The Astrophysical Journal, 2014
Comet C/2013 A1 (Siding Spring) will have a close encounter with Mars on October 19, 2014. We model the dynamical evolution of dust grains from the time of their ejection from the comet nucleus to the Mars close encounter, 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 grains with higher velocities will reach Mars, peaking approximately 90-100 minutes after the close approach of the nucleus, and consisting mostly of millimeter-radius grains ejected from the comet nucleus at a heliocentric distance of approximately 9 AU or larger. At higher velocities, younger grains from sub-millimeter to several millimeter can reach Mars too, 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 −7 grains/m 2 . We include a detailed analysis of how the expected fluence depends on the grain density, ejection velocity, and sizefrequency distribution, to account for current model uncertainties and in preparation of possible refined model values in the near future.
Letter to the Editor Comet C/2013 A1 (Siding Spring) as seen with the
2014
Received...; accepted... The thermal emission of comet C/2013 A1 (Siding Spring) was observed on March 31, 2013, at a heliocentric distance of 6.48 au using the PACS photometer camera of the Herschel Space Observatory. The comet was clearly active, showing a coma that could be traced to a distance of ∼10′′, i.e. ∼50000 km. Analysis of the radial intensity profiles of the coma provided dust mass and dust production rate; the derived grain size distribution characteristics indicate an overabundance of large grains in the thermal emission. We estimate that activity started about 6 months before these observations, at a heliocentric distance of ∼8 au.
Dust environment and dynamical history of a sample of short-period comets
Astronomy & Astrophysics, 2014
Aims. In this work, we present an extended study of the dust environment of a sample of short period comets and their dynamical history. With this aim, we characterized the dust tails when the comets are active, and we made a statistical study to determine their dynamical evolution. The targets selected were 22P/Kopff, 30P/Reinmuth 1, 78P/Gehrels 2, 115P/Maury, 118P/Shoemaker-Levy 4, 123P/West-Hartley, 157P/Tritton, 185/Petriew, and P/2011 W2 (Rinner). Methods. We use two different observational data: a set of images taken at the Observatorio de Sierra Nevada and the A f ρ curves provided by the amateur astronomical association Cometas-Obs. To model these observations, we use our Monte Carlo dust tail code. From this analysis, we derive the dust parameters, which best describe the dust environment: dust loss rates, ejection velocities, and size distribution of particles. On the other hand, we use a numerical integrator to study the dynamical history of the comets, which allows us to determine with a 90% of confidence level the time spent by these objects in the region of Jupiter Family Comets. Results. From the Monte Carlo dust tail code, we derived three categories attending to the amount of dust emitted: Weakly active (115P, 157P, and Rinner), moderately active (30P, 123P, and 185P), and highly active (22P, 78P, and 118P). The dynamical studies showed that the comets of this sample are young in the Jupiter Family region, where the youngest ones are 22P (∼ 100 yr), 78P (∼ 500 yr), and 118P (∼ 600 yr). The study points to a certain correlation between comet activity and time spent in the Jupiter Family region, although this trend is not always fulfilled. The largest particle sizes are not tightly constrained, so that the total dust mass derived should be regarded as lower limits.
Icarus
Striated features, or striae, form in cometary dust tails due to an as-yet unconstrained process or processes. For the first time we directly display the formation of striae, at C/2006 P1 McNaught, using data from the SOHO LASCO C3 coronagraph. The nature of this formation suggests both fragmentation and shadowing effects are important in the formation process. Using the SOHO data with STEREO-A and B data from the HI-1 and HI-2 instruments, we display the evolution of these striae for two weeks, with a temporal resolution of two hours or better. This includes a period of morphological change on 2007 January 13-14 that we attribute to Lorentz forces caused by the comet's dust tail crossing the heliospheric current sheet. The nature of this interaction also implies a mixing of different sized dust along the striae, implying that fragmentation must be continuous or cascading. To enable this analysis, we have developed a new technique-temporal mapping-that displays cometary dust tails directly in the radiation beta (ratio of radiation pressure to gravity) and dust ejection time phase space. This allows for the combination of various data sets and the removal of transient motion and scaling effects. Highlights • We directly observe the formation of striated features in a comet's dust tail for the first time at C/2006 P1 McNaught. • We show how the temporal mapping technique-plotting dust tails in terms of radiation pressure effects against time-aligns features between multiple observations from Earth and spacecraft. • The striated tail features are shown to remain at the same locations in temporal maps over time, demonstrating the accuracy of the technique. • The mapping technique highlights a period of morphological change during 2007 January 13-14, which we argue from a comparison with solar wind simulations is from changing Lorentz force effects on dust grains as they cross the heliospheric current sheet.