Short Period Jupiter Family Comets Research Articles

Optical observations and dust modelling of comet 156P/Russell-LINEAR

Comet 156P/Russell-LINEAR is a short period Jupiter family comet with an orbital period of 6.44 years. The results from spectroscopic, photometric, polarimetric observations and dust modelling studies are presented here. From the spectroscopic study, strong emissions from CN(Δν=0), C3 (λ4050 Å), C2(Δν=+1) and C2(Δν=0) can be observed during both the epochs of our observations. The Q(C2)/Q(CN) ratio classifies the comet as a typical comet. The imaging data reveals the presence of jets. The dust emission from the comet is observed to have a non-steady state outflow due to the presence of these strong jets which subside in later epochs, resulting in a steady state outflow. Polarimetric study at two different phase angles reveals the degree of polarization to be comparable to Jupiter family comets at similar phase angles. Localized variations in polarization values are observed in the coma. The dust modelling studies suggest the presence of high amount of silicate/low absorbing material and indicate the coma to be dominated by higher amount of large size grains with low porosity having power law size distribution index = 2.4. The observed activity and dust properties points to a similarity to another Jupiter family comet, 67P/Churyumov–Gerasimenko.

Solar-insolation-induced changes in the coma morphology of comet 67P/Churyumov-Gerasimenko

Context. 67P/Churyumov-Gerasimenko (67P/C-G) is a short-period Jupiter family comet with an orbital period of 6.55 years. Being the target comet of ESA’s Rosetta mission, 67P/C-G has become one of the most intensively studied minor bodies of the Solar System. The Rosetta Orbiter and the Philae Lander have brought us unique information about the structure and activity of the comet nucleus, as well as its activity along the orbit, composition of gas, and dust particles emitted into the coma. However, as Rosetta stayed in very close proximity to the cometary nucleus (less than 500 km with a few short excursions reaching up to 1500 km), it could not see the global picture of a coma at the scales reachable by telescopic observations (103 - 105 km). Aims. In this work we aim to connect in-situ observations made by Rosetta with the morphological evolution of the coma structures monitored by the ground-based observations. In particular, we concentrate on causal relationships between the coma morphology and evolution observed with the Nordic Optical Telescope (NOT) in the Canary Islands, and the seasonal changes of the insolation and the activity of the comet observed by the Rosetta instruments. Methods. Comet 67P/C-G was monitored with the NOT in imaging mode in two colors. Imaging optical observations were performed roughly on a weekly basis, which provides good coverage of short- and long-term variability. With the three dimensional modeling of the coma produced by active regions on the Southern Hemisphere, we aim to qualify the observed morphology by connecting it to the activity observed by Rosetta. Results. During our monitoring program, we detected major changes in the coma morphology of comet 67P/C-G. These were longterm and long-lasting changes. They do not represent any sudden outburst or short transient event, but are connected to seasonal changes of the surface insolation and the emergence of new active regions on the irregular shaped comet nucleus. We have also found significant deviations in morphological changes from the prediction models based on previous apparitions of 67P/C-G, like the time delay of the morphology changes and the reduced activity in the Northern Hemisphere. According to our modeling of coma structures and geometry of observations, the changes are clearly connected with the activity in the Southern Hemisphere observed by the Rosetta spacecraft.

Optical observations of comet 67P/Churyumov-Gerasimenko with the Nordic Optical Telescope

Context. 67P/Churyumov-Gerasimenko (67P) is a short-period Jupiter-family comet that was chosen as a target for the Rosetta mission by the European Space Agency (ESA). Monitoring of 67P with the Nordic Optical Telescope (NOT; La Palma, Spain) intends to aid this mission by providing ground-based reference information about the overall activity of the target and its astrometric position before the rendezvous. One motivation for our observations was to monitor sudden major increases in activity because they might have affected the Rosetta mission planning. None were observed. Ground-based photometric observations register the global activity of the comet, while the Rosetta spacecraft mostly measures local events. These data combined can lead to new insights into the comet behavior.Aims. The aim of this work is to perform the photometric and the astrometric monitoring of comet 67P with the NOT and to compare the results with the latest predictions for its position and activity. A new method of fitting extended-source components to the target surface brightness distribution was developed and applied to the data to estimate the size and contribution of the coma to the total brightness of the target.Methods. Comet 67P was monitored by the NOT in service mode during the period between 12.5.2013 and 11.11.2014. The very first observations were performed in the V band alone, but in the latest observations, the R band was used as well to estimate the color and nature of activity of the target. We applied a new method for estimating the coma size by deconvolving the point spread function profile from the image, which used Markov chain Monte Carlo and Bayesian statistics. This method will also be used for coma size estimations in further observations after the solar conjunction of 67P.Results. Photometric magnitudes in two colors were monitored during the period of observations. At the end of April 2014, the beginning of activity was observed. In late September 2014, a minor dip in cometary activity was measured. Otherwise, the activity of the comet was close to the expected values. For some of the observations, we were able to determine limits for the physical size and brightness of the coma by studying the surface brightness distribution of the target. The astrometric calibration results we obtained were consistent with the predictions of the ephemerides of the Minor Planet Center, but at the moment these results are superseded with the more precise astrometric data from the Rosetta spacecraft.

Single minerals, carbon- and ice-coated single minerals for calibration of GIADA onboard ROSETTA to comet 67P/Churyumov–Gerasimenko

In preparation of the rendezvous of the European Space Agency Rosetta spacecraft with short period Jupiter Family comet 67P/Churyumov–Gerasimenko we undertook the selection and characterization of mineral grains to serve as analogs of dust from the comet. Specifically, these dust analogs are used to calibrate the performance of the onboard Grain Impact Analyser and Dust Accumulator (GIADA) instrument at the comet. Our selection of suitable natural analog minerals was guided by the finding of an asteroid-like mineralogy in Jupiter Family comet Wild 2. We selected (1) anhydrous silicate minerals [forsterite and fayalite (end-members of the olivine solid solution series), enstatite, melilite, alkali-feldspar and anorthite], (2) hydrated layer silicates (kaolinite, serpentine, and talc), (3) pyrrhotite, and (4) corundum. Four size fractions, viz. 500–250µm, 250–100µm, 100–50µm and 50–20µm, were prepared for each analog mineral. In addition, each selected analog mineral, from each size bin, was coated with carbon layer. Similarly another set of analog grains were coated with a layer of sodium hexafluorosilicate (Na2SiF6) crystals representing comet water-ice, for what concerns their optical properties. Laboratory experiments to calibrate the GIADA performance using these analogs are currently underway. We report the availability of analogs that will enable the calibration of various instruments onboard Rosetta.

The Scattered Disk as the Source of the Jupiter Family Comets

The short-period Jupiter family comets (JFCs) are thought to originate in the Kuiper Belt; specifically, a dynamical subclass of the Kuiper Belt known as the is argued to be the dominant source of JFCs. However, the best estimates from observational surveys indicate that this source may fall short by more than 2 orders of magnitude of the estimates obtained from theoretical models of the dynamical evolution of Kuiper Belt objects into JFCs. We reexamine the scattered disk as a source of the JFCs and make a rigorous estimate of the discrepancy. We find that the uncertainties in the dynamical models combined with a change in the size distribution function of the scattered disk at faint magnitudes (small sizes) beyond the current observational limit offer a possible but problematic resolution to the discrepancy. We discuss several other possibilities: that the present population of JFCs is a large fluctuation above their long-term average, that larger scattered disk objects tidally break up into multiple fragments during close planetary encounters as their orbits evolve from the trans-Neptune zone to near Jupiter, or that there are alternative source populations that contribute significantly to the JFCs. Well-characterized observational investigations of the Centaurs, objects that are transitioning between the trans-Neptune Kuiper Belt region and the inner solar system, can test the predictions of the non-steady state and the tidal breakup hypotheses. The classical and resonant classes of the Kuiper Belt are worth reconsideration as significant additional or alternate sources of the JFCs.

Short-period Jupiter family comets after Stardust

The NASA Stardust mission has provided for laboratory study an extensive data set of cometary dust of known provenance (from comet 81P/Wild 2) yielding detailed insights into the composition of the comet. Combined with the results of data from other missions to short-period Jupiter family comets (JFC), this has greatly deepened the understanding of such objects. If depressions on the surface of comet 81P/Wild 2 are all taken as evidence of impact cratering, their number suggests a long occupancy in the outer region of the Solar System. The dust from comet 81P/Wild 2 has been shown to be heavily deficient in pre-Solar grains and rich in materials formed at high temperatures in the inner Solar System. Although it is too early to know if this is typical of JFC, it does argue for rapid and thorough mixing of materials in the disk on timescales related to comet formation, and may also suggest outward migration of small icy bodies after their formation. Thus, instead of providing mainly new knowledge of the pre-Solar materials expected to be rich in comets, Stardust and comet 81P/Wild 2 have instead focussed attention on large-scale transport processes during the critical period when cometary parent bodies were forming in the early Solar System.

Origins of Solar System Dust beyond Jupiter

The measurements of cosmic interplanetary dust by the instruments on board the Pioneer 10 and 11 spacecraft contain the dynamical signature of dust generated by Edgeworth-Kuiper Belt objects, as well as short period Oort Cloud comets and short period Jupiter family comets. While the dust concentration detected between Jupiter and Saturn is mainly due to the cometary components, the dust outside Saturn's orbit is dominated by grains originating from the Edgeworth-Kuiper Belt. In order to sustain a dust concentration that accounts for the Pioneer measurements, short period external Jupiter family comets, on orbits similar to comet 29P/Schwassmann-Wachmann-1, have to produce $8\times 10^4:{\rm g}:{\rm s}^{-1}$ of dust grains with sizes between 0.01 and $6:{\rm mm}$. A sustained production rate of $3\times 10^5:{\rm g}:{\rm s}^{-1}$ has to be provided by short period Oort cloud comets on 1P/Halley-like orbits. The comets can not, however, account for the dust flux measured outside Saturn's orbit. The measurements there can only be explained by a generation of dust grains in the Edgeworth-Kuiper belt by mutual collisions of the source objects and by impacts of interstellar dust grains onto the objects' surfaces. These processes have to release in total $5\times 10^7:{\rm g}:{\rm s}^{-1}$ of dust from the Edgeworth Kuiper belt objects in order to account for the amount of dust found by Pioneer beyond Saturn, making the Edgeworth-Kuiper disk the brightest extended feature of the Solar System when observed from afar.

Temporary Satellite Capture of Short-Period Jupiter Family Comets from the Perspective of Dynamical Systems

The Temporary Satellite Capture (TSC) of short-period comets, such as Oterma and Helin-Roman-Crockett, by Jupiter has intrigued astronomers for many years. A widely accepted approach to study TSC is to numerically integrate the equations of motion for the n-body problem using a wide range of initial conditions obtained from the heliocentric two-body problem; then, a search ensues for instances when the Joviocentric energy becomes negative. More recently, a preliminary analysis involving the application of Dynamical Systems Theory (DST) to the Sun-Jupiter-comet three-body problem has provided significant insight into the motion in the Sun-Jupiter system and offered a simple model to account for the TSC phenomena observed in Jupiter family short-period comets. The accuracy of this model can be immediately verified since ephemeris data is available for comet trajectories.

CCD photometry of distant comets II

R band CCD photometric observations of short period Jupiter family comets in the heliocentric region of 2.11 AU Rh 5:63 AU were performed using the 4.2 m William Herschel Telescope on La Palma in December 1998. 22 comets were targeted, including the comet-asteroid transition object 49P/Arend{Rigaux. Out of a total of ten detected comets, six were seen to display substantial outgassing (48P, 65P, 74P, 103P, 128P, and 139P), with the remaining four comets (7P, 9P, 22P, and 49P) being stellar in appearance. Nuclear radius measurements and relative dust production rates in terms of Af were measured for these comets, along with upper limits for the remaining twelve undetected comets (6P, 44P, 51P, 54P, 57P, 63P, 71P, 73P, 79P, 86P, 87P, and 100P). The inactive comets had nuclear radii in the range 1.8 km rN 4:4 km, while upper limits for the active and undetected comets (assuming they all lay within the eld of view) were between 0.6 km and 12.7 km, for an assumed albedo of 0.04. Even if one applies the previously measured maximum axis ratio of 2.6:1 and the minimum measured albedo of 0.02 to the undetected comets, their projected semi-major axes are all constrained to below 8 km. For the active comets, photometric proles of their dust comae were measured and are consistent with those of steady state coma models.