In response to last month's Call for NASA Discovery Comet Mission Summaries, the CHagall Mission was submitted and is summarized below. Other summaries of comet-related missions are still welcome for future issues.
CHagall: A Discovery Mission Proposal
CHagall – Comet Hartley Analyses to Gather Ancient Links to Life– is a voyage of discovery that generates an abundance of essential scientific insights into comets, the ancient organic- and volatile-rich building blocks of our Solar System, thereby bringing us closer to answering the question: “Where did we come from?” The CHagall mission interactively explores the heterogeneity of the highly active comet 103P/Hartley 2, the only comet whose water is known to match terrestrial isotopic ratios. Spending 95% of its mission life within 10 km of the comet, CHagall makes repeated, detailed measurements of the subsurface, surface, and innermost coma as the comet transitions from minimal to maximum activity. CHagall literally and figuratively breaks new scientific ground by repeatedly probing the variability of subsurface compositions, structures, and thermal properties before explosively excavating more primitive materials from depth for analysis by CHagall’s suite of remote sensing instruments. As the first integrated study of the physical and compositional heterogeneity of the surface and sub-surface of a comet, the CHagall mission will revolutionize our understanding of cometary formation and evolution, while paving the way for future missions to return cryogenic samples of highly volatile ices that are uniquely preserved on comets.
Jessica Sunshine, Principal Investigator
University of Maryland
Abstracts of recent PhD dissertations. Limited to 3000 characters.
Spectrophotometric Analysis of Cometary Nuclei From In Situ Observations
- IAPS - INAF, Via del fosso del cavaliere 100, Roma, Italy
Topic of this work are comets, small and elusive objects that may hold great secrets about the origin of the Solar System and life on Earth, being among the most primitive objects. The method of investigation addressed in this work is the visible and infrared spectrophotometry by imaging spectrometers, designed for the observation of remote planetary atmospheres and surfaces, capable to acquire hyperspectral data with high spatial and spectral resolution. The context under which this mission moves its steps is described in the first chapter. In the second chapter the performances of the VIRTIS instrument, onboard Rosetta spacecraft, are analyzed in detail. In particular the modeling of the signal to noise ratio is the main argument of this chapter. The third chapter shows simulations of possible spectra of the comet's nucleus, which are useful for both a comparison with real spectra, and for a planning of the observations. Hapke's radiative transfer model is used to invert acquired data to infer physical properties. The fourth chapter introduces a method for spectral modeling. It includes the information on the instrumental noise, permitting the analysis of the goodness of the models, and an estimation of the error of the retrieved parameters. The fifth chapter presents the spectral analysis of Tempel 1 and Hartley 2 whose data are coming from Deep Impact space mission and its extended investigation. The sixth chapter shows the photometric analysis of Lutetia asteroid, which was encountered by Rosetta during its cruise phase. This work have paved the way to the analysis of the final target of Rosetta: comet 67P/Churyumov-Gerasimenko. The tools presented are currently used by the VIRTIS Team to produce works on the comet, that are recommended to the reader. Since a complete analysis on the comet is outside the scope of this work, just preliminary results are shown here.
NASA ADS: 2015arXiv150308172R arXiv: 1503.08172
Abstracts of articles in press or recently published. Limited to 3000 characters.
Short-Term Variability of Comet C/2012 S1 (ISON) at 4.8 AU From the Sun
- Instituto de Astrofísica de Andalucia-CSIC, 18008-Granada, Spain
Context. We observed comet C/2012 S1 (ISON) during six nights in February 2013 when it was at 4.8 AU from the Sun. At this distance and time the comet was not very active and it was theoretically possible to detect photometric variations likely due to the rotation of the cometary nucleus.
Aims: The goal of this work is to obtain differential photometry of the comet inner coma using different aperture radii in order to derive a possible rotational period.
Methods: Large field of view images were obtained with a 4 k × 4 k CCD at the f/3 0.77 m telescope of La Hita Observatory in Spain. Aperture photometry was performed in order to get relative magnitude variation versus time. Using calibrated star fields we also obtained ISON's R-magnitudes versus time. We applied a Lomb-Scargle periodogram analysis to get possible periodicities for the observed brightness variations, directly related with the rotation of the cometary nucleus.
Results: The comet light curve obtained is very shallow, with a peak-to-peak amplitude of 0.03 ± 0.02 mag. A tentative synodic rotational period (single-peaked) of 14.4 ± 1.2 h for ISON's nucleus is obtained from our analysis, but there are other possibilities. We studied the possible effect of the seeing variations in the obtained periodicities during the same night, and from night to night. These seeing variations had no effect on the derived periodicity. We discuss and interpret all possible solutions for the rotational period of ISON's nucleus.
Astronomy & Astrophysics (Published)
DOI: 10.1051/0004-6361/201425265 NASA ADS: 2015A&A...575A..52S arXiv: 1501.05274
Density and Charge of Pristine Fluffy Particles From Comet 67P/Churyumov-Gerasimenko
- INAF – OATS, Trieste, Italy
- INAF – IIAPS, Rome, Italy
- “Parthenope” Univ., Naples, Italy
- JPL, Pasadena, CA 91109, USA
- Wigner Research Centre for Physics, Budapest, Hungary
- MPI Goettingen, Germany
- LESIA, Meudon, France
- INAF – OACN, Naples, Italy
- INAF – OAR, Roma, Italy
- CSIC, Granada, Spain
- ESA - ESTEC, The Netherlands
- MPI, Heidelberg, Germany
- Planetary and Space Sciences, UK.
- Laboratoire d'Astrophysique de Marseilles, France
- The University of Kent, UK
- UnispaceKent, UK
- Departamento de Física Aplicada, Granada, Spain
- INTA-CSIC, Madrid, Spain
- ISSI, Bern, Switzerland
- Selex-ES, Firenze, Italy
- Virginia Polytechnic Institute, VA 24061, USA
- University of Florida, USA
- ESA-ESAC, Madrid, Spain
The Grain Impact Analyzer and Dust Accumulator (GIADA) instrument on board ESA’s Rosetta mission is constraining the origin of the dust particles detected within the coma of comet 67P/Churyumov–Gerasimenko (67P). The collected particles belong to two families: (i) compact particles (ranging in size from 0.03 to 1mm), witnessing the presence of materials that underwent processing within the solar nebula and (ii) fluffy aggregates (ranging in size from 0.2 to 2.5 mm) of sub-micron grains that may be a record of a primitive component, probably linked to interstellar dust. The dynamics of the fluffy aggregates constrain their equivalent bulk density to <1 kg m−3. These aggregates are charged, fragmented, and decelerated by the spacecraft negative potential and enter GIADA in showers of fragments at speeds <1m s−1. The density of such optically thick aggregates is consistent with the low bulk density of the nucleus. The mass contribution of the fluffy aggregates to the refractory component of the nucleus is negligible and their coma brightness contribution is less than 15%.
Astrophysical Journal Letters (Published)
DOI: 10.1088/2041-8205/802/1/L12 NASA ADS: 2015ApJ...802L..12F
Imaging Polarimetry of Comet C/2013 V1 (Boattini) and Comet 290P/Jager Before and After Perihelion
- Department of Physics, Assam University, Silchar 788011, India
- Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263129, India
We report the results obtained from the optical polarimetric study of the light scattered by Comet C/2013 V1 (Boattini) and Comet 290P/Jager at lower phase angles. The polarimetric observations of two comets have been performed with the 1.04-metre Sampurnanand telescope of ARIES near Nainital in India on 4th & 5th of December, 2013 and on 24th April, 2014 using R photometric band (λ = 630 nm, Δλ=120nm). We covered observations in both the pre and post perihelion passage of Comet C/2013 V1 (Boattini) and Comet 290P/Jager at two phase angles ~ 13 deg and 27 deg. The degree of polarization changes from (-1.4±0.3)% to (+2.8±0.5)% for Comet C/2013 V1 (Boattini) and (-1.6±0.5)% to (+2.5±0.5)% for Comet 290P/Jager at phase angles ~ 13 deg and 27 deg respectively. The change in the physical properties of cometary dust is being well studied from the polarization maps obtained for both the period of observations. It is found that the aperture polarization values are comparable to those of other comets. The variation in the brightness profile of both the comets from the standard canonical nature is also being observed in both the solar and anti-solar direction during this phase which suggests the various physical evolution influencing the cometary comae.
Monthly Notices of the Royal Astronomical Society (In press)
NASA ADS: 2015arXiv150308151R arXiv: 1503.08151
Crater-Diameter Distribution on Comets 9P and 81P and Potential Meteoroid Streams Crossing Their Orbits
- Main Astronomical Observatory of NAS of Ukraine, Akademika Zabolotnoho 27, 03680 Kyiv, Ukraine
- Astronomical Institute of the Slovak Academy of Sciences, SK-05960, Tatranska Lomnica, Slovak Republic
We attempt to answer two questions concerning the impacts of stream meteoroids on the nuclei of comets 9P/Tempel 1 and 81P/Wild 2: firstly, how many streams cross the orbits of both comets and, secondly, what is the index of the differential mass distribution of impactors, s, when we assume that a prevailing number of the craters on the surfaces of cometary nuclei were created by stream meteoroids? We found that 110 and 129 potential streams originating from comets likely cross the orbits of 9P and 81P, respectively (and 103 potential streams cross the orbit of 1P/Halley, for comparison). If we consider the more compact streams originating from asteroids, the 9P and 81P pass through such streams 15,664 and 65,368 times. Neither these large numbers of passages imply, however, enough large impactors to excavate the whole observed variety of craters on studied comets. For all craters on 9P and 81P, s = 2.09+/-0.01 and s = 2.25+/-0.03, respectively. The craters on 81P seem to be, however, excavated by the impactors from four discernible sources. For two numerous enough sources we find s = 5.6+/-0.2 and s = 5.2+/-0.5. The difference between the indices for the set of all craters and the sets of their partial groups obviously implies an unknown cosmogonic consequence.
Icarus (In press)
Comets as Collisional Fragments of a Primordial Planetesimal Disk
- CNRS, Observatoire de la Cote d'Azur, Nice, France
- P.A.S. Space Research Center, Warsaw
- Dept. of Physics and Astronomy, Uppsala University
The Rosetta mission and its exquisite measurements have revived the debate on whether comets are pristine planetesimals or collisionally evolved objects. We investigate the collisional evolution experienced by the precursors of current comet nuclei during the early stages of the Solar System, in the context of the so-called "Nice Model". We consider two environments for the collisional evolution: (1) the trans-planetary planetesimal disk, from the time of gas removal until the disk was dispersed by the migration of the ice giants, and (2) the dispersing disk during the time that the scattered disk was formed. Simulations have been performed, using different methods in the two cases, to find the number of destructive collisions typically experienced by a comet nucleus of 2km radius. In the widely accepted scenario, where the dispersal of the planetesimal disk occurred at the time of the Late Heavy Bombardment about 4Gy ago, comet-sized planetesimals have a very small chance to survive against destructive collisions in the disk. On the extreme assumption that the disk was dispersed directly upon gas removal, there is a chance for a significant fraction of the planetesimals to remain intact. However, these survivors would still bear the marks of many non-destructive impacts. Thus, the Nice Model of Solar System evolution predicts that typical km-sized comet nuclei are predominantly fragments resulting from collisions experienced by larger parent bodies. An important goal for further research is to investigate, whether the observed properties of comet nuclei are compatible with such a collisional origin.
Astronomy & Astrophysics (In press)
NASA ADS: arXiv:1504.04512 arXiv: 1504.04512