The nucleus of Comet 67P/Churyumov-Gerasimenko: A new shape model and thermophysical analysis

Lowry, S. and Duddy, S.R. and Rozitis, B. and Green, S.F. and Fitzsimmons, A. and Snodgrass, C. and Hsieh, H.H. and Hainaut, O. (2012) The nucleus of Comet 67P/Churyumov-Gerasimenko: A new shape model and thermophysical analysis. Astronomy and Astrophysics, 548 . (A12) 1-15. ISSN 0004-6361. E-ISSN 1432-0746. (doi:https://doi.org/10.1051/0004-6361/201220116) (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided)

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Official URL
http://dx.doi.org/10.1051/0004-6361/201220116

Abstract

Context. Comet 67P/Churyumov-Gerasimenko is the target of the European Space Agency Rosetta spacecraft rendez-vous mission. Detailed physical characteristation of the comet before arrival is important for mission planning as well as providing a test bed for ground-based observing and data-analysis methods. Aims. To conduct a long-term observational programme to characterize the physical properties of the nucleus of the comet, via ground-based optical photometry, and to combine our new data with all available nucleus data from the literature. Methods. We applied aperture photometry techniques on our imaging data and combined the extracted rotational lightcurves with data from the literature. Optical lightcurve inversion techniques were applied to constrain the spin state of the nucleus and its broad shape. We performed a detailed surface thermal analysis with the shape model and optical photometry by incorporating both into the new Advanced Thermophysical Model (ATPM), along with all available Spitzer 8-24 ?m thermal-IR flux measurements from the literature. Results. A convex triangular-facet shape model was determined with axial ratios b/a = 1.239 and c/a = 0.819. These values can vary by as much as 7% in each axis and still result in a statistically significant fit to the observational data. Our best spin state solution has Psid = 12.76137 ± 0.00006 h, and a rotational pole orientated at Ecliptic coordinates ? = 78°(±10°), ? = + 58°(±10°). The nucleus phase darkening behaviour was measured and best characterized using the IAU HG system. Best fit parameters are: G = 0.11 ± 0.12 and H R(1,1,0) = 15.31 ± 0.07. Our shape model combined with the ATPM can satisfactorily reconcile all optical and thermal-IR data, with the fit to the Spitzer 24 ?m data taken in February 2004 being exceptionally good. We derive a range of mutually-consistent physical parameters for each thermal-IR data set, including effective radius, geometric albedo, surface thermal inertia and roughness fraction. Conclusions. The overall nucleus dimensions are well constrained and strongly imply a broad nucleus shape more akin to comet 9P/Tempel 1, rather than the highly elongated or "bi-lobed" nuclei seen for comets 103P/Hartley 2 or 8P/Tuttle. The derived low thermal inertia of <15 J m-2 K-1 s-1/2 is comparable with that measured for other comets scaled to similar heliocentric distances, and implies a surface regolith finer than lunar surface material. © 2012 ESO.

Item Type: Article
Additional information: Unmapped bibliographic data: C7 - A12 [EPrints field already has value set] LA - English [Field not mapped to EPrints] J2 - Astron. Astrophys. [Field not mapped to EPrints] AD - Centre for Astrophysics and Planetary Science, School of Physical Sciences (SEPnet), University of Kent, Canterbury CT2 7NH, United Kingdom [Field not mapped to EPrints] AD - Planetary and Space Sciences, Department of Physical Sciences, Open University, Milton Keynes, MK7 6AA, United Kingdom [Field not mapped to EPrints] AD - Astrophysics Research Centre, Queens University Belfast, Belfast, BT7 1NN, United Kingdom [Field not mapped to EPrints] AD - Max Planck Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany [Field not mapped to EPrints] AD - Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, United States [Field not mapped to EPrints] AD - European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei Munchen, Germany [Field not mapped to EPrints] DB - Scopus [Field not mapped to EPrints]
Uncontrolled keywords: Comets: individual: 67P/Churyumov-Gerasimenko, Infrared: planetary systems, Methods: data analysis, Techniques: photometric, Axial ratio, Best fit, Comet 9P/Tempel 1, Comets: individual: 67P/Churyumov-Gerasimenko, Data sets, Effective radius, European Space Agency, Flux measurements, Ground based, Heliocentric distances, Imaging data, Infrared: planetary systems, Inversion techniques, Lightcurves, Lunar surface, Methods:data analysis, Mission planning, Observational data, Optical photometry, Physical parameters, Rosetta, Shape model, Spin state, Spitzer, Techniques: photometric, Thermal inertia, Thermophysical, Astronomy, Equipment testing, Photometry, Space flight, Spin dynamics, Thermoanalysis, Surfaces
Subjects: Q Science > QB Astronomy
Divisions: Faculties > Sciences > School of Physical Sciences > Centre for Astrophysics and Planetary Sciences
Depositing User: Stephen Lowry
Date Deposited: 08 Dec 2015 22:11 UTC
Last Modified: 21 Dec 2015 16:04 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/52279 (The current URI for this page, for reference purposes)
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