Deep Impact: Excavating Comet Tempel 1

A’Hearn, Michael F.; Belton, M. J. S.; Delamere, W. A.; Kissel, J.; Klaasen, K. P.; McFadden, L. A.; Meech, К. J.; Melosh, H. J.; Schultz, P. H.; Sunshine, J. M.; Thomas, P. C.; Veverka, J.; Yeomans, D. K.; Baca, M.; Busko, I.; Crockett, Christopher; Collins, Steven M.; Desnoyer, M.; Eberhardy, C. A.; Ernst, C. M.; Farnham, T. L.; Feaga, Lori M.; Groussin, O.; Hampton, Donald; Ипатов, С. И.; Li, J. Y.; Lindler, Don J.; Lisse, C. M.; Mastrodemos, Nickolaos; Owen, W. M.; Richardson, James E.; Wellnitz, D. D.; White, R. L.

doi:10.1126/science.1118923

Cited by 740 publications

(268 citation statements)

References 21 publications

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“…The compact aggregates are assumed to have a fractal dimension , which corresponds to the value when the D p 2.5 maximum compression of fluffy aggregates is attained (Wada et al 2008). Our calculation using the superposition T-matrix method (TMM) showed that the geometric albedo of the compact aggregates is ∼0.04 at visible wavelengths (see Kimura, Kolokolova, & Mann 2003), and this value is identical to the albedo derived from an observation of the T1 surface (A'Hearn et al 2005). We also calculate (the ratio of solar rab ∼ 0.3 diation pressure to solar gravity) for the compact aggregates, using Mie theory with the optical constants deduced from the Maxwell-Garnett mixing rule (MG) (see Mukai et al 1992): This is also consistent with b for high-velocity ejecta within the DI ejecta plume (e.g., Meech et al 2005).…”

Section: Aggregate Modelsupporting

confidence: 63%

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Comet 9P/Tempel 1: Interpretation with theDeep ImpactResults

Yamamoto

Kimura

Zubko

et al. 2008

ApJ

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According to our common understandings, the original surface of a short-period comet nucleus has been lost by sublimation processes during its close approaches to the Sun. Sublimation results in the formation of a dust mantle on the retreated surface and in chemical differentiation of ices over tens or hundreds of meters below the mantle. In the course of NASA's Deep Impact mission, optical and infrared imaging observations of the ejecta plume were conducted by several researchers, but their interpretations of the data came as a big surprise: (1) The nucleus of comet 9P/Tempel 1 is free of a dust mantle but maintains its pristine crust of submicron-sized carbonaceous grains. (2) Primordial materials are accessible already at a depth of several tens of centimeters with abundant silicate grains of submicrometer sizes. In this study, we demonstrate that a standard model of cometary nuclei explains well available observational data: (1) A dust mantle with a thickness of ∼1-2 m builds up on the surface, where compact aggregates larger than tens of micrometers dominate. (2) Large fluffy aggregates are embedded in chemically differentiated layers as well as in the deepest part of the nucleus with primordial materials. We conclude that the Deep Impact results do not need any peculiar view of a comet nucleus.

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Section: Aggregate Modelsupporting

confidence: 63%

“…Plenty of DI observational results support the standard model: (1) The presence of a dust mantle on T1 is evidenced by a low thermal inertia of the nucleus estimated from its thermal maps (A'Hearn et al 2005).…”

Section: Introductionmentioning

confidence: 73%

Comet 9P/Tempel 1: Interpretation with theDeep ImpactResults

Yamamoto

Kimura

Zubko

et al. 2008

ApJ

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“…Furthermore, that lack of overall correlation between H 2 O, CO and CO 2 implies that the outgassing from the nucleus is not correlated, or that CO and CO 2 are not strictly embedded in H 2 O. For Temple 1, material was found in layers and supports the above idea (16). In summary, the coma composition has been measured over many rotational periods of the comet and a wide range of latitudes with high time resolution and compositional detail.…”

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confidence: 73%

Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko

Hässig

Altwegg

Balsiger

et al. 2015

Science

239

188

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Abstract:Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early Solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: H 2 O, CO, and CO 2 . These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface.One Sentence Summary: ROSINA/DFMS shows that 67P/Churyumov-Gerasimenko has a highly heterogeneous coma with large diurnal and possibly seasonal variations. Main Text:Initially, comets were classified depending on the location where they formed in the protoplanetary disc (1,2). This classification assumed a similar composition of the nucleus within a given formation region. No cometary nucleus composition has been sampled in situ. Rather, it is implicitly assumed that measurements of the outgassing of comets reveal the composition of the volatile components of the nucleus. However, compositional homogeneity of at least one comet was confirmed by studying outgassing from the fragments of the broken up comet Schwassmann-Wachmann 3 (3). Detailed observations of other cometary comae indicated that there is evidence of heterogeneity. Missions to comet Halley detected release of volatiles in multiple jet-like features that were dominantly seen on the sunlit side of the nucleus (4, 5). The Deep Impact mission detected asymmetries in composition in the coma of Tempel 1 (6). In particular, these remote sensing observations at Tempel 1 indicated an absence of correlation between H 2 O and CO 2 in the coma.Detailed, close up cometary images have also showed visible differences between different areas of cometary nuclei. These images suggested that heterogeneity in the coma of a comet may be related to heterogeneity of the nucleus. Observations by EPOXI at Hartley 2 in 2010 near perihelion indicated that the nucleus is complex, with two different sized lobes separated by a middle waist region that is smoother and lighter in color (7). Outgassing from sunlit surfaces of the nucleus revealed that the waist and one of the lobes were very active. A CO 2 source was detected at the small lobe of the comet, while the waist was more active in H 2 O and had a significantly lower CO 2 content. Based on these coma observations, it has been tentatively suggested that the heterogeneity in the comet's nucleus was primordial (7). Seasonal effects could not be ruled out because the observations also showed a complex rotational state for the comet (7). The smaller of the two lobes ...

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“…Excavation of Tempel 1 by a projectile carried by the Deep Impact spacecraft suggests a nucleus with volatiles hidden below a thin mantle of fine powdery material (A'Hearn et al, 2005). The surface of 67P/ChuryumovGerasimenko is characteristically similar to 9P/ Tempel 1 in terms of its phase function and it is anticipated to have a similar thermal inertia (Lamy et al, 2006).…”

Section: The Comet Ice Modelmentioning

confidence: 99%

Computer modelling of a penetrator thermal sensor

Paton

Kargl

Ball

et al. 2010

Advances in Space Research

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The Philae lander is part of the Rosetta mission to investigate comet 67P/Churyumov-Gerasimenko. It will use a harpoon like device to anchor itself onto the surface. The anchor will perhaps reach depths of 1-2 m. In the anchor is a temperature sensor that will measure the boundary temperature as part of the MUPUS experiment. As the anchor attains thermal equilibrium with the comet ice it may be possible to extract the thermal properties of the surrounding ice, such as the thermal diffusivity, by using the temperature sensor data. The anchor is not an optimal shape for a thermal probe and application of analytical solutions to the heat equation is inappropriate. We prepare a numerical model to fit temperature sensor data and extract the thermal diffusivity. Penetrator probes mechanically compact the material immediately surrounding them as they enter the target. If the thermal properties, composition and dimensions of the penetrator are known, then the thermal properties of this pristine material may be recovered although this will be a challenging measurement. We report on investigations, using a numerical thermal model, to simulate a variety of scenarios that the anchor may encounter and how they will affect the measurement.

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Deep Impact: Excavating Comet Tempel 1

Cited by 740 publications

References 21 publications

Comet 9P/Tempel 1: Interpretation with theDeep ImpactResults

Comet 9P/Tempel 1: Interpretation with theDeep ImpactResults

Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko

Computer modelling of a penetrator thermal sensor

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