Solar wind sputtering of dust on the surface of 67P/Churyumov-Gerasimenko

Würz, Peter; Rubin, Martin; Altwegg, Kathrin; Balsiger, H.; Berthelier, Jean‐Jacques; Bieler, André; Calmonte, Ursina; Keyser, Johan De; Fiethe, Björn; Fuselier, S. A.; Galli, André; Gasc, Sébastien; Gombosi, T. I.; Jäckel, A.; Roy, Léna Le; Mall, U.; Rème, H.; Tenishev, V.; Tzou, Chia-Yu

doi:10.1051/0004-6361/201525980

Cited by 58 publications

(77 citation statements)

References 38 publications

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“…They measure the strongest emissions for late 2014 at northern sub-spacecraft latitudes. Wurz et al (2015) report highest abundances of neutral H 2 O for northern (positive) latitudes in the coma of 67P. Those measurements were performed with the ROSINA-DFMS mass spectrometer during several days along a bound orbit at ≈10 km distance from the nucleus.…”

Section: Heterogeneity Effectsmentioning

confidence: 99%

Comparison of 3D kinetic and hydrodynamic models to ROSINA-COPS measurements of the neutral coma of 67P/Churyumov-Gerasimenko

Bieler

Altwegg

Balsiger

et al. 2015

A&A

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106

113

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ABSTRACT67P/Churyumov-Gerasimenko (67P) is a Jupiter-family comet and the object of investigation of the European Space Agency mission Rosetta. This report presents the first full 3D simulation results of 67P's neutral gas coma. In this study we include results from a direct simulation Monte Carlo method, a hydrodynamic code, and a purely geometric calculation which computes the total illuminated surface area on the nucleus. All models include the triangulated 3D shape model of 67P as well as realistic illumination and shadowing conditions. The basic concept is the assumption that these illumination conditions on the nucleus are the main driver for the gas activity of the comet. As a consequence, the total production rate of 67P varies as a function of solar insolation. The best agreement between the model and the data is achieved when gas fluxes on the night side are in the range of 7% to 10% of the maximum flux, accounting for contributions from the most volatile components. To validate the output of our numerical simulations we compare the results of all three models to in situ gas number density measurements from the ROSINA COPS instrument. We are able to reproduce the overall features of these local neutral number density measurements of ROSINA COPS for the time period between early August 2014 and January 1 2015 with all three models. Some details in the measurements are not reproduced and warrant further investigation and refinement of the models. However, the overall assumption that illumination conditions on the nucleus are at least an important driver of the gas activity is validated by the models. According to our simulation results we find the total production rate of 67P to be constant between August and November 2014 with a value of about 1 × 10 26 molecules s −1 .

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Section: Heterogeneity Effectsmentioning

confidence: 99%

Comparison of 3D kinetic and hydrodynamic models to ROSINA-COPS measurements of the neutral coma of 67P/Churyumov-Gerasimenko

Bieler

Altwegg

Balsiger

et al. 2015

A&A

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106

113

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“…Sputtering of dust refractory material from the surface of 67P (Wurz et al 2015) is observed. When Rosetta was 10 km from the comet in mid-October 2014, DFMS observed nonvolatile refractory species (Na, K, Si, and Ca) in the coma.…”

Section: Conditions At the Comet From Octobermentioning

confidence: 92%

“…At such low outgassing rates, the solar wind, while deflected because of pickup of cometary ions, has access to the nucleus. The non-volatile neutrals in the coma (see, Wurz et al 2015) are evidence of solar wind sputtering of these neutrals from the comet surface. Since the solar wind threads the entire neutral coma (see Fig.…”

Section: Discussionmentioning

confidence: 99%

ROSINA/DFMS and IES observations of 67P: Ion-neutral chemistry in the coma of a weakly outgassing comet

Fuselier

Altwegg

Balsiger

et al. 2015

A&A

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Context. The Rosetta encounter with comet 67P/Churyumov-Gerasimenko provides a unique opportunity for an in situ, up-close investigation of ion-neutral chemistry in the coma of a weakly outgassing comet far from the Sun. Aims. Observations of primary and secondary ions and modeling are used to investigate the role of ion-neutral chemistry within the thin coma. Methods. Observations from late October through mid-December 2014 show the continuous presence of the solar wind 30 km from the comet nucleus. These and other observations indicate that there is no contact surface and the solar wind has direct access to the nucleus. On several occasions during this time period, the Rosetta/ROSINA/Double Focusing Mass Spectrometer measured the low-energy ion composition in the coma. Organic volatiles and water group ions and their breakup products (masses 14 through 19), CO + , and CO + 2 (masses 28 and 44) and other mass peaks (at masses 26, 27, and possibly 30) were observed. Secondary ions include H 3 O + and HCO + (masses 19 and 29). These secondary ions indicate ion-neutral chemistry in the thin coma of the comet. A relatively simple model is constructed to account for the low H 3 O + /H 2 O + and HCO + /CO + ratios observed in a water dominated coma. Results from this simple model are compared with results from models that include a more detailed chemical reaction network. Results. At low outgassing rates, predictions from the simple model agree with observations and with results from more complex models that include much more chemistry. At higher outgassing rates, the ion-neutral chemistry is still limited and high HCO + /CO + ratios are predicted and observed. However, at higher outgassing rates, the model predicts high H 3 O + /H 2 O + ratios and the observed ratios are often low. These low ratios may be the result of the highly heterogeneous nature of the coma, where CO and CO 2 number densities can exceed that of water.

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“…Such surface production mechanisms have not been considered in models of cometary comae. We note that water ion-surface collisions may also contribute to the observed sputtering of other surface species, such as refractory elements (Wurz et al 2015).…”

Section: Discussionmentioning

confidence: 99%

Dynamic Deuterium Enrichment in Cometary Water via Eley–rideal Reactions

Yao

Giapis

2017

ApJ

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The deuterium-to-hydrogen ratio (D/H) in water found in the coma of Jupiter family comet (JFC) 67P/ Churyumov-Gerasimenko was reported to be (5.3±0.7)×10 −4 , the highest among comets and three times the value for other JFCs with an ocean-like ratio. This discrepancy suggests the diverse origins of JFCs and clouds the issue of the origin of Earth's oceanic water. Here we demonstrate that Eley-Rideal reactions between accelerated water ions and deuterated cometary surface analogs can lead to instantaneous deuterium enrichment in water scattered from the surface. The reaction proceeds with H 2 O + abstracting adsorbed D atoms, forming an excited H 2 DO * state, which dissociates subsequently to produce energetic HDO. Hydronium ions are also produced readily by the abstraction of H atoms, consistent with H 3 O + detection and abundance in various comets. Experiments with water isotopologs and kinematic analysis on deuterated platinum surfaces confirmed the dynamic abstraction mechanism. The instantaneous fractionation process is independent of the surface temperature and may operate on the surface of cometary nuclei or dust grains, composed of deuterium-rich silicates and carbonaceous chondrites. The requisite energetic water ions have been detected in the coma of 67P in two populations. This dynamic fractionation process may temporarily increase the water D/H ratio, especially as the comet gets closer to the Sun. The magnitude of the effect depends on the water ion energy-flux and the deuterium content of the exposed cometary surfaces.

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Solar wind sputtering of dust on the surface of 67P/Churyumov-Gerasimenko

Cited by 58 publications

References 38 publications

Comparison of 3D kinetic and hydrodynamic models to ROSINA-COPS measurements of the neutral coma of 67P/Churyumov-Gerasimenko

Comparison of 3D kinetic and hydrodynamic models to ROSINA-COPS measurements of the neutral coma of 67P/Churyumov-Gerasimenko

ROSINA/DFMS and IES observations of 67P: Ion-neutral chemistry in the coma of a weakly outgassing comet

Dynamic Deuterium Enrichment in Cometary Water via Eley–rideal Reactions

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