ROSINA/DFMS and IES observations of 67P: Ion-neutral chemistry in the coma of a weakly outgassing comet
ROSINA/DFMS and IES observations of 67P: Ion-neutral chemistry in the coma of a weakly outgassing comet
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67P 的 ROSINA/DFMS 和 IES 观测：弱排气彗星彗发中的离子中性化学
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发表时间：
2015
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影响因子：
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通讯作者：
P. Wurz
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作者：
S. Fuselier;K. Altwegg;H. Balsiger;J. Berthelier;A. Bieler;C. Briois;T. Broiles;J. Burch;U. Calmonte;G. Cessateur;M. Combi;J. Keyser;B. Fiethe;M. Galand;S. Gasc;T. Gombosi;H. Gunell;K. Hansen;M. Hässig;A. Jäckel;A. Korth;L. L. Roy;U. Mall;K. Mandt;S. Petrinec;S. Raghuram;H. Rème;M. Rinaldi;M. Rubin;T. Sémon;K. Trattner;C. Tzou;E. Vigren;J. Waite;P. Wurz
罗塞塔号与彗星67 P/Churyumov-Gerasimenko的相遇为在远离太阳的弱放气彗星的昏迷中进行原位近距离离子中性化学研究提供了一个独特的机会。
初级和次级离子的观测和建模被用来研究薄彗发中离子中性化学的作用。
方法.从2014年10月下旬到12月中旬的观测显示，在距离彗星核30公里处，太阳风持续存在。这些和其他观测表明，没有接触面，太阳风可以直接进入原子核。在此期间，Rosetta/ROSINA/双聚焦质谱仪多次测量了彗发中的低能离子组成。有机挥发物和水的基团离子及其分解产物（质量14至19），CO2+（质量28和44）的另一个质量峰（在质量26，27，并可能30）观察。二次离子包括H3 O +和HCO +（质量19和29）.这些二次离子表明彗星薄彗发中的离子中性化学。一个相对简单的模型被构造来解释在水主导的彗发中观察到的低H3 O+/H2O+和HCO + /CO +比率。从这个简单的模型的结果进行比较，包括一个更详细的化学反应网络的模型的结果。
在低释气率下，简单模型的预测与观察结果一致，并且与包括更多化学物质的更复杂模型的结果一致。在较高的放气速率下，离子中性化学仍然是有限的，并且预测和观察到高的HCO + /CO +比率。然而，在较高的出气率，该模型预测高H3 O+/H2 O +的比例和观察到的比例往往很低。这些低比率可能是彗发的高度不均匀性的结果，其中CO和CO2数密度可以超过水。
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.
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 2 + (masses 28 and 44) another 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.
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.