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Quantifying the Hypervolatile Abundances in Jupiter-family Comet 46P/Wirtanen
The Planetary Science Journal ( IF 3.8 ) Pub Date : 2021-02-04 , DOI: 10.3847/psj/abd71d
Adam J. McKay 1, 2 , Michael A. DiSanti 1, 3 , Anita L. Cochran 4 , Boncho P. Bonev 2 , Neil Dello Russo 5 , Ronald J. Vervack Jr. 5 , Erika Gibb 6 , Nathan X. Roth 1, 7 , Mohammad Saki 6 , Younas Khan 6 , Hideyo Kawakita 8
Affiliation  

We present analysis of IR and optical spectroscopy of Jupiter-family comet (JFC) 46P/Wirtanen obtained in 2019 January, when the comet had sufficient geocentric velocity to enable studies of the hypervolatiles CO and CH4, as well as [O i] emission. These species could not be studied near closest approach in mid-December because there was insufficient Doppler shift to separate the cometary emission from their corresponding telluric absorption lines. We employed the [O i] observations as a proxy for the CO2/H2O ratio, as CO2 cannot be observed directly from the ground, and space-based assets sensitive to CO2 were not able to observe 46P during this apparition. We focused our analysis on H2O, CO, CH4, C2H6, CH3OH, and CO2 (via [O i] emission). We detected strong emissions from H2O, C2H6, and CH3OH. Over the 3 nights, we found evidence for changing mixing ratios, mostly due to a variable H2O production rate. In 46P, C2H6 and CH3OH are enriched compared to cometary averages, with mixing ratios relative to H2O of ∼1% and ∼3%, respectively. Measurements of CH4 and CO have been especially rare in JFCs. We report significant 3σ upper limits on CH4/H2O < 0.97% and CO/H2O < 0.54%. They place CH4 being near-average or depleted, and CO being strongly depleted in 46P compared with Oort cloud comets. 46P has comparable CO/H2O to the few other measurements in JFCs, but enriched in C2H6 and CH3OH. Our inferred CO2/H2O mixing ratio is ∼15%, though accounting for systematic uncertainties from the lack of knowledge of [O i] photochemistry means a value between 10% and 20% is likely. The compositional profile of 46P is similar to another small, hyperactive comet: 103P/Hartley 2. The mechanism of CO2-driven water-rich ice grain production proposed for 103P/Hartley 2 may be operating on 46P as well.



中文翻译:

量化木星家族彗星46P / Wirtanen中的高挥发性丰度

我们对2019年1月获得的木星家族彗星(JFC)46P / Wirtanen的红外光谱和光谱学进行了分析,当时该彗星具有足够的地心线速度,可以研究高挥发性CO和CH 4以及[O i ]排放。由于没有足够的多普勒频移将彗星的发射与其相应的碲吸收线区分开来,因此无法在12月中旬附近研究这些物种。我们所用的〔O]观测作为CO的代理2 / H 2 O比,如CO 2不能直接从地面观察,以及CO基于空间的资产敏感2在这次幻影中无法观察到46P。我们将分析重点放在了H 2 O,CO,CH 4,C 2 H 6,CH 3 OH和CO 2(通过[O i ]发射)上。我们检测到H 2 O,C 2 H 6和CH 3 OH的强烈排放。在3个晚上的时间里,我们发现了改变混合比的证据,主要是由于H 2 O产生速率的变化。与彗星平均值相比,在46P中,C 2 H 6和CH 3 OH富集,相对于H 2的混合比O分别为〜1%和〜3%。在JFC中,CH 4和CO的测量尤为罕见。我们报告了CH 4 / H 2 O <0.97%和CO / H 2 O <0.54%的3σ上限。与奥特云彗星相比,它们使CH 4接近平均或已耗尽,而CO在46P中被严重耗尽。46P的CO / H 2 O可以与JFC中的其他几项测量值相提并论,但富含C 2 H 6和CH 3 OH。我们推断的CO 2 / H 2 O混合比约为15%,尽管由于缺乏对[O i光化学意味着该值可能在10%到20%之间。46P的组成特征类似于另一个小的活动过度的彗星:103P / Hartley2。针对103P / Hartley 2提出的CO 2驱动的富水冰粒生产机制也可能在46P上运行。

更新日期:2021-02-04
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