Having a nucleus darker than charcoal, comets are usually detected from Earth through the emissions from their coma. The coma is an envelope of gas that forms through the sublimation of ices from the nucleus as the comet gets closer to the Sun. In the far-ultraviolet portion of the spectrum, observations of comae have revealed the presence of atomic hydrogen and oxygen emissions. When observed over large spatial scales as seen from Earth, such emissions are dominated by resonance fluorescence pumped by solar radiation. Here, we analyse atomic emissions acquired close to the cometary nucleus by the Rosetta spacecraft and reveal their auroral nature. To identify their origin, we undertake a quantitative multi-instrument analysis of these emissions by combining coincident neutral gas, electron and far-ultraviolet observations. We establish that the atomic emissions detected from Rosetta around comet 67P/Churyumov-Gerasimenko at large heliocentric distances result from the dissociative excitation of cometary molecules by accelerated solar-wind electrons (and not by electrons produced from photo-ionization of cometary molecules). Like the discrete aurorae at Earth and Mars, this cometary aurora is driven by the interaction of the solar wind with the local environment. We also highlight how the oxygen line O i at wavelength 1,356 Å could be used as a tracer of solar-wind electron variability.

彗星的核比木炭更黑，通常是通过彗星的彗星散发来探测到的。彗星是气体的包裹层，当彗星靠近太阳时，它是通过核中冰的升华而形成的。在光谱的远紫外线部分，彗星的观测表明存在原子氢和氧排放。从地球上看，在较大的空间尺度上观察时，此类辐射主要由太阳辐射泵浦的共振荧光控制。在这里，我们分析了Rosetta航天器在彗核附近获得的原子发射，并揭示了其极光性。为了确定它们的来源，我们通过结合同时发生的中性气体，电子和远紫外观测，对这些排放物进行了定量的多仪器分析。我们确定，从彗星67P / Churyumov-Gerasimenko周围的罗塞塔号探测到的大太阳中心距的原子发射，是由加速的太阳风电子（而不是彗星分子光电离产生的电子）引起的彗星分子的解离激发引起的。像地球和火星上的离散极光一样，这种彗星极光是由太阳风与当地环境的相互作用驱动的。我们还将重点介绍氧气线O 这个彗星的极光是由太阳风与当地环境的相互作用驱动的。我们还将重点介绍氧气线O 这个彗星的极光是由太阳风与当地环境的相互作用驱动的。我们还将重点介绍氧气线O波长为1,356Å的i可用作太阳风电子可变性的示踪剂。