Exocomets are small bodies releasing gas and dust which orbit stars other than the Sun. Their existence was first inferred from the detection of variable absorption features in stellar spectra in the late 1980s using spectroscopy. More recently, they have been detected through photometric transits from space, and through far-IR/mm gas emission within debris disks. As (exo)comets are considered to contain the most pristine material accessible in stellar systems, they hold the potential to give us information about early stage formation and evolution conditions of extra Solar Systems. In the Solar System, comets carry the physical and chemical memory of the protoplanetary disk environment where they formed, providing relevant information on processes in the primordial solar nebula. The aim of this paper is to compare essential compositional properties between Solar System comets and exocomets. The paper aims to highlight commonalities and to discuss differences which may aid the communication between the involved research communities and perhaps also avoid misconceptions. Exocomets likely vary in their composition depending on their formation environment like Solar System comets do, and since exocomets are not resolved spatially, they pose a challenge when comparing them to high fidelity observations of Solar System comets. Observations of gas around main sequence stars, spectroscopic observations of "polluted" white dwarf atmospheres and spectroscopic observations of transiting exocomets suggest that exocomets may show compositional similarities with Solar System comets. The recent interstellar visitor 2I/Borisov showed gas, dust and nuclear properties similar to that of Solar System comets. This raises the tantalising prospect that observations of interstellar comets may help bridge the fields of exocomet and Solar System comets.

中文翻译：

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从太阳系角度看系外彗星

系外彗星是释放气体和尘埃的小天体，围绕太阳以外的恒星运行。它们的存在首先是从 1980 年代后期使用光谱学检测恒星光谱中的可变吸收特征而推断出来的。最近，它们通过来自太空的光度传输和碎片盘内的远红外/毫米气体发射被检测到。由于（外）彗星被认为包含恒星系统中最原始的物质，它们有可能为我们提供有关额外太阳系早期形成和演化条件的信息。在太阳系中，彗星携带着它们形成的原行星盘环境的物理和化学记忆，提供有关原始太阳星云过程的相关信息。本文的目的是比较太阳系彗星和系外彗星之间的基本组成特性。本文旨在强调共同点并讨论差异，这可能有助于相关研究团体之间的交流，也可能避免误解。系外彗星的组成可能会根据它们的形成环境而有所不同，就像太阳系彗星一样，并且由于系外彗星在空间上无法解析，因此在将它们与太阳系彗星的高保真观测进行比较时，它们构成了挑战。对主序星周围气体的观测、对“受污染”白矮星大气的光谱观测以及对凌日系外彗星的光谱观察表明，系外彗星可能与太阳系彗星的成分相似。最近的星际访客 2I/Borisov 显示出类似于太阳系彗星的气体、尘埃和核特性。这提出了一个诱人的前景，即对星际彗星的观测可能有助于弥合系外彗星和太阳系彗星的领域。