Université Grenoble Alpes, Centre National de la Recherche Scientifique (CNRS), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), 38000 Grenoble, France.
Institut Universitaire de France (IUF), Paris, France.
Science. 2020 Mar 13;367(6483). doi: 10.1126/science.aaw7462.
The measured nitrogen-to-carbon ratio in comets is lower than for the Sun, a discrepancy which could be alleviated if there is an unknown reservoir of nitrogen in comets. The nucleus of comet 67P/Churyumov-Gerasimenko exhibits an unidentified broad spectral reflectance feature around 3.2 micrometers, which is ubiquitous across its surface. On the basis of laboratory experiments, we attribute this absorption band to ammonium salts mixed with dust on the surface. The depth of the band indicates that semivolatile ammonium salts are a substantial reservoir of nitrogen in the comet, potentially dominating over refractory organic matter and more volatile species. Similar absorption features appear in the spectra of some asteroids, implying a compositional link between asteroids, comets, and the parent interstellar cloud.
彗星的氮碳比测量值低于太阳，这一差异可以通过在彗星中存在未知的氮储存库来缓解。彗星 67P/楚留莫夫-格拉希门克的核表现出在大约 3.2 微米处的未识别宽光谱反射特征，这在其表面普遍存在。基于实验室实验，我们将此吸收带归因于表面上的灰尘与铵盐的混合物。该带的深度表明，半挥发性的铵盐是彗星中氮的重要储存库，可能超过难熔有机物和更易挥发的物质。一些小行星的光谱中也出现了类似的吸收特征，这表明小行星、彗星和星际云母体之间存在组成上的联系。
