Mandt Kathleen E, Lustig-Yaeger Jacob, Luspay-Kuti Adrienn, Wurz Peter, Bodewits Dennis, Fuselier Stephen A, Mousis Olivier, Petrinec Steven M, Trattner Karlheinz J
NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
Johns Hopkins Applied Physics Laboratory, Laurel, MD 20723, USA.
Sci Adv. 2024 Nov 15;10(46):eadp2191. doi: 10.1126/sciadv.adp2191. Epub 2024 Nov 13.
Cometary comae are a mixture of gas and ice-covered dust. Processing on the surface and in the coma change the composition of ice on dust grains relative to that of the nucleus. As the ice on dust grains sublimates, the local coma composition changes. Rosetta observations of 67P/Churyumov-Gerasimenko previously reported one of the highest D/H values for a comet. However, reanalysis of more than 4000 water isotope measurements over the full mission shows that dust markedly increases local D/H. The isotope ratio measured at a distance from the nucleus where the gas is well mixed is close to terrestrial, like that of other Jupiter family comets. This lower D/H has implications for understanding comet formation and the role of comets in delivering water to Earth.
彗发是气体和覆冰尘埃的混合物。尘埃颗粒表面及其彗发中的物理过程会改变尘埃颗粒上冰的成分与彗核中冰成分的相对比例。随着尘埃颗粒上的冰升华，局部彗发成分会发生变化。此前罗塞塔号对67P/丘留莫夫－格拉西缅科彗星的观测报告显示，该彗星的氘氢比（D/H）是彗星中最高的之一。然而，对整个任务期间4000多次水同位素测量结果的重新分析表明，尘埃会显著提高局部D/H。在离彗核一定距离处（此处气体充分混合）测得的同位素比率接近地球值，与其他木星族彗星的情况类似。这种较低的D/H对于理解彗星形成以及彗星在向地球输送水的过程中所起的作用具有重要意义。
