Seligman Darryl Z, Farnocchia Davide, Micheli Marco, Hainaut Olivier R, Hsieh Henry H, Feinstein Adina D, Chesley Steven R, Taylor Aster G, Masiero Joseph, Meech Karen J
Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824.
Department of Astronomy and Carl Sagan Institute, Cornell University, Ithaca, NY 14853.
Proc Natl Acad Sci U S A. 2024 Dec 17;121(51):e2406424121. doi: 10.1073/pnas.2406424121. Epub 2024 Dec 9.
Small bodies are capable of delivering essential prerequisites for the development of life, such as volatiles and organics, to the terrestrial planets. For example, empirical evidence suggests that water was delivered to the Earth by hydrated planetesimals from distant regions of the Solar System. Recently, several morphologically inactive near-Earth objects were reported to experience significant nongravitational accelerations inconsistent with radiation-based effects, and possibly explained by volatile-driven outgassing. However, these "dark comets" display no evidence of comae in archival images, which are the defining feature of cometary activity. Here, we report detections of nongravitational accelerations on seven additional objects classified as inactive (doubling the population) that could also be explainable by asymmetric mass loss. A detailed search of archival survey and targeted data rendered no detection of dust activity in any of these objects in individual or stacked images. We calculate dust production limits of [Formula: see text]10, [Formula: see text], and [Formula: see text] kg s[Formula: see text] for 1998 FR[Formula: see text], 2001 ME[Formula: see text], and 2003 RM with these data, indicating little or no dust surrounding the objects during the observations. This set of dark comets reveals the delineation between two distinct populations: larger, "outer" dark comets on eccentric orbits that are end members of a continuum in activity level of comets, and smaller, "inner" dark comets on near-circular orbits that could signify a different different population. These objects may trace various stages in the life cycle of a previously undetected, but potentially numerous, volatile-rich population that may have provided essential material to the Earth.
小天体能够为类地行星输送生命发展的基本先决条件，比如挥发物和有机物。例如，经验证据表明，水是由来自太阳系遥远区域的含水小行星带到地球的。最近，有报道称，几颗形态上不活跃的近地天体经历了与基于辐射的效应不一致的显著非引力加速，这可能是由挥发物驱动的排气作用所解释的。然而，这些“暗彗星”在存档图像中没有显示出彗发的迹象，而彗发是彗星活动的决定性特征。在这里，我们报告在另外七个被归类为不活跃的天体上检测到了非引力加速（使这类天体的数量增加了一倍），这些加速也可能是由不对称质量损失所导致的。对存档巡天和定向数据的详细搜索在单个或叠加图像中均未检测到这些天体中有任何尘埃活动。利用这些数据，我们计算出1998 FR₂、2001 ME₁₀和2003 RM₅的尘埃产生极限分别为10⁻¹⁰、10⁻¹¹和10⁻¹² kg s⁻¹，这表明在观测期间这些天体周围几乎没有或根本没有尘埃。这组暗彗星揭示了两个不同群体之间的界限：处于偏心轨道上的较大“外层”暗彗星，它们是彗星活动水平连续统的终端成员；以及处于近圆形轨道上的较小“内层”暗彗星，它们可能代表着一个不同的群体。这些天体可能追踪了一个以前未被发现但数量可能众多的富含挥发物群体生命周期中的各个阶段，这个群体可能为地球提供了重要物质。
