Sample Exploration Systems La Cañada, California, USA.
Astrobiology. 2012 Aug;12(8):730-42. doi: 10.1089/ast.2011.0813.
Life Investigation For Enceladus (LIFE) presents a low-cost sample return mission to Enceladus, a body with high astrobiological potential. There is ample evidence that liquid water exists under ice coverage in the form of active geysers in the "tiger stripes" area of the southern Enceladus hemisphere. This active plume consists of gas and ice particles and enables the sampling of fresh materials from the interior that may originate from a liquid water source. The particles consist mostly of water ice and are 1-10 μ in diameter. The plume composition shows H(2)O, CO(2), CH(4), NH(3), Ar, and evidence that more complex organic species might be present. Since life on Earth exists whenever liquid water, organics, and energy coexist, understanding the chemical components of the emanating ice particles could indicate whether life is potentially present on Enceladus. The icy worlds of the outer planets are testing grounds for some of the theories for the origin of life on Earth. The LIFE mission concept is envisioned in two parts: first, to orbit Saturn (in order to achieve lower sampling speeds, approaching 2 km/s, and thus enable a softer sample collection impact than Stardust, and to make possible multiple flybys of Enceladus); second, to sample Enceladus' plume, the E ring of Saturn, and the Titan upper atmosphere. With new findings from these samples, NASA could provide detailed chemical and isotopic and, potentially, biological compositional context of the plume. Since the duration of the Enceladus plume is unpredictable, it is imperative that these samples are captured at the earliest flight opportunity. If LIFE is launched before 2019, it could take advantage of a Jupiter gravity assist, which would thus reduce mission lifetimes and launch vehicle costs. The LIFE concept offers science returns comparable to those of a Flagship mission but at the measurably lower sample return costs of a Discovery-class mission.
土卫二生命探测任务（LIFE）是一项低成本的土卫二样本返回任务，土卫二是一颗具有高天体生物学潜力的天体。有充分的证据表明，在土卫二南半球“老虎条纹”区域的冰层下，以活跃间歇泉的形式存在着液态水。这个活跃的羽流由气体和冰粒组成，可以从内部采集到可能来自液态水的新鲜物质。这些颗粒主要由水冰组成，直径为 1-10μm。羽流的成分表明存在 H(2)O、CO(2)、CH(4)、NH(3)、Ar，并且有证据表明可能存在更复杂的有机物质。由于地球上的生命只要存在液态水、有机物和能量，就会存在，因此了解散发的冰粒的化学组成可以表明土卫二上是否存在生命。外行星的冰态世界是地球生命起源理论的一些测试场地。LIFE 任务概念分为两部分：第一，环绕土星（以便实现更低的采样速度，接近 2km/s，从而使样本采集撞击比星尘更柔和，并有可能对土卫二进行多次飞越）；第二，对土卫二的羽流、土星的 E 环和土卫六的高层大气进行采样。通过对这些样本的新发现，美国宇航局可以提供关于羽流的详细化学、同位素，以及潜在的生物组成背景。由于土卫二羽流的持续时间是不可预测的，因此必须尽早在最早的飞行机会中捕获这些样本。如果 LIFE 任务在 2019 年之前发射，它可以利用木星的引力辅助，从而减少任务寿命和运载火箭成本。LIFE 概念提供的科学回报与旗舰任务相当，但样本返回成本可显著低于发现级任务。
