Wang Yifeng, Chan Marjorie A, Merino Enrique
Sandia National Laboratories, P. O. Box 5800, Albuquerque, New Mexico 87185-0779, USA.
Department of Geology and Geophysics, University Utah, Salt Lake City, Utah 84112-0111, USA.
Sci Rep. 2015 Jun 30;5:10792. doi: 10.1038/srep10792.
Widespread iron oxide precipitation from groundwater in fine-grained red beds displays various patterns, including nodulation, banding and scallops and fingers. Hematite nodules have been reported also from the Meridiani Planum site on Mars and interpreted as evidence for the ancient presence of water on the red planet. Here we show that such patterns can autonomously emerge from a previously unrecognized Ostwald ripening mechanism and they capture rich information regarding ancient chemical and hydrologic environments. A linear instability analysis of the reaction-transport equations suggests that a pattern transition from nodules to bands may result from a symmetry breaking of mineral dissolution and precipitation triggered by groundwater advection. Round nodules tend to develop under nearly stagnant hydrologic conditions, while repetitive bands form in the presence of persistent water flows. Since water circulation is a prerequisite for a sustainable subsurface life, a Martian site with iron oxide precipitation bands, if one were found, may offer a better chance for detecting extraterrestrial biosignatures on Mars than would sites with nodules.
细粒红层中地下水中广泛存在的氧化铁沉淀呈现出各种形态，包括结核状、带状以及扇贝状和指状。火星子午线平原地区也有赤铁矿结核的报道，并被解释为这颗红色星球古代存在水的证据。在此我们表明，这些形态能够通过一种此前未被认识的奥斯特瓦尔德熟化机制自动出现，并且它们捕捉到了关于古代化学和水文环境的丰富信息。对反应 - 输运方程的线性稳定性分析表明，从结核到带状的形态转变可能是由地下水平流引发的矿物溶解和沉淀的对称性破缺导致的。在水文条件近乎停滞的情况下往往会形成圆形结核，而在持续水流存在时会形成重复的带状。由于水循环是地下可持续生命存在的一个前提条件，所以如果在火星上发现一个有氧化铁沉淀带的地点，那么与有结核的地点相比，它可能为探测火星上的外星生物特征提供更好的机会。
