Dynamics of ice ages on Mars

摘要

火星上目光照射的波动要比地球上大得多，这是由于其轴心相对于轨 道平面的倾斜度等天文因素变化较大。火星上的气候变化也相应地比 地球上更强烈。现在，Norbert Schorghofer建立了一个新的气候模型， 该模型能够解释火星地表之下冰层在40个主要冰期和500万年时间里 的进退情况。这便解释了火星地表之下冰层当前的分布。另外，从时 间长而相对比较简单的火星冰层年龄地层学研究获得的知识，应能帮 助解释地球上更复杂的事件。%Unlike Earth, where astronomical climate forcing is comparatively small, Mars experiences dramatic changes in incident sunlight that are capable of redistributing ice on a global scale. The geographic extent of the subsurface ice found poleward of approximately ±60° latitude on both hemispheres of Mars coincides with the areas where ice is stable. However, the tilt of Mars' rotation axis (obliquity) changed considerably in the past several million years. Earlier work has shown that regions of ice stability, which are defined by temperature and atmospheric humidity, differed in the recent past from today's, and subsurface ice is expected to retreat quickly when unstable. Here I explain how the subsurface ice sheets could have evolved to the state in which we see them today. Simulations of the retreat and growth of ground ice as a result or sublimation loss and recharge reveal forty major ice ages over the past five million years. Today, this gives rise to pore ice at mid-latitudes and a three-layered depth distribution in the high latitudes of, from top to bottom, a dry layer, pore ice, and a massive ice sheet. Combined, these layers provide enough ice to be compatible with existing neutron and gamma-ray measurements.