Effect of orbital parameters on the habitability on planets

用一般环流模型研究了陆地行星（没有固定海洋的潮湿行星）和水行星（完全被海洋覆盖的行星）发生完全冻结状态（“雪球”状态）的条件，并特别参考了倾角。结果：1；陆地行星比水行星对完全冻结的抵抗力更强。2. 陆地行星和水系行星在倾斜状态下比在直立状态下表现出更强的完全冻结阻力。然而，在直立状态下，对倾角的依赖并不清楚。3. 在倾斜状态的陆地行星上，低纬度地区比中纬度地区更容易结冰。因此，陆地行星很有可能只在低纬度地区结冰（在低纬度地区结冰，而不冻结整个行星）。4. 在具有高倾角的水行星上，低纬度冻结发生在太阳常数较低的地方，而在具有高倾角的陆地行星上。在水行星上，太阳常数的范围比在陆地行星上要窄得多。因此，在水行星上，只有低纬度的冰冻是不可能的。对古火星的启示：为了在古火星的低纬度地区保持潮湿的地面，火星必须处于倾斜状态，或者有海洋。然而，在这种条件下，低纬度地区相对容易被永久积雪覆盖。因此，在低纬度保持不冻结的潮湿表面比在目前的倾角条件下保持火星不完全冻结要困难得多。2. 如果在火星水循环活跃、平均温度稳定下降的时候，倾角发生了显著变化，那么一定有一段时间只有低纬度地区被永久积雪覆盖。我们能否从地质记录中找到这样的证据是个有趣的问题。对行星宜居性的启示：富含水的水行星可能不是最适合生命的地方，而有水的陆地行星可能比有水的行星更好，因为有水的行星很容易陷入完全冻结的状态。2. 高倾角行星和低倾角行星孰优孰劣是一个难题。一个高倾角的行星是抵抗完全冻结，但经历严重的季节变化。最平静的气候出现在倾角45°的水行星上。少

The condition for the occurrence of a completely frozen state (a "snow-ball" state) is investigated with a general circulation model for both a land planet case (a wet planet without fixed ocean) and an aqua planet (a planet entirely covered by an ocean) with a particular reference to the obliquity. Results : 1. A land planet shows stronger resistance to the com-plete freezing than an aqua planet. 2. Both land and aqua planets in an oblique regime show stronger resis-tance to the complete freezing than those in an upright regime. However, the dependence on the obliquity is not clear within the upright regime. 3. On a land planet in an oblique regime, low latitude area is more suscep-tible to freezing than the mid latitude area. Thus, there is a good chance of low-latitude-only freezing (freezing of low latitude without freezing the entire planet) of a land planet. 4. On an aqua planet with high obliquity, low latitude freezing occurs at lower solar constant than on a land planet with h … More igh obliquity. The range of the solar constant that yields low-latitude-only freezing is much narrower on an aqua planet than that on a land planet. Thus, low-latitude-only freezing is unlikely on an aqua planet. Implications for the paleo-Mars : 1. In order to keep a wet ground at the low latitude area of paleo-Mars, the planet must be in the oblique regime, or with oceans. Under such conditions, however, the low latitude is relatively easily covered by permanent snow. Thus, it is more difficult to keep unfrozen wet surface on low latitude than to keep Mars from the completely frozen state under the condition of the present obliquity. 2. If the obliquity changed significantly while Martian water cycle was active and the average temperature was de-creasing steadily, there must have been a period while only the low latitude area is covered by permanent snow. It is an interesting question whether we can find such evidence from geological records. Implication for the Habitability on a Planet : 1. A water rich aqua planet may not be the best place for life, and a land planet with some water may be better than an aqua planet, because an aqua planet easily falls in a completely frozen state. 2. It is a difficult question whether high obliquity or low obliquity planet is prefer-able. A high obliquity planet is resistive to the complete freezing, but experiences severe seasonal change. The calmest climate is found on 45° obliquity aqua planet. Less