Latest research in planet formation indicates that Mars formed within a few million years (Myr) and remained as a planetary embryo that never grew to a more massive planet. It can also be expected from dynamical models that most of Mars' building blocks consisted of material that formed in orbital locations just beyond the ice line which could have contained ~0.1–0.2wt.% of H2O. By using these constraints, we estimate the nebula-captured and catastrophically outgassed volatile contents during the solidification of Mars' magma ocean and apply a hydrodynamic upper atmosphere model for the study of the soft X-ray and extreme ultraviolet (XUV) driven thermal escape of the martian protoatmosphere during the early active epoch of the young Sun. The amount of gas that has been captured from the protoplanetary disk into the planetary atmosphere is calculated by solving the hydrostatic structure equations in the protoplanetary nebula. Depending on nebular properties such as the dust grain depletion factor, planetesimal accretion rates and luminosities, hydrogen envelopes with masses ≥3×1019g to ≤6.5×1022g could have been captured from the nebula around early Mars. Depending on the before mentioned parameters, due to the planets low gravity and a solar XUV flux that was ~100 times stronger compared to the present value, our results indicate that early Mars would have lost its nebular captured hydrogen envelope after the nebula gas evaporated, during a fast period of ~0.1–7.5Myr. After the solidification of early Mars' magma ocean, catastrophically outgassed volatiles with the amount of ~50–250bar H2O and ~10–55bar CO2 could have been lost during ~0.4–12Myr, if the impact related energy flux of large planetesimals and small embryos to the planet's surface lasted long enough, that the steam atmosphere could have been prevented from condensing. If this was not the case, then our results suggest that the timescales for H2O condensation and ocean formation may have been shorter compared to the atmosphere evaporation timescale, so that one can speculate that sporadically periods, where some amount of liquid water may have been present on the planet's surface. However, depending on the amount of the outgassed volatiles, because of impacts and the high XUV-driven atmospheric escape rates, such sporadically wet surface conditions may have also not lasted much longer than ~0.4–12Myr. After the loss of the captured hydrogen envelope and outgassed volatiles during the first 100 Myr period of the young Sun, a warmer and probably wetter period may have evolved by a combination of volcanic outgassing and impact delivered volatiles ~4.0±0.2Gyr ago, when the solar XUV flux decreased to values that have been <10 times that of today's Sun.

中文翻译：

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逃离火星原始大气层和最初的水库存

行星形成的最新研究表明，火星在几百万年（Myr）内形成，并保持为行星胚胎，从未成长为更大的行星。从动力学模型中还可以预期，火星的大部分构建块由在刚好超过冰线的轨道位置形成的材料组成，其中可能含有约 0.1-0.2wt.% 的 H2O。通过使用这些约束，我们估计了火星岩浆海洋凝固过程中星云捕获和灾难性脱气的挥发物含量，并应用流体动力学高层大气模型来研究软 X 射线和极紫外 (XUV) 驱动的热逃逸。年轻太阳早期活跃时期的火星原始大气层。通过求解原行星状星云中的流体静力结构方程，可以计算出从原行星盘捕获到行星大气中的气体量。根据星云的特性，例如尘埃颗粒消耗因子、小行星吸积率和光度，可以从火星早期周围的星云中捕获质量≥3×1019g 至≤6.5×1022g 的氢包层。根据前面提到的参数，由于行星的低重力和比现值强约 100 倍的太阳 XUV 通量，我们的结果表明，在星云气体蒸发后，早期火星将失去其星云捕获的氢包层，在 ~0.1–7.5Myr 的快速期间。早期火星的岩浆海凝固后，如果大星子和小胚胎对行星表面的撞击相关的能量通量持续足够长的时间，那么在大约 0.4-12Myr 期间，灾难性地释放出约 50-250bar H2O 和约 10-55bar CO2 的挥发物可能会丢失本来可以防止蒸汽气氛凝结。如果情况并非如此，那么我们的结果表明，与大气蒸发时间尺度相比，H2O 冷凝和海洋形成的时间尺度可能更短，因此人们可以推测可能存在一定数量液态水的零星时期在地球表面。然而，根据脱气挥发物的数量，由于撞击和高 XUV 驱动的大气逃逸率，这种零星潮湿的表面条件也可能不会持续超过 ~0。4–12Myr。在年轻太阳的前 100 Myr 时期失去捕获的氢包层和脱气的挥发物后，火山脱气和撞击相结合可能演化出一个更暖和可能更湿润的时期，大约 4.0±0.2Gyr 之前，当太阳 XUV 通量下降到小于今天太阳的 10 倍。