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 ~0.1–0.2 wt.% 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 × 1019 g to ≤ 6.5 × 1022 g 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 ~0.1–7.5 Myr. After the solidification of early Mars' magma ocean, catastrophically outgassed volatiles with the amount of ~50–250 bar H2O and ~10–55 bar CO2 could have been lost during ~0.4–12 Myr, 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 ~0.4–12 Myr. 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 ± 0.2 Gyr ago, when the solar XUV flux decreased to values that have been 10 times that of today's Sun.
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机译：关于行星形成的最新研究表明，火星是在数百万年（Myr）内形成的，并且仍然是从未成长为更大质量行星的行星胚胎。从动力学模型还可以预期，火星的大多数构造块均由在冰线以外的轨道位置形成的材料组成，该材料可能含有约0.1–0.2 wt％的H2O。利用这些约束条件，我们估计了火星岩浆海洋凝固期间星云捕获和灾难性排放的挥发物含量，并应用流体动力学高层大气模型研究软X射线和极紫外（XUV）驱动的热逸散在年轻的太阳活跃初期，火星的原大气层。通过求解原行星云中的静水力结构方程，可以计算出从原行星盘捕获到行星大气中的气体量。取决于星尘特性，例如尘粒损耗因子，行星的增生速率和光度，质量≥3×10 10 19≤6.5×10 22 22 s的氢包膜是在火星早期从星云捕获的。根据前面提到的参数，由于行星的低重力和太阳XUV通量是当前值的100倍，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〜0.1–7.5 Myr的快速期内。在火星早期岩浆海洋凝固后，如果与撞击有关的大行星能量通量在〜0.4-12 Myr范围内可能损失约50–250 bar H2O和〜10–55 bar CO2的灾难性脱气挥发物行星表面的小胚持续了足够长的时间，以至于可以防止蒸汽气氛凝结。如果不是这种情况，那么我们的结果表明，与大气蒸发时间尺度相比，H2O凝结和海洋形成的时间尺度可能更短，因此人们可以推测零星的时期，其中可能存在一定量的液态水。在地球表面。然而，取决于所散发的挥发物的量，由于影响和XUV驱动的高空气逸出率，此类偶发湿润的表面条件可能持续的时间也不会长于〜0.4-12 Myr。在年轻的太阳的第一个100毫秒期间失去捕获的氢气包层并释放出挥发物后，火山脱气和撞击传递的挥发物结合在一起形成了一个更温暖甚至更湿润的时期，约4.0±0.2 Gyr之前，当太阳XUV通量下降到今天太阳的<10倍以下。
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