论灾难性蒸发的岩石行星可能存在的镁铁硅酸盐尘埃尾
On the likely magnesium-iron silicate dusty tails of catastrophically evaporating rocky planets
AI总结：
本研究提出了一个自洽的尘埃尾模型，通过模拟KIC 1255b和K2-22b的尘埃轨迹和光深，发现其尘埃可能由镁铁硅酸盐组成，支持了行星含尘埃外流经历温室效应-核冬天循环的观点。
摘要：
灾难性蒸发的岩石行星为研究小型行星的组成提供了独特的机会。通过模拟这些行星类似彗星的尘埃尾，可以限制它们的表面成分。在本研究中，我们提出了一个新的自洽尘埃尾模型：我们在物理上模拟了尘埃颗粒离开气体外流后的运动轨迹，包括对尘埃云光深的即时计算。我们模拟了两颗灾难性蒸发的行星：KIC 1255b和K2-22b。对于这两颗行星，我们发现尘埃可能由镁铁硅酸盐（olivine和pyroxene）组成，这与类地成分一致。我们将初始尘埃颗粒尺寸限制在约1.25-1.75 μm，平均（含尘埃）行星质量损失率限制在约3 M⊕ Gyr^-1。我们的模型表明，K2-22b前导尘埃尾的起源可能是外流几何形态与较低辐射压力对恒星引力之比的结合。我们发现行星附近尘埃云的光深为几倍。我们的成分限制支持了最近提出的观点，即这些行星的含尘埃外流经历温室效应-核冬天循环，从而产生了观测到的凌星深度时间变异性。镁铁硅酸盐具有必要的可见光到红外不透明度比，能够在高质量损失状态下引发这种循环。
英文摘要：
Catastrophically evaporating rocky planets provide a unique opportunity to study the composition of small planets. The surface composition of these planets can be constrained via modelling their comet-like tails of dust. In this work, we present a new self-consistent model of the dusty tails: we physically model the trajectory of the dust grains after they have left the gaseous outflow, including an on-the-fly calculation of the dust cloud's optical depth. We model two catastrophically evaporating planets: KIC 1255b and K2-22b. For both planets, we find the dust is likely composed of magnesium-iron silicates (olivine and pyroxene), consistent with an Earth-like composition. We constrain the initial dust grain sizes to be $\sim$ 1.25-1.75 $μ$m and the average (dusty) planetary mass-loss rate to be $\sim$ 3$M_\oplus \mathrm{Gyr^{-1}}$. Our model shows the origin of the leading tail of dust of K2-22b is likely a combination of the geometry of the outflow and a low radiation pressure force to stellar gravitational force ratio. We find the optical depth of the dust cloud to be a factor of a few in the vicinity of the planet. Our composition constraint supports the recently suggested idea that the dusty outflows of these planets go through a greenhouse effect-nuclear winter cycle, which gives origin to the observed transit depth time variability. Magnesium-iron silicates have the necessary visible-to-infrared opacity ratio to give origin to this cycle in the high mass-loss state.
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