Ultrahot disintegrating exoplanets have been detected with tails trailing behind and/or shooting ahead of them. These tails are believed to be made of dust that are formed out of the supersonic escaping flow that emanated from the permanent day side. Conserving angular momentum, this day-side escape flux would lead the planet in orbit. In order to explain the trailing tails in observation, radiation pressure, a repulsive force pushing the escape flow away from the host star, is considered to be necessary. We here investigate whether escape could be deflected to head away from the host star by the pressure gradient force. We demonstrate in an idealized framework that escape flux from the night side can occur, and sometimes, can be even stronger than the escape from the day-side. The night-side escape infers that escape flow could trail behind the planet in orbit by virtue of angular momentum conservation even without radiation pressure. We also find analytical approximations for both day-side and night-side escape fluxes, which may be applied to study planetary evolution of disintegrating planets.

已检测到超热分解的系外行星，尾巴落后于尾翼和/或朝前射击。这些尾巴被认为是由尘埃构成的，该尘埃是由永久日日发出的超音速逃逸流形成的。保持角动量，该日侧逃逸通量将导致行星进入轨道。为了解释观测中的尾巴，辐射压力是一种排斥力，它迫使逃逸流远离主恒星，因此是必要的。我们在这里研究压力梯度力是否可以使逃逸偏向远离主恒星。我们在一个理想化的框架中证明，从夜间逃逸可能会发生，有时甚至会比从白天逃逸更强大。夜间逃逸推断，即使没有辐射压力，借助角动量守恒，逃逸流也可能在轨道后方落后于行星。我们还发现了白天和夜晚逃逸通量的解析近似值，可用于研究崩解行星的行星演化。