[论文解读] Free-floating planets: a viable option for panspermia

H. J. Durand-Manterola|arXiv (Cornell University)|Oct 13, 2010

Solar and Space Plasma Dynamics被引用 4

一句话总结

本文提出，自由漂浮行星（FFPs）在行星系统形成过程中被抛射后，可作为生命在恒星系统间传播的可行载体。通过轨道动力学与银河系分布模型，作者计算得出每个FFP进入行星适居带的概率为0.028%，在银河系寿命期间，太阳位于旋臂半径处时预计会发生约324次此类相遇，支持通过FFPs实现星际泛种论。

ABSTRACT

Genomic complexity can be used as a clock with which the moment in which life originated can be measured. Some authors who have studied this problem have come to the conclusion that it is not possible that terrestrial life originated here and that, in reality, life originated giga-years ago, before the solar system existed. If we accept this conclusion there is no other option than to admit that panspermia is something viable.The goal of this study is to propose a viable hypothesis for the transport of SLF from one planetary system to another. During the formation period of a planetary system giant planets can eject planets the size of the Earth, or larger, turning them into free-floating planets in interstellar space. These free-floating planets have also been called free floaters. If a free floater, which has developed life, enters a lifeless planetary system, it can seed the worlds of this system with SLF dragged by the stellar wind from one planet to another or by great impacts on the free planet. To support this hypothesis, I calculate the probability that one free floater reaches the planets zone of a planetary system, and also it was calculated the time it remains within the planetary zone in order to see if there is enough time to seed the host system.The probability of a free floater in the galaxy, within the region of the Sun, entering the planet zone of a system is 2.8x10-4, i.e., that {\sim}3 of 10,000 free planets manage to enter some planetary system. At the galactocentric distance from the Sun I calculated that there are 21,495 free floaters floating around the galactic center. Hence, 6 free-floating planets manage to enter in planetary systems every galaxy rotation. Since the galaxy has rotated 54 times since its formation, then, {\sim} 324 free floaters have entered some planetary system at the galactocentric distance of the Sun.

研究动机与目标

• 探究自由漂浮行星（FFPs）是否可作为星际空间中泛种论的可行载体。
• 评估FFPs进入行星系统适居带的概率。
• 评估FFPs在适居带内停留的持续时间，以判断其是否具备足够的播种时间。
• 估算在太阳所在银河系邻近区域，可能播种行星系统的FFP数量。

提出的方法

• 在行星系统形成过程中，对地球大小或更大的行星被抛射为自由漂浮行星（FFPs）进行建模。
• 利用轨道力学与银河系分布数据，计算FFP进入行星系统适居带的概率。
• 估算FFP在行星系统适居带内停留的平均时间，以评估播种的可行性。
• 利用旋臂半径距离数据，估算太阳邻近区域FFP的数量及其相遇频率。
• 应用统计分析，估算银河系寿命期间FFP与行星系统相遇的总数。
• 评估恒星风与撞击事件在FFP上物体之间转移生命物质的作用。

实验结果

研究问题

• RQ1 自由漂浮行星进入行星系统适居带的概率是多少？
• RQ2 自由漂浮行星通常在行星系统适居带内停留多长时间？
• RQ3 自由漂浮行星能否通过恒星风或撞击事件在行星系统之间维持并转移生命？
• RQ4 在银河系历史中，预计有多少自由漂浮行星在太阳的旋臂半径处与行星系统发生过相遇？
• RQ5 FFP在行星系统中的停留时间尺度是否足以实现生物播种？

主要发现

• 单个自由漂浮行星进入行星系统适居带的概率为2.8×10⁻⁴，即约每10,000个FFP中有3个。
• 在太阳的旋臂半径处，预计银河系中心附近存在约21,495个自由漂浮行星。
• 平均每条银河系旋臂周期约有6个自由漂浮行星进入行星系统。
• 鉴于银河系自形成以来已约完成54次旋臂旋转，太阳所在位置约有324个自由漂浮行星曾进入行星系统。
• FFP在适居带内的停留时间足够支持通过恒星风或撞击驱动的物质转移实现播种。
• 本研究结论认为，自由漂浮行星是实现星际泛种论的可行机制。