外行星系统中通过光帆泄漏的SETI
SETI via Leakage from Light Sails in Exoplanetary Systems
摘要：
火箭推进的主要挑战是需要加速航天器自身燃料的负担，导致在向航天器添加推进剂时最大速度仅以对数增益。光帆提供了一个有吸引力的替代方案，其中燃料不是由航天器携带的，加速是由外部光源提供的。通过用光束辐射人工照射航天器，速度只受帆的面积、材料的耐热性和加速装置的功率使用的限制。在本文中，我们表明，从光帆推进装置在太阳系模拟周围的操作泄漏将是可检测的。为了证明这一点，我们建立了一个微波束驱动的光帆的发射和到达模型，该光帆是为了在围绕一颗恒星的轨道上的行星之间过境而建造的，并找到了几十GHz量级的最佳光束频率。这些光束的泄漏会产生通量密度为Jy的瞬变，在100秒/秒时持续时间为数十秒。由于行星系统内的大多数旅行都是在该系统内的可居住世界之间进行的，因此多重凌日的系外行星系统提供了最大的探测机会，特别是当行星在地球上的投影结合时。如果通过光束驱动的光帆进行行星际旅行在我们的银河系中很普遍，那么这种活动可以通过对附近凌日系外行星系统的无线电跟踪来揭示。预期的信号特性定义了搜寻地外文明（SETI）的新策略。
英文摘要：
The primary challenge of rocket propulsion is the burden of needing to accelerate the spacecraft's own fuel, resulting in only a logarithmic gain in maximum speed as propellant is added to the spacecraft. Light sails offer an attractive alternative in which fuel is not carried by the spacecraft, with acceleration being provided by an external source of light. By artificially illuminating the spacecraft with beamed radiation, speeds are only limited by the area of the sail, heat resistance of its material, and power use of the accelerating apparatus. In this paper, we show that leakage from a light sail propulsion apparatus in operation around a solar system analogue would be detectable. To demonstrate this, we model the launch and arrival of a microwave beam-driven light sail constructed for transit between planets in orbit around a single star, and find an optimal beam frequency on the order of tens of GHz. Leakage from these beams yields transients with flux densities of Jy and durations of tens of seconds at 100 pc. Because most travel within a planetary system would be conducted between the habitable worlds within that system, multiply-transiting exoplanetary systems offer the greatest chance of detection, especially when the planets are in projected conjunction as viewed from Earth. If interplanetary travel via beam-driven light sails is commonly employed in our galaxy, this activity could be revealed by radio follow-up of nearby transiting exoplanetary systems. The expected signal properties define a new strategy in the search for extraterrestrial intelligence (SETI).
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