For centuries, astronomers have discussed the possibility of inhabited worlds - from Herschel's 18th-century observations suggesting Mars may host life, to the systematic search for technosignatures that began in the 1960s using radio telescopes. Searching for artifacts in the solar system has received relatively little formal scientific interest and has faced significant technical and social challenges. Automated surveys and new observational techniques developed over the past decade now enable astronomers to survey parts of the sky for anomalous objects.
We briefly describe four methods for detecting extraterrestrial artifacts and probes within the Solar System and then focus on demonstrating one of these. The first makes use of pre-Sputnik images to search for flashes from glinting objects. The second method makes use of space-borne telescopes to search for artificial objects. A third approach involves examining the reflectance spectra of objects in Earth orbit, in search of the characteristic reddening that may imply long-term exposure of metallic surfaces to space weathering. We focus here on a fourth approach, which involves using Earth's shadow as a filter when searching for optically luminous objects in near-Earth space. We demonstrate a proof-of-concept of this method by conducting two searches for transients in images acquired by the Zwicky Transient Facility (ZTF), which has generated many repeated 30-second exposures of the same fields.
In this way, we identified previously uncatalogued events at short angular separations from the center of the shadow, motivating more extensive searches using this technique. We conclude that the Earth's shadow presents a new and exciting search domain for near-Earth SETI.
The Breakthrough Listen Search for Intelligent Life: A 3.95-8.00 GHz Search for Radio Technosignatures in the Restricted Earth Transit Zone
我们报告了在受限的地球过境区内搜索20颗恒星的人造窄带信号，这是为期十年的突破性聆听（BL）搜索外星智慧的一部分。限制地球凌日区是一个天空区域，从这个区域观察者可以看到地球以小于0.5的碰撞参量凌日。这片天空在几何学上是独一无二的，为外星智慧生物发现太阳系提供了一条潜在的途径。目标就在附近（7-143 pc），搜索覆盖了3.95-8.00 GHz的电磁频率范围。我们使用了罗伯特C。伯德绿岸望远镜执行这些观测与标准的BL数据记录器。我们在这些数据中搜索多普勒漂移率为$\pm 20$ Hz s $^{-1}$的人工窄带（$\sim$ Hz）信号。我们在目标HIP 109656上发现了一组潜在的候选信号，然后发现其与人为射频干扰的已知特性一致。在我们的观测中，我们没有发现来自外星智慧生物的无线电技术特征的证据。观测活动实现了最小可探测通量，这将允许探测发射，其强度分别为最近和最远恒星的阿雷西博雷达发射机信号能力的$10^{-3}$至$0.88$倍。我们的结论是，至少$8\%$的系统在150 pc内的限制地球过境区不具备在本次调查中搜索的发射机类型。据我们所知，这是第一次有针对性的搜索外星智慧的限制地球过境区。本文中使用的所有数据都可通过Breakthrough Listen Public Data Archive（http：//seti.berkeley.edu/bldr2）公开获取。
Laser-based mass spectrometry for the detection of signatures of life within our Solar System
Space Research and Planetary Sciences, Physics Institute, University of Bern（伯尔尼大学物理研究所空间研究与行星科学）；NCCR PlanetS, University of Bern（伯尔尼大学国家卓越研究中心“行星科学”）
