Approximately 22% of sun-like stars have Earth-like exoplanets. Advanced civilizations may exist on these, and significant effort has been expended on the theoretical analysis of planetary systems, and accompanying practical detection instruments.The longevity of technological civilizations is unknown, as is the probability of less advanced societies becoming technological. Accordingly, searching for pre-industrial extra-terrestrial societies may be more productive.Using the earth as a model, a consideration of possible detectible proxies suggests that observation of seasonal agriculture may be possible in the near future – particularly in ideal circumstances, for which quantitative analysis is provided. More speculatively, other detectible processes may include: species introduction; climate change; large urban fires and land-use or aquatic changes.Primitive societies may be both aware that their activities may be observed from other planets, and may deliberately adjust these activities to aid or conceal detection.

中文翻译：

---

探测系外行星上的前工业社会

大约 22% 的类太阳恒星拥有类地系外行星。先进的文明可能存在于这些之上，并且已经在行星系统的理论分析和伴随的实用检测仪器上付出了巨大的努力。技术文明的寿命是未知的，不太先进的社会成为技术的可能性也是未知的。因此，寻找前工业化的地外社会可能更有成效。以地球为模型，考虑可能的可检测代理表明，在不久的将来可能对季节性农业进行观察——尤其是在理想情况下，因为提供定量分析。更具推测性，其他可检测的过程可能包括：物种引入；气候变化；