Conclusion

In this paper, we investigated the distances at which technosignatures of the modern-day Earth could be detected with the astronomical instrumentation of the modern-day Earth in a formulation we called “Earth detecting Earth.” This paradigm focuses on limiting extrapolation to unknown technologies to understand the detectability of Earth by its constellation of technosignatures. We put various technosignatures across the electromagnetic spectrum onto a quantified “detectability” distance scale, including radio transmissions from different scales of radio transmitters, optical emission from nightside city lights, focusing lasers for AO, heat islands from cities, free-floating objects that could be pinged with radar, the belt of satellites around the planet, and objects such as rovers on non-Earth planetary surfaces.

The results of this investigation are shown in Figure 1 and summarized as follows.

1.  Radio remains the way that Earth is most detectable at ι = 1.

2.  Investment in atmospheric biosignature searches has opened up the door for atmospheric technosignature searches.

3.  Humanity’s remotely detectable impacts on Earth and the solar system span 12 orders of magnitude.

4.  Our modern-day planetary-scale impacts are modest compared to what is assumed in many technosignature papers.

5.  We have a multiwavelength constellation of technosignatures, with more of the constellation becoming visible the closer the observer becomes.

This should not be the only way of characterizing and sorting a portfolio of technosignature approaches but will be complemented by future work emphasizing aspects perpendicular to the minimal-extrapolation approach taken here.