The ultimate technosignature is an alien artifact. We should look for them near Earth. The great virtue of searching for artifacts is their lingering endurance in space, long after they go dead. I compare a Search for Extraterrestrial Artifacts (SETA) strategy of exploring near Earth for alien artifacts to the existing listening-to-stars SETI strategy. Stars come very close to Earth frequently. About two stars per million years come within a light year. An extraterrestrial civilization that passes nearby can see there’s an ecosystem here, due to the out-of-equilibrium atmosphere. They could send interstellar probes to investigate. The Moon and the Earth Trojans have the greatest probability of a successful search by us, ET archeology. I suggest resources devoted to imaging of our Moon’s surface, the Earth Trojans and Earth co-orbitals, and for probe missions to the latter two. The SETA concept can be falsified: if we investigate these near-Earth objects and don’t find artifacts, the concept is disproven for this region. Close inspection of bodies in these regions, which may hold primordial remnants of our early solar system, yields concrete astronomical research.

The existence of causal constraints introduces a temporal selection effect in the type of technosignatures that we can detect. I discuss the implications of this fact on the characteristic of detectable technosignatures, and in particular their longevity.

Dyson spheres are hypothetical structures that high-level civilizations may build to harvest energy in the form of starlight. As in any thermodynamic process, the conversion of stellar energy would involve the emission of waste heat. For Dyson spheres operating at temperatures in the range 100 - 1000 K, this energy would be emitted primarily in the mid-infrared. Here we present some models to estimate upper limits on the prevalence of Dyson spheres in the Milky Way based on the number of sources with mid-infrared excess. In the present analysis, we are only using 260,000 of the most nearby stars from the Gaia DR2 and AllWISE combined dataset, but the full search will include 10^7 - 10^8 objects, making it the largest search for Dyson spheres in the Milky Way carried out so far. In this small sample, we found that less than 1 in 10,000 stars display the mid-IR excess expected for a Dyson sphere, assuming a Dyson sphere with a temperature of 300 K and a covering factor > 0.9.

Searching for life on other planets and planetary bodies poses a number of challenges, especially given that there is currently no clear evidence that lifeforms can only conform to characteristics observed on Earth. While current astrobiology missions operate under the assumption that any astrobiological entities of interest will have similar properties to organisms on Earth (‘canonical’ lifeforms), the current convention of searching for direct evidence of such lifeforms (e.g. organic compounds, genetic material, etc.) is largely exclusionary to any biologically valid lifeforms which are not currently a part of the canonical model of life that is used to drive exploratory efforts. It is proposed that the definition of life be broadened to include any entities capable of maintaining homeostasis relative to an entropic environment. Thus, instead of the traditional strategy of searching for direct evidence of life conforming to Earth-based standards, i.e., looking for specific organic compounds, a new strategy could be used to indirectly identify lifeforms through their utilization of environmental resources (e.g. as energy sources).