The Nine Axes of Merit for Technosignature Searches
Sofia Z. Sheikh
International Journal of Astrobiology · 2020
Sofia Z. Sheikh proposes nine comparative axes, covering observational capability, cost, detectability, duration, ambiguity, extrapolation, inevitability, and information content, to systematically rank and communicate the trade-offs of competing technosignature search strategies.
Brief
Sheikh (2020) formalizes the Nine Axes of Merit framework, originating at the 2018 NASA Technosignatures Workshop in Houston, to compare technosignature search strategies across nine dimensions: Observational Capability, Cost, Ancillary Benefits, Detectability, Duration, Ambiguity, Extrapolation, Inevitability, and Information. The framework is applied qualitatively to three search classes, radio/optical communication, megastructure waste heat, and solar system artifacts, revealing that historical funding pressure has systematically overweighted the first three practical axes, leaving archival-data searches largely unexecuted despite requiring no new instrumentation. The axes are explicitly non-quantitative; assigning numeric scores requires priors about ETI occurrence rate, longevity, and energy use that the author characterizes as inherently subjective. An open-source plotting tool at github.com/sofsheikh/Axes-of-Merit generates customizable radar diagrams for research and publication.
Metadata
- Category
- Search
- Venue
- International Journal of Astrobiology
- Type
- Peer-reviewed
- Year
- 2020
- Authors
- Sofia Z. Sheikh
- arXiv
- 1908.02683
- Access
- Open access
- Length
- 4.0 M
- Programs
- NASA Technosignatures Workshop, Breakthrough Listen
- Instruments
- Green Bank Telescope
- Tags
- SETI, technosignature, search-strategy, megastructure, biosignature
Key points
- Nine axes codified at the 2018 NASA Technosignatures Workshop: Observational Capability, Cost, Ancillary Benefits, Detectability, Duration, Ambiguity, Extrapolation, Inevitability, and Information.p.1
- Funding scarcity has historically overweighted the first three practical axes, leaving a large set of science-focused searches, especially archival-data surveys requiring no new instrumentation, unperformed.p.8
- Waste heat from megastructures scores highest on Inevitability (thermodynamics guarantees emission if a megastructure exists) but lowest on Ambiguity (confusion with astrophysical dust) and Information (distant detection yields little beyond artifact confirmation).p.7
- Radio and optical communication score perfectly on Ambiguity, narrow-band emissions have no known natural source, and require zero extrapolation from Earth technology, but score poorly on Inevitability because intentional transmission assumes ETI sociological motivation to transmit.p.5
- Solar system artifacts score highest on Information, enabling in-situ analysis using archaeological methods, but poorly on Inevitability: there is no physically-motivated reason for interstellar artifact construction to be a common phenomenon.p.9
- Three candidate axes were rejected from the final model: Potential for Concealment (requires assuming concealment motivation), Physical Volume (assumes ETI rarity), and Size of Search Space (degenerate with Observational Capability and Detectability).p.9
- Quantitative scoring is explicitly ruled out: axis weights depend on priors about ETI occurrence rate, longevity, and energy use, none of which are known, making any such scoring necessarily subjective.p.10
- The discovery of fast radio bursts (Lorimer et al. 2007) is cited as evidence that SETI searches in parameter spaces assumed empty can yield significant ancillary astrophysical discoveries.p.5
Verbatim
“Every search for alien civilizations should be planned to give interesting results even when no aliens are discovered”
p.2“Extremely narrow-band radio emissions, on the other hand, do not have a natural source, and thus provide a thoroughly unambiguous signature of technology”
p.4“While prioritizing searches is important, especially with limited resources, breadth will serve us better than depth in technosignature searches.”
p.9“Instead the axes should be used as an illustrative tool to motivate the choice of a particular search strategy and openly communicate its shortcomings.”
p.10
Most interesting
- The framework was not conceived in a journal paper but in a working-group discussion at the 2018 NASA Technosignatures Workshop, then retroactively formalized for publication.
- Voyager 1, the most distant human-made object, only recently past the heliopause, is invoked to illustrate why solar system artifacts score poorly on Extrapolation: humanity has never sent an artifact between stellar systems.
- Waste heat technosignatures, first proposed by Dyson in 1960, rank as information-poor in this framework despite their inevitability advantage: a distant detection would yield 'little more than the knowledge that an artificial artifact exists.'
- The framework explicitly codifies Freeman Dyson's First Law of SETI Investigations as the definition of the Ancillary Benefits axis, requiring any search to be scientifically productive even on a null result.
- A signal-shape-agnostic communication search scores better on the Inevitability axis than targeted searches precisely because it makes fewer assumptions about ETI psychology and behavior.
- The Breakthrough Listen backend hardware developed for the Green Bank Telescope is cited as a concrete example of ancillary technological benefit that a SETI-motivated engineering investment can produce.