  Non-canonical phenomena - defined here as observables which are either
insufficiently characterized by existing theory, or otherwise represent
inconsistencies with prior observations - are of burgeoning interest in the
field of astrophysics, particularly due to their relevance as potential signs
of past and/or extant life in the universe (e.g. off-nominal spectroscopic data
from exoplanets). However, an inherent challenge in investigating such
phenomena is that, by definition, they do not conform to existing predictions,
thereby making it difficult to constrain search parameters and develop an
associated falsifiable hypothesis.
  In this Expert Recommendation, the authors evaluate the suitability of two
different approaches - conventional parameterized investigation (wherein
experimental design is tailored to optimally test a focused, explicitly
parameterized hypothesis of interest) and the alternative approach of anomaly
searches (wherein broad-spectrum observational data is collected with the aim
of searching for potential anomalies across a wide array of metrics) - in terms
of their efficacy in achieving scientific objectives in this context. The
authors provide guidelines on the appropriate use-cases for each paradigm, and
contextualize the discussion through its applications to the interdisciplinary
field of technosignatures (a discipline at the intersection of astrophysics and
astrobiology), which essentially specializes in searching for non-canonical
astrophysical phenomena.
