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Rio-Like Scales

The Rio scale of extraterrestrial contacts is similar to other sorts of scales and was inspired by them:

IAA SETI Permanent Committee: San Marino Scale for evalulating METI (active SETI) transmissions. It is
log10( (signal flux) / (quiet solar flux) ) + (character) ,
where the character value is

  • 5: Reply to an extraterrestrial signal or message (if they are not yet aware of us)
  • 4: Continuous, broadband transmission of a message to ETI
  • 3: Special signal targeting a specific star or stars, at a preselected time, in order to draw the attention of ETI astronomers
  • 2: Sustained, untargeted message with the intention to reach ETI
  • 1: A beacon without any message content (e.g., planetary radar)

Discovery of extra-terrestrial life: assessment by scales of its importance and associated risks | Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences proposes a “London Scale” in analogy with the Rio Scale. It is calculated as follows:
(quality) * (reliability)
where
(quality) = (type) + (nature) + (method) + (distance)

  • Type:
    • 5: completely alien life form
    • 4: likely to be non-terrestrial, but some uncertainty remains
    • 3: life definitely, but a previously unknown variant of terrestrial life (in structure or composition) (e.g. if DNA is present, different amino acids are used)
    • 2: terrestrial-type life form, but some uncertainty remains
    • 1: possible signature of life, but indirect information only (e.g. volatile, trace)
  • Nature:
    • 6: complex life (high level of organization)
    • 5: simple life (low level of organization)
    • 4: extant life with suspended functioning (like a spore)
    • 3: uncertain whether living or not (like a virus)
    • 2: fossilized life or remnants of life forms
    • 1: biomarkers (indirect evidence, like volatiles, metabolites, biochemical signatures, etc.)
  • Method:
    • 5: by analysing the result of a sample return mission (origin of the sample is well known)
    • 4: by analysing something found on Earth’s surface or in the atmosphere (e.g. meteorite and atmospheric sample)
    • 3: by a manned mission, in situ, on another celestial body
    • 2: by a surface robot, in situ, on another celestial body
    • 1: by remote sensing from the surface of the Earth or from satellites, flybys, etc.
  • Distance:
    • 4: zero distance (on Earth)
    • 3: inside the orbit of Jupiter (in situ research more easily possible)
    • 2: on or outside the orbit of Jupiter, but in the Solar System (in situ research possible, but difficult)
    • 1: beyond the Solar System (in situ research impossible)
  • Reliability:
    • 0.5: certain or highly reliable
    • 0.4: probably real
    • 0.3: testable, needs further evidence
    • 0.2: controversial, but not rejectable
    • 0.1: probably not real
    • 0: obviously fake or fraudulent
  • Their examples:
    • ALH84001 meteorite: (2+2+4+4) * 0.3 = 3.6.
    • The Hungarian dark-dune-spot – Mars-surface-organism hypothesis: (2+5+1+3) * 0.3 = 3.3
    • Hoyle–Wickramasinghe hypothesis of panspermia: (2+4+4+4) * (0.1 to 0.2) = 1.4 to 2.8
    • Red rain in Kerala, India: (2+3+4+4) * 0.1 = 1.3
  • Past hypotheses (my evaluation):
    • Mars wave of darkening: (2+5+1+3) * 0.2 = 2.2
      Listed as “controversial” because of plausible nonbiological hypotheses.
  • Recent hypotheses (my evaluation):
    • Martian methane: (1+1+2+3) * 0.2 = 1.4
      Listed as “controversial” because of plausible nonbiological hypotheses.
  • Possible future detections (my evaluation):
    • Exoplanet biota: (1+1+1+1) * 0.5 = 2
      Uses the best case of reliability for illustrative purposes, because all the quality features are worst-case ones.