Rio scale

The Rio scale was proposed in 2000 as a means of quantifying the significance of a SETI detection.^[1][2] The scale was designed by Iván Almár and Jill Tarter to help tell policy-makers how likely, from 0 to 10, it is that an extraterrestrial radio signal has been produced by an intelligent civilization.^[3]

The scale is inspired by the Torino scale, which is used to determine the impact risk associated with near-Earth objects. Just as the Torino scale takes into account how significant an object's impact on the planet would be, the Rio scale takes into account how much a public announcement of the discovery of extraterrestrial intelligence would probably impact society.

The IAA SETI Permanent Study Group officially adopted the Rio scale as a way of bringing perspective to claims of extraterrestrial intelligence (ETI) detection, and as an acknowledgement that even false ETI detections may have disastrous consequences.^[4][5]

The scale was modified in 2011 to include a consideration of whether contact was achieved through an interstellar message or a physical extraterrestrial artifact, including all indications of intelligent extraterrestrial life such as technosignatures.^[6] A 2.0 version of the scale was proposed in 2018.^[3][7][8]

Calculation

In its 2.0 version, the Rio Scale, R, of a given event is calculated as the product of two terms.^[9]

${\displaystyle R=Q\delta }$

The first term, Q, is the significance of the consequences of an event. It is determined considering three factors: the estimated distance to the source of the signal (a value between 0 and 4), the prospects for communicating with the source (a value between 0 and 4) and how likely is that the sender is aware of humanity (a value between -1 and 2). The value of each factor is determined by answering a question and Q is calculated by summing the three values.

The second term, δ, is the probability that the event actually occurred. Its value is determined by first calculating a term, J, based on three factors: the probability that the signal is real, the probability that it is not instrumental, and the probability that it is not natural or human-made. The values for these factors are determined by answering a questionnaire and J is calculated by summing them. δ is then calculated using the formula δ = 10^(10-J)/2.

The final R value, going from 0 to 10, is the likelihood that the observed event was produced by an intelligent civilization.

Rating scale

Rio value	Importance
10	Extraordinary
9	Outstanding
8	Far-reaching
7	High
6	Noteworthy
5	Intermediate
4	Moderate
3	Minor
2	Low
1	Insignificant
0	Nil

See also

• Quiet and loud aliens
• San Marino Scale

References

1. "The Rio Scale" (PDF).
2. Arbesman, Samuel. "Quantifying Alien Encounters: The Rio Scale". Wired. ISSN 1059-1028. Retrieved 2022-05-30.
3. Bartels, SPACE.com, Meghan. "To Fight Fake News, SETI Researchers Update Alien-Detection Scale". Scientific American. Retrieved 2022-05-30.
4. "How can you tell if that ET story is real? St Andrews scientists revise the Rio Scale for alien encounters".
5. Hall, Shannon. "Strange signals from 234 stars could be ET - or human error". New Scientist. Retrieved 2022-05-30.
6. Mike Wall (2016-10-28). "Mysterious Star Pulses May Be Alien Signals, Study Claims". Space.com. Retrieved 2022-05-30.
7. Tudhope, Christine. "Scientists revise the Rio Scale for reported alien encounters". phys.org. Retrieved 18 September 2022.
8. Bartels, Meghan (31 July 2018). "SETI Researchers Want to End the Alien-Detection Hype". Space.com. Retrieved 18 September 2022.
9. Forgan, Duncan; Wright, Jason; Tarter, Jill; Korpela, Eric; Siemion, Andrew; Almár, Iván; Piotelat, Elisabeth (August 2019). "Rio 2.0: revising the Rio scale for SETI detections". International Journal of Astrobiology. 18 (4): 336–344. Bibcode:2019IJAsB..18..336F. doi:10.1017/S1473550418000162. hdl:10023/16927.