Our recent discussions of active SETI, otherwise known as METI (Messaging to Extraterrestrial Intelligence), highlighted many of the key issues involved while demonstrating just how controversial the topic has become. But is there a way to look at METI experiments more objectively?
The San Marino Scale has been widely suggested as a method for assessing the risks we incur with deliberate transmissions from the Earth to other stars. Introduced by Iván Almár in 2005, the Scale is a work in progress that draws on the model of the Richter Scale, which quantifies the severity of earthquakes. The IAA SETI Permanent Study Group continues to work on it, hoping to measure “…the potential exposure of employing electromagnetic communications technology to announce Earth’s presence to our cosmic companions, or replying to a successful SETI detection.” More on the background of the Scale here.
Hungarian theorist Tibor Pacher has been calling my attention to the San Marino Scale for some time, and recently provided the link to a paper by Almár and Paul Shuch that looks at past METI transmissions. Note that this is a simple ordinal scale ranging from a risk factor of 1 (insignificant) and climbing to 10 (extraordinary). Almár and Shuch apply it to several widely known experiments, looking at them in terms of duration, directionality, information content and transmitter power, before assigning them a value on the scale.
The experiments are these:
- Evpatoria Planetary Radar Telescope: The source of three METI attempts, beginning with the Cosmic Call transmissions of 1999 and 2003, and including the so-called Teen Age Message to the Stars in 2001. The Evpatoria experiments targeted specific stars; their signal amplitude exceeded that of the quiet sun (see below) by about four orders of magnitude. Almár and Shuch assign them a San Marino Scale value of 7, which ranks as ‘high’ in significance.
- Arecibo Message: This was the first METI attempt ever made, sent in November of 1974 and targeting M13, a star cluster some 25,000 light years from Earth. By the paper’s calculations, the Arecibo message outshone the Sun by a factor of 105. The authors assign it a San Marino score of 8, ranking it as ‘far-reaching’ on the scale.
- Planetary Radar: This one is quite interesting. Planetary radars like that at Arecibo are routinely used (when funding is present!) to study near-Earth objects like asteroids and comets. Such transmissions are not intended as communications signals, but Alexander Zaitsev at Evpatoria has examined their potential for detectability over interstellar distances, and Almár and Shuch consider them inadvertent but de facto METI signals. Here we have a powerful signal but little information content, registering at a 6 on the San Marino Scale for ‘noteworthy.’
- Finally, and perhaps still more curious, is Allen Tough’s continuing work with the Invitation to ETI Initiative. Here we have no targeted interstellar transmissions but an attempt to reach out via the Internet. Thus even with the most powerful uplink signals to satellites, we are many orders of magnitude below the solar flux, so the intensity of the message can be discarded. On the other hand, the information content at the Invitation site is high, creating a combined San Marino score of 4, or ‘moderate.’ The Invitation strategy assumes an ETI civilization advanced enough to monitor terrestrial networks, and thus the presence of an ETI probe nearby.
A key in all such grading is the character of the information content in a message and the intensity of the transmitted signal. Almár and Shuch examine the latter in relation to the solar flux. Modeling a ‘quiet sun’ baseline (i.e., conditions of minimum solar noise), the researchers compare the outgoing signal to that flux. Obviously, the actual flux varies significantly, but the method is carefully chosen. From the paper:
By quantifying our transmissions relative to minimum solar flux, we are perhaps overstating the SNR [signal to noise ratio] which a given terrestrial transmission might impart on extraterrestrial receivers. This approach ensures that our resulting Intensity term, which contributes to the overall San Marino Scale value, is a best-case number as far as signal detectability is concerned. Since it is the potential negative consequences of transmission which we seek to quantify, we believe this conservative approach, which may slightly overstate signal impact, is appropriate to the function the San Marino Scale was intended to serve.
How useful are the San Marino Scale’s gradations? Are the distinctions between METI experiments helpful as we look to future possibilities? I’m glad to see an attempt being made to quantify the risks involved, but the Scale seems to be only a beginning given the complexity of the issues involved. And I agree with Tibor Pacher, who said this in a recent comment here:
I think it would be useful to devote some really interdisciplinary effort to investigate the role of such a measure like the San Marino Scale. Informatics, social sciences, law, etc. could say a lot about this; so I hope that people knowledgeable in these fields will pick up the issue.
‘Interdisciplinary’ is the key word for a topic with potential ramifications for our entire species. More details in the paper, which is Shuch and Almár, “Quantifying Past Transmissions Using the San Marino Scale,” available online. See also the same authors’ “The San Marino Scale: A New Analytical Tool for Assessing Transmission Risk,” Acta Astronautica 60 (January 2007), pp. 57-59, available here.