Dear friends,
I am writing to share tremendous news. Our group will receive funding from NASA to search for technosignatures! The budget excludes telescope costs and will mainly fund one graduate student for three years, but I am ecstatic anyway! Since the termination of the High Resolution Microwave Survey (HRMS) in 1993, NASA has hardly funded any SETI efforts, and most of such funding has gone to instrumentation development (although NASA awarded one grant in 2008 to fund the SETI@home project, a fact that I mistakenly left out from my October 2018 newsletter). NASA's long-awaited renewal of SETI support is an exciting turning point. I owe a debt of gratitude to all the people who have advocated for technosignature searches at the congressional level, to supportive civil servants at NASA, to the reviewers of our proposal, and to all our generous donors who have sustained our efforts since 2015. Our NASA funding is slated to start on January 1, 2021.
I am also pleased to report that the results of our 2018-2019 search are making their way through the review process at the Astronomical Journal. Our article quantifies the advantages of our search compared to the $100 million Breakthrough Listen (BL) initiative in terms of hit rate density (200 times larger), sensitivity (up to 25 times better), and frequency drift rate coverage (2–4 times larger). Although we did not detect ET, we made a few contributions that I believe are important to the field. First, we described a new technique for the identification of signals in dynamic spectra. Our approach relies on the topographic concept of prominence and enables the detection of ten times as many signals as other algorithms (Figure 1). Second, we implemented a signal injection and recovery analysis tool applicable to searches for narrowband signals. This tool allows us to inject artificial signals into the data and quantify the fraction of signals that are correctly recovered and classified. We found that our pipeline is highly but not perfectly efficient. Third, we quantified the signal loss of a tree algorithm that is commonly used in data processing pipelines to search for signals with unknown frequency drift rates. This algorithm reduces the number of computing cycles by taking some shortcuts at the expense of some signal degradation, which we have now quantified (Figure 2).
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Figure 1: Improvements in detection counts obtained with our new prominence-based algorithm.
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Figure 2: Efficiency of the UCLA (blue) and BL (red) data processing pipelines based on the use of a tree algorithm to detect signals at a variety of frequency drift rates. The UCLA search is substantially more efficient and samples a larger search space.
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The mid-September 2020 publication of a Nature Astronomy article titled "Phosphine gas in the cloud decks of Venus" was covered by over 60 major news outlets and generated over 4,700 news stories. The possible detection of a possible sign of life evidently caught the attention of reporters. The claim resulted in immediate attempts to confirm the detection and examine the range of plausible interpretations. It took just a few weeks for other teams to submit a variety of rebuttals. First, on October 15, analysis of existing infrared observations showed that phosphine is not detected in the atmosphere of Venus. Second, on October 19 and 29, reanalyses of the millimeter data associated with the initial detection claim showed that the 12th-order polynomial used to process the data artificially introduced features in the spectra. Two independent teams argued that the initial detection was simply erroneous. In the meantime, at least two teams suggested that volcanic – as opposed to biological – processes on Venus might explain the presence of phosphine, which is now very much in doubt. The episode was reminiscent of the ALH84001 episode, where microstructures in a Martian meteorite were initially attributed to fossilized life forms, until follow-up studies indicated more plausible abiogenic origins.
I see some unfortunate consequences as well as some redeeming aspects of the phosphine controversy. As is unfortunately common in news reporting, the rebuttals garnered far less attention than the initial sensational claim. Many non-experts may now hold the questionable belief that scientists have detected evidence of life on Venus. In addition to confounding public perception, the brouhaha may have detrimental consequences for the selection of Venus missions or instruments by space agencies. There are many important scientific questions about Venus, and the elusive search for phosphine may negatively influence which investigations get prioritized. On the other hand, any story that brings attention to Venus has some intrinsic benefit because this planet, much like SETI, has been neglected by NASA for almost 30 years. The timing of the publications allowed me to draw upon a real-time example when I described the scientific method to UCLA students who took our general education Astrobiology course this Fall. The data reduction blunder in the initial report is sobering, but it illustrates the self-correcting nature of science nonetheless.
The phosphine story epitomizes the difficulties associated with biosignature searches around exoplanets. The initial detection claims will likely be contentious, in part because signal strength decreases as the square of the distance. If biosignature detections are problematic with the planet next door, they are going to be extremely challenging with planets that are a million times further away. The interpretation of such proposed detections will almost certainly be controversial as well. As in the Venus example, research teams will offer abiogenic explanations for the presence of molecules in exoplanet atmospheres. How confident will we be that an actual biosignature has been detected? We should be prepared for a drawn-out process with no clear answer for years or decades.
For these reasons and many more, I am thrilled that NASA is investing in the search for technosignatures in addition to biosignatures. As always, I will keep you informed of our work and progress.
Warm regards,
Jean-Luc Margot
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