UCLA SETI Group newsletter 2018-02-21

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February 21, 2018

Dear friends,

I am happy to report that the results of our 2016 observations at the Green Bank Telescope have been submitted for publication. Our article is titled "A search for technosignatures from 14 planetary systems in the Kepler field with the Green Bank Telescope at 1.15-1.73 GHz" and includes 15 current or former UCLA students as co-authors. We also posted our article on the arXiv preprint server that is familiar to many astronomers as a vehicle for disseminating results in advance of publication, which prompted a reporter at Universe Today to write a story about our results. We focused on signals that natural sources cannot produce and detected about 850,000 candidates. Initial analysis revealed that most of these detections were due to anthropogenic radio-frequency interference (RFI). In particular, we found much RFI in the frequency band that is nominally protected for radio astronomy studies. Approximately 20 signals deserved further testing, which we describe in our article. Ultimately, none of these signals were attributable to an extraterrestrial source. Our article describes the fraction of the search volume that we investigated and the sensitivity of our search. It turns out that we can detect Arecibo-class transmitters at distances of 450 light years and transmitters that are 1000 times more effective than Arecibo at distances of 14,000 light years. This volume represents a large fraction of the Galaxy and we are eager to expand our search to additional planetary systems.

Signal-to-noise ratio (SNR) of detections as a function of transmitter distance from Earth, assuming search parameters identical to those used in our work. Colored lines represent transmitters that are 1–1000 times as powerful as the Arecibo Observatory (AO) planetary radar. Solid and dashed colored lines represent reception with the Green Bank Telescope and the Arecibo Observatory, respectively. The black horizontal line represents the threshold for detection used in our work. The black vertical line represents the distance to the center of the Galaxy.

Because we would like to expand our search, I perused NASA's annual omnibus solicitation for basic and applied research, titled "Research Opportunities in Space and Earth Science." The exobiology component of the solicitation could in principle accept SETI-related grant proposals because its stated goal is to "understand the origin, evolution, distribution, and future of life in the Universe." In particular, "research focused on understanding or characterizing nonradio technosignatures from extrasolar planets that may harbor intelligent life are included in this area." However, "proposals aimed at the identification and characterization of radio signals from extrasolar planets that may harbor intelligent life" are specifically excluded from the program. Apparently, NASA's current position is that a search for technosignatures in the optical or infrared part of the spectrum is worthy of consideration, whereas a similar search in the radio part of the spectrum is not. This arbitrariness does not seem to make a lot of sense. There is some hope that the committee on "Astrobiology Science Strategy for the Search for Life in the Universe" formed by the U.S. National Academies will adopt language that will encourage leveling the playing field. Whether such a recommendation would be adopted by NASA administrators and on what timescale remains to be seen. In the meantime, we will continue to rely on philanthropy to support our search.

Does the name "KIC 8462852" sound familiar? KIC stands for "Kepler Input Catalog" and the number refers to a particular star among the 13-million-strong database. The catalog includes stars observed by NASA's Kepler mission and also many other stars outside Kepler's field of view. KIC 8462852 was found to exhibit unusual, non-periodic light variations and has been known colloquially as "Tabby's star," named after astronomer Tabetha Boyajian who first reported the star's puzzling behavior. Speculations of all stripes were put forward to explain the phenomenon, including the idea that we might be witnessing a feat of astroengineering by an advanced civilization. Could it be that an alien megastructure is occasionally blocking the light from the star? A follow-up paper by Boyajian and her collaborators recently dismissed this notion: it's just dust, the authors say. The key observation is that the amount of dimming is not uniform across all colors. One would expect uniform dimming if an opaque structure was blocking the starlight. The observed dimming of Tabby's star is consistent with the presence of dust, although the source of the dust remains uncertain.

An artist's rendition of an uneven dust cloud obscuring some of the light from Tabby's star. Source: NASA.

In my next newsletter, I hope to tell you about our progress with the analysis of our TRAPPIST-1 observations and other planetary systems.

Warm regards,

Jean-Luc Margot