Free Astronomy Magazine January-February 2022

6 data, which only specific automated procedures (search algorithms) could possibly process. A trainee from Breakthrough Listen, Shane Smith, was entrusted with the long work of “creaming off” the data. He found himself having to look for the proverbial “needle in the haystack,” where the haystack was represented by over 4 million “hits,” or fre- quency intervals with some radio emission. As always in these cases, the first thing done was to eliminate all those signals clearly produced by human technologies and which cer- tainly could not have come from great distances beyond the Earth. This process involved the considera- tion of two main selection criteria. The first criterion was the determi- nation of whether the frequency of a given signal varied over time. In fact, we can expect that a transmit- ter placed on a planet orbiting a star other than the Sun is either moving away from or approaching the radio telescope that picks up the signal here on Earth, meaning that the sig- nal can be characterized as having a positive or negative radial accelera- tion (zero acceleration is instead typ- ical of local sources moving in the same reference frame as the detec- tor). The rotation of an exoplanet on its axis, as well as its orbital mo- tion, can vary the frequency of the T his image shows the star system closest to the Sun − the double star Alpha Centauri AB and its com- panion, the dim and distant Prox- ima Centauri. At the end of 2016, ESO signed an agreement with Breakthrough Initiatives to adapt the VLT instrumentation so that it could search for planets in the Alpha Centauri system, planets that could become the target of a launch of miniature space probes by Break- through Starshot Initiatives. [ESO/ B. Tafreshi (twanight.org )/Digitized Sky Survey 2. Acknowledgement: Davide De Martin/Mahdi Zamani]