fBLS is a novel technique for detecting transiting planets, based fBLS is a novel technique for detecting transiting planets, based on the fast-folding algorithm [1], extensively used in pulsar on the fast-folding algorithm [1], extensively used in pulsar astronomy [2]. astronomy [2]. fBLS is efficient and scalable. It can substantially reduce the fBLS is efficient and scalable. It can substantially reduce the computation time required to search for transiting planets. For computation time required to search for transiting planets. For example, when applied example, when applied to the to the Kepler Kepler data, fBLS reduces the data, fBLS reduces the computation time by a factor of up to ~3000. computation time by a factor of up to ~3000. fBLS is well suited to the analysis of PLATO lightcurves. We fBLS is well suited to the analysis of PLATO lightcurves. We currently adapt fBLS and extend its operation to efficiently detect currently adapt fBLS and extend its operation to efficiently detect planets with varying transit duration and timing [4]. planets with varying transit duration and timing [4]. We used fBLS We used fBLS to detect small rocky transiting planets with to detect small rocky transiting planets with periods shorter than one day, a period range for which the periods shorter than one day, a period range for which the computation is extensive [3]. We have discovered five new planet computation is extensive [3]. We have discovered five new planet candidates (Shahaf et al., in prep.) candidates (Shahaf et al., in prep.) For a given lightcurve of measurements, fBLS simultaneously produces binned and phase-folded lightcurves for an array of ‘sufficiently different’ trial periods, with arithmetic operations. This procedure is conceptually similar to FFT. For comparison, a standard BLS implementation requires operations. For each folded lightcurve we compute the BLS statistic [5], producing a standard BLS periodogram. Demonstration: Kepler-78b Figure 1: fBLS periodogram of Kepler-78. The left panel is a grayscale diagram demonstrating the fast-folding algorithm output for a narrow frequency range centered around the periodogram peak. The fBLS periodogram appears on the Right panel, where the BLS scores were calculated for each of the fast-folded profiles. The central peak is highlighted in yellow. The required single-core computation time for the settings used in this example is ~10 sec. Ultra-short period (USP) planets are exoplanets with orbital periods shorter than one day, which tend to be terrestrial. Studies of these extreme systems can shed light on planet formation, star-planet and planet-planet interaction, and orbital evolution. A fast folding algorithm to produce BLS A fast folding algorithm to produce BLS periodograms in search for transiting planets periodograms in search for transiting planets R E L A T E D L I T E R A T U R E [1] Staelin D. H., 1969, Proceedings of the IEEE, 57, 724 [2] Morello V., et al., 2020,MNRAS, 497, 4654 [3] Winn J. N., Sanchis-Ojeda R., Rappaport S., 2018, New Astron. Rev., 83, 37 [4] Shahaf S., Mazeh T., Zucker S., Fabrycky D., 2021, MNRAS, 505, 1293 [5] Kovács G., Zucker S., Mazeh T., 2002, A&A, 391, 369 Sahar Shahaf (1, 11), Barak Zackay (1), Pascal Guterman (111), Tsevi Mazeh (11), Shay Zucker (1v) and Simchon Faigler (11). A F F I L I A T I O N S (1) Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 7610001, Israel. (11) School of Physics and Astronomy, Tel Aviv University, Tel Aviv, 6997801, Israel. (111) Aix Marseille University, CNRS, CNES, LAM, Marseille, France. (1v) Porter School of the Environment and Earth Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel. C O N T A C T : sahar.shahaf@weizmann.ac.il Figure 2: Two examples of phase folded USP planet lightcurves with the same number of bins. Top—a new USP candidate, detected by fBLS. Bottom— Kepler-78b, plotted for reference. Vertical axis range is identical. Despite the shall