Preliminary estimates of the Zwicky Transient Facility 'Ayló'chaxnim asteroid population completeness

Creators: Bolin, B. T.; Ahumada, T.; van Dokkum, P.; Fremling, C.; Hardegree-Ullman, K. K.; Purdum, J. N.; Serabyn, E.; Southworth, J.

Abstract

Near-Earth asteroids (NEAs) are organized into five main classes: Amor, Apollo, Aten, Atira and 'Ayló'chaxnim. Asteroids belonging to the 'Ayló'chaxnim class are located entirely within the orbit of Venus making them difficult to detect by ground-based observatories. The first-known asteroid of this class, (594913) 'Ayló'chaxnim, was discovered by the Zwicky Transient Facility (ZTF) in 2020 January during a twilight search for asteroids at small solar elongations that ran between September 2019 and January 2020. Due to its large diameter of ~2 km, the discovery of (594913) 'Ayló'chaxnim is surprising because contemporary NEA population models predict a scarcity of asteroids of this size located inside the orbit of Venus. To compare the discovery of (594913) 'Ayló'chaxnim by ZTF with the predictions of NEA population models, we estimated the ZTF survey completeness at detecting 'Ayló'chaxnim asteroids and the number of 'Ayló'chaxnim asteroids expected to have been discovered by simulating observations of synthetic 'Ayló'chaxnim asteroids. We find that the 'Ayló'chaxnim population completeness of the survey is ~18% and there is only a 5% probability that a single 'Ayló'chaxnim asteroid would have been discovered. Given the small chance for (594913) 'Ayló'chaxnim to have been discovered, its presence is either a statistical fluke or it implies that asteroid population models may need to be revised.

Additional Information

© 2023 Elsevier. The authors would like to acknowledge Frank Masci for help with operating the software for identifying asteroids in ZTF data, helping with the completeness estimate, and providing helpful comments on the manuscript. The authors would also like to thank Alessandro Morbidelli for the useful discussion and for providing the synthetic asteroid population. C.F. acknowledges support from the Heising-Simons Foundation, United States (grant #2018-0907). Part of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA 80NM0018D0004. Based on observations obtained with the Samuel Oschin 48-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation, United States under Grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. Data availability. Data will be made available on request. Software. The Near-Earth Object Survey Simulation software (Naidu et al., 2021) are publicly available.

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