A kilometer-scale asteroid inside Venus's orbit

Creators: Ip, W.-H.; Bolin, B.; Masci, F. J.; Ye, Q.-Z.; Kramer, E. A.; Helou, G.; Ahumada, T.; Coughlin, M. W.; Graham, M. J.; Walters, R.; Deshmukh, K. P.; Fremling, C.; Lin, Z.-Y.; Milburn, J. W.; Purdum, J. N.; Quimby, R.; Bodewits, D.; Chang, C.-K.; Ngeow, C.-C.; Tan, H.; Zhai, C.; van Dokkum, P.; Granvik, M.; Harikane, Y.; Mowla, L. A.; Burdge, K. B.; Bellm, E. C.; De, K.; Cenko, S. B.; Copperwheat, C. M.; Dekany, R.; Duev, D. A.; Hale, D.; Kasliwal, M. M.; Kulkarni, S. R.; Kupfer, T.; Mahabal, A.; Mróz, P. J.; Neill, J. D.; Riddle, R.; Rodriguez, H.; Serabyn, E.; Smith, R. M.; Sollerman, J.; Soumagnac, M. T.; Southworth, J.; Yan, L.

Abstract

Near-Earth asteroid population models predict the existence of asteroids located inside the orbit of Venus. However, despite searches up to the end of 2019, none have been found. Here we report the discovery by the Zwicky Transient Facility of the first known asteroid located inside of Venus' orbit, 2020 AV₂, possessing an aphelion distance of 0.65 au and ∼2 km in size. While it is possible that 2020 AV₂ is the largest of its kind, we find that its discovery is surprising in the context of population models where the expected count is close to zero. If this discovery is not a statistical fluke, then 2020 AV₂ may come from a yet undiscovered source population of asteroids interior to Venus, and currently favored asteroid population models may need to be adjusted.

Additional Information

Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation 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. SED Machine is based upon work supported by the National Science Foundation under Grant No. 1106171 The KPED team thanks the National Science Foundation and the National Optical Astronomical Observatory for making the Kitt Peak 2.1-m telescope available. We thank the observatory staff at Kitt Peak for their efforts to assist Robo-AO KP operations. The KPED team thanks the National Science Foundation, the National Optical Astronomical Observatory, the Caltech Space Innovation Council and the Murty family for support in the building and operation of KPED. In addition, they thank the CHIMERA project for use of the Electron Multiplying CCD (EMCCD). The authors would like to thank Alessandro Morbidelli for useful discussion in the interpretation of the first inner-Venus asteroid discovery as well as providing the synthetic asteroid population used to model our survey efficiencies. M. W. Coughlin acknowledges support from the National Science Foundation with grant number PHY-2010970. C.F. gratefully acknowledges the support of his research by the Heising-Simons Foundation (#2018-0907). Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Authors Contributions. W.-H.I. helped initiate, design and secure P48 time for the ZTF Twilight. B.T.B. discovered 2020 AV₂ in the ZTF data and realized it had an orbit interior to Venus', led the study, wrote the manuscript, reviewed and scanned all candidate asteroid detections for the duration of this study, helped design and secure time for the Twilight survey and for follow-up, prepared and executed follow-up observations, reduced the photometric and spectroscopic data, did the astrometry, orbit determination, helped generate the synthetic NEA population, calculated the survey completeness and estimates of the inner-Venus asteroid population. F.J.M. served as the Science Data System Lead of the ZTF collaboration, wrote and maintained software for extraction of moving objects in ZTF data, calculated the survey completeness, maintained the ZTF data system, helped secure P48 time for the ZTF Twilight survey, helped design and initiate the Twilight survey. Q.Y. contributed code used to schedule the ZTF survey and contributed improvements to the moving object identification pipeline, and helped initiate and design the Twilight survey. E.K. monitored the NEA discovery performance of the ZTF survey. G.H. helped with the interpretation of the completeness calculation, helped prepare the manuscript, served as the Primary Investigator of the team observing NEAs with ZTF and as the Data Archive Director of the ZTF collaboration, helped design the cadence, secure P48 time for the ZTF Twilight survey and is one of its initiators. E.K. monitored the NEA discovery performance of the ZTF survey. G.H. served as the Primary Investigator of the team observing NEAs with ZTF and as the Data Archive Director of the ZTF collaboration, helped design the cadence, secure P48 time for the ZTF Twilight survey and is one of its initiators. E.K. monitored the NEA discovery performance of the ZTF survey. G.H. served as the Primary Investigator of the team observing NEAs with ZTF and as the Data Archive Director of the ZTF collaboration, helped design the cadence, secure P48 time for the ZTF Twilight survey and is one of its initiators. T.A. and M.C. performed follow-up observations of 2020 AV₂ with KPED and contributed to the reduction of photometry. M.G. served as the Project Scientist of ZTF, secured time with Keck I and took spectroscopic observations of 2020 AV₂ with Keck I/LRIS and reduced spectral data. R.W. performed follow-up observations of 2020 AV₂ with SEDM. K.P.D. contributed to planning follow-up observations of 2020 AV₂. C.F. contributed to the planning of spectroscopy observations of 2020 AV₂ with Keck and spectroscopic data reduction. Z.-Y.L. contributed to the interpretation of the 2020 AV₂ spectroscopy data. J.W.M. contributed to follow-up observations of 2020 AV₂. J.P. and R.Q. contributed to the reduction of photometry and follow-up observations of 2020 AV₂. C.-K.C., C.-C.N. and H.T. contributed to securing time with the P48 for ZTF Solar System observations. C.Z., C.M.C and J.S. were members of the team that conducts follow-up observations of ZTF Solar System discoveries. P.D. and L.A.M. helped secure time for follow-up observations of 2020 AV₂. M.G. helped generate the synthetic NEA population. K.B.B. and K.D. contributed to the reduction of Keck/LRIS spectroscopy data of 2020 AV₂. E.C.B. served as the Survey Scientist of the ZTF collaboration and scheduled the observations taken with the P48 during the ZTF Twilight survey. S.B.C. contributed to the planning of P48 time used in the Twilight survey. D.A.D, A.M. and P.J.M. wrote and maintained software and machine learning algorithms for the ZTF data pipeline and identification of sources in ZTF data. A.M. served as the Machine Learning Lead for the ZTF collaboration. R.D. served as the Project Manager of the ZTF collaboration and contributed to the design and construction of the ZTF camera. D.H. contributed to the design and construction of the ZTF camera. M.K. served as the Primary Investigator of the Global Relay of Observatories Watching Transients Happen (GROWTH) team for follow-up of ZTF discoveries. S.R.K. served as the Principal Investigator of the ZTF collaboration and survey. T.K. and M.T.S. contributed to the ZTF calibration pipeline. J.D.N. contributed to SEDM operations and observations of 2020 AV₂. R.R. contributed to maintaining ZTF operations. H.R. contributed to SEDM operations. E.S. contributed to KPED operations and observations of 2020 AV₂. R.M.S. served as the Lead Camera Engineer for the ZTF survey and lead the design and construction of the ZTF camera. J.S. contributed to SEDM operations and observations of 2020 AV₂. L.Y. contributed to planning and securing of telescope time for follow-up observations of 2020 AV₂.

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