Over recent years, newspapers have been filled with headlines such as "billions of Earths in the Milky Way alone". But how many Earthlike planets are there really?

Join us as we explore all of the different estimates for how many Earths there really are, how each team arrived at their answers, and why they seem to differ so wildy from each other, before finally we'll offer our own answer to this monumental question.

Written & presented by Prof David Kipping

This video is based on research conducted at the Cool Worlds Lab at Columbia University, New York. You can now support our research program directly here: https://www.coolworldslab.com/support

References:
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► Dong, S. & Zhu, Z., 2013, ApJ, 778, 11: https://arxiv.org/abs/1212.4853
► Petigura, E., Howard, A., Marcy, G. W., 2013, PNAS, 110, 19273: https://arxiv.org/abs/1311.6806
► ForemanMackey, D., Hogg., D. W. & Morton, T. D., 2014, ApJ, 795, 12: https://arxiv.org/abs/1406.3020
► Farr, W. M., Mandel, I., Aldridge, C., Stroud, K., 2014, arXiv:1412.4849: https://arxiv.org/abs/1412.4849
► Burke, C. J., Christiansen, J. L., Mullally F. et al., 2015, ApJ, 809, 19: https://arxiv.org/abs/1506.04175
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► Belikov, R., Stark, C., Batalha, N., et al., 2017: https://exoplanets.nasa.gov/system/in...
► Garrett, D., Savransky, D., Belikov, R., 2018, PASP, 130, 114403: https://arxiv.org/abs/1810.02847
► Mulders, G. D., Pascucci, I., Apai, D., Ciesla, F. J., 2018, AJ, 156, 24: https://arxiv.org/abs/1805.08211
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► Bryson, S., Coughlin, J., Batalha, N. M. et al., 2019, submitted: https://arxiv.org/abs/1906.03575
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Video materials & graphics used:
► Atacama timelapse by Timestorm Films:    • NOX ATACAMA | 8K  
► Spinning galaxy animation by Huy Trường Nguyễn:    • Galaxy Spinning  
► GJ 357 animations by NASA's Goddard Space Flight Center/Chris Smith: https://svs.gsfc.nasa.gov/13266
► Wheat field footage by xbility1:    • Hand on wheat field 2  
► Orion nebula animation from Space.com/NASA/ESA: https://www.space.com/39362orionneb...
► Bacteria videos from Nikon Small World competition: https://www.nikonsmallworld.com/galle...
► TESS & Kepler animations by NASA's Goddard Space Flight Center: https://svs.gsfc.nasa.gov/12884
► Mars flyby footage by Jan Fröjdman/NASA/JPL/University of Arizona: https://vimeo.com/207076450
► Trappist1 animation by ESO/L. Calçada/spaceengine.org: https://www.eso.org/public/videos/eso...
► Kepler Orrery V by Ethan Kruse:    • Kepler Orrery V  

Movies/TV scenes used:
► Agora (2010) Focus Features
► 300 (2006) Warner Bros. Pictures

Music used, in chronological order:
► "Selha" by Stephen Keech, licensed through SoundStripe.com: https://app.soundstripe.com/songs/7102
► "Waking Up" by Atlas, licensed through SoundStripe.com: https://app.soundstripe.com/songs/3984
► Cylinder Four (http://chriszabriskie.com/cylinders/) by Chris Zabriskie (http://chriszabriskie.com/); licensed under a Creative Commons Attribution license (https://creativecommons.org/licenses/...)
► Cylinder Two (http://chriszabriskie.com/cylinders/) by Chris Zabriskie (http://chriszabriskie.com/); licensed under a Creative Commons Attribution license (https://creativecommons.org/licenses/...)
► Cylinder Five (http://chriszabriskie.com/cylinders/) by Chris Zabriskie (http://chriszabriskie.com/); licensed under a Creative Commons Attribution license (https://creativecommons.org/licenses/...)
► Music from Neptune Flux, "We Were Never Meant to Live Here" by Chris Zabriskie (http://chriszabriskie.com/neptuneflux/); licensed under a Creative Commons Attribution license (https://creativecommons.org/licenses/...)

And also:
► Columbia University Department of Astronomy: http://www.astro.columbia.edu
► Cool Worlds Lab website: http://coolworlds.astro.columbia.edu

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