In the search for life in the cosmos, transiting exoplanets are currently our best targets. With thousands already detected, our search is entering a new era of discovery with upcoming large telescopes that will look for signs of ‘life’ in the atmospheres of transiting worlds. Previous work has explored the zone from which Earth would be visible while transiting the Sun1,2,3,4. However, these studies considered only the current position of stars, and did not include their changing vantage point over time. Here we report that 1,715 stars within 100 parsecs from the Sun are in the right position to have spotted life on a transiting Earth since early human civilization (about 5,000 years ago), with an additional 319 stars entering this special vantage point in the next 5,000 years. Among these stars are seven known exoplanet hosts, including Ross-128, which saw Earth transit the Sun in the past, and Teegarden’s Star and Trappist-1, which will start to see it in 29 and 1,642 years, respectively. We found that human-made radio waves have already swept over 75 of the closest stars on our list.
This is a preview of subscription content
Subscribe to Nature+
Get immediate online access to the entire Nature family of 50+ journals
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Code used in the analysis is available at https://github.com/jfaherty17/ETZ.
Shostak, S. & Villard, R. A Scheme for Targeting Optical SETI Observations. In Symp. Int. Astron. Union Vol. 213, 409–414 (Cambridge Univ. Press, 2004).
Filippova, L. N., Kardashev, N. S., Likhachev, S. F. & Strelnitskj, V. S. in Bioastronomy: The Search for Extraterrestial Life — The Exploration Broadens 254–258 (Springer, 2008).
Heller, R. & Pudritz, R. E. The search for extraterrestrial intelligence in Earth’s solar transit zone. Astrobiology 16, 259–270 (2016).
Kaltenegger, L. & Pepper, J. Which stars can see Earth as a transiting exoplanet? Mon. Not. R. Astron. Soc. Lett. 499, L111–L115 (2020).
Gaia Collaboration. Gaia Early Data Release 3. Summary of the contents and survey properties. Astron. Astrophys. 649, 61 (2020).
Gaia Collaboration. Gaia Early Data Release 3. The Gaia catalogue of nearby stars. Astron. Astrophys. 41, 10 (2020).
Marconi, S. G. Radio telegraphy. J. Am. Inst. Electr. Eng. 41, 561–570 (1922).
Gaia Collaboration. Gaia Data Release 2. Astron. Astrophys. 616, A10 (2018).
Kiman, R. et al. Exploring the age-dependent properties of M and L dwarfs using Gaia and SDSS. Astron. J. 157, 231 (2019).
Bochanski, J. J. et al. The luminosity and mass functions of low-mass stars in the galactic disk II. The field. Astron. J. 139, 2679–2699 (2010).
Sheikh, S. Z. et al. The breakthrough listen search for intelligent life: a 3.95–8.00 GHz search for radio technosignatures in the restricted Earth transit zone. Astron. J. 160, 29 (2020).
Zhang, Z.-S. et al. First SETI observations with China’s Five-hundred-meter Aperture Spherical Radio Telescope (FAST). Astrophys. J. 891, 174 (2020).
Zahnle, K. et al. Emergence of a habitable planet. Space Sci. Rev. 129, 35–78 (2007).
Lyons, T. W., Reinhard, C. T. & Planavsky, N. J. The rise of oxygen in Earth’s early ocean and atmosphere. Nature 506, 307–315 (2014).
Mojzsis, S. J. et al. Evidence for life on Earth before 3,800 million years ago. Nature 384, 55–59 (1996); correction 386, 738 (1997).
Agol, E. Transit survey for Earths in the habitable zone of white dwarfs. Astrophys. J. 731, L31 (2011).
Ramirez, R. M. & Kaltenegger, L. Habitable zone of post-main sequence stars. Astrophys. J. 823, 6 (2016).
Kozakis, T. & Kaltenegger, L. Atmospheres and UV environments of Earth-like planets throughout post-main-sequence evolution. Astrophys. J. 875, 99 (2019).
Vanderburg, A. et al. A giant planet candidate transiting a white dwarf. Nature 585, 363–367 (2020).
Kaltenegger, L. et al. The white dwarf opportunity: robust detections of molecules in Earth-like exoplanet atmospheres with the James Webb space telescope. Astrophys. J. 901, L1 (2020).
Zechmeister, M. et al. The CARMENES search for exoplanets around M dwarfs. Astron. Astrophys. 627, A49 (2019).
Kasting, J. F., Whitmire, D. P. & Reynolds, R. T. Habitable zones around main sequence stars. Icarus 101, 108–128 (1993).
Kaltenegger, L. How to characterize habitable worlds and signs of life. Annu. Rev. Astron. Astrophys. 55, 433–485 (2017).
Bryson, S. et al. A probabilistic approach to Kepler completeness and reliability for exoplanet occurrence rates. Astron. J. 159, 279 (2020).
Crutzen, P. J. The “anthropocene”. J. Phys. IV 12, 1–5 (2002).
Frank, A., Carroll-Nellenback, J., Alberti, M. & Kleidon, A. The Anthropocene generalized: evolution of exo-civilizations and their planetary feedback. Astrobiology 18, 503–518 (2018).
Kipping, D. M. & Teachey, A. A cloaking device for transiting planets. Mon. Not. R. Astron. Soc. 459, 1233–1241 (2016).
Kerins, E. Mutual detectability: a targeted SETI strategy that avoids the SETI paradox. Astron. J. 161, 39 (2020).
Kaltenegger, L., Traub, W. A. & Jucks, K. W. Spectral evolution of an Earth-like planet. Astron. J. 658, 598–616 (2007).
Kaltenegger, L., Lin, Z. & Madden, J. High-resolution transmission spectra of Earth through geological time. Astrophys. J. Lett. 892, 17 (2020).
Kaltenegger, L., Lin, Z. & Rugheimer, S. Finding signs of life on transiting Earth-like planets: high-resolution transmission spectra of Earth through time around FGKM host stars. Astrophys. J. 904, 10 (2020).
Lovelock, J. E. A physical basis for life detection experiments. Nature 207, 568–570 (1965).
Lederberg, J. Signs of life: criterion-system of exobiology. Nature 207, 9–13 (1965).
Fujii, Y. et al. Exoplanet biosignatures: observational prospects. Astrobiology 18, 739–778 (2018).
Catling, D. C. et al. Exoplanet biosignatures: a framework for their assessment. Astrobiology 18, 709–738 (2018).
Kasting, J. F., Kopparapu, R., Ramirez, R. M. & Harman, C. E. Remote life-detection criteria, habitable zone boundaries, and the frequency of Earth-like planets around M and late K stars. Proc. Natl Acad. Sci. USA 111, 12641–12646 (2014).
Tarter, J. The search for extraterrestrial intelligence (SETI). Annu. Rev. Astron. Astrophys. 39, 511–548 (2001).
Ricker, G. R. et al. Transiting Exoplanet Survey Satellite (TESS). In Proc. SPIE, Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave Vol. 9143 (eds Oschmann Jr, J. M. et al.) 914320 (SPIE, 2014).
Stassun, K. G. et al. The revised TESS input catalog and candidate target list. Astron. J. 158, 138 (2019).
Faherty, J. K. et al. A late-type L dwarf at 11 pc hiding in the Galactic plane characterized using Gaia DR2. Astrophys. J. 868, 44 (2018).
Caselden, D. et al. WiseView: visualizing motion and variability of faint WISE sources. Astrophysics Source Code Library https://ascl.net/1806.004 (2018).
Gagné, J. & Faherty, J. K. BANYAN. XIII. A first look at nearby young associations with Gaia Data Release 2. Astrophys. J. 862, 138 (2018).
Smart, R. L. et al. The Gaia ultracool dwarf sample – II. Structure at the end of the main sequence. Mon. Not. R. Astron. Soc. 485, 4423–4440 (2019).
Muirhead, P. S. et al. A catalog of cool dwarf targets for the transiting exoplanet survey satellite. Astron. J. 155, 180 (2018).
Anders, F. et al. Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18. Astron. Astrophys. 628, A94 (2019).
Cifuentes, C. et al. CARMENES input catalogue of M dwarfs. Astron. Astrophys. 642, A115 (2020).
Malo, L. et al. Bayesian analysis to identify new star candidates in nearby young stellar kinematic groups. Astrophys. J. 762, 88 (2013).
Bock, A. et al. OpenSpace: a system for astrographics. IEEE Trans. Vis. Comput. Graph. 26, 633–642 (2019).
Kozakis, T. & Kaltenegger, L. High-resolution spectra of Earth-like planets orbiting red giant host stars. Astrophys. J. 160, 225 (2020).
O’Malley-James, J. T., Cockell, C. S., Greaves, J. S. & Raven, J. A. Swansong biospheres II: the final signs of life on terrestrial planets near the end of their habitable lifetimes. Int. J. Astrobiol. 13, 229–243 (2014).
L.K. acknowledges support from the Carl Sagan Institute at Cornell and the Breakthrough Initiative. J.K.F. acknowledges support from the Heising Simons Foundation and the Research Corporation for Science Advancement (award 2019-1488). This work has made use of data from the European Space Agency (ESA) mission Gaia, processed by the Gaia Data Processing and Analysis Consortium DPAC20 (https://www.cosmos.esa.int/gaia, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research also used NASA’s Astrophysics Data System and the VizieR and SIMBAD databases operated at CDS, Strasbourg, France.
The authors declare no competing interests.
Peer review information Nature thanks the anonymous reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
A guide to Supplementary Tables 1 and 2.
Stars that can see Earth transit in the +/-5000-year period. This Table lists all characteristics for stars that can see Earth transit in the +/-5000-year period, sorted by distance from the Sun. The authors cross-matched their full sample against literature estimates of mass, effective temperature, radii, bolometric luminosity, metallicity, and log g for Gaia sources. Respective catalogue references for the parameter are noted in Table 1 and Table 2.
Exoplanet host stars that can see Earth transit in the +/-5000-year period. This table lists the characteristics of the seven known stars that can see Earth transit in the +/-5000-year period, that are known exoplanet host stars, sorted by distance from the Sun.
About this article
Cite this article
Kaltenegger, L., Faherty, J.K. Past, present and future stars that can see Earth as a transiting exoplanet. Nature 594, 505–507 (2021). https://doi.org/10.1038/s41586-021-03596-y