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The First Thousand Exoplanets: Twenty Years of Excitement and Discovery

Part of the Advances in Astrobiology and Biogeophysics book series (ASTROBIO)

Abstract

The recent “explosion” in the number of extrasolar planets, or exoplanets, is perhaps the most exciting phenomenon in all of science. Two decades ago, no planets were known beyond the Solar System, and now there are more than 770 confirmed exoplanets and several thousand more candidates, while the mass detection limit has marched steadily downwards from Jupiter mass in 1995 to Neptune mass in the early 2000s to Earth mass now. The vast majority of these exoplanets are detected indirectly, by their gravitational influence on the parent star or the partial eclipse they cause when they periodically pass in front of it. Doppler detection of the planet’s reflex motion yields a period and an estimate of the mass, while transits or eclipses yield the size. Exoplanet detection taxes the best observatories in space, yet useful contributions can be made by amateur astronomers armed with 6-inch telescopes. The early discoveries were surprising; no one predicted “hot Jupiters” or the wild diversity of exoplanet properties that has been seen. It is still unclear if the Solar System is “typical” or not, but at current detection limits at least 10 % of Sun-like stars harbor planets and architectures similar to the Solar System are now being found. Over a hundred multiple planet systems are known and the data are consistent with every star in the Milky Way having at least one planet, with an implication of millions of habitable, Earth-like planets, and of which could harbor life. Doppler and transit data can be combined to give average density, and additional methods are beginning to give diagnostics of atmospheric composition. When this work can be extended to rocky and low mass exoplanets, and the imprint of biology on a global atmosphere can be measured, this might be the way that life beyond Earth is finally detected for the first time.

Keywords

  • Solar System
  • Giant Planet
  • Terrestrial Planet
  • Habitable Zone
  • Extrasolar Planet

These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Acknowledgments

Astrobiology is not my research specialty so I gain knowledge and stay current thanks to the good graces and patience of many of my colleagues. In particular, this chapter has benefitted from conversations with John Baross, Alan Boss, Adam Burrows, David Charbonneau, Debra Fischer, Lisa Kaltenegger, Jonathan Lunine, Geoff Marcy, Sara Seager, and Giovanna Tinetti, Any errors or misrepresentations that remain are, however, purely my own.

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Correspondence to Chris Impey .

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Impey, C. (2013). The First Thousand Exoplanets: Twenty Years of Excitement and Discovery. In: Vakoch, D. (eds) Astrobiology, History, and Society. Advances in Astrobiology and Biogeophysics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-35983-5_10

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