with guest Dr. Natalie Batalha from San Jose State University
Over the past decade and a half, astronomers have used both ground-based and space-based telescopes to discover more than 400 "extrasolar" planets. The Kepler space-based mission uses a technique called transit photometry to search for these planets. In January 2010 the Kepler mission team announced the discovery of five new planets. Four of them are massive worlds similar in size to Jupiter; the fifth is smaller, more like Neptune or Uranus. The ultimate goal of the Kepler mission is to search out the existence of Earth-like planets.
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Produced by the Astronomical Society of the Pacific
Written and narrated by Carolyn Collins Petersen
Original music by Geodesium
Soundtrack production by Loch Ness Productions
Web page materials by Andrew Fraknoi
Special thanks to Dr. Seth Shostak and the SETI Institute
Special thanks to Dr. Natalie Batalha
Fraknoi (Foothill College & ASP)
Until the mid-1990s, the only planets astronomers knew about were the ones orbiting the Sun. But then, in a rapid series of technical breakthroughs, scientists developed a number of techniques for finding planets around other stars. In the most commonly used technique, astronomers measure the "pull" of a massive planet's gravity on its star, as the planet goes around. While the planet is too dim to detect directly, the planet's gravity causes the star to "wiggle" back and forth during its complete orbit, and it is this tiny wiggle that can now be found.
Another method looks for planets that, as seen from Earth, cross the face of their parent star in the course of orbiting it. When they do, they block a tiny fraction of the star's light. While this small decrease in light is hard (but not impossible) to measure from the ground, it is a much easier task from the airless realm of space. Looking for such planetary crossings (or transits) is the task of the Kepler mission, and it is expected to add many more planets and less massive planets to our inventory of planet discoveries.
As of the first few months of 2010, over 400 planets have now been found around stars in our cosmic neighborhood -- and more are being discovered all the time. This is one of the most active and successful areas of modern astronomy and no article or book can keep fully current on the torrent of new data. Still, the list below is a small selection of non-technical resources that you may find useful if you want to begin exploring the world of "extra-solar" planets (the ones beyond the Sun's influence.).
Painting of a close-by Jupiter planet crossing the face of its star
(NASA, ESA, G. Bacon)
Boss, Alan The Crowded Universe: The Search for Living Planets. 2009, Basic Books. A book brimming with optimism (and also full of good information) about the prospects of finding Earth-like worlds out there, by a noted astronomer.
Casoli, Fabinee & Encrenaz, Therese The New Worlds: Extrasolar Planets. 2007, Springer. Translated from the Italian edition, this is an illustrated guide to how we are discovering exoplanets.
Jones, Barrie The Search for Life Continued: Planets around Other Stars. 2008, Praxis/Springer. An introductory book by a British astronomer.
Carlisle, C. "The Race to Find Alien Earths" in Sky & Telescope, Jan. 2009, p. 28. On early discoveries of planets with masses comparable to Earth's and the Kepler mission to find many more of them.
Marcy, G. "The New Search for Distant Planets" in Astronomy, Oct. 2006, p. 30. Fine 7-page overview by the leading planet hunter of our time. (The same issue has a dramatic fold-out visual atlas of extrasolar planets.)
Naeye, R. "Planetary Harmony: Resonances are a Key to Deciphering How Planetary Systems Form and Evolve" In Sky & Telescope, Jan. 2005, p. 44. On theory and observations of other star systems with more than one planet.
Seager, S. "Alien Earths from A to Z" in Sky & Telescope, Jan. 2008, p. 22. How we learn what planets around other stars are made of and the range of possible planets we might expect.
Seager, S. "Unveiling Distant Worlds" in Sky & Telescope, Feb. 2006, p. 28. Nice introduction to the types of planets we are finding and the methods astronomers use.
Expolanets Database and California Planet Search is a site that highlights the work of the original American team of planet hunters (Marcy and Butler) and their colleagues, but has useful background information as well:
PlanetQuest (from the Exoplanet Exploration Program at the Jet Propulsion Lab) is probably the best site for students and beginners, with introductory materials and nice illustrations, but it focuses mostly on NASA work and missions:
The Planetary Society Exoplanets Pages are also very nice, with a dynamic catalog of planets found and good explanations:
The Extra-solar Planets Encyclopedia, maintained by Jean Schneider, Paris Observatory, has the best catalog of planet discoveries and useful background material (some of it more technical):
Where the Kepler Mission will be taking images
(box superimposed on the a photo of the night sky by Carter Roberts)
Doyle, L., et al. "Searching for the Shadows of Other Earths" in Scientific American, Sep. 2000, p. 58. On using transits to find extrasolar planets, and a preview of the Kepler mission to do this from space.
Jayawardhana, R. "Are Super-sized Earths the New Frontier?" in Astronomy, Nov. 2008, p. 26. On first discoveries of planets with masses comparable to Earth's.
Kepler Mission Web Site (Public web site for the telescope with good information, images, educational materials):
News Items about the Kepler Mission (from Astronomy Magazine):
Mar. 2009 article about Kepler in The New York Times:
A Brief Introduction to the Kepler Mission by Seth Shostak:
Painting of a planet with 13 times the mass of the Earth (plus a moon) orbiting a red dwarf star
(David Aguilar, CfA)
Activities from the Kepler Mission:
An Australian educator has a project to link students with Kepler data and activities at:
The PlanetQuest Student Activities Guide highlights four short activities and some information on NASA projects:
How Do We Find Planets Around Other Stars (a demonstration activity from the JPL/ASP Night Sky Network):
Where are the Distant Worlds (an activity to map stars that have planets from the Night Sky Network):