Open Questions: Extrasolar Planets

Artist's concept of TrES-2
See PlanetQuest for information

Introduction

Isolated planets

Recommended references: Web sites

Recommended references: Magazine/journal articles

Recommended references: Books

Introduction

Recommended references: Web sites

Site indexes

Open Directory Project: Extrasolar Planets: Categorized and annotated links. A version of this list is at Google, with entries sorted in "page rank" order. May also be found at Netscape.
Useful Links to Darwin-related Information: Located at a site about the proposed Darwin mission. In addition to the links related to extrasolar planets, there are also links related to exobiology, SETI, and similar topics.
Galaxy: Extrasolar Planets: Categorized site directory. Entries usually include descriptive annotations.
Links to Other Sites on Planet Detection: List provided by the NASA Kepler Mission.

Sites with general resources

University of California Planet Search Project: Good site by the team which has found the largest number of extrasolar planets. Contains a table of discovered planets, news, published papers, external links, and other useful resources. Material for a more general audience is here.
Extrasolar Planets Encyclopedia: Good articles and other information about extrasolar planet research, compiled by Jean Schneider. Includes a catalog of known extrasolar planets.
The Geneva Extrasolar Planet Search Programmes: Home page for an extrasolar planet search team. Includes a table of known exoplanets.
Planet Search and Stellar Kinematics: Home page of a research group involved in extrasolar plant search, at the Observatoire Astronomique de l'Université de Genève
Known Planetary Systems: Table of data on known extrasolar planetary systems, maintained by Alexander J. Willman, Jr..
Exoplanets: Comprehensive list of candidate planets and related information, by Eric Mamajek.
Planet Quest: Extrasolar Planets: Web site based at NASA's Jet Propulsion Laboratory, covering all aspects of searching for extrasolar planets.
Planet Quest: New Worlds Atlas: A database of known extrasolar planets.
NASA Navigator Program: An umbrella organization for NASA projects to detect and study extrasolar planets. "The primary goal of these interrelated missions is to discover and characterize planetary systems and Earth-like planets around nearby stars. The missions are designed to build on each other's success, each providing an essential step forward toward the goal of discovering habitable planets and evidence of life beyond." Missions include SIM PlanetQuest and Terrestrial Planet Finder. The site includes a great deal of background information.
Keck Interferometer: "The Keck Interferometer combines light from the twin Keck telescopes to measure the emission from dust orbiting nearby stars and to directly detect and characterizse hot gas giant planets in other solar systems." Site describes many aspects of the research program. Part of NASA's Planet Quest site.
Kepler Mission: Kepler "is a special purpose space mission in the NASA Headquarters Discovery Program for detecting terrestrial planets, that is, rocky and Earth-size, around other stars." The mission is scheduled for launch in 2007. The Web site provides information about the mission, scientific background, a substantial bibliography of additional reading, and external links.
Planet Quest Missions: Kepler: "Kepler, a NASA Discovery mission, is a spaceborne telescope designed to look for Earth-like planets around stars beyond our solar system." Part of NASA's Planet Quest site.
Space Interferometry Mission: A NASA research mission "scheduled for launch in 2009, [which] will determine the positions and distances of stars several hundred times more accurately than any previous program. This accuracy will allow SIM to determine the distances to stars throughout the galaxy and to probe nearby stars for Earth-sized planets." Part of NASA's Planet Quest site.
Terrestrial Planet Finder: NASA project to develop a space-based telescope especially for detecting Earth-like extrasolar planets. It is currently scheduled for launch about 2015. "The Terrestrial Planet Finder (TPF) will study all aspects of planets outside our solar system: from their formation and development in disks of dust and gas around newly forming stars to the presence and features of those planets orbiting the nearest stars; from the numbers at various sizes and places to their suitability as an abode for life." Part of NASA's Planet Quest site.
Corot: "The COROT space telescope is a mission of astronomy led by CNES in association with French laboratories (CNRS) and with several international partners (European countries, Brazil)." The mission is scheduled to be launched in December, 2006. This site is maintained by CNES, the French space agency.
Corot: This is the Corot site maintained by ESA, the European Space Agency. It provides general information about Corot and extrasolar planets
Darwin: Home page of the European Space Agency's mission to search for signs of life on extrasolar planets. The mission, planned for about 2015, will use six telescopes, each at least 1.5 meters in diameter, in orbit at the L2 point. The "main objective is to detect and characterise Earth-like worlds. To do this, Darwin will survey 1000 of the closest stars, primarily looking for small, rocky planets. It will provide images of these worlds as points of lights." Spectroscopes will be used to detect and analyze any atmosphere such planets may possess. Darwin will also be capable of performing other ultra-high-resolution astronomical research in areas such as star and planet formation, galactic evolution, black holes, and the center of the Milky Way.
Darwin space infrared interferometer project: A site by Alan Penny about the European Space Agency mission planned for about 2015, which will (among other things) be capable of searching for signs of life on Earth like planetws orbiting nearby stars. Includes good external links.
Microlensing Planet Search Project: Home page of a research project that searches for extrasolar planets using the gravitational microlensing technique.
MicroFUN: Microlensing Follow-Up Network: "MicroFUN is an informal consortium of observers dedicated to photometric monitoring of interesting microlensing events in the Galactic Bulge. Our primary scientific objective is to observe high-magnification microlensing events that give the best potential for detecting extra-solar planets orbiting the lensing star."
The Optical Gravitational Lensing Experiment: "The Optical Gravitational Lensing Experiment (OGLE) is a long term observational program with the main goal to search for dark, unseen matter using the microlensing phenomena." Detection of distant extrasolar planets is one possible product of the experiment.
OGLE - The Optical Gravitational Lensing Experiment: Another page about OGLE, with information on scientific results, such as First Detection of an Extrasolar Planet with Microlensing.
The Anglo-Australian Planet Search: "The Anglo-Australian Planet Search (AAPS) is a long-term program being carried out on the 3.9m Anglo-Australian Telescope (AAT) to search for giant planets around 200 nearby Solar-type stars." The site includes research news and a brief description of planet search technique.
PLANET Homepage: PLANET stands for Probing Lensing Anomalies NETwork. "PLANET uses a network of five 1m-class optical telescopes distributed in longitude around the southern hemisphere in order to perform quasi-continuous round-the-clock precision monitoring of Galactic bulge microlensing events."
HARPS: High Accuracy Radial velocity Planet Searcher>: Homepage of experimental equipment used in the search for extrasolar planets at the La Silla facility of the European Southern Observatory.
TrES: The Transatlantic Exoplanet Survey: "TrES, the Transatlantic Exoplanet Survey, is a network of three small-aperture telescopes ... searching the sky for transiting planets."
Dr. Gilda E. Ballester: Home page of an astronomer who has participated in extrasolar planet research. Press release announcements of several discoveries are listed. Ballester also maintains pages about Detection of Hot Hydrogen in the Atmosphere of the Extrasolar Planet HD209458b and The signature of hot hydrogen in the atmosphere of the extrasolar planet HD 209458b.

Surveys, overviews, tutorials

Extrasolar planet: Article from Wikipedia.
Extrasolar Planets: A ScienceWeek "symposium" consisting of excerpts and summaries of articles from various sources.
Extrasolar Planets: Good overview information on techniques used for detecting extrasolar planets.
Pursuing the Invisible with Einstein's Lens: Explanation of "microlensing", as used in detection of extrasolar planets in the SIM PlanetQuest experiment. Other objects that are otherwise invisible can be detected with microlensing, such as brown dwarf stars and concentrations of dark matter. The article is from the PlanetQuest site.
Optical Vortex Coronagraph Figures: Information about an instrument called an "optical vortex" that makes it possible to obtain direct images of extrasolar planets.
Planet Finds Could Impact Planet Formation Theories: June 2007 article about discovery of two planets of the star HD 155358. The planets are unusual because of their low density and the low metal content of their parent star.
Gravitational lensing brings extrasolar planets into focus: June 2004 article from Physics World, by Keith Horne. "Astronomers have used gravitational microlensing to detect a cool planet orbiting a star some 15,000 light-years away."
Extrasolar planets: January 2001 article from Physics World, by Andrew Collier Cameron. "Astronomers have detected over 50 giant planets outside our solar system and made remarkable progress in determining their properties. But the real prize would be an Earth-like planet that could harbour life."
Finding New Worlds: Theoretical Conjecture Versus Hands-on Astronomy: February 2007 article from Space.com about discussions and debates taking place among astronomers who study extrasolar planets. One of the more significant debates cocerns the formation and orbital evolution of giant planets.
Cyber Planets: Building Virtual Worlds to Explore Signs of Real Life: December 2002 article from Space.com. Provides an interview with Vikki Meadows, who oversees a computer simulation project called the Virtual Planetary Laboratory, which is investigating what observable properties a planet capable of sustaining some form of life should have.
Astronomers on Brink of Watershed in Planet Discoveries: June 2002 article from Space.com. Describes new technique for discovering extrasolar planets which involves detecting fluctuations in light from a star due to planetary transits.
Amid a Flurry of Planet Discoveries, the True Tally: June 2002 article from Space.com. Consists of an interview with researcher Debra Fischer, discussing results to date and future prospects.
Other Worlds Not So Strange, Top Planet Hunter Says: May 2002 article from Space.com. Discusses recent discoveries of extrasolar planetary systems that more closely resemble our own.
Hubble Telescope: Surprise Tool in Search for Life: May 2002 article from Space.com. Explains how the Hubble telescope is being used to investigate extrasolar planets.
Detecting Other Worlds VIII: Radio Detection: May 2002 article from Space.com. Describes how radio telescopes can be used to search for extrasolar planets.
Detecting Other Worlds VII: Direct Imaging: February 2002 article from Space.com. Describes future satellite missions that may be able to detect extrasolar planets by direct imaging.
Changing Phases: Detecting Other Worlds With The Fade-In/Fade-Out Method: November 2001 article from Space.com. Describes how extrasolar planets may be detected by their variation in brightness as they circle their parent star.
Timing Eclipsing Binary Stars or The 'Do-Si-Do' Method: October 2001 article from Space.com. Describes a special method of detecting extrasolar planets orbiting an eclipsing binary star system.
Detecting Other Worlds: The Photometric Transit or 'Wink' Method: August 2001 article from Space.com. Describes how variation in light from a star may indicate the existence of one or more planets.
Detecting Other Worlds: The 'Pulse' Method: July 2001 article from Space.com. Describes a special method of detecting extrasolar planets orbiting a pulsar.
Detecting Other Worlds: The 'Flash' (Gravitational Lens) Method: June 2001 article from Space.com. Describes how gravitational lensing can be used to search for extrasolar planets.
Detecting Other Worlds: The Wobble Method: May 2001 article from Space.com. Describes how irregularities in the motion of stars may indicate the existence of one or more planets.
Future Missions to Search for Earth-like Planets: November 2000 article from Space.com. Describes six candidate missions that could search for Earth-like planets.
The Search for Extrasolar Planets: Very good longer 1997 article by George H. Bell.
Cannibal star ate planet: May 2001 news article from PhysicsWeb about a star that show evidence of having consumed one of its planets.
Extrasolar planets: January 2001 article from Physics World, by Andrew Collier Cameron. "Astronomers have detected over 50 giant planets outside our solar system and made remarkable progress in determining their properties. But the real prize would be an Earth-like planet that could harbour life."
Light glimpsed from extra-solar planet: December 1999 news article from PhysicsWeb about an extrasolar planet believed to have been discovered, by reflected light, in orbit around tau Bootis.
Eclipse confirms extrasolar planet: November 1999 news article from PhysicsWeb about the confirmation of an extrasolar planet by the eclipse method.
First evidence for planet orbiting a binary star: November 1999 news article from PhysicsWeb.
Multi-planet system startles astronomers: April 1999 news article from PhysicsWeb.
Stars Swallow Planets and Researchers Have Proof: May 2001 Scientific American news article about planets consumed by their stars.
Wandering Lonely as a Planet: October 2000 Scientific American article about planetary mass objects detected away from the vicinity of any star.
Protostellar and Protoplanetary Systems: Outline/notes of a talk by James Imamura that discusses formation of planetary systems.
Another Planet is Found that Circles its Own Sun: 1995 article from the Philadelphia Inquirer. Seems to have good links.
Pulsar Planets: About the discover by Alexander Wolszczan of the first extrasolar planets in 1991, with references in the technical and popular literature.
Tall Tales of Distant Planets: Science Notes article by Solana Pyne concerning the information that extrasolar gas giant planets may provide about the process of planetary formation.
In Search of Small Planets: Excellent Science Notes article by Jessa Netting on the Kepler satellite telescope to search for small extrasolar planets.
Giant Planets Orbiting Faraway Stars: March 1998 article from a Scientific American special issue.
Significant Others: April 1999 Scientific American In Focus article, subtitled "The discovery of a nearby solar system renders our corner of space a little bit less lonely."
A Parade of New Planets: May 1996 Scientific American In Focus article, subtitled "Astronomers are sighting new planets circling distant stars."
A planet in our own backyard: August 2000 news article about discovery of a Jupiter-mass planet orbiting Epsilon Eridani.
Planet hunters net another six: December 1999 news article about discovery of six more extrasolar planets.
Gotcha! A planet's shadow provides proof: November 1999 news article about observation of the transit of an extrasolar planet in front of its star.

Recommended references: Magazine/journal articles

Search for Other Earths
Tim Appenzeller
National Geographic, December 2004, pp. 68-95: Since many Jupiter-size planets have been found orbiting nearby stars, it is quite likely that Earthlike planets exist also. The problem is how to detect them.
[Additional resources]
Burning Down to Rock
Charles Choi
Scientific American, May 2004
Unlocking New Worlds
Robert Naeye
Astronomy, November 2002, pp. 48-53: About 100 extrasolar planets have been identified to date. There are four different methods of detecting such planets, and each strains the limits of observational precision in order to identify solar systems that more closely resemble our own.
Dusty Disks May Reveal Hidden Worlds
Ron Cowen
Science Week, May 4, 2002, pp. 280-281: Disks of dust and debris around stars are much easier to observe than planets, but patterns in the disks may still indicate the existence of planets.
Can We Find Another Earth?
Michael D. Lemonick
Discover, March 2002, pp. 32-37: Novel telescope designs based on the principle of interferometry may make it possible within 20 years to directly detect planets as small as Earth orbiting other stars.
We Are Not Alone
Oliver Morton
Wired, June 2001, pp. 162-169: Finding extrasolar planets has become one of NASA's clearest long-term goals. The relatively simple and inexpensive Kepler spacecraft, which would detect extrasolar planets by measuring minute dips in stellar brightness during planetary transits, may be the key tool.
Captured on Camera: Are They Planets?
Ron Cowen
Science News, May 26, 2001, pp. 333-335: Astronomers are now searching for very young stars within 200 light years of Earth which may have planets observable in infrared.
Discovering Worlds in Transit
Laurance R. Doyle; Hans-Jörg-Deeg; Jon M. Jenkins
Astronomy, March 2001, pp. 38-43: All extra-solar planets detected so far have been identified by means of Doppler shifts caused by wobbles in stellar motion due to the presence of very massive planets. A different technique is required to detect Earth-size planets -- observation of very small dips in stellar brightness that occur when a planet transits in front of its star.
Searching for Shadows of Other Earths
Laurance R. Doyle; Hans-Jörg Deeg; Timothy M. Brown
Scientific American, September 2000, pp. 58-65: Until recently, only giant planets could be detected in other solar systems. Very sensitive measurements of stellar brigntness now make it possible to detect Earth-like planets if they pass in front of their star on their orbit.
Field Guide to New Planets
Kathy A. Svitil
Discover, March 2000, pp. 48-55: 29 extrasolar planets had been detected as of the writing of this article. Although such planets must be very massive to be detected at all, hence quite unlike Earth, they are quickly adding to our knowledge of planetary systems.
Spying on Planetary Nurseries
Ray Jayawardhana
Astronomy, November 1998, pp. 62-67: Within the last year images of dust disks around young stars have been obtained. Such disks are probably similar to earliest stage of formation of our own Solar system.
Wanted: Life-Bearing Planets
Doug McInnis
Astronomy, April 1998, pp. 38-43: All of the extrasolar planets discovered so far have been similar in size to Jupiter, much larger than Earth. A variety of new observational techniques and equipment will search for Earth-size planets over the next 20 years.
Impossible Planets
Sam Flamsteed
Discover, September 1997, pp. 78-83: The extrasolar planets discovered so far have all been very massive - necessarily so, in order to have been discovered at all. The solar systems they are part of may be rather different from ours and have formed in different ways.
The Strange New Planetary Zoo
Robert Naeye
Astronomy, April 1997, pp. 42-49: Many of the extrasolar planets discovered so far are surprising for their size and proximity to their host star. Some of the objects may even be "brown dwarfs", and planet-like objects have even been found in orbit around pulsars (neutron stars).
Extrasolar Planets
Alan P. Boss
Physics Today, September 1996, pp. 32-38: Not only have planets similar to those of the Solar System been discovered associated with other stars, but also more exotic objects, such as brown dwarf stars and circumstellar disks.
Searching for Life on Other Planets
J. Roger P. Angel; Neville J. Woolf
Scientific American, April 1996, pp. 60-66: Although we are now able to detect planets of other stars, determining whether they probably harbor life is a much more difficult problem. A space-based telescope using sensitive spectroscopic equipment is proposed.

Recommended references: Books

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