The image above involves some artistic license. As suggested on Behind the Speculations, gas giants orbiting a sun-like star at distances similar to the Earth are likely to have clouds of water ice, with white a characteristic color. These water clouds may be obscured by higher layers of gas, primarily methane. Methane scatters blue light weakly, so these deeper cloud regions will have a slight bluish tinge.
For imaginative visions of exoplanets and the future, visit this 'Planetology' page and other pages on the Orion's Arm website.

The first confirmed discovery of extrasolar planets (planets around another star - also called exoplanets) occured in 1992. Radio astronomers Aleksander Wolszczan and Dale Frail announced the discovery of planets around a pulsar. In 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi). This discovery was made at the Observatoire de Haute-Provence and ushered in the modern era of exoplanetary discovery.

Technological advances allowed astronomers to detect exoplanets indirectly by determining their gravitational influence on the motion of their parent stars. The planets are usually discovered by measuring the change in Doppler shift of the star's light, resulting from the star orbiting a common center of mass with a companion planet.

Several extrasolar planets were detected by observing the variation in a star's apparent luminosity as a planet passed or transited in front of it. The occasional transit of Venus across the sun is an example from our own Solar System.

By the fall of 2010, almost 500 exoplanets had been discovered. Most of them are huge and hot gas planets (similar or larger in mass to Saturn or Jupiter) orbiting very close to their sun.

Given the current early stage in planet searching technology, this preponderance of giant planet discoveries in close solar orbit should not be surprising. These would be the most noticeable planetary bodies given the degree of sensitivity of the available instruments.

As sensitivity increases in the future and new methodologies become common, the average range in planet distance from the parent star should increase and the average observed planet size should decrease. Astronomers have recently discovered that terrestrial planets might form around many, if not most, of the nearby sun-like stars in our galaxy.

If you want to keep apprised of the latest scientific findings and theories regarding exoplanets, check out the Exoplanet News. It is a monthly newsletter listing abstracts of the latest findings in the exoplanet field.

Planet Searchers

The California Planet Survey team is one of the most successful planet searchers. These scientists use telescopes at the University of California's Lick Observatory near San Jose and the Keck Observatory in Hawaii. The Geneva Extrasolar Planet Search includes a number of observational programs managed out of Versoix in France near Geneva, Switzerland. The Anglo-Australian Planet Search team uses the Anglo-Australian Observatory near Coonabarabran, NSW, Australia. SuperWASP is the UK's extra-solar planet detection program involving a consortium of eight academic institutions monitoring the sky for planetary transit events.

Interstellar Travel - An obvious problem with finding exoplanets, including the holy grail of a planet habitable by human beings, is the current impossibility of traveling to other stars. Some investigators are actively searching for ways to solve this problem. An Advanced Space Propulsion Workshop sponsored by NASA occured in November 2010. This paper, Progress in revolutionary propulsion physics, discusses methods currently being investigated and can be downloaded from the Cornell University library. The article, Tau Zero Takes Aim at Interstellar Propulsion, gives a realistic overview of the situation and details a specific effort to find answers.

Latest Findings

In June 2010, the Kepler team (also see table below and video description of the Kepler mission) announced they had identified more than 700 “candidate” exoplanets after the first 43 days of data collection, including six candidate planetary systems that appeared to contain more than one transiting planet in them. The Exoclimes 2010 Conference in Exeter, UK brought together scientists exploring the diversity of exoplanet atmospheres.

If you want to learn more about what is happening on the frontiers of outer space research, including the newest findings regarding exoplanets, check out these excellent video lectures sponsored by the SETI Institute. If the link is broken, go to You Tube and search under 'Seti'. Here is a video on the exoplanet search by Lick Observatory overlooking the Silicon Valley of California.

Lick Observatory - Seeker of exoplanets as seen from a favorite hiking trail

Exoplanet Resources - The most complete up-to-date catalog of discovered exoplanets may be found at the Extrasolar Planet Encyclopedia maintained by the Paris Observatory. In September 2010 the count was up to 490 planets. The NASA PlanetQuest site gives a good overview of the search for planets around other stars. The PlanetQuest site has a continually updated atlas of all exoplanets discovered.

The Planetary Society presents current extrasolar planet discoveries with a good explanation of current methods for finding these planets. It even includes a 3-D map of stars with planets in our stellar neighborhood. The Exoplanet Data Explorer is an interactive table and plotter for exploring and displaying data from the Exoplanet Orbit Database, a carefully constructed compilation of quality, spectroscopic orbital parameters of exoplanets orbiting normal stars. A German website (English version) focuses on some of the more interesting exoplanets. The Guide to Extrasolar Planets (last updated in 2005) contains a wealth of information on these discoveries.

Systemic is a collaboration of astronomers and interested individuals aimed at understanding the possible structure and composition of extrasolar planetary systems. The Tau Zero Foundation focuses on the subject of "practical starflight." Its associated Centauri Dreams is a news blog covering the latest developments in the hunt for planets beyond our solar system, progress in spaceflight technology, and the sociological implications of interstellar exploration.

'Alien Earths' enables you to build a hypothetical extrasolar planetary system and see how it functions over time. Click on 'planet families' under 'games and activities' to give it a try.

The table below summarizes known current and future instruments and missions participating in the search for planets around other stars:

Instruments & Space Missions Searching for Extrasolar Planets
COROT	Spitzer Space Telescope	Large Binocular Telescope Interferometer	EPOCh
Keck Interferometer	MOST	Hubble Space Telescope	Automated Planet Finder Telescope
Epoxi	HARPS	Kepler Mission	TEDI
Future Exoplanet Missions & Instruments
SIM PlanetQuest	Lyot	Terrestrial Planet Finder	GAIA
New Earths Facility	Thirty Meter Telescope	European Extremely Large Telescope	James Webb Space Telescope
		WFIRST

Actual travel to the stars and landing on new Earths? Such a journey can't occur based on current* scientific knowledge. Faster than light travel requires a major jump into the unknown in technology and our understanding of the universe. Given the significant mysteries associated with our current knowledge (dark energy, dark matter, other dimensions and alternative universes, to name a few), a revolutionary discovery in space travel within 200 years may not be wildly unreasonable.

*Although at least one scientist had presented a theory that would enable such travel through 'hyperspace'. His ideas were not accepted by his peers.