Billions of worlds in Milky Way

• Billions of habitable worlds in Milky Way
• Astronomers hunting for rocky planets with the right temperature to support life estimate there may be tens of billions of them in our galaxy alone. A European team said that about 40 percent of red dwarf stars - the most common type in the Milky Way - have a so-called "super-Earth" planet orbiting in a habitable zone that would allow water to flow on the surface. Since there are around 160 billion red dwarfs in the Milky Way, the number of worlds that are potentially warm enough and wet enough to support life is enormous. Here's a look at artistic samplings of some far-away worlds:
• This artist's impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. The other two more distant stars, Gliese 667 A and B appear in the sky also to the right. Astronomers have estimated that there are tens of billions of such rocky worlds orbiting faint red dwarf stars in the Milky Way alone.

• An artist rendering illustrates the newly discovered world (HAT-P-1) that has baffled astronomers, since the planet is much larger than theory predicts, scientists said September 14, 2006. HAT-P-1 has a radius about 1.38 times Jupiter's but contains only half Jupiter's mass.
• An artist's illustration of Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star, is seen in this undated handout picture released by NASA, December 5, 2011. Kepler-22b, the most Earth-like planet ever discovered is circling a star 600 light years away, a key finding in an ongoing quest to learn if life exists beyond Earth, scientists said.
• An artist's impression shows a unique type of exoplanet discovered with the Hubble Space Telescope. The planet is so close it to its star that it completes an orbit in 10.5 hours. The planet is only 750,000 miles from the star, or 1/130th the distance between Earth and the Sun. The Jupiter-sized planet orbits an unnamed red dwarf star that lies in the direction of the Galactic Centre; the exact stellar distance is unknown.

An artist's rendering image released to Reuters on October 19, 2009 shows an exoplanet 6 times the Earth-size circulating around its low-mass host star at a distance equal to 1/20th of the Earth-Sun distance. The host star is a companion to two other low-mass stars, which are seen here in the distance (L). European astronomers announced they had found 32 new planets orbiting stars outside our solar system and said on Monday they believe their find means that 40 percent or more of Sun-like stars have such planets.

In this artist's conception released by NASA February 2, 2011, Kepler-11 is a sun-like star around which six planets orbit. At times, two or more planets pass in front of the star at once, as shown in a simultaneous transit of three planets observed by NASA's Kepler spacecraft on August 26, 2010. 

Scientists using NASA's Spitzer Space Telescope observed a fledgling solar system like the one depicted in this artist's concept, finding deep within it enough water vapor to fill all the oceans on Earth five times. The scientists peered at an embryonic star called IRAS 4B located in our Milky Way galaxy about 1,000 light years from Earth in the constellation Perseus.

An artist's impression shows a Jupiter-sized planet passing in front of its parent star. Such events are called transits. When the planet transits the star, the star's apparent brightness drops by a few percent for a short period. Through this technique, astronomers can use the Hubble Space Telescope to search for planets across the galaxy by measuring periodic changes in a star's luminosity. The first class of exoplanets found by this technique are the so-called "hot Jupiters," which are so close to their stars they complete an orbit within days, or even hours.

NASA handout image shows an artist's concept of the circumbinary planet Kepler-16b - the first planet known to definitively orbit two stars. The cold planet, with its gaseous surface, is not thought to be habitable. The largest of the two stars, a K dwarf, is about 69 percent the mass of our sun, and the smallest, a red dwarf, is about 20 percent the sun's mass. These star pairs are called eclipsing binaries

Astronomers searching the skies for distant planets have detected two Saturn-sized worlds orbiting distant suns, the smallest planets found thus far outside our solar system. The discovery boosted the likelihood that even smaller planets - perhaps the size of Earth - exist elsewhere in the universe, Professor Steve Vogt of the University of California-Santa Cruz said. This artists concept shows a view of the discovered planet orbiting 79 Ceti.

NASA handout image shows an artist's 

concept of the circumbinary planet 

Kepler-16b - the first planet known to 

definitively orbit two stars. The cold 

planet, with its gaseous surface, is not

 thought to be habitable. The largest of 

the two stars, a K dwarf, is about 69 

percent the mass of our sun, and the

 smallest, a red dwarf, is about 20 percent 

the sun's mass. These star pairs are 

called eclipsing binaries.

NASA handout image of an artist's concept illustrating an icy planet-forming disk around a young star called TW Hydrae, located about 175 light-years away in the Hydra, or Sea Serpent, constellation. Astronomers using the Herschel Space Observatory detected copious amounts of cool water vapor, illustrated in blue, emanating from the star's planet-forming disk of dust and gas. The water vapor, which probably comes from icy grains in the disk, is located in the frigid outer regions of the star system, where comets will take shape.

A newly discovered planet, designated by the unglamorous identifier of OGLE-2005-BLG-390Lb, orbits a red star five times less massive than the Sun and located at a distance of about 20,000 light years, in this undated artist's impression. A new planet-hunting technique has detected the most Earth-like planet yet around a star other than our sun, raising hopes of finding a space rock that might support life, astronomers reported on January 25, 2006.

  

A handout photo from the European Space Agency released December 10, 2008 shows an artist's impression of the Jupiter-size extrasolar planet, HD 189733b, being eclipsed by its parent star. Astronomers using the Hubble Space Telescope have measured carbon dioxide and carbon monoxide in the planet's atmosphere. The planet is a ?hot Jupiter?, so close to its parent star that it completes an orbit in only 2.2 days.

Handout picture released June 14, 2005 shows an artist's conception of a newly discovered planet being shown as a hot, rocky, geologically active world glowing in the deep red light of its nearby parent star, the M dwarf Gliese 876. The heat and the reddish light are among the few things about the new planet that are certain, depending on the thickness and composition of its atmosphere - if any - it could range from being a barren, cratered ball of rock like Mercury or the Moon, to being a featureless, cloud-shrouded cue-ball like Venus.

A rich starry sky fills the view from an ancient gas-giant planet in the core of the globular star cluster M4, as imagined in this artist's concept. The 13-billion-year-old planet orbits a helium white-dwarf star and the millisecond pulsar B1620-26, seen at lower left. The globular cluster is deficient in heavier elements for making planets, so the existence of such a world implies that planet formation may have been quite efficient in the early universe.

NASA's Hubble Space Telescope has taken the first visible-light snapshot of a planet circling another star in this image released by NASA November 13, 2008. Estimated to be no more than three times Jupiter's mass, the planet, called Fomalhaut b, orbits the bright southern star Fomalhaut, located 25 light-years away in the constellation Piscis Australis, or the "Southern Fish."

Image shows composite image of Elephant's Trunk Nebula, an elongated dark globule within the emission nebula IC 1396 in the constellation of Cepheus, one of the first images from the new Spitzer Space Telescope released by NASA on December 18, 2003. The new Spitzer Space Telescope, that looks at the cosmos with infrared detectors, has lifted the dust veils from newborn stars and a bumptious comet, and revealed the detail in the spiral arms of a neighboring galaxy.

A handout image received April 5, 2005 from the University of Jena and the European Space Observatory ( ESO) shows the first photograph of a planet (B) beyond our solar system and the star, GQ Lupi (A) around which it orbits. The planet is thought to be one to two times as massive as Jupiter, according to the scientists who imaged it. It orbits a star similar to a young version of our Sun.

A new view of the Whirlpool Galaxy, one of the two largest and sharpest images Hubble Space Telescope has ever taken, is released by NASA on Hubble's 15th anniversary April 25, 2005. The new Whirlpool Galaxy image showcases the spiral galaxy's curving arms where newborn stars reside and its yellowish central core that serves as home for older stars. During the 15 years Hubble has orbited the Earth, it has taken more than 700,000 photos of the cosmos.

A California astronomer has discovered what he believes is the 10th planet in our solar system, a group of NASA-funded researchers said on July 29, 2005. The new planet, known as 2003UB313, has been identified as the most distant object ever detected orbiting the sun, California Institute of Technology astronomer Michael Brown said. This artist's concept shows planet 2003UB313 at the lonely outer fringes of our solar system. Our sun can be seen in the distance. The new planet, which is yet to be formally named, is at least as big as Pluto and about three times farther away from the Sun than Pluto.