An extrasolar planet, or exoplanet: a small review with recent developments

An extrasolar planet, or exoplanet, is a planet beyond the Solar System, orbiting around another star. As of December 2008, 331 exoplanets are listed in the Extrasolar Planets Encyclopaedia. The vast majority have been detected through radial velocity observations and other indirect methods rather than actual imaging. Most announced exoplanets are massive gas giant planets thought to resemble Jupiter, but this is a selection effect due to limitations in detection technology. Projections based on recent detections of much smaller worlds suggest that lightweight, rocky planets will eventually be found to outnumber extrasolar gas giants.Extrasolar planets became a subject of scientific investigation in the mid-19th century. Many astronomers supposed that such planets existed, but they had no way of knowing how common they were or how similar they might be to the planets of the Solar System. The first confirmed radial velocity detection was made in 1995, revealing a gas giant planet in a four-day orbit around the nearby G-type star 51 Pegasi. The frequency of detections has tended to increase on an annual basis since then. It is estimated that at least 10% of sun-like stars have planets, and the true proportion may be much higher. The discovery of extrasolar planets sharpens the question of whether some might support extraterrestrial life.Currently, Gliese 581 d, the third planet of the red dwarf star Gliese 581 (approximately 20 light years from Earth), appears to be the best example yet discovered of a possible terrestrial exoplanet that orbits close to the habitable zone surrounding its star. Although Gliese 581 d appears to reside outside the so-called "Goldilocks Zone", a potential greenhouse effect might raise the planet's surface temperature high enough to support liquid water.[…]

Recent developments on extrasolar planet, or exoplanet:

• Hubble Telescope Finds Carbon Dioxide On An Extrasolar Planet:
  NASA's Hubble Space Telescope has discovered carbon dioxide in the atmosphere of a planet orbiting another star. This breakthrough is an important step toward finding chemical biotracers of extraterrestrial life.[1]
• Oxygen And Carbon Found In Atmosphere Of An Extrasolar Planet: NASA's Hubble Space Telescope has detected, for the first time ever, the presence of oxygen and carbon in the atmosphere of a planet outside our solar system.[2]
• Alpha Centauri Should Harbor Detectable, Earth-like Planets: A rocky planet similar to Earth may be orbiting one of our nearest stellar neighbors and could be detected using existing techniques, according to astronomers. The closest stars to our Sun are in the three-star system called Alpha Centauri, a popular destination for interstellar travel in works of science fiction. Computer simulations of planet formation show that terrestrial planets are likely to have formed around the star Alpha Centauri B and to be orbiting in the "habitable zone" where liquid water can exist on the planet's surface. Such planets could be observed using a dedicated telescope.[3]
• Chance Of Finding Earthlike Planets On The Rise, UK Astronomers Believe: Using a revolutionary new camera, UK astronomers have a real chance of being the first to find Earth-like planets around other stars. Since the early 1990s, astronomers have found more than 200 planets in orbit around stars other than our Sun (so-called 'extrasolar' planets). These have been detected through two techniques that are particularly sensitive to massive planets in orbit close to their parent star.[4]
• Hazy Red Sunset On Extrasolar Planet: The NASA/ESA Hubble Space Telescope has given astronomers a fascinating new insight into the atmosphere of a planet in orbit around another star. The observations provide evidence of the presence of hazes in the atmosphere of the planet HD 189733b.[5]
• Unique Extrasolar Planet Orbits Fast-rotating Hot Star: Three undergraduate students, from Leiden University in the Netherlands, have discovered an extrasolar planet. The extraordinary find, which turned up during their research project, is about five times as massive as Jupiter. This is also the first planet discovered orbiting a fast-rotating hot star.[6]