This artist rendition shows a hot giant gaseous exoplanet orbiting near its home star.
Credit: NASA, ESA, G. Bacon (STScI) and N. Madhusudhan (UC)
Planets orbiting outside our solar system are known as exoplanets or extrasolar planets. Since the 1990s, astronomers have discovered more than 1,800 exoplanets belonging to over 1,130 planetary systems, consisting of planets around stars or multiple star systems. Astronomers using NASA's Hubble Space Telescope (HST) have found that the atmospheres of three exoplanets are almost devoid of water vapor.
These three planets, termed HD 189733b, HD 209458b, and WASP-12b, lie between 60 and 900 light-years away from Earth. They are gas giants, like Jupiter, the largest planet in our solar system, with temperatures ranging between 800 and 2,200 C. They seemed ideal targets for searching for water vapor. Surprisingly, however, these exoplanets turned out to be dry, containing only one-tenth to one one-thousandth the amount of water predicted by current planet-formation theories.
These results urge scientists to develop detectors that are more sensitive for detecting water signature.
Exoplanets show various intriguing characteristics. Hot Jupiters are a class of extrasolar planets whose composition is similar to Jupiter’s, but have high temperatures, as they orbit very close to their stars, while Jupiter is a cold planet, orbiting the Sun at about 800 million km.
One of the best examples of hot Jupiters is the exoplanet 51 Pegasi b. Discovered in 1995, it was the first extrasolar planet found orbiting a Sun-like star, a star with a size and temperature similar to the those of the Sun. The hot Jupiter 51 Pegasus b amazingly orbits its host star every 4 days, approximately!
A super-Earth is an exoplanet with a mass greater than Earth's, but significantly smaller than the mass of the planet Neptune, which is 17 times the terrestrial mass.
References
NASA
www.nasa.gov/