15 January 2012
An artist’s rendition of three newly discovered exoplanets. Planets orbiting a star outside the Solar System are termed exoplanets, or extrasolar planets. The new exoplanets were discovered using data collected by NASA’s Kepler spacecraft. They all have been estimated to be smaller than Earth in size.
Credit: NASA/JPL-Caltech
Astronomers using data from NASA's Kepler spacecraft have discovered the three smallest exoplanets ever spotted around a star beyond our Solar System. (Planets orbiting other stars are termed exoplanets, or extrasolar planets.) The exoplanets’ parent star is known as KOI-961. The three exoplanets are estimated to be smaller than Earth (12,756 km across) in size. The smallest of them is about the size of Mars (approximately 6,800 km across).
All three planets are thought to be rocky, like Earth, but orbit very close to their star. This makes them too hot to be in the habitable zone, a region around a star where liquid water could exist on the surface of a planet. Of the over 700 exoplanets confirmed, only a few are believed to be rocky.
"Astronomers are just beginning to confirm thousands of planet candidates uncovered by Kepler so far," said Doug Hudgins, Kepler program scientist at NASA Headquarters. "Finding one as small as Mars is amazing, and hints that there may be a bounty of rocky planets all around us."
Kepler searches for exoplanets by continuously monitoring over 150,000 stars, within a small patch of sky, looking for tiny dips in their brightness caused by crossing, or transiting objects. At least three transit observations are required to verify the existence of an exoplanet. Further observations from ground-based telescopes are also needed to confirm the discoveries. The latest discovery was made by a team led by astronomers at the California Institute of Technology.
Kepler’s Field of View
This image shows the constellations of Cygnus, Lyra and Aquila. Kepler’s field of view is a fixed small area, located between Cygnus, The Swan, and Lyra, The Harp. It contains over 150,000 stars.
Credit: NASA
The three planets circle very near to their star, taking less than two days, to orbit around it. KOI-961 is a red dwarf star, smaller and cooler than our Sun.
Red dwarfs are the smallest and coolest stars. They are also the most common stars in our Galaxy. The discovery of three rocky planets around one red dwarf suggests that rocky planets could abound in the Galaxy.
The discovery follows a series of recent milestones of the Kepler mission. In December 2011, scientists announced Kepler's first confirmed planet in the habitable zone of a Sun-like star: a planet 2.4 times the size of Earth, called Kepler-22b. Later in the month, the team announced the discovery of the first Earth-sized planets orbiting a Sun-like star, called Kepler-20e and Kepler-20f.
The Kepler observatory was launched into space in March 2009. It was placed into an orbit around the Sun, on a mission expected to last at least 3.5-years.
References
NASA
www.nasa.gov/
Kepler Mission
http://www.nasa.gov/mission_pages/kepler/main/index.html
Wikipedia
Aymen Mohamed Ibrahem
Senior Astronomy Specialist