Astronomers have discovered 28 new planets outside of our solar system, increasing to 236 the number of known exoplanets, revealing that planets can exist around a broad spectrum of stellar types-from tiny, dim stars to giants.
"We added 12 percent to the total in the last year, and we're very proud of that," said one of the study team members Jason Wright of the University of California at Berkeley. "This provides new planetary systems so that we can study their properties as an ensemble."
The planets are among 37 new objects spotted within the past year. Seven of the objects are failed stars called brown dwarfs, with masses that dwarf the largest, Jupiter-sized planets but too small to sustain the nuclear reactions necessary for stellar ignition.
John Johnson of the University of California at Berkeley and his colleagues presented the findings here today at a meeting of the American Astronomical Society (AAS).
One of the exoplanets, orbiting a red M dwarf just 30 light-years from Earth, was discovered two years ago, but recent observations have allowed astronomers to pin down its mass, radius and density. The ice-giant planet circles the star Gliese 436 (GJ 436) and has a radius and density that are surprisingly similar to that of Neptune.
Weighing in at 22.4 Earth-masses, the exoplanet is the first Neptune-sized planet observed to transit a star. The previous record holder, dubbed HD 140926b, weighed in at 100 Earth masses, and Jupiter is 320 Earth masses.
At least four of the newly spotted planets belong to multiple-planet systems, supporting the idea that at least 30 percent of all planet-parent stars have more than one planetary companion. Since smaller planets and those outside our solar system are trickier to detect, Wright predicts this percentage will continue to rise as detection methods improve.
And three of the just-discovered planets circle stars that boast masses between 1.6 and 1.9 times that of our Sun. Planets orbiting these so-called A- and F-type stars, which are typically difficult to detect because they rotate fast and have pulsating atmospheres.
29 May 2007
28 new exoplanets discovered
ZUI this from Space,com (posted 28 May):