March 20, 2006
(PLANETQUEST) -- The current month already has brought four new discoveries of planets beyond our solar system - including a new type of rocky, frozen world dubbed a "super-Earth."
With the new announcements, the tally of known worlds beyond our solar system now stands at 162.
1 Rocky Planet
Researchers last Monday said they had detected a roughly 13 Earth-mass planet orbiting a red dwarf star about 9,000 light-years away. This newfound world is probably a mixture of rock and ice, with a diameter several times that of Earth, according to a Harvard-Smithsonian Center for Astrophysics release. It orbits its star at about the distance of the asteroid belt in our solar system, which is between Mars and Jupiter. Its distant location chills it to -330 degrees Fahrenheit, suggesting that although this world is similar in structure to the Earth, it is too cold for liquid water or life.
The team said their findings suggest that similar icy super-Earths may exist around about one-third of all main sequence stars -- that is, normal stars in their main period of life. Theory predicts that smaller planets should be easier to form than larger ones around low-mass stars. Since most Milky Way stars are red dwarfs (dim, cool, low-mass stars), solar systems dominated by super-Earths may be more common in the galaxy than those with giant Jupiters.
The discovery was made using the mircolensing technique by MircoFUN, a collaboration of researchers led by Andrew Gould of Ohio State University. Microlensing is an effect where the gravity of a foreground star magnifies the light of a more distant star. If the foreground star possesses a planet, the planet's gravity can distort the light further, thereby signaling its presence.
3 Gas Giants
Researchers reported this month three new gas-giant planets discovered using the Anglo-Australian Telescope. One of the planets, labeled HD 187085 b, is three-fourths the mass of Jupiter and orbits a star located 146.7 light-years away in the consetllation Sagittarius. The other planet, labeled HD 20782 b, is slightly larger than Jupiter and orbits a star 117 light-years away. Both planets follow highly eccentric, or elongated, orbital paths.
Another team reported the discovery of the planet HD 73526 c, a second companion to a star located about 323 light-years away in the constellation Vela. The new planet is about 1.5 times the mass of Jupiter. All three planets were found using radial velocity, or Doppler spectroscopy, which detects the to-and-fro wobble of a star caused by an orbital companion.
Written by Randal Jackson/PlanetQuest
