for National Geographic News
A previously unproven tool in the planet-hunting arsenal has finally netted its quarry—and it's found an unusual cosmic duo.
Using a technique called astrometry, scientists have spotted an extrasolar planet that's thought to be the same size as its parent star.
By contrast, Jupiter, the largest planet in our solar system, is only a tenth the width of the sun.
The newfound gas giant, called VB 10b, orbits a red dwarf star, a relatively cool, small star less than half the mass of the sun. Although both are roughly the size of Jupiter, the planet orbits the star because the star is much more massive.
VB 10b's discovery is the culmination of a 12-year search using an instrument at California's Palomar Observatory.
(Related: "'Hidden' Planet Found in Old Hubble Image.")
The telescope attachment specializes in astrometry, a technique first tried 50 years ago that measures the minute back-and-forth motions of a star created by the gravitational tug of an unseen planet.
Most of the previous planet-hunting attempts have had more luck with the radial velocity—or Doppler wobble—method, which measures stellar movement toward and away from Earth.
Radial velocity and other techniques are better at finding very massive worlds in tight orbits around their stars.
Astrometry, on the other hand, could open the door to finding a whole new class of planets that were difficult to spot before, said study author Stuart Shaklan of NASA's Jet Propulsion Laboratory (JPL) in California.
"It allows you to see planets further from their stars," Shaklan said, because the greater the distance between the two bodies, the more a star seems to shift. "It's also a technique that works well on [spotting] very faint stars.
That aspect of the technique, however, remains unproven. VB 10b, which lies about 20 light-years away in the constellation Aquila, orbits its tiny star at the same distance at which Mercury orbits our sun.
VB 10b is called a "cold Jupiter," because its star is small and dim enough that the planet is not scorched despite its close proximity.
Astronomers think planetary systems with cold Jupiters might be miniature versions of our own, with rocky inner planets and outer gas giants.
It's conceivable that VB 10b has rocky neighbors, Shaklan said, but this would have to be verified with other telescopes.
"This is an exciting discovery, because it shows that planets can be found around extremely lightweight stars," Wesley Traub, a planet hunter at JPL who was not involved in the study, said in a statement.
"This is a hint that nature likes to form planets, even around stars very different from the sun.
Findings will be detailed in an upcoming issue of the Astrophysical Journal.
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