The latest exoplanet we've discovered is an imposing giant, almost the same size as the star it orbits. It's also the first planet found using a fifty-year-old technique designed to find planets at greater distances from their suns.
Steven Pravdo and Stuart Shaklan of NASA's Jet Propulsion Laboratory led the twelve-year effort responsible for discovering the exoplanet, which has been designated VB 10b after its star, VB 10. The red dwarf star, roughly a twelfth the size of our sun, is just twenty lightyears away, making it one of the closest stars with an exoplanet. VB 10 is also only one of a handful of red dwarfs with confirmed exoplanets.
VB 10b is the first planet discovered using the astrometry method. It works on the principle that a planet does not exactly orbit its star. Instead, both celestial bodies orbit around their common center of gravity, although in most cases the huge mass disparity between the two makes their center of gravity and the star itself practically the same thing, which tends to reduce this method's effectiveness. For instance, alien astronomers would almost certainly be unable to detect any of the planets around our sun using the astrometry method.
This particular exoplanet, however, was pretty much the perfect candidate to be found using this method. Six times the size of Jupiter, VB 10b is nearly as massive as the star, greatly exaggerating the star's motion around their center of gravity. It's also relatively distant from its sun, which again causes the red dwarf to trace an unusually large arc around its center of gravity. Finally, its close proximity to our solar system made it far easier to detect VB 10's exoplanet-induced motion.
Even with all those favorable conditions, it still took Pravdo and Shaklan twelve years searching through thirty different star systems to find conclusive evidence, and even then their discovery was, as New Scientist puts it, "equivalent to measuring the width of a human hair from a distance of about 3 kilometres." This is pretty much why I find exoplanet-hunting the most awesomely absurd endeavor in modern science.
The long-awaited success of the astrometry technique provides astronomers with a way of locating planets that are relatively far away from their stars. The most successful technique for finding exoplanets is to locate shifts in the star's light spectrum that indicate an orbiting planet is causing the star to wobble. This is known as the radial velocity technique. Another method is to find variations in the star's brightness as a planet passes in front of it relative to our vantage point. Both of these work best when the exoplanet is close to the star it orbits.
VB 10b is, in absolute terms, pretty close to its star, as it's roughly the same distance from VB 10 that Mercury is from our sun. However, the tiny mass of the star makes its distance more comparable to that of Jupiter in terms of the warmth it receives and the gravitational effects that act upon it. This actually opens up the possibility of rocky inner planets between VB 10 and VB 10b. Such planets might be detectable with Europe's wonderfully named Very Large Telescope, which could use the radial velocity technique to search for them.
The planet's discovery could also change our understanding of what sorts of stars can have planetary systems. Red dwarfs are by far the most common kind of star, comprising roughly seventy percent of all stars. As more and more exoplanets are discovered around red dwarfs - and the massive size of VB 10b relative to VB 10 suggest such stars can support pretty much any kind of planet - the evidence mounts that planets are far, far more common that once was thought.
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