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First planet found via astrometry! June 1, 2009

Posted by CosmicThespian in Discoveries, News, Planet Gallery.
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A team of astronomers at the NASA Jet Propulsion Laboratory (JPL) announced last week that they are the first group to find an exoplanet using the astrometric wobble method!

As I discussed in one of my first blog articles, planets gravitationally tug on their host stars as they orbit around them.  Astronomers have long known that if they wanted to find distant planets, they would need to first find stars that appeared to wobble on the celestial sphere.  Unfortunately, these wobbles are impossibly small and up until now no team has ever been able to measure them.  The wobbles we have been detecting have been found via doppler shifts in the light from these planet hosting stars.

Drs. Steven Pravdo and Stuart Shaklan have broken through that barrier!  For the past 12 years, they have been experimenting with an instrument specifically designed to directly detect the slight wobble of distant stars on the Palomar Hale Telescope.  Over those twelve years, they’ve only had access to the telescope a few times each year.  But it appears all of their efforts have finally paid off!

The planet is a big one: six times more massive than Jupiter!  It orbits a very tiny star, VB 10, roughly 20 light years away in the constellation Aquila.  The size of its orbit is similar to Mercury’s, but because its sun is so very faint, the planet receives about as much light from its sun as Jupiter does from our own.

Schematic of the VB 10 system compared to our own.

Schematic of the VB 10 system compared to our own. Image credit: NASA/JPL-Caltech

The diminutive size of the star coupled with the mass of the planet are, no doubt, what led to a successful discovery.  If you recall from my original article on detecting wobbles, the name of the game here is the location of the center of mass of the system.  A high mass planet orbiting a low mass star will move the system’s barycenter further from the center of the star thus leading to a larger wobble of the distant sun.  Despite this advantage, the wobble is still incredibly tiny: the span of the wobble is no larger than the width of a human hair seen at over a mile-and-a-half away!

VB 10 is particularly tiny and for a time was the smallest star known.  It is a type of star known as a ‘red dwarf’.  It weighs in at just one-twelfth the mass of our Sun and isn’t much bigger than Jupiter!  In fact, despite the significant difference in mass between VB 10 and its new-found planet, the two would actually be roughly the same size!

This is an exciting new chapter in the unfolding saga of exoplanet discovery and is an important reminder of the potential of astrometric surveys.  Future space missions will take advantage of this technique to find Earth-like planets by the dozen in the next decade or so.  This journey of 1000 miles has taken its first step!

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