Click on the image for the movie
This movie shows the star VB 10 moving across the sky over a period of
nine years. Astronomers nabbed a planet circling this star using a method
called astrometry—the first successful application of the method to
planet hunting.
The planet, called VB 10b, tugs on the star, causing it to wobble back and
forth—but you can't see the planet or the wobble in the movie. You
can see what is called proper motion.
Proper motion reflects the star's velocity. All stars move around in space
at different speeds, including our sun. The closer a star is to us, the
more it will appear to move relative to stars that are farther away (to
picture this, think about a car speeding by in front of you and very far
from you—its motion is less obvious when viewed from far away).
In the astrometry planet-hunting technique, researchers attempt to measure
very tiny wobbles in stars—the result of planets yanking them
around. The method requires precise observations of a star's position on
the sky. But to do this, the star's proper motion, and a cyclic "parallax"
motion caused by Earth's changing vantage point as it orbits the sun, must
be measured and subtracted.
This was done for the VB 10 star to identify its orbiting planet.
Measurements were made of the star's position over a period of about 9
years. While the proper motion causes the star to move 1.5 arcseconds per
year, the parallax motion (not seen in this movie) induces a movement of
1/6th an arcsecond per year (about 1/12th the size of the star images).
The planet-induced wobble is responsible for moving the star just
6/1000ths of an arcsecond—a motion so tiny that it took a special
JPL-built astrometry instrument and a five-meter telescope at the Palomar
Observatory to see. (An arcsecond is 1/3600th of a degree across the sky.)
The blue line in the movie shows a magnified picture of the orbit of the
VB 10 planet, represented in red. The motion shown for this orbit is
accurately timed to correspond to the time in the actual images making up
the movie.
The California Institute of Technology and NASA's Jet Propulsion
Laboratory, both in Pasadena, are partners in the Palomar Observatory,
near San Diego, Calif.