This artist's concept shows the smallest star known to host a planet. The planet, called VB 10b, was discovered using astrometry, a method in which the wobble induced by a planet on its star is measured precisely on the sky.
The dim, red star, called VB 10, is a so-called M-dwarf, located 20 light-years away in the constellation Aquila. It has only one-twelfth the mass, and one-tenth the size, of our sun. The planet is a gas giant similar in size to Jupiter but with six times the mass. Though the planet is less massive than its star, the two orbs would have a similar diameter.
VB 10b orbits its star about every 9 months at a distance of 50 million kilometers (30 million miles).
Image credit: NASA/JPL-Caltech
This artist's diagram compares our solar system (below) to the VB 10 star system. Astronomers successfully used the astrometry planet-hunting method for the first time to discover a gas planet, called VB 10b, around a very tiny star, VB 10. All of the bodies in this diagram are shown in circular insets at the same relative scales.
The VB 10 star is one of the smallest known -- and holds the record for the smallest known to host a planet. It's a dim, red M-dwarf with only one-tenth the size, and one-twelfth the mass, of our sun. Its planet, on the other hand, is quite hefty, with six times the mass of Jupiter. Though the planet is less massive than the star, the two orbs would be about the same size.
The VB 10 system is essentially a shrunken version of our solar system. Even though its planet is at a similar distance from its star as Mercury is from our sun, it wouldn't receive as much heat and would be classified as a "cold Jupiter" similar to our own. If any rocky planets do orbit in the VB 10 system, they would be located even closer in than VB 10b, and could lie within the star's habitable zone -- a region where temperatures are right for water to be liquid.
Astrometry involves measuring the wobble of a star on the sky, caused by an unseen planet yanking it back and forth. Because the VB 10b planet is so big relative to its star, it really tugs the star around. The red circle seen at the center of the VB 10 system shows just how big this wobble is. Because our sun is more massive than VB 10, its planets do not cause it to wobble nearly as much.
Image credit: NASA/JPL-Caltech
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.
Image credit: NASA/JPL-Caltech/Palomar
