Thursday, May 28, 2009

A New Exoplanet from an Old Technique

Back when I was a kid space exploration was flying high, astronauts were on the Moon, there were big plans for orbital cities and an astronomer had just announced the discovery of a system of planets orbiting a nearby star. It didn’t take much for my imagination to leap forward to my eventual trip into space. I was even sure that things would progress to the point where we would eventually be sending missions to explore the planets in orbit around Barnard’s Star. Alas, just about all of that has evaporated, even the planets.

Barnard’s Star is red dwarf star located just six light years from our solar system. Its small size and close proximity make it a great target to hunt for exoplanets. Back in the late 1960s astronomer Peter van de Kamp announced (see The Myserious Companions of Barnard's Star from Time Magazine's April 25, 1969 issue) the discovery of two planets in orbit about Barnard’s Star. B1, was slightly more massive than Jupiter and had an orbital period of 26 years and B2 was slightly less massive than Jupiter and had an orbital period of 12 years. All of this was pretty reasonable compared to our own solar system and life was good.

Peter Van de Kamp used a technique known as astrometry. The idea is to take very precise images of the star’s exact position relative to any background stars. As a planet orbits about the star its gravity will slightly pull the star toward the planet, making a change in its position. If all goes well a repeatable wobble, directly related to the orbital period of the planet will be detected.

van de Kamp knew that Barnard’s star was small, which was good because that makes it easier for a planet to deflect its position. He also knew that it was close, which was also good because it makes the tiny wobble easier to find. Unfortuately, what he didn’t know was that his technique was flawed. No other survey technique has been able to confirm his observations. Barnard’s Star apparently has no planets.

Planet hunters have not given up and new techniques have arisen. The number of known exoplanets now stands at almost 350. But what of van de Kamp’s method of astrometry? It was all but dead for many years, but two JPL astronomers resurrected it. For a little over a decade Steven Pravdo and Stuart Shaklan have been coming to Palomar to use their instrument called STEPS (STellar Planet Survey).

STEPS, seen above, is a large-format CCD camera that gets occasionally mounted at the Hale Telescope’s Cassegrain focus. The CCD has 4096 x 4096 pixels. The payoff of years of observing, an exoplanet discovery, is a difficult one to make. The elusive wobble that Peter van de Kamp thought he had found is small, just 1 milli-arcsecond in size -- that is the angle subtended by a human hair (about 50 microns wide) as seen from a distance of 30 miles!

I am happy to tell you that Pravdo and Shaklan have indeed found an exoplanet using this technique!

The tiny star known as VB 10 is located 20 light years away in the constellation Aquila and is now the smallest star known to have an exoplanet. The planet, VB 10b, is six times more massive than Jupiter, but just about the same size as Jupiter. Notice in the artwork above that the two are pretty close to being the same size.

VB 10b has a nine month orbital period and is just 30 million miles from its star, that puts it a little closer to its star than Mercury is to ours. See below for the comparison.

This is not Palomar's first exoplanet, but congratulations still go out to Steven Pravdo and Stuart Shaklan on their discovery and for mastering the astrometric method of planet hunting.

You can read more about their find from JPL (it even has a movie) here, or here from Bad Astronomy or even here from

No comments: