The Martlet
1 November 2001
by Chris Bodenbender
One of astronomy's most successful planet hunters talked about his prominent role in the discovery of planets beyond our solar system at the University Centre this month.
Dr. Paul Butler gave a lecture on campus as part of the American Astronomical Society (AAS) Second Century Lecture series. This was the first lecture to be held in Canada since the series started in 1999.
"Our goal over the next decade is to learn what fraction of sun-like stars have planets and what fraction of these planetary systems are similar to the solar system," Butler said.
A decade ago, finding planets orbiting other stars was the stuff of science fiction. But the dozens of giant planets orbiting distant stars like our sun, detected since the mid-1990s, have made scientists reconsider theories about planetary systems while questioning the possibility of life elsewhere in the universe.
Since planets are very small, they don't emit light on their own and orbit their suns too close to make them.
In 1996 Butler uncovered the first-known extra-solar planet, orbiting 80 light-years away in the Big Dipper constellation. This discovery wouldn't have been possible without the help of computers.
What was detected was not the planet itself but the effect that it has on its star.
In a planetary system both planet and star orbit the common centre of mass. This centre is closest to the more massive body, the star. For instance, since the mass of our sun is 1,000 times larger than the mass of Jupiter, the orbit that the sun follows is 1,000 times smaller than the orbit of Jupiter. This orbital motion of a star can be detected due to the Doppler effect on its emitted light.
When a star moves away from us during its orbital motion, the light that reaches us from that star shows a slightly redshifted spectrum, while when it moves towards us it is slightly blueshifted. This is the Doppler effect.
The extend of the difference from redshift to blueshift is a direct indication of the diameter of the star's orbit, which is directly linked to the mass of the planet.
The time it takes the star to orbit is also the time that the planet takes for one orbit. The size of the planet can be determined due to transit, the dimming of the star's light when the planet crosses our line of sight in front of the star.
If the light is dimmed by 1.5 percent that means the planet has 1.5 percent of the surface area of the sun. In the case that the sun is about the same as ours, a dimming of 1.5 percent indicates a planet with 40 times the radius of Jupiter.
With these methods scientists like Butler can determine the size, mass and chemical composition of the planet.
"The early hints suggest that the solar system may be the odd bird in the planetary zoo," said Butler.
The key to finding a planetary system like ours is to find a system with a true Jupiter analog, since Jupiter's location and attributes are essential for the stability of the solar system and with that for the existence of life.
Butler concluded that the necessary technology exists to find another solar system, but more money is needed for better telescopes, like dedicated telescopes, for example. These telescopes are locked onto one star for a long time.
