Extrasolar Planet Basics

What are extrasolar planets?

Extrasolar planets (which are also known as exoplanets) are planets that orbit stars other than the Sun. About two dozen are discovered each year. As of 2006, 190 extrasolar planets have been found . Extrasolar planets more closely resemble the Giant planets (Jupiter, Saturn, Uranus, and Neptune) of our planetary system. These planets are gas giants that orbit close to their host star .

How do scientists detect extrasolar planets?

There are four methods used to find extrasolar planets: radial velocity, astrometry, transit method, and optical detection.

Radial Velocity Measures slight changes in the position of a star as it is tugged by a planet’s gravitational pull. The changes in direction are measured through the Doppler effect. The Doppler effect measures changes in frequency of light waves as the star moves closer and further away from the observer.

Astrometry Uses precise measurements to tell the extent of motion of the star, which then can help find the mass and orbit of the planet. The movement can be found using other stars as a backdrop. The other stars appear to be motionless because they are far away.

Transit Method If a planet passes through a star and an observer’s line of sight, it blocks a slight amount of the star’s light, which reduces brightness. Sensitive instruments are used to detect the reduction in brightness. Reduction in brightness occurs for a few hours every year if the planet orbits the star in the same way the Earth orbits the Sun.

Optical Detection Planets do not give off their own light, which makes them harder to find. Technology is used to block out light at certain frequencies. Another way is to use a coronograph, which blocks the star’s glare. The coronograph blocks out everything but the star’s corona (colored rings that surround a star when it shines through a thin cloud), and the planet is then exposed.

How are extrasolar planets named?

Extrasolar planets are named after the star in which they orbit. They appear with a lower case letter (starting with ‘b’) after the name of the star. Scientists start with a lower case ‘b’ because a lower case ‘a’ is designated for the star .

Information found at: http://en.wikipedia.org/wiki/Extrasolar_planets http://planetquest.jpl.nasa.gov/science/origins.cfm