Extrasolar Planets


Detection Methods

The past ten years have shown an explosive growth in the detection of extasolar planets due to three primary detection methods.

  1. Astrometric Detection Method
  2. Doppler Detection Method
  3. Transit Detection Method

The first two methods are based on the fact that a planet orbiting a star will cause the star to "wobble" in space. The first method detects the component of this wobble that is horizontal to our line of site, and is based simply on observing the position of the star over time. The second method detects the component of the wobble that is radial to us, (i.e. directly towards or away from us), and is based on the doppler shift in the star's light as the star moves towards or away from us. The third method is based on detecting the small drop in apparent luminosity of a star as a planet transits in front of it, between the star and the Earth.


So far the planets that have been found around other stars have tended to be very large, (Jupiter size), but have been found in orbits very close to their parent star. This has required us to revisit our theories of solar system formation, and is suggesting that after a solar system forms, it is likely that gravitational interactions and resonances between the planets will alter their initial orbits, possibly causing the entire composition and structure of the solar system to change dramatically.

The following image is a link to a chart showing the size and distance from their stars of the typical extrasolar planets found to date.

Img: th_chart

Update -- Professional/Amateur Team Discover New Extrasolar Planet

This is an exciting update for me because it demonstrates how real science can be done by amateur astronomers and that collaborative efforts between professional and amateur astronomers can be very fruitful, (plus one of the amateurs, Ron Bissinger, is right here in Pleasanton!).

Ron was working with Dr. Peter McCullough of the Space Telescope Science Institute in Baltimore, MD, and a team of 3 other amateur astronomers from around the world to find new extrasolar planets using the third method I've described, the transit detection method.

The professional/amateur collaboration worked as follows. An automated camera setup in Maui scans the sky nightly and collects data from which a computer program sifts through looking for candidate stars for extrasolar planets based on their light curves. The data from the sky survey is not accurate enough to verify an extrasolar planet, so McCullough's team takes the list and identifies the most promising candidates for further observation. This list is then given to the four amateur astronomers to perform more accurate observations from their own home observatories. If a star is found in their more detailed observation to display the characteristic curve of an orbiting extrasolar planet (below I've linked to Ron Bissinger's site where you can read how the shape of the light curve is different for an extrasolar planet than for an eclipsing binary star, a distinction I had not made when describing the method), it is scheduled for confirming spectroscopic observation at a large observatory.

On June 23, 2005, Ron identified a light curve from one of the candidate stars that he felt must be an extrasolar planet. He notified the rest of the team who then made confirming observations. The star was then observed from University of Texas’s McDonald Observatory, to obtain spectroscopic data that verified the existence of the planet.

My congratulations to Dr. McCullough, Ron, and the rest of the team!

Ron Bissinger's Account of the Discovery

Press Release

The Future

The pace of planet discovery does not seem to be slowing down at all, and there are many new methods of detection that are being investigated. Also we are beginning to discover smaller sized planets, on the order of Neptune rather than Jupiter. It is only a matter of time before we will detect Earth sized planets. All of these issues will be the subject of future additions to this site.

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