Surveys for Extra Solar Planets
Hugh Jones is co-Principal Investigator of The Anglo-Australian Planet Search.
The Anglo-Australian planet search is targeting 250 nearby stars brighter than V=7.5 in the Southern Hemisphere. A Jupiter-like planet exerts a small gravitational pull on its parent star, causing the star to wobble with a velocity of 1 to 100 meters per second depending on the orbital distance and mass of the planet. This motion can be detected via the Doppler Effect. The light emitted by a star moving toward the Earth will be Doppler shifted to shorter (bluer) wavelengths, while a star receding from the Earth will emit light shifted to longer (redder) wavelengths. The effect is extremely subtle and has no effect on the apparent colour of the star. A star with a Jupiter-mass planet will be revealed by the periodic Doppler shift of its light. After one or two orbital periods the information from the Doppler measurements allows us to calculate the orbit and the mass of the unseen planet. Our current measurement precision is 3 meters per second (a brisk walk). For comparison, Jupiter causes the Sun to wobble with a velocity of 12.5 meters per second over a 12 year period. Saturn induces a 2.7 meter per second wobble on the Sun with a 30 year period. The other planets are too small to produce a measurable effect on the Sun.
David Pinfield is the Principal Investigator of the WFCAM Transit Survey.
The WFCAM Transit Survey (WTS) will identify and study rocky planets using the transit technique, by targeting low mass M dwarfs in the near infrared. While the survey data itself can reveal the orbital period and size of the planets, radial velocity follow-up will provide planet mass and density. Planetary atmospheric properties will come from transmission spectra and secondary eclipse measurements. M dwarfs provide a particularly sensitive probe for small planet transits, will show larger Doppler wobbles than higher mass stars, and have lower star/planet brightness contrast ratios. Indeed, for the lowest mass M dwarfs this survey could find planets that may be habitable. WTS has been awarded 200 nights with WFCAM, with at least 90 nights by the end of 2009.