Extrasolar Planet Search

OGLE-2005-BLG-390Lb

The Age of Miniaturization:Smaller is Better

OGLE-2005-BLG-390Lb is believed to be the smallest exoplanet. For now.

Background:Extrasolar Planet = Exoplanet = Planet orbiting a star other than the Sun.

• 188 extrasolar planets have been discovered with a wide range of masses and orbital periods, but planets of Neptune’s mass or less have not hitherto been detected at separations of more than 0.15 AU from normal stars.

• OGLE-2005-BLG-390Lb is a 5.5(-2.7 to +5.5) Earth-mass planetary companion at a separation of 2.6(-0.6 to +1.5) AU from a 0.22(-0.11 to +0.21) solar mass M-dwarf star (68% confidence intervals)

• Its detection suggests that such cool, sub-Neptune-mass planets may be more common than gas giant planets, as predicted by the core accretion theory.

Discoveries:• 1989 – 1

1995 – 11996 – 61997 – 11998 – 61999 onwards: >10/yearAs of April 18th 2006: 188 planets are confirmed (and not retracted yet) according to the Paris Observatory Extrasolar Planets Encyclopedia

Of these 188, the spread of detection is as follows:Radial Velocity – 176Microlensing – 4Imaging – 4Pulsars – 4

1. Radial Velocity (doppler shift)2. Astrometry (uses proper motion, extremely limited)3. Gravitational Microlensing (planet and parent star pass in front of background star)4.Transit Method (planet passes in front of parent star) 5. Circumstellar Disks (measure dust cloud distortions caused by orbiting planets)6. Direct Observation with Spitzer

Main Detection Methods:

Gravitational Microlensing

• Microlensing is most sensitive to planets in Earth-to-Jupiter-like orbits with semi-major axes in the range 1-5 AU.

• The sensitivity of the microlensing method to low-mass planets is restricted by the finite angular size of the source stars.

• Microlensing determines directly only the planet-to-star mass ratio and the projected separation

• The team derived probability densities with Bayesian analyasis.

MicroLensing for OGLE-2005-BLG-390Lb

Results of Bayesian AnalysisPlanetary Host Star is with:• 95% probability a Main Sequence Star• 4% probability a White Dwarf• <1% probability a neutron star/black hole

Fitting for Main Sequence star lens

Going Forward• Planets with separations of ~0.1 AU will be detected routinely by the radial

velocity method or space observations of planetary transits in the coming years

• Our best chance to increase our understanding of such planets over orbits of 1-10 AU in the next 5-10 years is by future interferometer programs and more advanced microlensing surveys.

Useful Links

• The actual research paper:”Discovery of a cool planet of 5.5 Earth Masses through gravitational microlensing.

• http://arxiv.org/ftp/astro-ph/papers/0601/0601563.pdf

• Original Hubble Release: “Astronomers Find Smallest Extrasolar Planet Yet Around Normal Star”• http://hubblesite.org/newscenter/newsdesk/archive/releases/2006/06/full/

• Relevant article in Sky and Telescope: “Low Mass Exoplanet”• http://skyandtelescope.com/news/article_1667_1.asp

• Useful wikipedia resource for Extrasolar Planet information:• http://en.wikipedia.org/wiki/Extrasolar_planet

• Paris observatory, Excellent, updated cataloging of Extrasolar planets• http://vo.obspm.fr/exoplanetes/encyclo/catalog.php

• Optical Vortex – Looking directly at Extrasolar Planets ( “nulling” out the parent star light by exploiting its wave nature)

• http://aip.org/pnu/2005/755.html