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Extrasolar Planet Search
The Age of Miniaturization:
Smaller is Better
OGLE-2005-BLG-390Lb is
believed to be the smallest
exoplanet. For now.
OGLE-2005-BLG-390Lb
Background:
Extrasolar Planet = Exoplanet = Planet orbiting a star other than the Sun.
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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:
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1989 – 1
1995 – 1
1996 – 6
1997 – 1
1998 – 6
1999 onwards: >10/year
As 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
– 176
Microlensing
–4
Imaging
–4
Pulsars
–4
Main Detection Methods:
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
Gravitational Microlensing
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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 Analysis
Planetary 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
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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
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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
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Original Hubble Release: “Astronomers Find Smallest Extrasolar Planet Yet Around Normal Star”
http://hubblesite.org/newscenter/newsdesk/archive/releases/2006/06/full/
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Relevant article in Sky and Telescope: “Low Mass Exoplanet”
http://skyandtelescope.com/news/article_1667_1.asp
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Useful wikipedia resource for Extrasolar Planet information:
http://en.wikipedia.org/wiki/Extrasolar_planet
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Paris observatory, Excellent, updated cataloging of Extrasolar planets
http://vo.obspm.fr/exoplanetes/encyclo/catalog.php
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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
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