Our Milky Way  galaxy contains a minimum of 100 billion planets according to a detailed  statistical study based on the detection of three extrasolar planets by  an observational technique called microlensing.

Kailash Sahu,  of the Space Telescope Science Institute in Baltimore, Md., is part of  an international team reporting today that our galaxy contains a minimum  of one planet for every star on average. This means that there is  likely to be a minimum of 1,500 planets within just 50 light-years of  Earth.

The results are  based on observations taken over six years by the PLANET (Probing  Lensing Anomalies NETwork) collaboration, which Sahu co-founded in 1995.  The study concludes that there are far more Earth-sized planets than  bloated Jupiter-sized worlds. This is based on calibrating a planetary  mass function that shows the number of planets increases for lower mass  worlds. A rough estimate from this survey would point to the existence  of more than 10 billion terrestrial planets across our galaxy.

The results are being published in the January 12 issue of the British science journal Nature.

The team's  conclusions are gleaned from a planet search technique called  microlensing. The technique takes advantage of the random motions of  stars, which are generally too small to be noticed. If one star passes  precisely in front of another star, the gravity of the foreground star  bends the light from the background star.

This means that  the foreground star acts like a giant lens amplifying the light from  the background star. A planetary companion around the foreground star  can produce additional brightening of the background star. This  additional brightening reveals the planet, which is otherwise too faint  to be seen by telescopes.

See the webside for more details :http://hubblesite.org/newscenter/archive/releases/2012/07/full/ (SY)