Astronomers Say There Are At Least 100 Billion Planets in the Milky Way

Posted on January 11, 2012

Astronomers have shared findings from new analysis - using data based on gravitational microlensing observations - that indicates nearly every star in the sky has at least one planet. The research was published in the journal Nature and released at the 219th American Astronomical Society (AAS) meeting.

There are at least 100 billion stars in our galaxy, the Milky Way. This means the Milky Way is home to at least 100 billion planets. The researchers also estimate there are about 10 billion stars with planets in the habitable zone, which means there are likely to be billions of habitable planets in the Milky Way.

Uffe Grae Jorgensen, head of the research group Astrophysics and Planetary Science at the Niels Bohr Institute at the University of Copenhagen, says, "Our results show that planets orbiting around stars are more the rule than the exception. In a typical solar system approximately four planets have their orbits in the terrestrial zone, which is the distance from the star where you can find solid planets. On average, there are 1.6 planets in the area around the stars that corresponds to the area between Venus and Saturn."

Above is a graphic illustrating the gravitational microlensing method. The method requires that you have two stars that lie on a straight line in relation to us on Earth. The light from the background star is amplified by the gravity of the foreground star, which thus acts as a magnifying glass. When astronomers observe the light from the background star there might be a little extra bump on the light curve if there is a planet around the foreground star.

Jorgensen says, "Our microlensing data complements the other two methods by identifying small and large planets in the area midway between the transit and radial velocity measurements. Together, the three methods are, for the first time, able to say something about how common our own solar system is, as well as how many stars appear to have Earth-size planets in the orbital area where liquid what could, in principle, exist as lakes, rivers and oceans - that is to say, where life as we know it from Earth could exist in principle."

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