Planets Around Stars

The first planet around another star was discovered as recently as 1995, and already today we know from the use of several different techniques that a few thousand of them exist. We are now able, for the first time, to put a number on how many Earth-like planets exist in the Galaxy. 


Our team at the MiNDSTEp Consortium uses the so-called microlensing method, which is particularly sensitive to planets like those in our own solar system. The results complement those of the Kepler satellite and many years of radial velocity planet hunting. Put together, the three methods estimate that 10 billion stars in the Milky Way will have a planet in its habitable zone. This means that a typical star in the Milky Way Galaxy has 1.6 planets of 5 Earth-masses or more, orbiting in the region corresponding to that between Venus and Saturn in our solar system.


The habitable zone is the distance from the star where the temperature is right for liquid water, and, therefore, in principle right for the existence of life as we know it on Earth. On average, a typical star will have about 4 small rocky planets in the inner part of its planetary system. This is the region where we find Mercury, Venus, Earth, and Mars in our own solar system. In the outer part, where we find the gas-giants Jupiter, Saturn, Uranus and Neptune in our own solar system, a typical solar system is empty. Our solar system is, therefore, fairly typical in its inner part, but very atypical in its outer part. The fact that there are so many planets in the habitable zone and yet no signs of technical civilizations, probably shows that the development of intelligent life requires much more than just an Earth-like planet within the habitable zone.


You can read more about the result of the first 6 years of our observations published in Nature on January 12, 2012.


Read the University of Copenhagen Niels Bohr Institute’s press-release here.


Find out more about the MiNDSTEp Consortium.


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