Washington, Jan 12 (ANI): Most of the Milky Way's 100 billion stars have Earth-like habitable exoplanets orbiting around them, researchers say.
Using a method that is highly sensitive to planets that lie in a habitable zone around the host stars, astronomers, including members from the Niels Bohr Institute, have discovered that it is very common for stars to have exoplanets.
"Our results show that planets orbiting around stars are more the rule than the exception," said astronomer Uffe Grae Jorgensen, head of the research group Astrophysics and Planetary Science at the Niels Bohr Institute at the University of Copenhagen.
Over 1000 exoplanets have been found in our galaxy, the Milky Way, and most have been found using either the radial velocity method or the transit method, both of which are best suited to be able to find planets that are large and relatively close to their host star.
In order to find planets similar to the planets from our own solar system, researchers used a third method - gravitational microlensing observations, which require very special conditions concerning the stars location in the galaxy.
Jorgensen explained that there is a need to have two stars that lie on a straight line in relation to us here on Earth. Then the light from the background star is amplified by the gravity of the foreground star, which thus acts as a magnifying glass.
When the stars pass close by each other in the sky, astronomers can observe the light from the background star first increase and then decrease again. If there is a planet around the foreground star, there might be a little extra bump on the light curve. But if the planet is very close to the star, the bump 'drowns' on the light curve, and if the planet is very far from star, it cannot be seen.
Since it is rare that two planets pass by each other closely enough to create a microlens, researchers therefore implemented a strategic search on two levels.
Every starry night the research group scanned 100 million stars using telescopes in Chile and New Zealand. If the scanning identified a stellar location with a possible microlensing effect, it automatically registered and all researchers were notified.
"In a six year period from 2002 to 2007, we observed 500 stars at high resolution. In 10 of the stars we directly see the lens effect of a planet, and for the others we could use statistical arguments to determine how many planets the stars had on average," Jorgensen said.
"To be exact, we found that the zone that corresponds to the area between Venus and Saturn in our solar system had and average of 1.6 planets the size of five Earth masses or more."
The microlensing results complemented the best existing transit and radial velocity measurements.
"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," Jorgensen added.
The study has been published in journal Nature. (ANI)
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