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Fifty new alien worlds, including 16 "super Earths," have been found—the largest extrasolar planet haul announced at one time, astronomers say. The discoveries bring the total number of known extrasolar planets, or exoplanets, to 645.

"The harvest of discoveries ... has exceeded all expectations, and includes an exceptionally rich population of super-Earths and Neptune-type planets hosted by stars very similar to our sun," study leader Michel Mayor, an astronomer at the University of Geneva in Switzerland, said in a statement.

One of the newly discovered worlds, dubbed HD 85512b, lies at the edge of its star's habitable zone—the region around a star where liquid water, and thus life as we know it, can exist.

The planetary treasure trove was found using an instrument called HARPS—short for High Accuracy Radial Velocity Planet Searcher—at the European Southern Observatory's La Silla facility in Chile. Radial velocity, also known as the Doppler wobble technique, involves searching for wobbles in a star's light that indicate the gravitational pull of an orbiting planet.

The method most easily finds very massive planets that orbit close to their host stars. But in recent years astronomers have used radial velocity to find or confirm a number of planets down to a few times Earth's mass.

In fact, HARPS alone has detected about two-thirds of all known exoplanets with masses less than that of Neptune. In 2007, for instance, HARPS discovered another super-Earth, called Gliese 581d, that may lie within the habitable zone of its star.

For the new study, astronomers used HARPS to observe 376 sunlike stars in our home galaxy, the Milky Way.

Based on the number and variety of planets found around these stars, the team estimates that about 40 percent of all sunlike stars in the galaxy host at least one planet that is less massive than the gas giant Saturn.

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