Thirty-two new alien orbs have just been added to the growing list of exoplanets, including several that qualify as "super-Earths," meaning they have a mass only a few times that of our planet and could potentially harbor Earth-like environments.

In the past five years, the High Accuracy Radial Velocity Planet Searcher, a special exoplanet-hunting device attached to a 3.6-meter telescope in La Silla, Chile, has spotted more than 75 alien planets, including 24 of the 28 known exoplanets with a mass less than 20 times that of Earth.

Given the high frequency of low-mass planets discovered by HARPS, the researchers think between 39 and 58 percent of solar-type stars host a planet with a mass of less than 50 Earth-masses.

"These findings consolidate the results of simulations of planet formation predicting a large population of super-Earths," astrophysicist Stephane Udry of Geneva University wrote in an email to Wired.com. "The formation models furthermore predict an even larger population of Earth-mass planets, providing solid scientific justifications for the development of ambitious programs (in space and on the ground) to look for those Earth-type planets."

Udry's announcement of the HARPS team's findings Monday at an exoplanet conference in Portugal marks the end of the first phase of HARPS research, and scientists say the project has been even more successful than they originally expected.

The HARPS instrument detects hidden exoplanets by looking for stellar "wobble," or a slight change in the radial velocity of potential host stars. The high-precision spectrograph can pick up even tiny fluctuations in a star's radial velocity — differences in speed of as little as 2.2 miles per hour — which are caused by the gravitational pull of a nearby planet.

The HARPS scientists focused their exoplanet-hunting efforts on certain kinds of stars, including stars similar to our sun and those with low mass (called Mdwarfs) or low metal content.

"By targeting M dwarfs and harnessing the precision of HARPS, we have been able to search for exoplanets in the mass and temperature regime of super-Earths," co-author Xavier Bonfils of the Joseph Fourier University in France said in a press release, "some even close to or inside the habitable zone around the star."

Image: Artist's impression of Gliese 667C, a six Earth-mass exoplanet that circulates around its low-mass host star at a distance only 1/20th of the Earth-Sun distance. The host star is a companion to two other low-mass stars, which are seen here in the distance. ESO/L. Calçada

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