Astronomers announced on Monday the discovery of 32 extrasolar planets, some just five times the mass of Earth and others five times heftier than giant Jupiter.
The findings significantly boost the number of planets closer to Earth in size and help astronomers better understand what types of stars birth what kinds of planets.
The new alien planets, which bring the known count beyond 400, were found with the HARPS spectrograph on the European Southern Observatory's 3.6-m telescope in La Silla, Chile. The HARPS (High Accuracy Radial Velocity Planet Searcher) program surveyed about 2,000 stars over five years, with the particular aim of looking at solar-type stars for low-mass planets.
Most of the known exoplanets found previously are very large — typically many times the size of Jupiter — so the newfound smaller planets bolster the known population of lower mass planets by 30 percent, said study team member Xavier Bonfils of LAOG in Grenoble, France.
It is not known if any of them are Earthlike, however, given the technology used to find them. The researchers look for dips in starlight to tell them that a planet has passed in front of the star. But they cannotsee the planet's surface or detect any potential atmosphere, important considerations in determining whether or not a planet might be habitable.
"It would be really difficult for HARPS to find a real Earth," said Stephane Udry of Geneva Observatory in Switzerland, who works with the discovery team.
Several of the discovered planets are in multiple-planet systems. The planets have orbital periods of anywhere from five Earth days to several thousand days (Earth's orbit is 365 days).
The survey also showed that, as models have predicted, solar-type stars have plenty of low-mass planets — an intriguing finding in the search for other potential Earths out there. The HARPS data suggest that at least 40 percent of solar-type stars have these smaller planets.
"These low-mass planets are everywhere basically," Udry said in a teleconference from a conference in Porto, Portugal.
Among the worlds found were also several giant gas planets around metal-poor stars. (Metals are any element heavier than hydrogen and helium, the main components of stars.) Such stars are thought to be less favorable for the formation of planets, which form in the metal-rich disc around young stars.
The finding showed that "giant planets can still exist around metal-poor stars," said Nuno Santos of the University of Porto in Portugal.
The survey also found four new exoplanets around M dwarf stars, which are relatively cool, low-mass stars. This finding challenges planet formation theory, the researchers said, as current models suggest it is difficult for planets to form around such stars.
The new findings suggest that exoplanets are quite common in our galaxy, the researchers said.
Employing the adage that nature abhors a vacuum, Udry said, "if there is place to put a planet, it will put a planet there."