Planet search finds lots of little guys

Prospects for abundant Earthlike worlds keep improving

Planet hunters have unlocked a treasure chest of alien worlds to reveal more than 50 newly discovered planets, including at least 16 not much bigger than Earth and one small, sparkling nugget: a 3.6-Earth-mass planet, parked just inside its star’s life-friendly zone.

A PLACE LIKE HOME The super-Earth HD 85512b (illustrated above) is one of more than 50 newly discovered exoplanets announced September 12 by the Swiss-led HARPS team. HD 85512b is on the inner edge of its star’s life-friendly zone. M. Kornmesser/ESO

“We can say that most of the stars have planets, and most of them have low-mass planets,” says astronomer Francesco Pepe, a member of the Geneva Observatory’s HARPS team that presented their new finds September 12 during the Extreme Solar Systems conference in Moran, Wyoming. HARPS finds distant worlds by focusing on wobbly stars that are being pulled in different directions by orbiting bodies. The update brings the team’s eight-year discovery total to more than 150 planets.

An accompanying study that will appear in an upcoming issue of Astronomy & Astrophysics presents the team’s long-awaited characterization of its planetary population – and suggests that more than 50 percent of sunlike stars sport a planet. The little guys among them – with masses between Earth’s and Neptune’s – occur primarily in planetary systems. The latest planet dump suggests that roughly 70 to 80 percent of low-mass planets might live in multiplanet neighborhoods, Pepe says.

“The handwriting is more than on the wall now. We can see that most stars have planetary systems, probably like our own,” says astronomer Debra Fischer of Yale University. “This paper is a home-run hit for the Geneva team.”

The new collection suggests that lighter planets are more common in extrasolar systems than heavier Jupiter-like ones. Though the discovery of Earth-sized planets remains in the future, when such planets do come out of the darkness astronomers predict they will be yet more common.

It’s likely that results from HARPS and NASA’s Kepler space telescope will inform some of the terms in the Drake Equation, Fischer notes, referring to SETI Institute astronomer Frank Drake, whose 1961 equation predicts how many detectable extraterrestrial civilizations exist in the Milky Way. Among other things, the equation considers the fraction of sunlike stars in the galaxy that host planets, and the fraction of those planets that are Earthlike.

While surveys haven’t detected any Earth-massed planets yet, they’re getting close. HARPS previously bagged a planet with 1.8 Earth-masses; and the newly discovered planet HD 85512b, which lives in the habitable zone around its star in the constellation Vela, is only 3.6 Earth-masses. As instruments become more precise and planet-finding missions like Kepler continue to stare at stars, finding Earth-like planets in life-friendly orbits looms.

“The floodgates are about to open,” Fischer says. “Between what Kepler is doing and these Doppler surveys, we’re really on the threshold of seeing a whole population of planets in this so-called habitable zone.”

Within a decade, astronomers hope to aim telescopes like the planned European Extremely Large Telescope at target exoplanets to sniff out the presence of oxygen or other biomarkers in their atmospheres from across intragalactic space. Right now, there are no instruments capable of doing this – but there will be. “The main science goal is not detecting exoplanets, but characterizing them,” says Markus Kissler-Patig of the European Southern Observatory, noting that the next few years present a “fantastic opportunity” for amassing a catalog of target planets.

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