Exo Earths

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Expand view Topic review: Exo Earths

Exo Earths

by falkor » Tue Sep 20, 2011 7:06 pm

one is among the most Earth-like yet, another orbits two suns
Image The Saturn-sized planet Kepler-16b
Rocky, Earth-like planets may be less common than many hoped, and unexpectedly 'noisy' stars are slowing the hunt. Moreover, astronomers cannot learn much beyond the basics — mass or size and orbit — of the planets they do find. "What we need is a telescope in space that can image and take spectra of truly Earth-like planets," Marcy says. "We still need that desperately."

For now, however, indirect methods are keeping astronomers busy. One trove of discoveries came from a European team that watches stars for the slight wobble that signals the gravitational pull of an unseen planet. Their instrument, the High Accuracy Radial velocity Planet Searcher (HARPS), which is attached to a 3.6-metre telescope at the European Southern Observatory in La Silla, Chile, yielded 41 new planets, including one of the most Earth-like yet. At 3.6 times the mass of Earth, it sits in the 'habitable zone' around its star, the Goldilocks range of distances at which a planet's surface would be neither too hot nor too cold for water to be liquid.
Image Kepler Catalogue
There was also news from astronomers working with Kepler, a NASA space telescope that stares fixedly at a field of about 155,000 stars in search of transits: the very slight dip in the brightness of a star as a planet crosses in front. The Kepler team announced that they have now detected 1,781 candidate planets, including 123 that are Earth-sized
Among the objects was a novelty: a circumbinary, or a planet orbiting a pair of stars.

Both groups are now confident enough to start making pronouncements about the statistics of planets in orbit close to a star — the kind that both Kepler and HARPS are most sensitive to. The HARPS team, for instance, estimates that about half of Sun-like stars have at least one planet with an orbital period of 100 days or fewer, and that many of these systems boast several such planets. Greg Laughlin, an astronomer at the University of California, Santa Cruz, points out that the Solar System — in which only Mercury has such a short period (88 days) — might end up looking like the oddball