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Flickers from a Far-Off Planet

8 August 1997 8:00 pm
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Southern strategy.

A network of telescopes in the Southern Hemisphere has uncovered a strong candidate for a planet circling a star thousands of light years from Earth. The network, called PLANET* and consisting of telescopes in South Africa, Australia, and South America, monitors stars in the Milky Way's crowded central bulge 24 hours a day for apparent brightenings. These could indicate another, dimmer star with a retinue of planets drifting across the line of sight, bending the bulge star's light with their gravitational field.

The signals PLANET detected earlier this summer and is now analyzing are "exactly what one would expect for a Jupiter-mass planet orbiting around a solar-mass star," says Abraham Loeb, a theorist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. He cautions that the team still needs to complete mathematical modeling of the event to nail down the arrangement of bodies that produced it. Another international collaboration called GMAN monitored the same star and saw a similar pattern of brightening and dimming, according to GMAN member David Bennett of the University of Notre Dame in Indiana.

The PLANET network of telescopes keeps watch on the bulge of the galaxy, which is visible in the southern sky.

This planet-finding technique builds on a strategy for finding dim stars and stellar cinders: scanning the sky for stars that gradually brighten over weeks or months. As a dim object drifts across the line of sight to the star, its gravity acts like a single magnifying glass slowly passing in front of a distant streetlight. Adding a planet is akin to spattering water on the magnifying glass, embellishing the more gradual curve with rapid spikes in brightness.

The glimmer that galvanized the PLANET and GMAN teams began with a sharp spike around 19 June, followed by a slow rise in brightness and--by some accounts--a strange, double-humped peak around 24 July before a final dimming. The candidate planet circling this putative dim star seems massive, like the handful of other extrasolar planets detected so far. But this search method could be sensitive enough to detect planets as small as Earth, unlike techniques that rely on finding a "wobble" in the parent star as a giant planet whirls around it. On the down side, it gives just a brief glimpse of the planet, and because of the very gradual convergence of light bent by gravity, any planets it reveals are so far out in the galactic blackness that they can't be studied by any other method.

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