Magazine article Science News

Core Finding: Latest, Oddest Planet Hints at How Orbs Form

Magazine article Science News

Core Finding: Latest, Oddest Planet Hints at How Orbs Form

Article excerpt

The 160 extrasolar planets discovered over the past decade constitute an odd menagerie. They include giant, Jupiter-like bodies with temperatures hot enough to melt metal, planets in orbits nearly as elongated as the paths of comets, and at least one distant cousin of Earth. But the planet announced last week seems the most bizarre of all. It displays the heaviest core of any planet yet detected.

With an orbit whose radius is only one-tenth that of Mercury's path around the sun, the planet has a searing surface temperature of 1,500 kelvins, and it whips around the sunlike star HD 149026 in just 2.88 days. It's likely to provide crucial new understanding of how planets form, says codiscoverer Bun'ei Sato of the Okayama Astrophysical Observatory in Japan.

"None of the models predicted that nature could make a planet like the one we are studying," says Sato. His team announced the discovery June 30, and details will appear in an upcoming Astrophysical Journal.

The scientists have studied the planet in two ways. First, Sato's team observed wobbles of the star HD 149026. Astronomers have detected nearly all other extrasolar planets by measuring such variations in velocity, which are caused by the tug of an orbiting object.

A second set of observations floored astronomers. An unusual alignment of the planet, its star, and Earth enabled the team to measure the starlight that the planet blocked each time that it passed between its star and Earth. The researchers found that although the planet is 20 percent more massive than Saturn, it blocks only about half the light that the giant planet would. …

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