Wednesday, July 11, 2007

Benchmark survey shows that giant outer extrasolar planets are rare

Astronomers who used powerful telescopes in Arizona and Chile in a survey for planets around nearby stars have discovered that extrasolar planets more massive than Jupiter are extremely rare in other outer solar systems.

University of Arizona astronomers and their collaborators from the European Southern Observatory, Max Planck Institute for Astronomy at Heidelberg, Italy's Arcetri Observatory, the W.M. Keck Observatory and the Harvard-Smithsonian Center for Astrophysics just concluded a benchmark 3-year survey using direct detection techniques sensitive to planets farther from their stars. The survey looked at 54 young, nearby stars that were among the best candidates for having detectable giant Jupiter-like planets at distances beyond 5 astronomical units (AU), or the distance between Jupiter and the sun. (One AU is the distance between Earth and the sun.)

Since 1995, astronomers have found more than 230 "super Jupiters" orbiting very close to their parent stars using the radial velocity method. This indirect planet-detecting technique measures the slight back-and-forth motion of the star as it is tugged by an unseen planet's gravity. Scientists have written more than 2,000 scholarly papers about these giant Jupiter-like planets within a few Earth-to-sun distances of their stars.

However, the radial velocity method presently used is most sensitive to planets close to their stars. The technique reveals little about extrasolar planets farther out in nearby solar systems.

Astronomers need other techniques to map extrasolar planets beyond 5 AU so they can determine what the "average" planetary system looks like -- and whether ours is a typical solar system.

The 3-year survey didn't turn up even one giant extrasolar planet in the outer part of any nearby solar system.


Ah, pulling away the curtain on sampling biases!

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