双子座行星成像仪已被送入太空

After nearly a decade of development, construction and testing, the world's most advanced instrument for directly imaging and analyzing¹ planets orbiting around other stars is pointing skyward and collecting light from distant worlds. "Even these early first-light images are almost a factor of 10 better than the previous generation of instruments. In one minute, we were seeing planets that used to take us an hour to detect," says Bruce Macintosh of Lawrence Livermore National Laboratory, who led the team who built the instrument.

 

For the past decade, Lawrence Livermore has been leading a multi-institutional team in the design, engineering, building and optimization² of the instrument, called the Gemini Planet Imager (GPI), which will be used for high-contrast imaging to better study faint planets or dusty disks next to bright stars. Astronomers³ -- including a team at LLNL-- have made direct images of a handful of extrasolar planets by adapting astronomical⁴ cameras built for other purposes. GPI is the first fully⁵ optimized⁶ planet imager, designed from the ground up for exoplanet imaging deployed⁷ on one of the world's biggest telescopes, the 8-meter Gemini South telescope in Chile.

 

Probing the environments of distant stars in a search for planets has required the development of next-generation, high-contrast adaptive optics (AO) systems, in which Livermore is a leader. These systems are sometimes referred to as extreme AO.

 

Macintosh said direct imaging of planets is challenging because planets such as Jupiter are a billion times fainter than their parent stars. "Detection of the youngest and brightest planets is barely within reach of today's AO systems," he said. "To see other solar systems, we need new tools."

 

And those new tools are installed in the Gemini Planet Imager with the most advanced AO system in the world. In addition to leading the whole project, LLNL also was responsible for the AO system. Designed to be the world's "most sophisticated" astronomical system for compensating⁸ turbulence⁹ in the Earth's atmosphere -- an ongoing¹⁰ problem for ground-based telescopes -- the system senses atmospheric¹¹ turbulence and corrects it with a a 2-centimeter-square deformable¹² mirror with 4,000 actuators. This deformable mirror is made of etched silicon¹³, similar to microchips, rather than the large reflective glass mirrors used on other AO systems. This allows GPI to be compact and stable. The new mirror corrects for atmospheric distortions by adjusting its shape 1,000 times per second with accuracy better than 1 nanometer. Together with the other parts of GPI, astronomers can directly image extra-solar planets that are 1 million to 10 million times fainter than their host stars.

 

GPI carried out its first observations in November 2013 -- during an extremely smooth debut¹⁴ for an extraordinarily¹⁵ complex astronomical instrument the size of a small car. "The GPI team's huge amount of high quality work has begun to pay off and now holds the promise of many years of important science to come," said LLNL Project Manager David Palmer.

 

For GPI's first observations, it targeted previously¹⁶ known planetary systems -- the 4-planet HR8799 system (co-discovered by an LLNL-led team at the Gemini and Keck Observatory¹⁷ in 2008) and the Beta Pictoris system, among others. GPI has obtained the first-ever spectrum¹⁸ of the very young planet Beta Pictoris b.

 

The first-light team also used the instrument's unique polarization mode -- tuned¹⁹ to look at starlight scattered²⁰ by tiny particles -- in order to study a ring of dust orbiting the very young star HR4796. With previous instruments, only the edges of this dust ring (which may be the debris²¹ remaining from planet formation) could be seen. GPI can follow the entire circumference²² of the ring. The images were released today at the 223rd meeting of the American Astronomical Society in Washington D.C., Jan. 5-9.

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