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Cosmic Diary

How GPI Works to See Planets

6 Aug 2015, 22:09 UTC
How GPI Works to See Planets
(200 words excerpt, click title or image to see full post)

I sometimes compare the challenge of directly detecting a Jupiter orbiting a nearby star to finding a glowing needle in a haystack. Oh, and by the way, the haystack is on fire.
It’s about as hard as seeing a candle a foot away from a spotlight (1 million candlepower) at a distance of 100 miles.
Why is doing this so difficult? There are three primary reasons:
1. We observe through atmospheric turbulence, which blurs our view of the star-planet system and scatters starlight, obscuring the faint planet beneath.
2. Light obeys a wave property called diffraction, which scatters light from a planet’s host star throughout the image, obscuring the planet. This effect occurs even in near-perfect optical systems above the atmosphere, like the Hubble Space Telescope.
3. The optics within telescopes and instruments are imperfect, which further distorts the optical wavefront and introduces speckles, or tiny images of the star that look like false planets, into the image.
The Gemini Planet Imager was designed to control and suppress these effects. The four components of GPI that do this are: an Adaptive Optics system, a coronagraph, a sensor that spectroscopically differentiates planets from starlight, and data post-processing techniques.
The Adaptive Optics ...

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