A new instrument, attached to one of the most powerful telescopes in the world, has opened its infrared eye for the first time, taking snapshots of a nearby planet orbiting another star and a ring of proto-planetary stellar dust.
The sophisticated car-sized instrument, called the Gemini Planet Imager (GPI), is attached to the 8-meter Gemini South telescope in Chile and represents a new era in exoplanetary discovery. The GPI, which has been in development since 2003, is capable of not only resolving the dim light from an exoplanet orbiting close to its parent star; it can also analyze the planet’s atmospheric composition and temperature.
The majority of ground-based exoplanet surveys watch for stars’ “wobbles” to betray the gravitational presence of massive exoplanets in orbit -- known as the “radial velocity technique.” Another powerful technique for discovering smaller exoplanets in tight orbits around their star is employed by NASA’s Kepler space telescope. As an exoplanet passes in front of its host star, a small dip in brightness can be detected by Kepler’s sensitive optics – this is known as a "transit."
Other methods for exoplanetary detection are possible (such as microlensing), but the “Holy Grail” for astronomers is to use a powerful telescope to directly image star systems, picking out tiny dots of light in orbit. This feat has been achieved a handful of times (most notably the 2008 Hubble and Keck/Gemini announcements of directly imaging exoplanets around the stars Fomalhaut and HR 8799) its wholesale use as an effective exoplanet-hunting tool has been limited by technology, a limit that the GPI has now dramatically lifted.
Through the ingenious combination of adaptive optics -- a laser system used on some observatories that can actively counteract the blurring effects of turbulence in the Earth’s atmosphere -- and an active obscuring coronagraph perfectly covering the star (to counteract the glaring effect of the starlight), GPI has the power to distinguish star from exoplanet to unparalleled precision.
“Most planets that we know about to date are only known because of indirect methods that tell us a planet is there, a bit about its orbit and mass, but not much else,” said Bruce Macintosh of the Lawrence Livermore National Laboratory, who led the team that developed GPI. “With GPI we directly image planets around stars -- it’s a bit like being able to dissect the system and really dive into the planet’s atmospheric makeup and characteristics.”