Following almost 10 years of development, the Gemini Observatory has debuted an advanced planet imaging instrument and captured a direct image of exoplanet Beta Pictoris b, signifying a breakthrough in our ability to analyze extrasolar planets. Called the Gemini Planet Imager (GPI), the tool uses an advanced optics system with an infrared spectograph to retrieve direct images of young planets orbiting distant stars.
The GPI, a collaborative project developed by institutes in several countries, was first put to the test last November when it was deployed at the 8-meter Gemini South telescope in Chile. The first-light team targeted the Beta Pictoris system and were able to capture direct images of Beta Pictoris b some 63 light years away.
Detecting exoplanets using direct imaging in the past has proven difficult, as planets close enough to a parent star to be considered a candidate for life are typically obscured by its overpowering light. As such, the majority of known exoplanets have been detected using indirect methods. Examples of these include the transit method, which relies on the detection of a drop in the brightness of the parent star as the planet passes in front of it, and the Transit Timing Variation method which compares deviations in orbit caused by gravitational pull with computer-based predictions.
Though high-tech imaging equipment enabling direct observation has been developed in the past, it has involved considerable telescope time to capture the images. The instrument used last year to view exoplanets HR8977b,c,d, and e required 30 - 45 minutes to collect each set of images and infrared spectra. By comparison, the GPI retrieved the image of Beta Pictoris b in 60 seconds.
"Even these early first-light images are almost a factor of 10 better than the previous generation of instruments," said Bruce Macintosh of the Lawrence Livermore National Laboratory (LLNL) and leader of the project team. "In one minute, we are seeing planets that used to take us an hour to detect."
In building the instrument, the team behind the GPI developed what it describes as an advanced optics system. The system uses the infrared spectograph to dissect light from the planets and is able to measure and correct for atmospheric turbulence a thousand times per second. It incorporates a deformable mirror and specially developed masks which work to block the brightness of parent stars.
By viewing the planets directly, scientists will be able to retrieve data that offers a greater insight into critical properties of the planets, such as the atmosphere and temperature.
"Most planets that we know about to date are only known because of indirect methods that tells us a planet is there, a bit about its orbit and mass, but not much else," Macintosh explains. "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."
In addition, the GPI is able to detect polarized light, which will enable further study of disks of scattered light that orbit young stars, believed to be dust leftover from their birth. Previously only the edges of these disks could be studied, but the ability to separate the polarized and regular light will allow further observation, potentially telling us more about the stars themselves.
The team used the GPI's polarization mode to observe dust orbiting the young star HR4796A. The photo seen below demonstrates the visibility of the ring in normal light (left) and in polarization mode with the normal light removed (right).
The team holds high hopes for the GPI and in 2014 will undertake a large-scale survey with the aim of observing 600 young stars and the giant planets orbiting them. Currently, the instrument is only capable of seeing exoplanets the size of Jupiter or larger, though Macintosh foresees advances in technology that will enable the detection of planets much smaller.
"Some day, there will be an instrument that will look a lot like GPI, on a telescope in space," he says. "And the images and spectra that will come out of that instrument will show a little blue dot that is another Earth."
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