ARCHIVED - The Sophisticated Science of Playing Peek-A-Boo With Distant Planets
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September 06, 2006— Ottawa, Ontario
Over the course of the last decade, astronomers have meticulously analyzed the unusual wobbles of more than 150 stars and concluded that there are planets orbiting around them. However, we have yet to get a look at these newfound worlds, a problem that researchers with the NRC Herzberg Institute of Astrophysics intend to solve.
|Gemini North Telescope|
NRC-HIA is part of a multinational team working on the Gemini Planetary Imager (GPI), an intricate mechanical and electronic optical system that will make it possible to resolve the extraordinarily dim light reflected by these planets. By 2010, this combination of hardware and software should be ready to operate on either one of the identical Gemini telescopes, which are located at the world's two prime viewing sites, in Hawaii and Chile.
The heart of this new instrumentation will be a coronagraph, which is essentially the equivalent of a screen that you would carefully position between your eye and the sun, so that you could see something else in the sky. This same technique will block the light of a star so that its nearby planet can come into view.
"A coronagraph is basically just a piece of black metal that you would put in front of the bright light," says Jean-Pierre Véran, an adaptive optics specialist with NRC-HIA's Astronomy Technology Research Group (Victoria) and HIA GPI co-Principal Investigator. "In reality, it's more complicated."
Complicated indeed. He explains that the complications begin with the fact that the starlight being blocked — which may already be invisible without the help of a telescope — can be hundreds of millions of times brighter than that of the planet that is being sought. The image could still be lost in the small amount of the star's light that will diffract around the edges of the coronagraph.
The screen must therefore work in concert with a spectrographic detector that can distinguish between a planetary image and this scattered light, as well as software to further resolve that image from surrounding background noise, including the light diffracting from the spider vanes supporting the telescope's various mirrors.
Those mirrors will take full advantage of adaptive optics, a field in which the HIA is a world leader. While the initial images from space are captured on a primary mirror some eight metres in diameter, a separate mirror will take those images and rapidly correct them for the blurring effect caused by layers of the earth's atmosphere with different temperatures.
The underside of this mirror is to be outfitted with an array of some 2,000 piezoelectric actuators, which can delicately deform the mirror's surface in response to an electric current. By carefully altering the mirror's shape at a rate of thousands of times per second, these actuators will correct for distortions in starlight, which will be essential for the coronograph to do its job.
The GPI project, which is being led by the Lawrence Livermore National Laboratory, has just completed its conceptual design phase, with another two years' worth of work ahead before construction can start. About a quarter of the US$21 million budget is going toward the adaptive optics work at NRC-HIA, with other expertise coming from partners such as the Jet Propulsion Laboratory, the University of California Los Angeles Infrared Instrumentation Laboratory, the University of Montréal, and the American Museum of Natural History.
According to NRC-HIA GPI Project Manager Les Saddlemyer, there is bound to be a great deal of public interest in the first confirmed picture of a planet outside our solar system. But he says the ongoing scientific impact of this new viewing capability will be even greater.
"As soon as you can take a picture of a planet, you can now take a spectrum of the planet, and you can determine things like whether there are various gases in the atmosphere, things that could lead you to some knowledge about the characteristics of the planet," he says. "What's really going to be significant is that people can say this is how planets form, this is what they look like, here's how they are evolving."
Over time, the resulting inventory of dozens or even hundreds of planets should tell us a great deal about what makes a world. Providing the means for this undertaking, adds Saddlemyer, is what drives the desire to meet the considerable technical challenges posed by the GPI.
"It's a very interesting marriage of ground-breaking science and cutting-edge technology," he says.
And we will finally be able to begin this exciting new phase in the exploration of our universe when we no longer have to analyse the suspicious wobbling of stars, and can look directly at distant planets.
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