The National Research Council Canada Herzberg Institute of Astrophysics (NRC-HIA) and an international team of researchers became the first to capture images of three planets circling a star other than the Earth's Sun.
“On behalf of the Government of Canada, I want to congratulate Dr. Marois and the other Canadian scientists for their remarkable and historic discovery,” said the Honourable Gary Goodyear, Minister of State, Science and Technology. “This achievement adds to our country's long and proud history of scientific success.”
The team, led by NRC-HIA astronomer Dr. Christian Marois, used high-powered telescopes to capture these images. They were then able to identify three planets larger than Jupiter orbiting a star known as HR 8799. This star is 130 light years from Earth in the constellation of Pegasus. It is faintly visible to the naked eye.
“We have known for a decade through indirect techniques that the Sun was not the only star to have planets in orbit around it,”said Dr. Marois. “We finally have an actual image of an entire solar system. This is a milestone in the search for planetary systems around stars.”
A team of Canadian, U.S. and British astronomers used the Gemini North and Keck telescopes on the summit of Mauna Kea in Hawaii to capture infrared images of the planets. The images were confirmed using advanced instrumentation and image-processing technology.
“NRC is proud of its world-class expertise that has lead once again an international team of scientists,” said NRC President Dr. Pierre Coulombe. “This important discovery will have a significant impact on astronomy for years to come.”
HR 8799 is about 1.5 times the mass of the Sun. It is also much brighter and significantly younger. Astronomers estimate the star is about 60 million years old.
“It's amazing to have a picture showing not one but three planets,” said Dr. Bruce Macintosh, a scientist at the Lawrence Livermore National Laboratory and a project collaborator. “The discovery of the HR 8799 system is a crucial step on the road to the ultimate imaging of another Earth.”
These findings will be published in the November issue of Science, an international weekly science journal.
Recognized globally for research and innovation, Canada's National Research Council (NRC) is a leader in the development of an innovative, knowledge-based economy for Canada through science and technology.
Media Relations Officer
National Research Council Canada
Tel: (613) 990-6091
Cell: (613) 853-5611
NRC Herzberg Institute for Astrophysics
Tel: (250) 363-6951
The HR 8799 system
In some ways, this planetary system seems to be a scaled-up version of Earth's Solar System orbiting a larger and brighter star. The planets around HR 8799 are young enough that they are still glowing from heat released when they formed, estimated to be 60 million years ago. Analysis of the brightness of the objects at multiple wavelengths shows that these objects are about seven and ten times the mass of Jupiter. As in our Solar System, these giant planets orbit in the outer regions – distant from their star at roughly 25, 40 and 70 times the distance between Earth and its Sun. The furthest planet orbits just inside a disk of dusty debris, similar to that produced by the comets of the Kuiper Belt of our Solar System (just beyond the orbit of Neptune at 30 times the Earth–Sun distance).
The parent star HR 8799 has about 1.5 times the mass of the Sun and is 5 times more luminous but is significantly younger than the Sun. Infrared observations by satellites have shown evidence for a massive disk of cold dust orbiting the star. Dr. Benjamin Zuckerman is a professor of physics and astronomy at the University of California, Los Angeles (UCLA) and a co-author on the Science paper. He has been studying dust disks orbiting nearby stars for decades and states, “HR 8799's dust disk stands out as one of the most massive in orbit around any star within 300 light years of Earth.”
Analysis of available data indicates that the star is about 60 million years old. “No one technique can yield a precise age for the star and its planets, so our age estimate is based on three independent lines of evidence that involve the spectrum and luminosity of HR 8799 and its motion in our Milky Way galaxy,” Dr. Zuckerman noted. Planets do not have any internal source of energy; they are thus slowly cooling down and becoming less luminous with time. Co-author Dr. Travis Barman, an astronomer at Lowell Observatory in Arizona, commented that “knowledge of the age of HR 8799 is critical for linking the observed luminosities of the planets with their masses. The younger/older the planets, the smaller/larger would be their masses.” The derived luminosities show that the three companions are massive planets. “Detailed comparison with theoretical model atmospheres confirms that all three planets possess complex atmospheres with dusty clouds partially trapping and re-radiating the escaping heat,” Dr. Barman remarked.
Artwork of the system is available at the following URL: www.gemini.edu/threeplanetart
Direct vs. indirect detection
More than two hundred exoplanets have been detected in the past decade, but almost all are known through indirect studies of their gravitational tug on their parent star. The indirect technique only measures the mass and orbit of the planet. “By making an image that shows the planet directly, we can study its properties in detail – measure its temperature and composition and try to understand its atmospheric structure,” said Dr. Bruce Macintosh, a scientist at the Lawrence Livermore National Laboratory in California who has been co-leading the attempts to image an extrasolar planet for almost a decade.
Up to now, only a few brown dwarfs (objects with a mass in between stars and planets, also known as failed stars) and some ambiguous objects near or above the boundary between brown dwarfs and planets have been detected by direct imaging. All of these are orbiting at large distances from their star and are not believed to have formed in the same way as the planets of Earth's Solar System did.
Telescopes and techniques
The team of Canadian, American and British astronomers used the Gemini North and Keck telescopes on Mauna Kea in Hawaii to take infrared images and, using advanced instrumentation and image processing, they discovered three faint objects close to HR 8799. Comparison of images from different years show that the three objects are all moving with and orbiting around the star, proving that they are associated with it rather than just being unrelated background objects coincidentally aligned in the field of view.
The Gemini and Keck observations were possible due to adaptive optics systems that significantly reduce the blurring caused by Earth's atmosphere. At Gemini, the largest of Canada's optical telescopes, the observations relied on the Altair adaptive optics instrument designed and built by the National Research Council of Canada (NRC). In addition, the detection of all three planets was made possible by an advanced observation strategy, called Angular Differential Imaging, which helps to separate the light of the host star to reveal the faint images of the planets.
Angular Differential Imaging ( ADI )
The Angular Differential Imaging (ADI) technique is a specialized observational and data reduction method that uses the intrinsic slow field-of-view rotation of altitude/azimuth mount telescopes. During an acquisition, the infrared camera is kept aligned with the telescope while the sky orientation is slowly rotating. A data reduction pipeline is then used to construct and subtract a reference star image that does not contain the flux of the planets. Residual images are then rotated to align the field and median combined to enhance the sensitivity to planets.
HR 8799 observations are part of a survey of 80 young, dusty, and massive stars located in the solar neighbourhood. The survey will use the Keck, Gemini North and VLT telescope's adaptive optics capabilities to constrain the Jupiter-mass planet populations in a range of separations inaccessible to other exoplanet detection techniques, i.e., separations similar to the outer giant planets of Earth's Solar System. “We discovered this system after observing only a few stars,” said NRC astronomer Dr. Christian Marois. “That may indicate that Jupiter-mass planets at separations similar to the giant planets of our Solar System are frequent around stars more massive than the Sun. HR 8799's planetary system will be studied in much detail in the years to come and it will surely be a prime target for future next generation exoplanet finding instruments and dedicated space missions.”
HR 8799's planets were detectable because they were quite massive, young and orbiting far from their star. To study the giant planets of solar systems like our own will require new and more advanced instruments. The NRC Herzberg Institute of Astrophysics (NRC-HIA) is a major part of a U.S. and Canadian team, led by Dr. Bruce Macintosh, building a next-generation adaptive optics system called the Gemini Planet Imager (GPI - http://gpi.berkeley.edu ). GPI is designed from the ground up to take images and spectra of extrasolar planets, and will be more than ten times more powerful than Altair. When deployed in 2011 it will be able to take spectra of planets equal in mass to Jupiter orbiting nearby solar-type stars.
Ultimately, astronomers are working towards images and spectroscopic studies of truly Earth-like planets, but that will require specialized space telescopes that are still on the drawing board.