Watching an Exoplanet in Motion Around a Distant Star

A note by Franck Marchis, Communications Lead and EPO of GPI and the Exoplanets Research Thrust Chair.

The Gemini Planet Imager on the Gemini South telescope. In the photo, GPI comprises the three box-like components attached to the telescope and hanging closest to the observatory floor. Other box-like components on the telescope are other instruments. Image: Manuel Paredes/Gemini Observatory/AURA.

In a major breakthrough for exoplanet discovery and exploration, the Gemini Planet Imager (GPI) is proving to be one of most powerful and effective instruments ever invented for directly imaging planets in orbit around other stars.

The behind-the-scenes story of this project sheds light on the complexities and challenges of designing and building a truly game-changing instrument. We started work more than thirteen years ago under the leadership of Bruce Macintosh and the auspices of the Center for Adaptive Optics. At that time, a number of scientists, most from California and Canada, met to discuss building a groundbreaking adaptive optics (AO) system powerful enough to confront -- and overcome -- the challenging of directly collecting photons from young Jupiter-like exoplanets. The discovery of 51 Eri b (link here), which was announced last month, is the culmination of that effort.

Today, GPI is fully operational and in the process of observing ~600 bright and nearby stars as part of an 900h-survey to search for exoplanets and their circumstellar disks. There's no way to predict how many we will find, but the survey has already generated interesting and groundbreaking data -- allowing scientists, for example, to study exoplanet Beta Pictoris b. The little white dot moving in the video below is the faint glow of this young and warm exoplanet, which is 60 light years away and was observed nine times by GPI between November 2013 and April 2015. Collecting an image of this planet and its star allows us to infer the orbit and composition of the planet, and measure its temperature. In time, GPI and its successor instruments will allow us to do far more.

Images like these make us confident that another revolution in human understanding of the cosmos has begun. Twentieth-century astronomers fundamentally changed our understanding of the universe and our place in it when they mapped asteroids, comets and satellites in our solar system and beyond. Their twenty-first century counterparts have begun work on what may well be an even greater revolution by expanding our knowledge of the Milky Way and mapping far more distant objects such as stars and exoplanets.

We've just begun work on this difficult but revolutionary task. GPI and the next generation of ground- and space-based telescopes equipped with advanced AO technology are the key to finding earth-like exoworlds, including ones that other forms of life may call home.

Read the Press release below

beta pictoris b
This artist’s view shows the planet orbiting the young star Beta Pictoris. Credit: ESO L. Calçada/N. Risinger (

TORONTO - A team of astronomers has given us our best view yet of an exoplanet moving in its orbit around a distant star. A series of images captured between November 2013 to April 2015 shows the exoplanet β Pic b as it moves through 1 ½ years of its 22-year orbital period.

First discovered in 2008, β Pic b is a gas giant planet ten to twelve times the mass of Jupiter, with an orbit roughly the diameter of Saturn’s. It is part of the dynamic and complex system of the star β Pictoris which lies over 60 light-years from Earth. The system includes comets, orbiting gas clouds, and an enormous debris disk that in our Solar System would extend from Neptune’s orbit to nearly two thousand times the Sun/Earth distance.

Because the planet and debris disk interact gravitationally, the system provides astronomers with an ideal laboratory to test theories on the formation of planetary systems beyond ours.

Maxwell Millar-Blanchaer, a PhD-candidate in the Department of Astronomy & Astrophysics, University of Toronto, is lead author of a paper to be published September 16th in the Astrophysical Journal. The paper describes observations of the β Pictoris system made with the Gemini Planet Imager (GPI) instrument on the Gemini South telescope in Chile.

“The images in the series represent the most accurate measurements of the planet’s position ever made,” says Millar-Blanchaer. “In addition, with GPI, we’re able to see both the disk and the planet at the exact same time. With our combined knowledge of the disk and the planet we’re really able to get a sense of the planetary system’s architecture and how everything interacts.”

The paper includes refinements to measurements of the exoplanet’s orbit and the ring of material circling the star which shed light on the dynamic relationship between the two. It also includes the most accurate measurement of the mass of β Pictoris to date and shows it is very unlikely that β Pic b will pass directly between us and its parent star.

Astronomers have discovered nearly two thousand exoplanets in the past two decades but most have been detected with instruments—like the Kepler space telescope—that use the transit method of detection: astronomers detect a faint drop in a star’s brightness as an exoplanet transits or passes between us and the star, but do not see the exoplanet itself.

With GPI, astronomers image the actual planet—a remarkable feat given that an orbiting world typically appears a million times fainter than its parent star. This is possible because GPI’s adaptive optics sharpen the image of the target star by cancelling out the distortion caused by the Earth’s atmosphere; it then blocks the bright image of the star with a device called a coronagraph, revealing the exoplanet.

Laurent Pueyo is with the Space Telescope Science Institute and a co-author on the paper. “It’s fortunate that we caught β Pic b just as it was heading back—as seen from our vantage point—toward β Pictoris,” says Pueyo. “This means we can make more observations before it gets too close to its parent star and that will allow us to measure its orbit even more precisely.”

GPI is a groundbreaking instrument that was developed by an international team led by Stanford University’s Prof. Bruce Macintosh (a U of T alumnus) and the University of California Berkeley’s Prof. James Graham (former director of the Dunlap Institute for Astronomy & Astrophysics, U of T).

In August 2015, the team announced its first exoplanet discovery: a young Jupiter-like exoplanet designated 51 Eri b. It is the first exoplanet to be discovered as part of the GPI Exoplanet Survey (GPIES) which will target 600 stars over the next three years.


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