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A team of astronomers including a PhD candidate in the University of Toronto's department of astronomy and astrophysics has given us our best view yet of an exoplanet moving around a distant star.

A series of images captured between November 2013 and April 2015 shows the exoplanet β Pic b as it moves through 1.5 years of its 22-year orbital period.

Discovered in 2008, β Pic b is a gas giant 10 to 12 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 more than 60 light years from Earth. The system includes comets, orbiting gas clouds, and an enormous debris disc that in our solar system would extend from Neptune’s orbit to nearly 2,000 times the distance from the Earth to the sun.

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.

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Published on Sept. 16 in the Astrophysical Journal, the paper describes observations of the β Pictoris system made with the groundbreaking Gemini Planet Imager (GPI) instrument on the Gemini South telescope in Chile.

“The images represent the most accurate measurements of the planet’s position ever made,” says PhD candidate and lead author Maxwell Millar-Blanchaer. “We’re able to see both the disc and the planet at the same time. With our combined knowledge of the disc and the planet, we’re really able to get a sense of the planetary system’s architecture and how everything interacts.”

Refinements to measurements of the exoplanet’s orbit and the ring of material circling the star shed light on the dynamic relationship between the two. The paper also includes the most accurate measurement of the mass of β Pictoris to date.

This value makes it very unlikely that β Pic b will pass directly between us and its parent star.
Astronomers have discovered nearly 2,000 exoplanets in the past two decades. Most have been detected with instruments – like the Kepler space telescope – that use the transit method of detection, whereby the planet causes a faint drop in a star’s brightness but cannot be resolved 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 distortion caused by the Earth’s atmosphere. The system then blocks the star with a device called a coronagraph, revealing the exoplanet.

“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 Laurent Pueyo, a co-author of the paper. “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 was developed by an international team led by Stanford University’s Bruce Macintosh, a U of T alumnus, and the University of California Berkeley’s James Graham, a former director of U of T's Dunlap Institute for Astronomy & Astrophysics.

In August 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, which will target 600 stars over the next three years.