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Watch an exoplanet orbit a distant star

Astronomers have obtained direct images of an exoplanet moving around a star 63 light-years from Earth.

Beta Pictorus b, animated over 1.5 years of its 22-year orbital period. M. Millar-Blanchaer, University of Toronto; R. Marchis (SETI Institute)

Exoplanets, or planets outside the solar system, are notoriously difficult to see. We know they exist, but these planets are not usually seen directly.

Planets only reflect the light of the stars, and stars are so bright that the any light reflected off the planet is very faint in comparison. Typically, stars are a million times brighter than their orbiting planets.

The presence of exoplanets is extrapolated by observing the star it orbits. When the star's light dims, astronomers are able to determine that a planet is passing in front of it and blocking some of the light from reaching Earth. At time of writing, NASA's exoplanet archive lists 1,890 confirmed exoplanets located by the Kepler mission.

Using the Chile-based Gemini South telescope's Gemini Planet Imager (GPI) instrument, a team of researchers led by PhD candidate Maxwell Millar-Blanchaer was able to take a series of images of a planet in orbit around a star named Beta Pictorus, which lies approximately 63 light-years from Earth in the direction of the constellation of Pictor.

The planet's name is Beta Pictoris b, discovered in 2008, and it's a gas giant. The system of Beta Pictorus is a complex one. It contains a massive debris disk, an orbiting gas clouds and comets.

Beta Pictorus b, with a radius 65 percent larger than Jupiter's, is a relatively young planet, orbiting a very young star only somewhere between 8 million and 20 million years old. Beta Pictorus b interacts gravitationally with the debris disk, within which, scientists theorise, planetary formation may still be ongoing. This makes the Beta Pictorus system and planet Beta Pictorus b excellent for studying planetary formation theories.

The planet was imaged from November 2013 to April 2015, capturing 1.5 years of its 22-year orbital period. The Gemini Planet Imager occludes the light from Beta Pictorus, allowing the camera to capture direct images of the planet, resulting in some of the best photos of Beta Pictorus b yet.

"The images in the series represent the most accurate measurements of the planet's position ever made," Millar-Blanchaer said. "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 team's paper, published this week in The Astrophysical Journal, also refines orbital measurements of the star and the debris disk, clarifying their relationship. It also refines the mass of the star Beta Pictorus, which comes in at around 1.6 solar masses, and demonstrates that Beta Pictorus b is unlikely ever to pass directly between Beta Pictorus and Earth.

"It's remarkable that Gemini is not only able to directly image exoplanets but is also capable of effectively making movies of them orbiting their parent star," said Chris Davis, astronomy division program director at the National Science Foundation, which helps fund the Gemini telescopes.

"The disk of gas and dust from which planets are currently forming was one of the first to be observed and is a fabulous laboratory for the study of young solar systems."