Given the scale of our own Solar System, the system circling the star Beta Pictoris can’t help but give us pause. Imagine not only the orbiting clouds of gas, dust and debris that we would expect around a young star (8-20 million years old) with a solar system in formation, but also a gas giant planet some ten to twelve times the mass of Jupiter, in an orbit something like Saturn’s. Now factor in this: The disk in question, if translated into our own system’s terms, would extend from about the orbit of Neptune to almost 2000 AU.
Now we have a view of Beta Pictoris b as it moves through a small slice (one and a half years) of a 22 year orbital period. The work of Maxwell Millar-Blanchaer (a doctoral candidate at the University of Toronto) and colleagues, the imagery appears in a paper published yesterday by The Astrophysical Journal. Millar-Blanchaer used observations from the Gemini Planet Imager on the Gemini South telescope in Chile to image Beta Pictoris b, the work being part of the GPI Exoplanet Survey, which will examine some 600 stars in the coming three years.
“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.”
Image: A series of images taken between November 2013 to April 2015 with the Gemini Planet Imager (GPI) on the Gemini South telescope in Chile shows the exoplanet β Pic b orbiting the star β Pictoris, which lies over 60 light-years from Earth. In the images, the star is at the center of the left-hand edge of the frame; it is hidden by the Gemini Planet Imager’s coronagraph. We are looking at the planet’s orbit almost edge-on; the planet is closer to the Earth than the star. Credit: M. Millar-Blanchaer, University of Toronto; F. Marchis, SETI Institute.
The intensively studied Beta Pictoris disk is known for a disk asymmetry (one side of the disk is longer and thinner than the other) and a ‘warp’ that has been thought to be the result of disk ‘sculpting’ by the known planet — a 1997 study argued that a planet with an inclination of between 3 and 5 degrees could account for the observed perturbation, with the subsequent discovery of Beta Pictoris b lending weight to the idea. The other possibility posed in the literature was that the disk is actually composed of two disks that appear superimposed in our view, with a roughly 3 degree difference in position angle.
The new paper refines measurements of the planet’s orbit and the circumstellar disk, showing an inner disk that is slightly offset from the main outer disk. The results also indicate that the sculpting effect cannot be accounted for purely through Beta Pictoris b. From the paper:
When considered together, the disk model and the orbital fit indicate that the dynamics of the inner edge of the disk are not consistent with sculpting by the planet β Pic b alone. This could be explained by an as-of-yet undetected planet in-between the known planet and the inner edge of the disk. Under this scenario the less massive, further out planet would dynamically influence the inner regions of disk, while the more massive β Pic b would have a greater effect at larger radii, causing the well known warp. If there is in fact another planet at this location, this will have significant consequences for our understanding of the planet formation history and dynamical evolution of this system.
Beta Pictoris, some 63 light years away in the constellation Pictor (the Painter’s Easel), is a system that is sure to see intensified investigation. In this case, we’re seeing images of the debris disk in polarized light that, as the paper notes, reach angular separations that have been inaccessible to both space- and ground-based telescopes. Learning more will require more sophisticated dust grain models that will allow researchers to further test their theories about the inner part of the disk.
The paper is Millar-Blanchaer et al., “β Pictoris’ inner disk in polarized light and new orbital parameters for β Pictoris b,” published September 16 2015 by The Astrophysical Journal (abstract / preprint). A University of Toronto news release is available.