Nancy A. Levenson
Science Highlights
Figure 1.
Polarization component
(Stokes I) of the β Pictoris
system. A purple x marks
the location of the star,
blocked by a mask in
the observation. The
horizontal dashed line
shows the position
angle of the outer disk.
The planet is separated
from the star by 0.4
arcseconds, visible on the
right side of the image,
offset above the dashed
line. This image is 1.3
arcseconds on a side.
A variety of instruments deliver amazing results: The visiting TEXES
spectrograph detects an uncommon amount of water vapor in a
debris ring where terrestrial planets develop; The Gemini Planet
Imager resolves the Beta Pictoris system to unprecedented angular
scales; and GeMS/GSAOI probes the crowded heart of a globular
cluster to new depths with exceptional clarity.
Best View of an Exoplanet Orbit
Observations using the Gemini Planet Imager (GPI) provide images and polarization measurements of the β Pictoris (β Pic) system that probe angular scales smaller than ever before, from ground or space (Figure 1). The dynamical interactions of exoplanet β Pic b and
a debris disk offer tests of planet formation models. A further advantage of the new data is
that they cover observations of the disk and planet together for more than a year, reducing
errors in measurements of their relative positions.
Maxwell Millar-Blanchaer (University of Toronto) and colleagues use the polarimetric observations especially to develop a model for the disk itself. They show that the 10 - 12 MJup
planet is not aligned with the large-scale disk. Ten new astrometric measurements, obtained over a 14-month period, combined with earlier data yield the planet’s
orbital properties and the mass of the central star accurately: 1.61 ± 0.05 MSun.
The planet, orbiting at roughly the same distance as Saturn in our Solar System, can account for some dynamical features of the disk, such as its warp.
However, it cannot fully account for several other features. In particular, β Pic
b is not responsible for clearing the region to the observed inner disk edge
at 23 astronomical units. Another planet could be the cause, but it would
have to be very faint to avoid detection so far. Complete results are published in The Astrophysical Journal; part of a press release also appears on the
following Gemini website, which provides a summary of the work, including
additional illustrations and an animation of the data showing the planet’s