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We use Atacama Large Millimeter/submillimeter Array Band 5 scienceverification observations of the red supergiant VY CMa to study thepolarization of SiO thermal/masers lines and dust continuum at ~1.7 mmwavelength. We analyse both linear and circular polarization and derive themagnetic field strength and structure, assuming the polarization of the linesoriginates from the Zeeman effect, and that of the dust originates from aligneddust grains. We also discuss other effects that could give rise to the observedpolarization.  We detect, for the first time, significant polarization (~3%) of thecircumstellar dust emission at millimeter wavelengths. The polarization isuniform with an electric vector position angle of $\sim8^\circ$. Varying levelsof linear polarization are detected for the J=4-3 28SiO v=0, 1, 2, and 29SiOv=0, 1 lines, with the strongest polarization fraction of ~30% found for the29SiO v=1 maser. The linear polarization vectors rotate with velocity,consistent with earlier observations. We also find significant (up to ~1%)circular polarization in several lines, consistent with previous measurements.We conclude that the detection is robust against calibration and regularinstrumental errors, although we cannot yet fully rule out non-standardinstrumental effects.  Emission from magnetically aligned grains is the most likely origin of theobserved continuum polarization. This implies that the dust is embedded in amagnetic field >13 mG. The maser line polarization traces the magnetic fieldstructure. The magnetic field in the gas and dust is consistent with anapproximately toroidal field configuration, but only higher angular resolutionobservations will be able to reveal more detailed field structure. If thecircular polarization is due to Zeeman splitting, it indicates a magnetic fieldstrength of ~1-3 Gauss, consistent with previous maser observations.

Magnetically aligned dust and SiO maser polarization in the envelope of the red supergiant VY CMa