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We present ALMA observations of the largest protoplanetary disk in the OrionNebula, 114-426. Detectable 345 GHz (856 micron) dust continuum is producedonly in the 350 AU central region of the ~1000 AU diameter silhouette seenagainst the bright H-alpha background in HST images. Assuming optically thindust emission at 345 GHz, a gas-to-dust ratio of 100, and a grain temperatureof 20 K, the disk gas-mass is estimated to be 3.1 +/- 0.6 Jupiter masses. Ifmost solids and ices have have been incorporated into large grains, however,this value is a lower limit. The disk is not detected in dense-gas tracers suchas HCO+ J=4-3, HCN J=4-3, or CS =7-6. These results may indicate that the114-426 disk is evolved and depleted in some light organic compounds found inmolecular clouds. The CO J=3-2 line is seen in absorption against the bright 50to 80 K background of the Orion A molecular cloud over the full spatial extentand a little beyond the dust continuum emission. The CO absorption reaches adepth of 27 K below the background CO emission at VLSR ~6.7 km/s about 0.52arcseconds (210 AU) northeast and 12 K below the background CO emission at VLSR~ 9.7 km/s about 0.34 arcseconds (140 AU) southwest of the suspected locationof the central star, implying that the embedded star has a mass less than 1Solar mass .

ALMA Observations of the Largest Proto-Planetary Disk in the Orion Nebula, 114-426: A CO Silhouette