| Summary: | Full disk images of Mars have been obtained with the use of the Very Large Array (VLA) to map the radar reflected flux density. The transmitter system was the 70-m antenna of the Deep Space Network at Goldstone, California. The surface of Mars was illuminated with continuous wave radiation at a wavelength of 3,5 cm. The reflected energy was mapped in individual 12-minute snapshots with the VLA in its largest configuration; fringe spacings as small as 67 km were obtained. The images reveal near-surface features including a region in the Tharsis volcano area, over 2000 km in east-west extent, that displayed no echo to the very low level of the radar system noise. The feature, called Stealth, is interpreted as a deposit of dust or ash with a density less than about 0.5 gram per cubic centimeter and free of rocks larger than 1 cm across. The deposit must be several meters thick and may be much deeper. The strongest reflecting geological feature was the south polar ice cap, which was reduced in size to the residual south polar ice cap at the season of observation. The cap image is interpreted as arising from nearly pure CO_2 or H_2O ice with a small amount of martian dust (less than 2 percent by volume) and a depth greater than 2 to 5 m. Only one anomalous reflecting feature was identified outside of the Tharsis region, although the Elysium region was poorly sampled in this experiment and the north pole was not visible from Earth. © 1991 American Association for the Advancement of Science. 14 May 1991; Accepted 12 August 1991. We thank the observing staffs at the VLA and the 70-m facilities for their attention and care in performing the observations; D. Paige and B. Jakosky for discussions about martian geology; and several members of the VLA professional staff including K. Sowinsky and T. Cornwell concerning the endlessly complex data processing; and J. Head, L. Keszthelyi, A. Ingersoll, H. Kieffer, S. Murchie, and R. Simpson for comments concerning the manuscript. Supported under NASA grant NAGW 1499 and ...
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