No abstract

Systematic Mariner 9 monitoring of the space and time distribution of Martian bright and dark markings, the streaks and splotches, indicates a range of global correlations. The time variable classical dark markings owe their configurations and variability to their constituent streaks and splotches, produced by windblown dust. Streaks and splotches are consistent wind direction indicators. Correlation of global streak patterns with general circulation models shows that velocities ∼50 to 90 m/sec above the boundary layer are necessary to initiate grain motion on the surface and to produce streaks and splotches. Detailed examples of changes in Syrtis Major, Lunae Palus, and Promethei Sinus are generally consistent with removal of bright sand and dust and uncovering of darker underlying material as the active agent in such changes, although dark mobile material probably also exists on Mars. The generation of streaks and the progressive albedo changes observed require only threshold velocities of about 2 m/sec for about 1 day at the grain surface. We propose that the dark collar observed following the north polar cap in its retreat is produced by the scouring of bright overlying dust from the polar peripheral ground by winds driven by the temperature differences between frosted and unfrosted terrain. The stability of bright streaks and the variability of dark streaks and splotches, as well as their contrast, can be the result of size differences of the constituent particles.

The surgical procedure and the device are reasonably safe. Adverse events were consistent with shunt procedures for hydrocephalus in this older population. The endpoint data show a trend in favor of the treated group. A larger, randomized, double-blinded, controlled, clinical trial is underway.

The first photographs ever returned from the surface of Mars were obtained by two facsimile cameras aboard the Viking 1 lander, including black-and-white and color, 0.12 degrees and 0.04 degrees resolution, and monoscopic and stereoscopic images. The surface, on the western slopes of Chtyse Planitia, is a boulder-strewn deeply reddish desert, with distant eminences-some of which may be the rims of impact craters-surmounted by a pink sky. Both impact and aeolian processes are evident. After dissipation of a small dust cloud stirred by the landing maneuvers, no subsequent signs of movement were detected on the landscape, and nothing has been observed that is indicative of macroscopic biology at this time and place.

Viking 2 lander began imaging the surface of Mars at Utopia Planitia on 3 September 1976. The surface is a boulder-strewn reddish desert cut by troughs that probably form a polygonal network. A plateau can be seen to the east of the spacecraft, which for the most probable lander location is approximately the direction of a tongue of ejecta from the crater Mie. Boulders at the lander 2 site are generally more vesicular than those near lander i. Fines at both lander sites appear to be very fine-grained and to be bound in a duricrust. The pinkish color of the sky, similar to that observed at the lander I site, indicates suspension of surface material. However, the atmospheric optical depth is less than that at the lander I site. After dissipation of a cloud of dust stirred during landing, no changes other than those stemming from sampling activities have been detected in the landscape. No signs of large organisms are apparent at either landing site.