The opposition effect of the moon: the contribution of coherent backscatter.

The opposition effect, the sharp surge in brightness of an astronomical object observed near zero phase angle, which has been known for more than a century, has generally been explained by shadow hiding. The reflectances of several Apollo lunar soil samples have been measured as a function of phase angle in linearly and circularly polarized light. All samples exhibited a decrease in the linear polarization ratio and an increase in the circular polarization ratio in the opposition peak. This provides unequivocal proof that most of the lunar opposition effect is caused by coherent backscatter, not shadow hiding. This result has major implications for the interpretation of photometric observations of bodies in the solar system, including the Earth.

Radioiodinated DNA as potential tumor-imaging agent.

Radiolabeled heat-denatured DNA and some related nucleic acids localize in tumor tissue following i.v. administration. Retention of radioactivity by tumors is longer than for other organs and localization of tumor tissues is possible by scintigraphic techniques 8-24 hr after injection.

Lunar soil: iron and titanium bands in the glass fraction.

A study of absorption bands in simulated lunar glasses resulted in the discovery of a Ti(4+)-O(2-) charge transfer band at 0.26 micrometer and two Fe(2+)-Ti(4+) bands at 0.34 and 0.42 micrometer. These results indicate that the properties of lunar soil are somewhat affected by the glass content but are controlled by other factors.

Enzymatic synthesis of duplex circular phiX174 DNA containing phosphoramidate bonds in the (-) strand.

Duplex circular phiX174 DNA (RF I) containing some phosphoramidate links in the backbone chain of the (-) strand was synthesized by reaction of 5'-amino-5'-deoxythymidine 5'-triphosphate, dCTP, dGTP, and 3H-dATP with DNA polymerase I and DNA ligase (T4) on a (+) strand phiX174 amber 3 DNA template. The yield of duplex DNA was higher when dTTP was included along with the amino analog in the initial reaction system or was added late in the synthesis. RF I DNA was observed as a rapidly sedimenting species in an alkaline sucrose gradient, and the presence of phosphoramidate linkages was demonstrated by the unusual lability of the duplex DNA in a weakly acidic solution.

Mercury's Surface: Preliminary Description and Interpretation from Mariner 10 Pictures.

The surface morphology and optical properties of Mercury resemble those of the moon in remarkable detail and record a very similar sequence of events. Chemical and mineralogical similarity of the outer layers of Mercury and the moon is implied; Mercury is probably a differentiated planet with a large iron-rich core. Differentiation is inferred to have occurred very early. No evidence of atmospheric modification of landforms has been found. Large-scale scarps and ridges unlike lunar or martian features may reflect a unique period of planetary compression near the end of heavy bombardment by small planetesimals.

Mariner 10 pictures of mercury: first results.

Mercury has a heavily cratered surface cotntaining basins up to at least 1300 kilometers diameter flooded with mare-like material. Many features are closely similar to those on the moon, but significant structural differences exist. Major chemical differentiation before termination of accretion is implied.

Venus: atmospheric motion and structure from mariner 10 pictures.

The Mariner 10 television camieras imaged the planet Venus in the visible and near ultraviolet for a period of 8 days at resolutions ranging from 100 meters to 130 kilometers. Tle general pattern of the atmospheric circulation in the upper tropospheric/lower stratospheric region is displayed in the pictures. Atmospheric flow is symmetrical between north and south hemispheres. The equatorial motions are zonal (east-west) at approxiimnately 100 meters per second, consistent with the previously inferred 4-day retrograde rotation. Angular velocity increases with latitude. The subsolar region, and the region downwind from it, show evidence of large-scale convection that persists in spite of the main zonal motion. Dynamical interaction between the zonal motion and the relatively stationary region of convection is evidenced by bowlike waves.

Venus clouds: a dirty hydrochloric Acid model.

The spectral and polarization data for Venus are consistent with micrometer-sized aerosol cloud particles of hydrochloric acid with soluble and insoluble iron compounds, whose source could be volcanic or crustal dust. The yellow color of the clouds could be due to absorption bands in the near ultraviolet involving ferric iron and chlorine complexes. The ultraviolet features could arise from variations in the concentrations of iron and hydrochloric acid in the cloud particles.

Solar radiation effects in lunar samples.

Optical properties of the pulverized crystalline rocks from the Apollo 11 samples are different from the optical properties of lunar soil. Changes in these properties were induced in the samples by ultraviolet and x-irradiation, standing, and heating. The albedo and spectrum of the soil differed significantly from expected values.

Radiation bleaching of thin lunar surface layer.

The thin, lighter-colored, upper layer of lunar soil shown in the television pictures from several Surveyor missions may be due to reversible bleaching by solar radiation. Of several possible bleaching reactions, the one considered most important is the photoreduction of Fe(+3) to Fe(+2).

Lunar surface: composition inferred from optical properties.

The optical characteristics (intensity, polarization, spectrum, and albedo) of the moon surface are compared with those of rock and meteorite powders. The only materials whose optical properties match those of the lunar surface are basic rocks containing lattice iron but little or no free iron, and then only after irradiation of these rocks by a simulated solar wind. Optical properties of chondritic meteorite powders differ from those of the moon in significant respects. The lunar crust is probably not chondritic, but is similar in composition to terrestrial iron-rich basalts. These results are independent of those from the Surveyor V alpha-scattering experiment and, in addition, provide a basis for extrapolating the Surveyor V analysis to other areas of the moon. The Surveyor V experiment has thus confirmed the value of earth-based optical techniques for the study of the structure and composition of the surfaces of other planets.

Luna 9 pictures: implications.

Evidence from Luna 9 does not preclude the possibility that the moon may have a surface made up largely of very fine rock particles. The degree to which they attach to each other and the resulting firmness of the ground cannot yet be closely estimated.