Vitrification darkening of rock powders: implications for optical properties of the lunar surface

Laboratory experiments show that albedoes as low as those on the Moon can be produced by vacuum vitrification and associated chemical fractionation of ordinary terrestrial basaltic material. Vitrification is established as an unequivocal process that can account for the low albedo and apparent local darkening with age of the lunar surface. The spectral reflectance curves of glass powders are significantly different than those of the parent rock mineralogy; thus, the presence of ubiquitous glass in lunar surface material complicates compositional determinations by interpretation of spectral reflectance curves. Vitrification of rocks on the Moon may highly modify the chemical composition of the resulting glass; thus, glass fragments found in lunar fines cannot be assumed to represent bulk parent rock material. Progressive impact vitrification of lunar surface material throughout the Moon's history may have led to a fine-grain, opaque, refractory-rich material we call ultimate glass. This unidentified and, at this point, hypothetical component may exist in dark regolith material; if found, it may be a useful indicator of regolith maturity.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.     

Decametric radio spectra and positions during the flare of August 28, 1966: 1522 UT

During a period of intense decametric continuum arising near the center of the sun, there occurred additional very strong emission closely associated with the flare beginning at 1522 UT on August 28, 1966. Owing to strong ionospheric absorption from about 1527 UT on, which eliminated telecommunications interference, the frequency range over which the flare-associated emission appears is unusually large, from the upper limit of the spectrograph, 41 MHz, to about 11 MHz, where external reflection cuts off the solar signals. Strong bursts of Type III (fast drift) occur from 1527 to 1531 UT, and a complex Type II (slow drift) from 1532 to 1547 UT. As the Type-II burst progresses at frequencies from 15 to 25 MHz, Northward position shifts of many solar radii probably take place; at higher frequencies the burst moves in a complicated pattern through a much narrower range of distances to the North of the sun. Type-IV emission, from 1540 UT on, moves a large distance to the sun's North, and then, after 1600 UT, returns to a stable position quite close to the sun.     

On the interpretation of the “inverse phase effect” for CO2 equivalent widths on Venus

Computations of the equivalent widths of absorption lines as a function of planetary phase angle are made for a homogeneous cloud with particles having the properties (shape, refractive index, and size distribution) deduced from polarimetry of Venus. The computed equivalent widths show an “inverse phase effect” comparable to that which is observed for CO₂ lines on Venus. This result verifies a recent suggestion of Regas et al. that the existence of an inverse phase effect does not by itself imply the presence of multiple layers of scattering particles in the atmosphere of Venus.