The Richtmyer Memorial Lecture: A Physicist Looks at Mars

Response of the Richtmyer Memorial Lecturer to the American Association of Physics Teachers, 1 February 1972

Small Cloud Chamber for Use with Unmanned Balloons

A small lightweight cloud chamber, designed for high altitude cosmic-ray researches, has been operated successfully in unmanned balloon flights up to an 80,000-ft. altitude. In view of the current interest in high altitude cosmic-ray studies, it seems appropriate to describe briefly some of the design features of the present apparatus

Anisotropic Projector

An optical projector having different magnifications, 5× and 50×, in two rectangular directions is described. Although the device is designed principally for rapid measurement of cloud‐chamber track curvatures, it has been applied to various situations in which plane‐to‐plane imaging at constant magnification is desired. Simple plano‐convex cylindrical lenses are used as the image‐forming elements. These give quite satisfactory linearity and resolution at the maximum magnification

One year's processing and interpretation — An overview

A total of 201 complete television frames of Mars were returned by Mariners 6 and 7 in late July and early August of 1969. During the subsequent year over 3500 different versions of those frames were generated by computer processing involving the production of about 35,000 individual photographic prints and large amounts of computer printout as well. This extensive data processing and distribution required the significant participation of about fifteen scientists, engineers, and technicians, mainly at the Jet Propulsion Laboratory. During that same year, the processed data were analyzed and interpreted by approximately twenty-five scientists and technicians at six different institutions. The special supplement of which this is the introductory paper presents most of the scientific findings that have accrued during the first year following the Mariner 6 and 7 flybys of Mars. It constitutes a final report on the television experiment, although significant efforts are continuing. Preliminary results were presented in three papers published in August and October of 1969 [Leighton et al., 1969a, b, c]. Smith [1970] presented information about the size, shape, and surprisingly low albedo of the martian satellite Phobos. Information concerning various aspects of the camera and data systems has also been published recently [Danielson, 1970]

The Vibrational Spectrum and Specific Heat of a Face-Centered Cubic Crystal

The frequency spectrum of a face-centered cubic crystal lattice is found by actually modeling the constant-frequency surfaces of the secular determinant in plaster of Paris and measuring the volume enclosed between successive surfaces. The frequency spectrum so obtained is used in the evaluation of the specific heat of a general crystal of the type treated, and numerical values are presented for the element silver. The present theory (that of Born and v. Karman) is in much better agreement with experimental values for temperatures below 100°K than is the Debye theory. Certain anomalies in the specific heat curves of silver and potassium chloride at temperatures below 10°K are not explicable in terms of the atomic model that is used

The energy spectrum of the decay particles and the mass and spin of the mesotron

Energy values determined from curvature measurements of 75 cloud-chamber tracks of decay particles of cosmic-ray mesotrons at sea level, in a magnetic field of 7250 gauss, are here reported. The observed spectrum extends from 9 Mev to 55 Mev with an apparently continuous distribution of intermediate energy values and a mean energy of 34 Mev. The shape of the spectrum and the value of its upper limit are strong evidence that the mesotron disintegrates into an electron and two neutrinos. It is concluded that the mesotron has half-integral spin. The value of the observed upper limit of the energy spectrum corresponds to a mass value of the mesotron equal to 217±4 electron masses

Mariner Mars 1969: Atmospheric results

Results of investigation of probable atmospheric effects appearing in Mariner '69 TV pictures that have undergone noise removal and preliminary decalibration are described. Two distinct types of haze are distinguished: north polar haze, seen prominently against the face of the planet in blue photographs, and thin haze, usually identified by its appearance on the limb and not strongly colored. Thin haze is surprisingly widespread, particularly in the southern hemisphere. Discrete bright features, which may be evidence for condensation on the ground or in the atmosphere, are described. These occur where bright features have often been seen from earth, in a region where very large multiple-ringed structures seem to dominate the surface morphology. The speculation that these may be evidence for local water-vapor exchange between ground and atmosphere is raised, and some constraints on local subsurface water-vapor sources in the Mars tropics are described. Finally, some implications of the Mariner '69 results for atmospheric exploration by Mariner '71 are briefly discussed

The surface of Mars 4. South polar cap

The south polar cap of Mars occupies a region of cratered terrain. Immediately outside the shrinking cap craters appear no more modified than those in areas farther north that are not annually frost covered. Craters showing through the frost mantle are locally as abundant as elsewhere on Mars. Only in a central region close to the pole are craters sparse. Both far- and near-encounter views reveal a highly irregular pole-cap edge. Photos of the same sector taken six days apart are near duplicates, suggesting that the irregularity is primarily ground controlled. No evidence of the classical polar collar is seen. Within the marginal zone, frost is preserved largely in crater bottoms and on slopes inclined away from the sun. Preferential retention in low spots supports the earlier suggestion that the Mountains of Mitchel may actually be depressions. An argument based on insolation as the prime factor in frost wastage and the narrow width of the marginal zone suggests that slopes of topographic features therein are mostly gentle, on the order of a few degrees. The frost cover of the pole-cap interior may range widely in thickness, obscuring parts of some craters and seemingly enhancing topographic visibility elsewhere, possibly through variations in thickness and reflectivity. Unusually bright areas on the cap surface, and differences in luminance between bright rims and the more somber floors of craters and other depressions, may be due in large part to differences in related frost textures and to the local history of evaporation and sublimation. Irregularly angular depressions within the polecap frost termed ‘etch pits’ may be the product of differential ablation or the undermining by wind of a slabby surficial crust. Encircling the south pole is a region of subdued relief with a paucity of craters, which displays enigmatic quasi-linear markings believed to be ground features. Although no satisfactory explanation of these markings has been formulated, it seems likely that this region has been occupied repeatedly by perennial masses of CO_2 ice, formed and maintained during those phases of the martian precessional cycle that resulted in short cool summers in the southern hemisphere. Such ice masses may play a role in producing the unusual features of the central polar region. Physical relationships suggest a local maximum frost thickness as great as tens of meters. The possibility should be kept in mind that remnants of perennial CO_2 ice of still greater thickness may exist locally, for example, in the ‘etch pit’ area