Planetary Astronomy; an Appraisal of Ground-Based Opportunities (1968) / Chapter Skim
Currently Skimming:
Planetary Surfaces
Planetary Surfaces
Pages 14-25
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 14... ...
The surfaces of the outer planets -- if solid surfaces indeed exist -- are blanketed by extremely deep and opaque atmospheres and are virtually inaccessible to study.
|
From page 15... ...
These structures appear to move relative to each other at the same latitudes, as well as to display systematic differences in rotation for zones located at different latitudes. The rotation periods of these features around the Jovian axis can vary from the planetary average of just under 10 h by as much as ± 5 min; the rotational period is shortest near the equator.
|
From page 16... ...
The significance of the different period of the moving cloud pattern as seen in the ultraviolet also remains to be determined, but the differences are probably a manifestation of the complex planetary atmospheric circulation whose nature is entirely obscure. The rotations of Uranus and Neptune have been determined spectroscopically in the same way as for Saturn, but the precision of current values is inadequate.
|
From page 17... ...
In addition, measurements at the longer radio wavelengths yield data on subsurface emission, while measurements at shorter wavelengths can provide information on the degree and nature of atmospheric absorption. Radio Measurements -- Low Resolution Planetary emission is most simply measured by including the entire disk of the planet; these measurements require less sensitivity and resolving power.
|
From page 18... ...
Radio Measurements -- High Resolution Although present knowledge of planetary surface temperatures has, at radio wavelengths, been based primarily on the observed emission from the entire disk of each planet, it is important to consider what has been achieved, or might be in the future, with significant improvements in radio facilities. The emphasis should be laid on increasing angular resolution and sensitivity at wavelengths which have already been used extensively.
|
From page 19... ...
These measurements show that the lunar surface has a very poor ability to conduct heat. Mild and broad variations of thermal conductivity have so far correlated with an age classification system recently developed by lunar geologists and based on the degree of rounding of originally sharp surface features.
|
From page 20... ...
SURFACE STRUCTURE The detailed structure or geography of a planetary surface, in addition to its intrinsic interest, often provides insight into the nature of internal and external forces acting to modify that surface. High-resolution photographs from the surface of the Earth and from orbiting and landing space probes have provided a wealth of information about the lunar surface.
|
From page 21... ...
PLANETARY COMPOSITION Detailed analysis of planetary composition requires the soft landing of payloads on the planets. Surveyor V made the first such analysis of a very limited area of the lunar surface by measuring the backscatter of alpha par
|
From page 22... ...
The apparently short length of time between nucleosynthesis and meteorite formation, together with indications that all stony meteorites cooled sufficiently within about a million years to retain xenon, are of fundamental importance to an understanding of the origin of the solar system. Continued work on the xenon isotopes and other rare gases, coupled with careful petrological and geochemical studies of the meteorites, will give a more accurate time scale for the early stage of the formation of the solar system.
|
From page 23... ...
Planetary surfaces exhibit a range of colors and polarizations, but, with the exception of the vaguest generalizations, it is almost impossible to associate these data with any particular mineral or rock. Spectroscopic studies of the infrared radiation from planetary surfaces have had particular appeal, because silicate minerals exhibit several infrared absorption bands and are thought to be dominant on many planetary surfaces.
|
From page 24... ...
It should then be possible to correlate spectra with composition and extrapolate to regions where remotely obtained spectra, but no direct information, are available. SURFACE VARIATIONS The sources of variation within the planetary system are diverse: the changing polar caps of Mars and the associated wave of darkening are surface effects; the changing patterns of Jupiter's belts are atmospheric effects; and the changing brightness of asteroids may be the effect of surface roughness, albedo, irregular shape, or all three.
|
From page 25... ...
The cloud belts of Jupiter have long been noted for their variability. A detailed study of the changing appearance of its apparent disk is of value, not only for meteorological information but also because of possible relations between the clouds, the interior of the planet, and its magnetic field (see Chapter?
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.