Venus Strategy for Exploration (1970) / Chapter Skim
Currently Skimming:
4 LOWER ATMOSPHERE
4 LOWER ATMOSPHERE
Pages 30-49
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 30... ...
One of the most difficult planetary measurements is the determination of wind velocity in a way that is useful to the theory of general planetary circulations. Radar techniques can measure the motion of an entry probe as it approaches the ground.
|
From page 31... ...
Second, the very slow planetary rotation and the dense, ubiquitous cloud cover indicate a different thermal and dynamical control of the planetary flow pattern. Thus we can present meteorological theory with a different set of circumstances than those presented by the earth.
|
From page 32... ...
Any knowledge of the state represented by Venus may be overwhelmingly important. PHYSICAL STRUCTURE OF THE LOWER ATMOSPHERE Direct measurements of temperature and pressure, with simple and reliable instruments, are among the primary tasks that should be undertaken in any future investigation of the lower atsmosphere of Venus by spacecraft.
|
From page 33... ...
It is important that three small entry probes should accompany a larger entry vehicle into the atmosphere of Venus. There are several factors, discussed later, which constrain the entry point of the main probe to lie within 35° of the subearth point.
|
From page 34... ...
This kind of measurement will complement and reinforce the data obtained from entry probes. RADIATIVE HEAT BUDGET Venus is characterized by two features that provide a chal lenge to our understanding of atmospheric science: high sur face temperatures (700 K)
|
From page 35... ...
The relative simplicity and compactness of solar-flux sensors renders it feasible to place such sensors on board all probes. Thermal flux plates have been employed in terrestrial meteorology to measure infrared cooling rates.
|
From page 36... ...
Those volatile elements, such as nitrogen, mercury, and the rare gases, which would be in capable of forming condensed compounds at the present surface temperature of Venus, would currently reside in the atmosphere. ~hus an analysis of the abundances of these elements in the atmosphere would contribute directly to an understanding of the origin of the entire planet and, by comparison with the atmospheres of the earth and Mars, might permit the develop ment of consistent models for the origins of the terrestrial planets.
|
From page 37... ...
It can be seen that cempesitiDnal data .on the lcwer atmDsphere and surface temperatures at widely separated pcints are bath relevant te the surface mineralegy and petrclcgy, and that the results .of such measurements weuld be useful in the design .of future petrDlcgical, mineralDgical, and geechemical experiments. Current epinien .on the nature .of the cleuds .ofVenus favars the view that the clauds are farmed by ccndensaticI'l.of gaseaus censtituents .of the atmesphere.
|
From page 38... ...
The atmospheric composition as a function of altitude, tied as it is to the problem of the location, mass, and opti cal properties of cloud layers, assumes considerable importance when one attempts to understand the thermal structure and ther mal balance of the atmosphere. The atmospheric opacity in the infrared regions is strongly dependent on the abundances of trace atmospheric constituents.
|
From page 39... ...
The vertical sampling frequency should be sufficient so that at least two analyses could be conducted at widely separated altitudes above the visible cloud layer, at least two more between the 250 and 400 K levels, and at least one or two in the deep atmosphere. At least one analysis capable of giving the He, Ne, and Ar isotopic composition is essential.
|
From page 40... ...
In the event that the cloud particles are not condensa tion products, the changes in the particle-size spectrum may provide clues to electrostatic processes active in agglomera tion and coagulation that increase particle size. Carbon di oxide is an excellent insulator, and frictionally produced electrification is a distinct possibility.
|
From page 41... ...
Whether cloud particles are condensation elements or dust scoured from the planet's surface has important ramifications in the atmosphere's dynamics and heat budget. The solar flux transported through the atmosphere depends on the absorption and scattering properties of the atmospheric constituents.
|
From page 42... ...
A nephe lometer will allow the visibility near the planet's surface to be determined. Infrared CZoud Sensor Infrared sensors may be employed to derive data on the vertical distribution of cloud particles that emit the measured infrared radiances.
|
From page 43... ...
The trument thus provides a vertical profile of effective cloud density in a particularly simple way. Condensimete~-EVapopimete~ An essential datum in studying the clouds whether they are in equilibrium with the gas phase or 'Vlhethey are solid matter raised from the planet I s surface by the action of winds.
|
From page 44... ...
We cannot hope to obtain this informa tion for all cloud layers in a simple manner, but the upper most cloud layer can be observed directly by visual and ther mal imaging. A limited number of high-contrast images with a horizontal resolution of about 2 km or better (such as might be obtained by the Venus/Mercury flyby)
|
From page 45... ...
The response time of the atmosphere of Venus to solar heating is long compared to a Venus day, up to a level approximately coincident with the cloud top. The atmosphere below that level experiences an average heating like the earth, symmetric about the rotation axis, highest at the equator, and vanishing at the poles.
|
From page 46... ...
Further, the relation ship between the Hadley and the 4-day circulation, if any, needs observational and theoretical elucidation. Motions of planetary atmospheres result from horizontal and vertical density gradients.
|
From page 47... ...
a temperature measured to 1 percent accuracy is also desirable. To determine the lapse rate between successive determinations to within 3 percent of the adiabatic value, a relative accuracy of 0.2 K will be required, but even 1 K is useful.
|
From page 48... ...
This will provide essential information on light levels and contrast of the cloud features of Venus, but it will pass by too rapidly to provide the coverage in time desired for wind measurements. A simple thermal radiometer, looking down in a window region of the spectrum, would allow temperature maps of the cloud surface to be drawn.
|
From page 49... ...
There may even b~ a few kilometers of isothermal atmosphere. If this is so, the surface temperature will provide a measure of the atmospheric temperature in the lowest one or two scale heights.
|
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.