394 
Mars. The greater uniformity of the Martian surface 
should lead to more pronounced regularities in weather; 
thus one may be justified in combining observations 
from different years and in accepting a very short 
climatological record with more confidence than would 
be possible for Earth. The severe Martian aridity, as 
manifested by the scarcity of clouds, should also con- 
tribute to this greater uniformity of weather from year 
to year and day to day, since insolation and outgoing 
radiation are not subject to the erratic and complex 
interference experienced on Earth. 
The fact that the Martian year is almost twice ours 
means that the temperature contrast between the sum- 
mer and winter hemispheres ought to be larger on 
Mars. Here on Earth one can deal with the circulation 
qualitatively by assuming it to be driven by the tem- 
perature difference between equator and poles. While 
this would not be completely invalid on Mars it would 
seem that the temperature contrast between the hemi- 
spheres should also be an important factor. That is, 
COSMICAL METEOROLOGY ~ 
larly, helium almost certainly is abundant [3, p. 316]. 
Unfortunately, neither hydrogen nor helium show 
strong spectral lines in the accessible regions of the 
spectrum at the temperatures of the visible surfaces 
of these planets (below 155K) and therefore estimates 
of the amounts of these molecules in the atmospheres 
of the outer planets must be extremely crude. Hydrogen 
and helium differ greatly from most other gases in some 
of their physical constants such as specific heat and, of 
course, molecular weight, so that, for example, the 
adiabatic lapse rate and the relation between pressure, 
temperature, and density are not well known. 
Methane and ammonia are the only constituents of 
the major planets which have been identified spectro- 
scopically. In the atmospheres of all four planets, 
methane is more abundant than ammonia; but the rela- 
tive abundance of the two gases is not constant. The 
absorption of light by methane becomes more pro- 
nounced in the spectra of the more distant planets, 
whereas the ammonia absorption almost disappears. 
ISO =—-:180 
Osc es e 
210 240 270 300 330 
N 
Fie. 2.—A schematic streamline map for Mars in Northern Hemisphere winter. This is the normal telescopic view with 
south at the top. To obtain the usual meteorological view, merely invert the page. The arrows represent observed cloud- 
drift directions. Taken from [2]. 
the long Martian seasons would seem to promote an 
exchange of air between hemispheres as a major feature 
of the circulation. One can check this conclusion by 
computing the magnitude of the interhemispheric ex- 
change from the known rate of transfer of water vapor 
from the dissipating icecap to the forming one [2]. 
This calculation mdicates the necessity for a wind of 
the order of 10-15 m sec blowing from the warm to the 
cold hemisphere all around the equator, at low levels. 
This constitutes an appreciable interhemispheric flow. 
The Characteristics of the Atmospheres of the Major 
Planets 
The four major planets are, in order of distance from 
the sun, Jupiter, Saturn, Uranus, and Neptune. Jupi- 
ter’s linear dimensions are 11 times larger than those 
of the Earth; Neptune’s, 3.9 times larger. The other 
two planets are intermediate. All four planets are mas- 
sive enough to retain hydrogen and, because of the 
cosmic preponderance of hydrogen, it is very likely the 
most important constituent of the major planets. Simi- 
The surfaces of all these planets are sufficiently cold so 
that ammonia can exist in its frozen state. The vapor 
pressure of the gas in equilibrium with this frozen am- 
monia becomes smaller for the more distant planets, so 
that hardly any gaseous ammonia can exist in the at- 
mosphere of Neptune. Ammonia is practically “frozen 
out” on this planet. 
The spectrograph not only indicates the presence of 
ammonia, but also permits an estimate of the total 
amount of ammonia in the line of sight between us and 
the visible ‘‘surface.” If we then assume that the at- 
mosphere is thoroughly mixed, and if we know the ap- 
proximate mean molecular weight of the other gases, 
we can calculate the partial pressure of ammonia at the 
“surface,” the level of the visible markings. Since the 
vapor is presumably saturated or nearly saturated 
with respect to frozen ammonia, measurements of the 
strength of absorption by ammonia can be used to 
determine the planet’s temperature. Such considera- 
tions lead to a temperature of 150K for Jupiter, about 
45 degrees warmer than the temperature expected if 
