Ionosphere

“ But apparently a part—perhaps 10 tons per second—escapes from Io and is captured by the Jovian magnetosphere. Another part contributes to an ionosphere—a tenuous atmosphere of electrons and ions—that surrounds Io. The injection of several tons of particles each second into the magnetosphere has dramatic consequences that can be seen even from Earth.
Direct evidence of an atmosphere on Io was obtained during the Voyager 1 flyby by the IRIS. In the region near the volcano Loki and its associated “lava lake,” infrared spectra clearly showed the signature of sulfur dioxide gas. ”

“ From the early 1950s pulsed oblique ionosphere sounders had shown that the normal ionosphere is much more stable than had previously been thought to be. The physical reason for this is that the incredibly tenuous ionized gas which does the reflecting has a molasses-like viscosity. Of course, there are daily and seasonal changes, but over limited periods of half an hour or so, the F layer at a given location is actually quite well-behaved. It bounces back signals in a nearly constant direction and with nearly constant amplitude—just what is required for good radar performance. ”

“ The free electrons absorb some of the ultraviolet energy that initially set them free and form an ionized layer. Since the atmosphere is bombarded by ultraviolet waves of differing frequencies, several ionized layers are formed at different altitudes. Ultraviolet waves of higher frequencies penetrate the most, so they produce ionized layers in the lower portion of the ionosphere. Conversely, ultraviolet waves of lower frequencies penetrate the least, so they form layers in the upper regions of the ionosphere. ”

“ A probe of the Jovian atmosphere is obtained each time a spacecraft passes behind the planet as seen from the Earth. Passage through the ionosphere and atmosphere alters the phase of the radio telemetry signal, and subsequent computer analysis allows members of the Radio Science Team to reconstruct the profile of the atmosphere. Shown here is the atmospheric temperature as a function of pressure as derived from the Voyager 1 X-band occultation data, corresponding to a point at latitude 12°S, longitude 63°. ”

“ Though no fixed conclusions are yet established about the causes of the brilliant auroral display, yet, as the results of laborious observations, we are assured that the stabler centre of our solar system holds in its powerful sway the several planets at their respective distances, supplying them all with their seasonable light and heat, vibrating sympathetic chords in all, and even controlling under certain—though to us still unknown—laws the electric streamers that flit, apparently lawlessly, in the distant earth’s atmosphere. ”

“ From the fact that one half of the atmosphere, including nearly all of its water vapor, lies below an elevation of three and one half miles, it becomes evident that the greater part of the absorption of the sun’s rays must take place in the lower strata. On clear days the atmosphere absorbs nearly one half of the sun’s heat rays; the remainder reaches the surface of the earth, warms it and in turn is radiated back into the air,—with this difference: that as earth radiation the wave motion of the rays is longer and slower than it was when the rays entered our atmosphere as solar radiation. ”

“ Two elements of meteorology, the temperature and the pressure of the atmosphere, have the very directest bearing upon astronomical work. And this in two ways. An instrument is sensible to heat and cold, and undergoes changes of form, size, or scale, which, however absolutely minute, yet become, with the increased delicacy of modern work, not merely appreciable, but important. So too [245] with the density of the atmosphere: the light from a distant star, entering our atmosphere, suffers refraction; and being thus bent out of its path, the star appears higher in the heavens than it really is. ”

“ The point is that in each case—that of a solidified globe like the earth, surrounded by a comparatively rare atmosphere; that of a partially cooled globe, like Jupiter, enveloped in a dense atmosphere of great depth; and that of a completely gaseous globe like the sun, possessing a sort of shell of partly condensed gases—certain regions near the equator are those in which the greatest disturbance is visible, and in every case, probably, the force of rotation is a powerful factor in the production of these zones of commotion. ”

“ Thus we learn that every particle of matter, and every body in the universe has its aetherial atmosphere so to speak, to which it is held bound by the universal Law of Gravitation. In the case of a satellite or planet or sun or star, that atmosphere will be more or less spherical in shape, decreasing in density as it recedes from the attracting body. ”

“ But the earth, lacking a sufficient surplus of electricity to extend its aurora from the equator to the poles, must content itself by displaying its brilliant light and beauty near its poles, only occasionally extending it half way to the equator. The fact that the earth creates its own aurora shows it manufactures its own light. Every flash of lightning in our midnight sky, every blazing meteor in our atmosphere, prove the earth and planets evolve their own light and heat. ”

“ In the bygone era of which we are speaking the pressure of the atmosphere on the water's surface was 700 lb. or 800 lb. to the square inch; and therefore it could be heated up to a high temperature without evaporating rapidly.
Another thing began to happen in those days. All bodies in space attract one another; the Sun attracts its planets; the planets attract the Sun and their satellites; and the satellites in their turn attract the planets. Ages before the earth had a moon these forces were at work. ”

“ In the upper atmosphere of a planet, the lighter gases tend to diffuse, rising above their heavier neighbors, and unusual chemical reactions take place as the action of sunlight breaks some chemical bonds and stimulates the formation of others. The study of these tenuous regions of planetary atmospheres is called aeronomy. Many of the exotic chemical processes that occur can best be studied by examining radiation of very short wavelength, and it is to these problems that much of the work of the UVS team is directed. ”

“ PRESSURES IN STELLAR ATMOSPHERES THE theory of thermal ionization enables us to make an analysis of the spectrum of the stellar reversing layer by predicting the number of atoms of any given kind that will be effective in absorbing light from the interior of the star, under given conditions, and by comparing the predicted values with the observed intensities of the corresponding absorption lines. The results depend partly on definite physical constants associated with the atoms—the ionization and excitation potentials, and the arrangement of the electrons around the nucleus. ”

“ We shall also find in such electric currents an explanation of sun-spots. It is not meant that a full knowledge can be obtained of their minute constitution, nor is it necessary; but the equatorial belt of six degrees, nearly free from sun-spots, we can readily understand to be caused—since sun-spots are depressions in the photosphere down to the deeper and denser cloud strata beneath—by the equatorial piling up of the sun’s atmosphere by its rotation. ”

“ Obeying a law which has been demonstrated in the laboratory, the particles then follow the lines of force toward the poles. While they are above the equatorial regions they do not become luminescent, because at the great elevation that they there occupy there is virtually no atmosphere; but as they pass on toward the north and the south they begin to descend with the lines of force, curving down to meet at the poles; and, encountering a part of the atmosphere comparable in density with what remains in an exhausted Crookes tube, they produce a glow of cathode rays. ”

“ Clouds of them may be supposed to be continually swept away from the sun into surrounding space, moving mostly in or near the plane of the solar equator, where the greatest activity, as indicated by sunspots and related phenomena, is taking place. As they pass outward into space many of them encounter the earth. If the earth, like the moon, had no atmosphere the particles would impinge directly on its surface, giving it a negative electric charge. ”

“ Thus, there is a constant current in the higher regions of the atmosphere, proceeding from the equator northward and southward to the poles; and, if the earth were at rest, there would be a constant wind in the lower regions of the atmosphere blowing directly from the poles to the equator, while in equatorial regions the two streamlets would meet, and neutralize each other’s influence. But the earth is not at rest! ”

“ This process would be gradual, because the molecules of a gas fly in all directions, only a small proportion having their trajectories directly away from the center of the globe on which they are held. But a singular consequence of this theory is that interplanetary space must contain an enormous number of such wandering molecules, and every attracting body must draw more or less of them to its surface, thus forming an atmosphere for itself. ”

“ This, to the eye, certainly looks like a definite shell, but some theorists have been so impressed with the difficulty of conceiving that a gaseous body like the Sun could, under the conditions of such stupendous temperatures as there exist, have any defined limit at all, that they deny that what we see on the Sun is a real boundary, and argue that it only appears so to us through the effects of the anomalous refraction or dispersion of light. ”

“ The rotation of the earth on its axis forces the terrestrial atmosphere, by its centrifugal motion, in undue proportion, around the equatorial belt, causing the same sort of atmospheric thinning at the poles which we see in the solar photosphere at its corresponding parts. ”

“ The observations are also sensitive to special processes in the Jovian atmosphere resulting from the magnetosphere. At the very top of the atmosphere, energetic charged particles interacting with the atmospheric molecules produce ultraviolet aurorae that indicate the location and nature of the bombarding electrons and ions. Emissions from atoms in the extended gas clouds around Io and possibly around other satellites were also expected to be observable. ”

“ If the points in which the carbons when prolonged would intercept the sphere are called the poles, and the line where the horizontal plane through the arc would intercept the sphere is called the equator, we might consider the sphere divided up by lines of latitude into zones, each of which would be differently illuminated. The total quantity of light or the total illumination of each zone is the product of the area of the zone and the intensity of the light falling on the zone measured in candle-power. ”

“ But an atmosphere 2,000 times rarer than our air can scarcely be regarded as an atmosphere at all. The contents of an air-pump receiver can seldom be rarefied to a greater extent than to about 1/1000 of the density of air at the earth’s surface, with the best of pneumatic machines; and the lunar atmosphere, if it exist at all, is thus proved to be twice as attenuated as what we are accustomed to recognise as a vacuum. ”

“ Although even in the hottest stars three ionizations is the greatest number observed, most of the elements that constitute the stellar atmosphere are appreciably ionized at temperatures greater than 4000°, so that the partial electron pressure is at least half the total pressure. ”

“ Direction of Ray of Heat.--The question as to the path which a ray of heat takes may best be attacked by finding out what is the path which a ray of light takes in its progress through the Aether. When we come to deal with light, we shall find that it has been experimentally proved that the path of a ray of light is that of a straight line through space; so that if we have any body emitting light, the rays of light will proceed from that body in straight lines, with decreasing intensity, according to the law of inverse squares, the same as Gravitation. ”

“ The concentrated rays of the Sun at midday of course bring them so closely together, and direct, that the Earth’s revolution comes squarely across them, as can be demonstrated across the teeth of a comb, thus showing a greater pressure than drawn obliquely.
That heat can come directly from the Sun seems an impossibility without some medium of contact, which through the coldness and a barrenness of space does not seem to exist. ”

“ This ingenious theory, in brief, is that the rotation of the sun on its axis causes a suction in the manner of a fan, at the poles, and a tangential projection, at the equator, of a disk-like stream of gaseous matter into space. The light and heat of the sun, dispersed through space, slowly but continuously act upon the compound gases with which space is universally pervaded to disassociate them into their elements. ”

“ If we conceive the entire globe spotted with high and low areas, we may picture the air surging upward in the lows, flowing outward under the isothermal layer, descending 374in the highs, then flowing outward along the earth’s surface toward the lows in a continuous cycle. Thus, chiefly is maintained the vast and multifold circulation of the atmosphere over the entire world. ”

“ If we take account, however, of the direct influence of temperature on ionization, which acts much more strongly in the opposite direction, we must expect equal ionization in the more advanced types for much smaller g and higher luminosities, contrary to the empirical reduction curves. ”