Io: a surface evaporite deposit?

A model is suggested for Io's surface composition involving evaporite salt deposits, rich in sodium and sulfur. According to this model, these deposits were produced as a result of the migration of salt-saturated aqueous solutions to Io's surface from a warm or hot interior followed by loss of the water to space. This model satisfies cosmochemical constraints based on Io's initial composition, current density, and thermal history. Salt-rich assemblages are easily derivable from the leaching of carbonaceous chondritic material; the chemical and optical properties of such deposits, after modification by irradiation, can be used to explain Io's overall albedo and spectral reflectance, its dark reddish poles, and the observed sodium emission as well as or better than other currently suggested materials.     

Io: ground-based observations of hot spots

Observations of Io in eclipse demonstrate conclusively that Io emits substantial amounts of radiation at 4.8 and 3.8 micrometers and a measurable amount at 2.2 micrometers. Color temperatures derived from the observations fit blackbody emission at 560 K. The required source area to yield the observed 4.8-micrometer flux is approximately 5 x 10(-5) of the disk of Io and is most likely comprised of small hot spots in the vicinity of the volcanoes.     

Jupiter: its infrared spectrum from 16 to 40 micrometers

Spectral measurements of the thermal radiation from Jupiter in the band from 16 to 40 micrometers are analyzed under the assumption that pressure-broadened molecular hydrogen transitions are responsible for the bulk of the infrared opacity over most of this spectral interval. Both the vertical pressure-temperature profile and the molecular hydrogen mixing ratio are determined. The derived value ofthe molecular hydrogen mixing ratio, 0.89 +/- 0.11, is consistent with the solar value of 0.86.     

Io: longitudinal distribution of sulfur dioxide frost

Twenty spectra of Io (0.26 to 0.33 micrometer), acquired with the International Ultraviolet Explorer spacecraft, have been studied. There is a strong ultraviolet absorption shortward of 0.33 micrometer that is consistent with earlier ground-based spectrophotometry; its strength is strongly dependent on Io's rotational phase angle at the time of observation. This spectral feature and its variation are interpreted as indicative of a longitudinal variation in the distribution of sulfur dioxide frost on Io. The frost is most abundant at orbital longitudes 72 degrees to 137 degrees and least abundant at longitudes 250 degrees to 323 degrees . Variations in spectral reflectivity between 0.4 and 0.5 micrometer, reported in earlier ground-based spectral studies, correlate inversely with variations in reflectivity between 0.26 and 0.33 micrometer. It is concluded that this is because the Io surface component with the highest visible reflectivity (sulfur dioxide frost) has the lowest ultraviolet reflectivity. At least one other component is present and may be sulfur allotropes or alkali sulfides. This model is consistent with ground-based ultraviolet, visible, and infrared spectrophotometry. Comparison with Voyager color photographs indicates that the sulfur dioxide frost is in greatest concentration in the "white" areas on Io and the other sulfurous components are in greatest concentration in the "red" areas.     

Galileo at Io: results from high-resolution imaging

During late 1999/early 2000, the solid state imaging experiment on the Galileo spacecraft returned more than 100 high-resolution (5 to 500 meters per pixel) images of volcanically active Io. We observed an active lava lake, an active curtain of lava, active lava flows, calderas, mountains, plateaus, and plains. Several of the sulfur dioxide-rich plumes are erupting from distal flows, rather than from the source of silicate lava (caldera or fissure, often with red pyroclastic deposits). Most of the active flows in equatorial regions are being emplaced slowly beneath insulated crust, but rapidly emplaced channelized flows are also found at all latitudes. There is no evidence for high-viscosity lava, but some bright flows may consist of sulfur rather than mafic silicates. The mountains, plateaus, and calderas are strongly influenced by tectonics and gravitational collapse. Sapping channels and scarps suggest that many portions of the upper approximately 1 kilometer are rich in volatiles.     

Io: evidence for silicate volcanism in 1986

Infrared observations of Io during the 1986 apparition of Jupiter indicate that a large eruptive event occurred on the leading side of Io on 7 August 1986, Universal Time. Measurements made at 4.8, 8.7, and 20 micrometers suggest that the source of the event was about 15 kilometers in radius with a model temperature of approximately 900 Kelvin. Together with previously reported events, these measurements indicate that high-temperature volcanic activity on the leading side of Io may be more frequent than previously thought. The inferred temperature is significantly above the boiling point of sulfur in a vacuum(715 Kelvin) and thus constitutes strong evidence for active silicate volcanism on the surface of Io.     

Attenuation on an Earth-space path measured in the wavelength range of 8 to 14 micrometers

A telescope operating over the wavelength range of 8 to 14 micrometers has been added to the Crawford Hill sun tracker for the purpose of measuring attenuation in that atmospheric window. Over a 9-month period the attenuation (typically from clouds) exceeded 10, 20, and 30 decibels for 48, 43, and 34 percent of the time.     

Earth as an intense planetary radio source: similarities to jupiter and saturn

Observations from spacecraft have revealed naturally occurring radio emission emanating from two regions near Earth. The characteristics of these two sources suggest a correlation with areas of known electron precipitation. The possibility of a similar production mechanism for observed nonthermal radio emissions from other planetary magnetospheres permits the polar magnetic field strengths of Jupiter and Saturn to be predicted.     

From dimming to brightening: decadal changes in solar radiation at Earth's surface

Variations in solar radiation incident at Earth's surface profoundly affect the human and terrestrial environment. A decline in solar radiation at land surfaces has become apparent in many observational records up to 1990, a phenomenon known as global dimming. Newly available surface observations from 1990 to the present, primarily from the Northern Hemisphere, show that the dimming did not persist into the 1990s. Instead, a widespread brightening has been observed since the late 1980s. This reversal is reconcilable with changes in cloudiness and atmospheric transmission and may substantially affect surface climate, the hydrological cycle, glaciers, and ecosystems.     

A Magnetic Signature at Io: Initial Report from the Galileo Magnetometer

During the inbound pass of the Galileo spacecraft, the magnetometer acquired 1 minute averaged measurements of the magnetic field along the trajectory as the spacecraft flew by Io. A field decrease, of nearly 40 percent of the background jovian field at closest approach to Io, was recorded. Plasma sources alone appear incapable of generating perturbations as large as those observed and an induced source for the observed moment implies an amount of free iron in the mantle much greater than expected. On the other hand, an intrinsic magnetic field of amplitude consistent with dynamo action at Io would explain the observations. It seems plausible that Io, like Earth and Mercury, is a magnetized solid planet.     

Hemolysis near an ultrasonically pulsating gas bubble

A small volume of an erythrocyte suspension was subjected to the action of a manipulated gas bubble set into stable oscillation at 20 kilohertz. Release of hemoglobin occurred when the oscillation amplitude exceeded a critical threshold. Hydrodynamic stresses resulting from acoustically induced small-scale eddying motion near the bubble may be the mechanism of hemolysis.     

Io volcanism seen by new horizons: a major eruption of the Tvashtar volcano

Jupiter's moon Io is known to host active volcanoes. In February and March 2007, the New Horizons spacecraft obtained a global snapshot of Io's volcanism. A 350-kilometer-high volcanic plume was seen to emanate from the Tvashtar volcano (62 degrees N, 122 degrees W), and its motion was observed. The plume's morphology and dynamics support nonballistic models of large Io plumes and also suggest that most visible plume particles condensed within the plume rather than being ejected from the source. In images taken in Jupiter eclipse, nonthermal visible-wavelength emission was seen from individual volcanoes near Io's sub-Jupiter and anti-Jupiter points. Near-infrared emission from the brightest volcanoes indicates minimum magma temperatures in the 1150- to 1335-kelvin range, consistent with basaltic composition.     

Electron acceleration by a wake field forced by an intense ultrashort laser pulse

Plasmas are an attractive medium for the next generation of particle accelerators because they can support electric fields greater than several hundred gigavolts per meter. These accelerating fields are generated by relativistic plasma waves-space-charge oscillations-that can be excited when a high-intensity laser propagates through a plasma. Large currents of background electrons can then be trapped and subsequently accelerated by these relativistic waves. In the forced laser wake field regime, where the laser pulse length is of the order of the plasma wavelength, we show that a gain in maximum electron energy of up to 200 megaelectronvolts can be achieved, along with an improvement in the quality of the ultrashort electron beam.     

Optical matter: crystallization and binding in intense optical fields

Properly fashioned electromagnetic fields coupled to microscopic dielectric objects can be used to create arrays of extended crystalline and noncrystalline structures. Organization can be achieved in two ways: In the first, dielectric matter is transported in direct response to the externally applied standing wave optical fields. In the second, the external optical fields induce interactions between dielectric objects that can also result in the creation of complex structures. In either case, these new ordered structures, whose existence depends on the presence of both light and polarizable matter, are referred to as optical matter.     

Plasma waves near venus: initial observations

The Pioneer Venus electric field detector observes significant effects of the interaction of the solar wind with the ionosphere of Venus all along the orbiter trajectory. Information is obtained on plasma oscillations emitted by suprathermal electrons beyond the bows shock, on sharp and diffuse shock structures, and on waveparticle interaction phenomena that are important near the boundary of the dayside ionosphere.     

Magnetite: Behavior near the Single-Domain Threshold

Maximum values for the single-domain threshold d(0) and superpara-magnetic threshold d(8) in pure magnetite are found to be 570+/-50 and 350+/-50 angstroms, respectively. Particles larger than do but smaller than about 0.25 micron have size-dependent saturation remanences and coercive forces like those of multidomain particles, but intense and stable thermoremanent magnetization like that of single-domain particles. The presence of magnetite grains in this size range could account for the essentially single-domain character of stable natural remanence in many volcanic and intrusive rocks.     

Atmospheric Absorption Anomalies in the Ultraviolet near an Altitude of 50 Kilometers

Rocket-borne radiometer determinations of ozone distributions by absorption of ultraviolet sunlight show anomalous eflects near 3000 angstroms. The instrument uses four 40-angstrom filters in the spectral region between 2650 and 3300 angstroms. At altitudes below 40 kilometers, signals from filters centered near 3000 angstroms appear reduced at least 25 percent below calculated values. However, at higher altitudes an unpredicted sharp increase in signals is observed. These effects are inconsistent with ozone absorption and cannot be ascribed to instrument characteristics. A previously unobserved absorption band of an atmospheric constituent, possibly the metastable excited states of molecular oxygen O(2)((1)Delta(g)) or O(2)((1)Sigma(g)+) can account for the anomalous effects.     

Elephant seals: genetic variation and near extinction

Blood samples from northern elephant seals (Mirounga angustirostris), representing five breeding colonies in California and Mexico, were surveyed electrophoretically for protein variation reflecting underlying genetic differences. No polymorphisms were found among 21 proteins encoded by 24 loci. This uniform homozygosity may be a consequence of fixation of alleles brought about by the decimation of this species by sealers in the last century.