The magnetic fields of Mercury,Venus and Mars

Just as clearly as Mariner 10 established that Mercury has an intrinsic magnetic field, the Pioneer Venus orbiter has established that Venus has no significant intrinsic field. This is perhaps the opposite of what might be expected. Mercury, a small planet might be expected to cool rapidly and its internal dynamo to cease, while Venus, which is almost as large as the Earth, should not have lost much heat. On the contrary the source of energy of the Mercury dynamo appears to be extant whereas that of Venus appears to be extinct.The existence of a Martian magnetic field is controversial. No unambiguous signature of a Martian magnetic field has been reported. If the field on the nightside of Mars is of planetary rather than solar origin the Russian Mars spacecraft observations indicate the Martian dipole lies near the planetary equator rather than its pole.     

Schumann resonance frequency and conductivity in the nighttime ionosphere of Mars: A source for lightning

We have solved the Maxwellian equations of electromagnetic waves which oscillate within the cavity formed in the lower ionosphere of Mars between 0 and 70?km. The electrical conductivity and Schumann Resonance (SR) frequencies are calculated in the lower ionosphere of Mars, in the presence of a major dust storm that occurred in Martian Year (MY) 25 at low latitude region (25°–35°S). It is found that the atmospheric conductivity reduced by one to two orders of magnitude in the presence of a dust storm. It represents a small dust layer at about 25–30?km altitudes where lightning can occur. We also found that the SR frequencies peak at?～18?km with values 19.9, 34.5 and 48.8?Hz for the modes l?=?1, 2 and 3, respectively, in the non-homogeneous medium. Our results indicate that practical or measurable values of SR are dependent on the altitudes.     

A quantitative assay of biologically important compounds in simulated primitive Earth experiments.

A CH4-N2-H2OV gas mixture was subjected to a high voltage (20 kV), high frequency (0.3 MHz) electric discharge. The energy input in the electric discharge was varied from 0.016 to 3.048 MJ mol-1. The chemical yields (G), expressed as the number of molecules formed or destroyed per 100 eV of energy input were calculated for several products. The G values calculated at the lowest energy input were (-CH4) = 6.48; (-N2) = 2.51; (C2H2) = 1.16; (HCN) = 0.215; (CH3CHO) = 0.115; (CH3CH2CHO) = 0.00161; (CH3(CH2)2CHO) = 0.0165; ((CH2CO2H)2) = 0.0000339; (CH4 --> Solid material) = 0.196; (N2 --> Solid material) = 0.00355. This is the first report in prebiotic studies in which the G values of various products in electric discharge experiments are determined. This type of study is needed in order to get a better insight into the relative role of electric discharges on the primitive Earth.     

Neutral atmosphere and crustal magnetization as factors determining differences in plasma convection and magnetic fields distribution in the ionospheres of Mars and Venus

The pattern of the magnetic field/plasma convection can be, to some extent, recovered from the magnetic field measurements by employing either theoretical or numerical models. We use the MAG/ER day-time measurements of the magnetic field at the altitudes from 90 to 180 km during the elliptical orbits of MGS. Analysis of the altitude variation of the characteristics of the large-scale magnetic fields, which were measured some distance away from strong crustal magnetic anomalies, is summarized. The low density of the Martian atmosphere together with the crustal magnetization result in critical differences in plasma convection which are followed by remarkable differences of the magnetic field features within the ionosphere of Venus and Mars (even in its northern hemisphere where the crustal magnetization is, on the average, low) and distribution of currents.     

Heterogeneous solid/gas chemistry of organic compounds related to comets,meteorites, Titan,and Mars: Laboratory and in lower Earth orbit experiments

To understand the evolution of organic molecules involved in extraterrestrial environments and with exobiological implications, many experimental programs in the laboratory are devoted to photochemical studies in the gaseous phase as well as in the solid state. The validity of such studies and their applications to extraterrestrial environments can be questioned as long as experiments conducted in space conditions, with the full solar spectrum, especially in the short wavelength domain, have not been implemented. The experiments that are described here will be carried out on a FOTON capsule, using the BIOPAN facility, and on the International Space Station, using the EXPOSE facility. Vented and sealed exposition cells will be used, which will allow us to study the chemical evolution in the gaseous phase as well as heterogeneous processes, such as the degradation of solid compounds and the release of gaseous fragments.     

Gravitropism of basidiomycetous fungi--on Earth and in microgravity.

In order to achieve perfect positioning of their lamellae for spore dispersal, fruiting bodies of higher fungi rely on the omnipresent force gravity. Only accurate negatively gravitropic orientation of the fruiting body cap will guarantee successful reproduction. A spaceflight experiment during the STS-55 Spacelab mission in 1993 confirmed that the factor gravity is employed for spatial orientation. Most likely every hypha in the transition zone between the stipe and the cap region is capable of sensing gravity. Sensing presumably involves slight sedimentation of nuclei which subsequently causes deformation of the net-like arrangement of F-actin filament strands. Hyphal elongation is probably driven by hormone-controlled activation and redistribution of vesicle traffic and vesicle incorporation into the vacuoles and cell walls to subsequently cause increased water uptake and turgor pressure. Stipe bending is achieved by way of differential growth of the flanks of the upper-most stipe region. After reorientation to a horizontal position, elongation of the upper flank hyphae decreases 40% while elongation of the lower flank slightly increases. On the cellular level gravity-stimulated vesicle accumulation was observed in hyphae of the lower flank.     

Dose equivalent, absorbed dose and charge spectrum investigation in low Earth orbit.

Particle intensity, dose equivalent and absorbed dose have been measured on board the space shuttle Endeavour during STS-108 in December 2001 by Dublin Institute for Advanced Studies (DIAS). The dose estimates are based on very accurate measurements of recoils produced in CR-39 by cosmic ray primary and secondary protons and heavier nuclei and by secondary neutrons. The corresponding LET spectra were used to determine dose equivalent and absorbed dose values. Estimates of the total flux of Z > or = 2 nuclei have been undertaken and a preliminary charge spectrum was measured. Some comparisons are made with preliminary data obtained on STS-105 (ISS Expedition) and other missions using CR-39 detectors.     

Earth benefits of interdisciplinary CELSS-related research by the NSCORT in Bioregenerative Life Support.

Earth benefits of research from the NSCORT in Bioregenerative Life Support will include the following: development of active control mechanisms for light, CO2, and temperature to maximize photosynthesis of crop plants during important phases of crop development; automation of crop culture systems; creation of novel culture systems for optimum productivity; creation of value-added crops with superior nutritional, yield, and waste-process characteristics; environmental control of food and toxicant composition of crops; new process technologies and novel food products for safe, nutritious, palatable vegetarian diets; creation of menus for healthful vegetarian diets with psychological acceptability; enzymatic procedures to degrade recalcitrant crop residues occurring in municipal waste; control-system strategies to ensure sustainabilty of a CELSS that will enable management of diverse complex systems on Earth.     

Production of hydrocarbons and nitriles by electrical processes in Titan's atmosphere.

Although lightning has not been observed in Titan's atmosphere, the presence of methane rain in the troposphere suggests the possibility of electrical activity in the form of corona and/or lightning discharges. Here we examine the chemical effects of these electrical processes on a Titan simulated atmosphere composed of CH4 in N2 at various mixing ratios. Corona discharges were simulated in two different experimental arrays. For the detection of reactive intermediates we used a mass spectrometer to study the main positive ions arising by bombarding low-energy electrons from a hot filament into low-pressure methane. The final stable products, generated by applying a high voltage in a coaxial reactor with either positive or negative polarity, were separated and detected by gas chromatography-Fourier transform infrared spectroscopy and electron impact mass spectrometry (GC-FTIR-MS). Lightning discharges were simulated by a hot and dense plasma generated by a Nd-YAG laser and the final products were separated and detected by GC-FTIR-MS. Corona discharges produce linear and branched hydrocarbons as well as nitriles whereas lightning discharges generate mainly unsaturated hydrocarbons and nitriles. Lightning discharges are about 2 orders of magnitude more efficient in product formation than corona discharges.     

Production and evolution of carbonaceous material by ion irradiation in space.

We review recent experimental studies concerning the evolution, driven by ion irradiation, of carbonaceous material from frozen gas to a refractory molecular solid. Under further irradiation the latter changes to a polymer-like material and ultimately to amorphous carbon. Most of the results have been obtained by "in situ" and remote IR and Raman spectroscopy. The results have been applied to demonstrate that molecular solids may be easily formed by irradiation of frozen mantles in dense interstellar clouds. Polymer-like material and amorphous carbons may result by further irradiation of organic mantles on grains in the diffuse interstellar medium. Those grains, during the aggregation to form extended bodies like comets (T-Tau phase of the Sun), are further modified. These latter are also irradiated, after the comet formation, during their long stay in the Oort cloud. In particular it has been suggested that comet may develop an ion-produced cometary organic crust that laboratory evidences show to be stable against temperature increases experienced during passages near the Sun. The comparison between the Raman spectra of some IDP (Interplanetary Dust Particles) and the Raman spectra of some ion-produced amorphous carbons, is also discussed.     

Formation of bioorganic compounds in simulated planetary atmospheres by high energy particles or photons.

Various types of organic compounds have been detected in Jupiter, Titan, and cometary coma. It is probable that organic compounds were formed in primitive Earth and Mars atmospheres. Cosmic rays and solar UV are believed to be two major energy sources for organic formation in space. We examined energetics of organic formation in simulated planetary atmospheres. Gas mixtures including a C-source (carbon monoxide or methane) and a N-source (nitrogen or ammonia) was irradiated with the followings: High energy protons or electrons from accelerators, gamma-rays from 60Co, UV light from a deuterium lamp, and soft X-rays or UV light from an electron synchrotron. Amino acids were detected in the products of particles, gamma-rays and soft X-rays irradiation from each gas mixture examined. UV light gave, however, no amino acid precursors in the gas mixture of carbon monoxide, nitrogen and nitrogen. It gave only a trace of them in the gas mixture of carbon monoxide, ammonia and water or that of methane, nitrogen and water. Yield of amino acid precursors by photons greatly depended on their wavelength. These results suggest that nitrogen-containing organic compounds like amino acid precursors were formed chiefly with high energy particles, not UV photons, in Titan or primitive Earth/Mars atmospheres where ammonia is not available as a predominant N-source.     

A step in embryonic axis specification in Xenopus laevis is simulated by cytoplasmic displacements elicited by gravity and centrifugal force.

Determination of the body pattern in Xenopus embryos is known to involve at least six steps. One of these steps can be experimentally simulated by inclining the fertilized egg with respect to gravity or centrifugal force (10-30 g x 4 min, directed 90 degrees to the animal-vegetal axis). In these eggs, the dorsal structures of the body axis form from the side of the egg that was uppermost in the gravitational or centrifugal field. This topography is seen even if the sperm entry point side (the prospective ventral side in control eggs) was uppermost. In addition, conjoined twin embryos form at very high frequencies in response to certain conditions of single or double centrifugation. Cytological analysis shows that the dorsal structures invariably form from the side(s) of the egg away from which vegetal cytoplasm was displaced. This is similar to the situation in the unperturbed egg, where the subcortical cytoplasm of the vegetal hemisphere rotates some 30 degrees relative to the surface, and the dorsal structures form from the side of the egg away from which the subcortical cytoplasm moved. The displacements elicited by centrifugation probably substitute for the normal displacements brought about by the subcortical rotation. These and other data suggest that the subcortical rotation is a crucial step in the process of axis determination. The subcortical rotation is an autonomous activity of the activated egg, and can displace cytoplasm against gravity. I believe that the subcortical rotation will function normally at microgravity, and I expect that overall development and axis polarity at microgravity will be normal. This will be tested in spaceflight.     

Vertical distribution of SO2 in upper cloud layer of Venus and Origin of U.V.-absorption

It is shown that decline of spherical albedo of Venus toward the ultraviolet can be explained by the presence of two absorbing agents: a) SO₂, for which abundance is 10¹¹ cm^?3 at height 68 km and scale height is about 1 km; b) some unknown aerosol absorbent, possibly a 1% FeCl₃ admixture in a sulfuric acid concentrated solution. A mechanism of aerosol formation is proposed.     

Electron densities and temperatures in the Venus ionosphere: Effects of solar EUV,solar wind pressure and magnetic field

The Venus ionosphere is influenced by variations in both solar EUV flux and solar wind conditions. On the dayside the location of the topside of the ionosphere, the ionopause, is controlled by solar wind dynamic pressure. Within the dayside ionosphere, however, electron density is affected mainly by solar EUV variations, and is relatively unaffected by solar wind variations and associated magnetic fields induced within the ionosphere. The existence of a substantial nightside ionosphere of Venus is thought to be due to the rapid nightward transport of dayside ionospheric plasma across the terminator. Typical solar wind conditions do not strongly affect this transport and consequently have little direct influence on nightside ionospheric conditions, except on occasions of extremely high solar wind dynamic pressure. However, both nightside electron density and temperature are affected by the presence of magnetic field, as in the case of ionospheric holes.     

Characterization of complex organic compounds formed in simulated planetary atmospheres by the action of high energy particles.

A wide variety of organic compounds, which are not simple organics but also complex organics, have been found in planets and comets. We reported that complex organics was formed in simulated planetary atmospheres by the action of high energy particles. Here we characterized the experimental products by using chromatographic and mass spectrometric techniques. A gaseous mixture of CO, N2 and H2O was irradiated with high energy protons (major components of cosmic rays). Water-soluble non-volatile substances, which gave amino acids after acid-hydrolysis, were characterized by HPLC and mass spectrometry. Major part of the products were complex compounds with molecular weight of several hundreds. Amino acid precursors were produced even when no water was incorporated with the starting materials. It was suggested that complex molecules including amino acid precursors were formed not in solution from simple molecules like HCN, but directly in gaseous phase.     

Production and action of cytokines in space.

B6MP102 cells, a continuously cultured murine bone marrow macrophage cell line, were tested for secretion of tumor necrosis factor-alpha and Interleukin-1 during space flight. We found that B6MP102 cells secreted more tumor necrosis factor-alpha and interleukin-1 when stimulated in space with lipopolysaccharide than controls similarly stimulated on earth. This compared to increased secretion of interferon-beta and -gamma by lymphocytes that was measured on the same shuttle flights. Although space flight enhanced B6MP102 secretion of tumor necrosis factor-alpha, an experiment on a subsequent space flight (STS-50) found that cellular cytotoxicity, mediated by tumor necrosis factor-alpha, was inhibited.     

Proton flare and magnetic storm effect in the vicinity of the Earth.

We have developed a model and associated computational procedure for estimating energetic proton exposures during a major solar proton event that occur in combination with a large magnetic storm. Transmission functions for solar protons are computed using geomagnetic vertical cutoff data for quiescent and disturbed conditions. Predicted exposures in low altitude polar orbit are found to be orders of magnitude greater for severe magnetic storm conditions than are corresponding exposures in the absence of major disturbances. We examine the response scenario for the events of November 1960 as an example.     

Critical issues in connection with human missions to Mars: protection of and from the Martian environment.

Human missions to Mars are planned to happen within this century. Activities associated therewith will interact with the environment of Mars in two reciprocal ways: (i) the mission needs to be protected from the natural environmental elements that can be harmful to human health, the equipment or to their operations; (ii) the specific natural environment of Mars should be protected so that it retains its value for scientific and other purposes. The following environmental elements need to be considered in order to protect humans and the equipment on the planetary surface: (i) cosmic ionizing radiation, (ii) solar particle events; (iii) solar ultraviolet radiation; (iv) reduced gravity; (v) thin atmosphere; (vi) extremes in temperatures and their fluctuations; and (vii) surface dust. In order to protect the planetary environment, the requirements for planetary protection as adopted by COSPAR for lander missions need to be revised in view of human presence on the planet. Landers carrying equipment for exobiological investigations require special consideration to reduce contamination by terrestrial microorganisms and organic matter to the greatest feasible extent. Records of human activities on the planet's surface should be maintained in sufficient detail that future scientific experimenters can determine whether environmental modifications have resulted from explorations.     

Excitations of nonmigrating diurnal tides in the mesosphere and lower thermosphere simulated by the Kyushu-GCM

Excitation mechanisms of nonmigrating diurnal tides in the MLT region simulated by the Kyushu-GCM are examined. It is shown that the westward propagating diurnal tide with zonal wavenumber s = 2 is mainly excited by nonlinear interactions between the migrating diurnal tide and the stationary planetary wave with zonal wavenumber s = 1, while the nonlinear excitation of the standing diurnal tide with zonal wavenumber s = 0 is less important than the excitation by tropospheric heating. Nonlinear interactions between the migrating diurnal tide and the stationary planetary wave with zonal wavenumber s = 2 are not dominant to excite the westward propagating diurnal tide with zonal wavenumber s = 3, and it is shown that the excitation by tropospheric heating is comparable to the nonlinear excitation. It is also shown that other nonmigrating diurnal tides are excited by tropospheric heating.