A cosmochemical view of cosmic rays and solar particles

The composition of cosmic rays and solar particles is reviewed with emphasis on the question of whether they are representative samples of Galactic and solar matter. The composition of solar particles changes with energy and from flare to flare. A strong excess of heavy elements at energies below a few MeV/nuc decreases with energy, and at energies above 15 MeV/nuc the composition of solar particles resembles that of galactic cosmic rays somewhat better than that of the solar atmosphere. The elements Ne through Pb have remarkably similar abundances in cosmic ray sources and in the matter of the solar system. The lighter elements are depleted in cosmic rays, whereas U and Th may be enriched or not, depending on whether the meteoritic or solar abundance of Th is used. Two prototype sources of cosmic rays are considered: gas with solar system composition but enriched in elements with Z > 8 during acceleration and emission (by analogy with solar particle emission), and highly evolved matter enriched in r-process elements such as U, Th and transuranic elements. The energy-dependence of cosmic ray composition suggests that both sources may contribute at different energies.Miller Institute Professor, 1972–73.     

Mars Phobos and Deimos Survey (M-PADS) – A martian Moons orbiter and Phobos lander

We describe a Mars ‘Micro Mission’ for detailed study of the martian satellites Phobos and Deimos. The mission involves two ∼330 kg spacecraft equipped with solar electric propulsion to reach Mars orbit. The two spacecraft are stacked for launch: an orbiter for remote investigation of the moons and in situ studies of their environment in Mars orbit, and another carrying a lander for in situ measurements on the surface of Phobos (or alternatively Deimos). Phobos and Deimos remain only partially studied, and Deimos less well than Phobos. Mars has almost always been the primary mission objective, while the more dedicated Phobos project (1988–89) failed to realise its full potential. Many questions remain concerning the moons’ origins, evolution, physical nature and composition. Current missions, such as Mars Express, are extending our knowledge of Phobos in some areas but largely neglect Deimos. The objectives of M-PADS focus on: origins and evolution, interactions with Mars, volatiles and interiors, surface features, and differences. The consequent measurement requirements imply both landed and remote sensing payloads. M-PADS is expected to accommodate a 60 kg orbital payload and a 16 kg lander payload. M-PADS resulted from a BNSC-funded study carried out in 2003 to define candidate Mars Micro Mission concepts for ESA’s Aurora programme.     

STARDUST: finessing expensive cometary sample returns

The STARDUST Discovery mission will collect samples of cometary coma and interstellar dust and return them to Earth. Five years after launch in February 1999, coma dust in the 1- to 100-micrometers size range will be captured by impact into ultra-low-density silica aerogel during a 6 kms-1 flyby of Comet Wild 2. The returned samples will be investigated at laboratories where the most critical information on these primitive materials is retained. The Jet Propulsion Laboratory will provide project management with Lockheed Martin Astronauts as the spacecraft industrial partner. STARDUST management will aggressively and innovatively achieve cost control through the use of Total Quality Management principles, the chief of which will be organization in a Project Engineering and Integration Team that "flattens" the traditional hierarchical structure by including all project elements from the beginning, in a concurrent engineering framework focusing on evolving Integrated Mission Capability.     

Debris swarms seen by SMEI

The large 3° × 60° fields-of-view of the Solar Mass Ejection Imager (SMEI) instruments are oriented on the stabilized Coriolis satellite to image most of the sky each Sun-synchronous orbit. Besides observing coronal mass ejections, the SMEI mission objective, SMEI also has detected a plethora of Earth-orbiting satellites (resident space objects or RSOs) brighter than ∼8th magnitude at a rate of about 1 per minute. Occasionally, SMEI sees an RSO swarm: a sudden onset of a large number of RSOs, many more than the nominal rate, upto dozens detected in a 4-s frame. These swarms usually last for a few minutes. A sample of six such RSO ensembles is analyzed in this paper in which the distance and the direction of the velocity vector for individual objects are estimated. We present the observational evidence indicating that the swarms must be near-field objects traveling in orbits near that of Coriolis, and that the relatively speeds between the objects and Coriolis are low. Further, analyses indicate that the RSOs are quite close (<20 m) and are generally moving radially away from the satellite. The predicted encounter geometries for Coriolis passing through or near a small debris cloud is, generally, quite inconsistent with the observations. The most likely explanation consistent with the observations is that SMEI is seeing debris being ejected from the Coriolis spacecraft itself. An analysis of distance and brightness for a subset of the RSOs indicates that the median diameter of the debris particles is ∼80 μm.     

Infrared Irradiance Calibration

Infrared astronomical measurements are calibrated against reference sources, usually primary standard stars that are, in turn, calibrated either by direct or indirect means. A direct calibration compares the star with a certified source, typically a blackbody. Indirect methods extrapolate a direct measurement of the flux at one wavelength to the flux at another. Historically, α Lyr (Vega) has been used as the primary standard as it is bright, easily accessible from the northern hemisphere, and is well calibrated in the visual. Until recently, the direct absolute infrared calibrations of α Lyr and those derived from the absolute solar flux scaled to the observed spectral energy distributions of solar type stars increasingly diverged with wavelength from those obtained using a model atmosphere to extrapolate the absolute visual flux of Vega into the infrared. The exception is the direct calibration by the 1996/97 Midcourse Space Experiment of the absolute fluxes for a number of the commonly used infrared standard stars, including Vega.In the mid-1980s, the Air Force Geophysics Laboratory began a program that led to the establishment of a network of stars with which to calibrate infrared space-based sensors. α Lyr and a CMa were adopted as the fundamental references and the absolute 1.2 to 35 µm infrared spectral energy distributions for the 616 secondary standard stars in the network were derived through spectral and photometric comparisons with the primary standards. The stars are also used for calibration at ground-based infrared observatories. For applications in which the network stars may not be bright enough, particularly at the longer infrared wavelengths, planets and the larger asteroids are used. Planets and asteroids move and rather sophisticated thermal modeling of the bodies is required to predict the disk-integrated brightness at a specific time with reasonable accuracy. The Infrared Space Observatory applied such a sophisticated ‘thermo-physical’ model to the largest asteroids to support calibration of the sensors to a claimed accuracy of within 5%. The AFRL program also created a spectral atlas of the brightest stars in the sky that, although they are variable, may be used for calibration if the large(r) attendant uncertainties are acceptable.     

Daily variations of the geomagnetic field

The atmospheric dynamo theory of the daily magnetic variations (S) has received substantial support from recent observational and theoretical work. In particular, several features of the variations, such as their remarkable enhancement close to the dip equator and other effects indicating a strong control by the main geomagnetic field, are well explained by the dynamo theory. Also the detection of ionospheric currents by instrumental rockets has confirmed an essential part of the theory.Considerable impetus was given to their study by the acquirement of much new data on magnetic variations during the IGY-IQSY period. Additional observations in the Pacific area were obtained during the IQSY by the establishment of four island stations equipped with newly developed magnetometers. A major advance at other stations was the development of automatic standard observatories using nuclear magnetometers.Several methods for the world-wide analysis of the S-field have been developed. A possibility now being studied is the completely automatic evaluation and construction by computers of ionospheric current charts for any day and any epoch UT.Some theoretical and statistical papers are briefly reviewed. These include discussions of the day-to-day variability of S, seasonal changes of the S-field, the nature of the equatorial electrojet, the possibility of solar wind effects contributing to the daily variations, and the modification of the dynamo theory to take account of the possible flow of electric current from the ionosphere along magnetic lines of force in the magnetosphere.Finally, an attempt to extend the dynamo theory of S by treating the ionosphere as a three-dimensional medium, instead of regarding it as a thin shell, has revealed that, although the relations between the horizontal components of electric field and current density in the dynamo layer are given with reasonable accuracy by the well-known layer equations, the assumption, implicit in the thin shell treatment, that the horizontal currents are non-divergent is not in fact true. Hence a revision of some earlier theoretical work on S appears necessary.     

Microorganisms metabolizing on clay grains in 3-km-deep Greenland basal ice

We have discovered > 10(8) microbial cells/cm3 attached to clay grains in the bottom 13 m of the GISP2 (Greenland Ice Sheet Project) ice core. Their concentration correlates with huge excesses of CO2 and CH4. We show that Fe-reducing bacteria produce most of the excess CO2 and methanogenic archaea produce the excess CH4. The number of attached cells per clay grain is proportional to grain perimeter rather than to area, which implies that nutrients are accessed at grain edges. We conclude that Fe-reducing microbes immobilized on clay surfaces metabolize via "shuttle" molecules that transport electrons to grain edges, where they reduce Fe(III) ions at edges to Fe(II) while organic acid ions are oxidized to CO2. Driven by the concentration gradient, electrons on Fe(II) ions at grain edges "hop" to Fe(III) ions inward in the same edges and oxidize them. The original Fe(III) ions can then attach new electrons from shuttle molecules at the edges. Our mechanism explains how Fe-reducers can reduce essentially all Fe(III) in clay minerals. We estimate that the Fe(III) in clay grains in the GISP2 silty ice can sustain Fe-reducing bacteria at the ambient temperature of -9 degrees C for approximately 10(6) years. F420 autofluorescence imaging shows that > 2.4% of the cells are methanogens, which account for the excess methane.     

Infrared astronomy on the midcourse space experiment

The Midcourse Space Experiment (MSX) is a multiple objective experiment scheduled to fly by the end of 1994. Infrared photometry and interferometry will be obtained by a solid hydrogen cooled, off-axis telescope of 35 cm unobscured primary aperture. The sensitivities of the line scanned arrays are comparable to IRAS bands 1 and 2 but the spatial resolution is some 30 times better. Nine broadly defined astronomy experiments are planned for the 18 month cryogen phase of the mission. Four of these experiments survey regions not adequately covered by previous infrared missions: the zodiacal cloud near the sun and the anti-solar direction, the Galactic Plane where IRAS sensitivities were limited by confusion and the gaps left by the IRAS survey. The higher sensitivity obtained from raster scans will probe Galactic structure and create intermediate spatial resolution maps of extended sources such as HII regions, the Magellanic Clouds and nearby galaxies. Measurements are also planned on a number of solar system objects such as planets, asteroids, the dust bands, comets and cometary debris trails. Moderate resolution spectra of a number of bright, discrete, extended sources will be obtained as well as low resolution spectral mapping along the Galactic Plane and Zodiacal dust cloud.     

Common freshwater cyanobacteria grow in 100% CO2

Cyanobacteria and similar organisms produced most of the oxygen found in Earth's atmosphere, which implies that early photosynthetic organisms would have lived in an atmosphere that was rich in CO2 and poor in O2. We investigated the tolerance of several cyanobacteria to very high (>20 kPa) concentrations of atmospheric CO2. Cultures of Synechococcus PCC7942, Synechocystis PCC7942, Plectonema boryanum, and Anabaena sp. were grown in liquid culture sparged with CO2-enriched air. All four strains grew when transferred from ambient CO2 to 20 kPa partial pressure of CO2 (pCO2), but none of them tolerated direct transfer to 40 kPa pCO2. Synechococcus and Anabaena survived 101 kPa (100%) pCO2 when pressure was gradually increased by 15 kPa per day, and Plectonema actively grew under these conditions. All four strains grew in an anoxic atmosphere of 5 kPa pCO2 in N2. Strains that were sensitive to high CO2 were also sensitive to low initial pH (pH 5-6). However, low pH in itself was not sufficient to prevent growth. Although mechanisms of damage and survival are still under investigation, we have shown that modern cyanobacteria can survive under Earth's primordial conditions and that cyanobacteria-like organisms could have flourished under conditions on early Mars, which probably had an atmosphere similar to early Earth's.     

Density and Temperature in Wind Tunnels Using Electron Beams

In a paper presented at the last meeting of the International Congress on Instrumentation in Aerospace Simulation Facilities, a method of measuring gas density by radiation scattering was presented. Since that time, the method has been further developed using scattering of 50-keV electrons and has been applied in a wind tunnel using air as a test gas. Test section temperature and density were in the neighborhood of 150°K and 6×10-8 g/cm3. In this application, accuracies better than 1.0 percent appear to be attainable, together with excellent spatial and temporal resolution. The application is described, and comprehensive design data are presented. In addition, the density measurements have been supplemented by measurements of the local rotational temperature, utilizing nitrogen molecular band radiation excited by a second electron beam. Comparisons between the density and temperature measurements and flow properties obtained by standard gas-dynamic calculations are made.