Genetic susceptibility to radiation.

In the context of space radiation, it is important to know whether the human population includes genetically predisposed radiosensitive subsets. One possibility is that haploinsufficiency for ATM confers radiosensitivity, and this defect involves 1-3% of the population. Using knock-out mice we chose to study cataractogenesis in the lens and oncogenic transformation in mouse embryo fibroblasts to assay for effects of ATM deficiency. Radiation induced cataracts appeared earlier in the heterozygous versus wild-type animals following exposure to either gamma rays or 1 GeV/nucleon iron ions. In addition, it was found that embryo fibroblasts of Atm heterozygotes showed an increased incidence of oncogenic transformation compared with their normal litter-matched counterparts. From these data we suggest that Ataxia Telangiectasia heterozygotes could indeed represent a societally significant radio sensitive subpopulation. Knock-out mice are now available for other genes including BRCA1 and 2, and Mrad9. An exciting possibility is the creation of double heterozygotes for pairs of mutated genes that function in the same signal transduction pathway, and consequently confer even greater radiosensitivity.     

A parametric study of space radiation exposures to critical body organs for low earth orbit missions.

The geomagnetically-trapped and galactic cosmic radiation environments are two of the major sources of naturally-occurring space radiation exposure to astronauts in low earth orbit. The exposure is dependent primarily on altitude, spacecraft shielding, crew stay-times, and solar cycle effects for a 28.5 deg orbital inclination. Based on Space Shuttle experience, the calculated results of a parametric study are presented for several mission scenarios using a computerized anatomical man model and are compared with the NASA crew exposure limits for several critical body organs.     

Life support systems and optimal isotope composition in cosmonaut habitats for long-term missions.

Differences in the isotope content of the biogenous chemicals of cosmonaut habitats are given a theoretical consideration. Rationale is given to the hypothesis according to which the biochemical and biophysical processes in plants. animals, and humans must be impacted by the isotopes of all the biogenous chemicals in cosmonaut habitats. Organisms were found to persistently make preference of lighter fractions of stable isotopes from the biogenous chemicals. In most of the compounds the light fraction of stable isotopes constitutes the greater portion by mass. However, the optimal isotope composition of biogenous chemicals is still unknown and necessitates biochemical, toxicological, biological and other kinds of research. The functions of a life support system should also include production and maintenance of an optimal isotope composition for habitats, i.e. water, oxygen, food stuffs in order to improve metabolism in and performance of cosmonauts.     

New ways to rotation rates

Progress in determining rotation rates of Algol primary stars from light curves is assessed. Included are elementary ideas on why the new method works, how to carry out solutions, and how and when to apply the constraint on rotational lobe filling. Some comments are made on desirable improvements for measuring rotation from line broadening. A few remarks are made about the problem of identifying likely fast rotating Algols.     

Long-term preservation of microbial ecosystems in permafrost.

It has been established that significant numbers (up to 10 million cells per gram of sample) of living microorganisms of various ecological and morphological groups have been preserved under permafrost conditions, at temperatures ranging from -9 to -13 degrees C and depths of up to 100 m, for thousands and sometimes millions of years. Preserved since the formation of permafrost in sand-clay sediments of the Pliocene-Quaternary period and in paleosols and peats buried among them, these cells art the only living organisms that have survived for a geologically significant period of time. The complexity of the microbial community preserved varies with the age of the permafrost. Eukaryotes are found only in Holocene sediments; while prokaryotes are found to greater ages, i.e., Pliocene and Pleistocene. The diversity of microorganisms decreases with increasing age of sediments, and as a result cocci and corynebacteria are predominant. Enzyme activity (catalase and hydrolytic enzymes) and photosynthetic pigments (chlorophyll and pheophytin have also been detected in permafrost sediments. These results permit us to outline some approaches to the search for traces of life in the permafrost of Martian sediments by borehole core sampling. It is in the deep horizons (and not on the planet surface), isolated by permafrost from the external conditions, that results similar to those obtained on Earth can be expected.     

ROSAT observations of the Chamaeleon star forming cloud

Two soft X-ray images of the Chamaeleon I star forming cloud obtained with the ROSAT Position Sensitive Proportional Counter are presented. Seventy reliable, and perhaps 19 additional, X-ray sources are found. Up to Ninety percent of these sources are certainly or probably identified with T Tauri stars formed in the cloud. Twenty to 35 are probably previously unrecognized ‘weak’ T Tauri (WTT) stars. T Tauri X-ray luminosities range from log , or 10² – 10⁴ times solar levels, with mean in the 0.2–2.5 keV band. The X-ray luminosities of well-studied Chamaeleon cloud members are correlated with a complex of four stellar properties: effective temperature, mass, radius and bolometric luminosity. The spatial distribution, H-R diagram locations of the stars indicate WTT and CTT are coeval. The total premain sequence population of the cloud is likely to be > 100 stars, with WTT stars outnumbering ‘classical’ T Tauri (CTT) stars by 2:1.