Lunar soil is a natural detector of cosmic rays (CRs) of different origins (solar and Galactic). Analysis of the depth profiles of cosmogenic isotopes (14C, 41Ca, 36Cl, 10Be, 26Al, and 53Mn) allows the intensity of a CR to be reconstructed on time scales of 3–4 half-lives of the corresponding isotope. The average flux of CRs and an additional source of accelerated particles with a hard spectrum are required to fit data on 10Be. The explosion of a nearby supernova 2–3 Ma ago can serve as such a source.

The lunar soil is an integral detector of cosmic rays (CRs) of different origin (Solar and Galactic). Analysis of the deep profiles of cosmogenic isotopes (14C, 41Ca, 36Cl, 10Be, 26Al, 53Mn) allows us to restore the intensity of CR on time scales of 3–4 half-lives of the corresponding isotope. To coordinate data on 10Be, it is required (in addition to the average flux of CRs) the presence of an additional source of accelerated particles with hard spectrum. Such a source can be, for example, an outbreak of a nearby SN 2–3 million years ago.

The work considers the modelling of nearby supernova (SN) effects on Earth's biosphere via cosmic rays (CRs) accelerated by shockwaves. The rise of the radiation background on Earth resulted from the external irradiation by CR high-energy particles and internal radiation in organisms by the decay of cosmogenic 14C is evaluated. We have taken into account that the CR flux near Earth goes up steeply when the shockwave crosses the Solar System, while in previous works the CR transport was considered as purely diffusive. Our simulations demonstrate a high rise of the external ionization of the environments at Earth's surface by atmospheric cascade particles that penetrate the first 70-100 m of water depth. Also, the cosmogenic 14C decay is able to irradiate the entire biosphere and deep ocean organisms. We analyzed the probable increase in mutation rate and estimated the distance between Earth and an SN, where the lethal effects of irradiation are possible. Our simulations demonstrate that for SN energy of around 1051 erg the lethal distance could be ∼18 pc.

Comet nuclei in the outer Solar system are constantly irradiated by cosmic rays at low temperatures. Accumulated high concentrations of radicals can undergo fast recombination with significant heating of cometary surface layers. We present the model of comet activity at large heliocentric distances caused by the recombination of radicals. We found that the considered mechanism can cause activity of comets in distant regions of the Solar system, even at the Oort cloud distances. Outbursts in distant comet reservoirs can be a new source of dust and ice particles contributing to the recently discovered anomalous diffuse light in the cosmic extragalactic background optic light and the unexpectedly high flux of dust particles detected by the New Horizons dust counter at the edge of the Kuiper belt. The orbits of small-radii comets in the Oort cloud are highly influenced by cometary outbursts. This effect may account for the observed decrease in the number of small -radius long-period comets.

Cometary nuclei located in the Oort cloud accumulate high concentration of radicals in surface layers under cosmic ray irradiation at low temperatures. Recombination of radicals induced by an increase in the surface temperature of a comet by a close passing star, O/B stars, or nearby supernovae leads to the heating of the ice layer with the releasing of volatiles from the amorphous ice. When high gas pressure builds up beneath the cometary surface, dust and gas are ejected. The resulting jet of gas and dust can change the comet’s orbit in the Oort cloud. The studied non-gravitational mechanism can effectively expel comets with a radius of ≤1 km from the Oort cloud into the inner part of the Solar system. The total effect of cometary outbursts on the stability of cometary orbits during the evolution of Solar system can result in a decrease in the number of long-period small-radius comets.

Observations of young rapidly rotating G-type stars show that a large number of super-powerful flares occur on them. According to the early Sun activity model proposed by (Airapetian et al., 2016), it is assumed that during the first 700 million years there were 250 flares per day with an energy release comparable to the Carrington event of 1859. Within the framework of this model, the high intensity of irradiation of the Earth’s atmosphere by solar cosmic rays (SCR) led to the formation of a large amount of greenhouse gases in ion-molecular reactions. Their high concentration in the atmosphere of the early Earth made it possible to solve the so-called “early Sun” paradox, where high climate temperatures existed on Earth at a reduced luminosity (by 20–30

We have estimated the values of solar modulation parameter Ф on several time scales: 20 kyr, 2 Myr, and 6 Myr, using GEANT4.10 nuclear code and experimental data on 14C, 26Al, and 10Be activity in a Apollo 15 drill core. We report the inaccuracies of direct GEANT4 application to the problem and propose a calibration procedure based on terrestrial radiocarbon data to correct the calculations of GCR interaction with the Moon’s surface. Those corrections are justified by recent comparisons of the Lunar Neutron Probe data with neutron fluxes calculated via GEANT4. The resulted mean Ф over the last 2 kyr and 2 Myr are in good agreement with modern understanding of levels of solar activity. However, the 6 Myr estimate suggest strong additional source of high-energy GCR particles, which could be attributed to a close Supernova explosion 2–3 Myr ago.

The depth profiles of cosmogenic isotopes in the lunar regolith depend on the flux and spectrum of Galactic and solar cosmic rays (GCRs and SCRs) and, therefore, depend on solar activity on a time scale comparable to the lifetime of these isotopes. In this work, we analyzed the content of various radionuclides ( 14 C, 26 Al, 10 Be, and 53 Mn) in samples obtained by the Apollo 15 mission. Comparing the results of modeling performed for the average GCR flow using the GEANT4.10 package with experimental data, we obtained a correction factor for the calculated formation rates of Y 0 ~ 0.6 for all the considered radionuclides. We attribute this result to the overestimated value of the flux of secondary particles in the lunar soil in the calculation using the GEANT4.10 package. This conclusion is supported by independent laboratory experiments. The estimated 10 Be depth profile can be consistent with the experimental data only if the additional (apart from the GCR) contribution of protons accelerated on the shock wave from a nearby supernova ~2.5 million years ago is taken into account. We also calculated the 53 Mn depth profile (with the longest half-life of those we considered), which can also be described taking the contribution of the supernova into account. We note that three long-lived isotopes, 26 Al, 10 Be, and 53 Mn, with different half-lives were modeled with the same average modulation potential. This allowed us to conclude that solar activity did not undergo noticeable changes on a time scale of about 10 million years.

Young fast-rotating G-class stars show large number of powerful flares.It is assumed that in the first 700 million years of the existence of the Sun, 250 flares per day take place with a hard spectrum and energy release comparable to the Carrington event.Solar cosmic rays (SCRs) bombarding the atmosphere produce carbon and nitrogen isotopes by nuclear reactions in the atmospheres of terrestrial planets.The ratios of 13 C/ 12 C and 15 N/ 14 N in the planets' atmospheres increase as a result of the accumulation of heavy isotopes over the early Sun's activity period.The production of these isotopes depends on the estimated value of the proton power-law index and on the composition of early atmospheres.At the same time, the absence of magnetic fields on Venus and Mars creates the possibility of a greater effect from the effect of SCRs.The modern isotope ratios of 13 С/ 12 C and 15 N/ 14 N in the atmospheres of Earth, Mars and Venus set limitations on the early Sun activity.In the atmosphere of early Mars (if its mass equals to modern) the isotope ratio of 14 C/ 12 C would increase by tens of percent, and 15 N/ 14 N -several times, which contradicts the measurements.To explain the increase of isotope ratios one can assume that the frequency of powerful flares in the early Sun should have been smaller or the energy spectrum -softer.On Venus the isotopic ratios under the influence of SCRs increase within the measurement error.

ABSTRACT The effect of radical accumulation in ice, under high energy particle irradiation at low temperature followed by the energy release during heating, has been proposed as a possible cause of cometary outbursts. Water ice samples were subjected to 15 MeV protons to simulate the cosmic ray irradiation of comet nuclei. The irradiation with 0.9 MeV electrons was performed to model a similar process on icy satellites located in radiation belts of planets. We observed the release of accumulated energy 20 J g−1 during the heating of the proton-irradiated ice with two pulses of fast self-heating of the sample at 84 and 110 K. Similar energy release occurred between 82 and 110 K in the electron-irradiated ice. Our calculations suggest that the recombination of radicals accumulated in the surface layer of a comet nucleus under cosmic ray bombardment can trigger the cometary outbursts far from the Sun.

Ionizing radiation is an important environmental factor affecting the dynamics of biospheric processes in the past and present, as well as limiting the spread of life outside the Earth. The effect of radiation on microorganisms has been studied for decades, but studies of the response of natural microbial ecosystems are still scarce. We have studied the effect of 100 kGy gamma irradiation under low pressure (1 Torr) and low temperature (–50°C) on microbial community of the ancient Antarctic permafrost sedimentary rock. After irradiation, the total number of prokaryotic cells determined by epifluorescence microscopy, as well as the number of metabolically active bacterial and archaeal cells detected by fluorescence in situ hybridization remained at the control level, while the number of cultured heterotrophic bacteria decreased by an order of magnitude. Using the multisubstrate testing method, it has been found that the microbial complex retained a high potential metabolic activity and functional diversity after exposure to a combination of extreme physical factors. The resistance demonstrated by the microbial community significantly exceeded the generally accepted estimates of the prokaryotes’ radioresistance and indicated an underestimation of the microorganisms' radioresistance in natural habitats and the important role of mineral heterophase environment and irradiation conditions (pressure, temperature). The study confirmed the potential for long-term cryopreservation of viable terrestrial-like microorganisms in the Martian regolith, as well as the possibility of transferring anabiotic life forms as a part of small bodies in the space environment.

Ionizing radiation is one of the main factors that destroy biomolecules in extraterrestrial conditions. The effects of radiation depend on the conditions of the exposure (pressure, temperature, presence of various chemicals). We have studied the stability of enzymes (catalase and dehydrogenases) in the soil under irradiation with accelerated electrons in doses up to 100 kGy at low pressure (0.01 Torr) and low temperature (–130°C). After exposure to a dose of 100 kGy, the catalase activity remained at the control level, while the dehydrogenase activity decreased by a factor of five. The results of the study suggest the possibility of long-term preservation of active enzymes in the Martian regolith until they are inactivated due to the accumulation of radiation damage. Taking into account the intensity of ionizing radiation in the surface layer of the Martian regolith, we believe that a decrease in dehydrogenase activity by a factor of 10, 100, and 1000 from the initial level could occur within 1.9, 3.8, and 5.7 Myr, respectively, while catalase could remain active for even longer periods. The data support the possibility of detecting enzymatic activity by landers in the course of planned space missions.