A. K. Pavlov

Irradiated interplanetary dust particles as a possible solution for the deuterium/hydrogen paradox of Earth's oceans

Determining the source of Earths oceans is a longstanding problem in planetary science. Possible sources of water include water ice or water of hydration of silicate minerals in the original material from which the bulk Earth accreted and water brought in by late-arriving planetesimals during the heavy bombardment period (4.5-3.8 Gyr ago) [Chyba, 1989, 1991]. Comets are an attractive source of water because their origin in the outer solar system is consistent with the long timescale for heavy bombardment. However, the high deuterium/hydrogen (D/H) ratio of the three comets that have been studied, Halley, Hyakutake, and Hale-Bopp, indicates that Earth must have had a source with a low-D/H ratio as well. Here we suggest that solar wind-implanted hydrogen on interplanetary dust particles (IDPs) provided the necessary low-D/H component of Earths water inventory.

Gamma-ray bursts and the production of cosmogenic radionuclides in the Earth’s atmosphere

An explanation is offered for the impulsive increase in the concentration of cosmogenic radiocarbon in annual tree rings (Δ14C ∼ 12‰) from AD ≃775. A possible cause of such an increase could be the high-energy emission from a Galactic gamma-ray burst. It is shown that such an event should not lead to an increase in the total production of 10Be in the atmosphere, as distinct from the effect of cosmic-ray fluxes on the atmosphere. At the same time, the production of an appreciable amount of 36Cl, which can be detected in Greenland and Antarctica ice samples of the corresponding age, should be expected. This allows the effects caused by a gamma-ray burst and anomalously powerful proton events to be distinguished.

“Isotopic footprints” of gamma-ray and proton events and anomalous signal in radiocarbon in 775 AD

The production of the cosmogenic radionuclides 14C, 10Be, and 36Cl in the Earth’s atmosphere under the action of powerful impulsive proton and gamma-ray events (superpowerful solar flares and Galactic gamma-ray bursts) is considered. The possible “isotopic footprint” in natural archives (the concentrations of these isotopes in dated polar ice cores and annual tree rings) has been calculated by taking into account geophysical processes. The results obtained have been applied to analyzing the anomalous increase in the concentration of radiocarbon measured in tree rings dated 774–775 AD. Arguments for the fact that the most likely cause of this increase is the high-energy emission from a Galactic gamma-ray burst are adduced.

Changes in the solar wind’s isotope component, due to interaction between solar flare particles and the photosphere

Possible mechanisms responsible for changes in the solar wind’s isotope component caused by interaction between solar flare protons and helium isotopes with photospheric nuclei are considered. Depth profiles of the rates of 6Li, 7Li, 7Be, 14C production in the solar atmosphere are simulated using the GEANT4 software package. It is concluded that anomalous isotopic compositions of the solar wind relative to the average values can form during the coronal mass ejections.

Influence of cosmic rays on biomarkers on the mars

Detection of the organic substance on the Mars is one of the main targets of the current and future Martian landing missions. In this study, we calculated the ionization of the Martian soil by solar and Galactic cosmic rays at its various depths. It is shown that complex organic molecules (biomarkers) with a mass more than 300 a.m.u. at a depth of ≤10 cm degrade for a time less than one milliard years.

Interaction of Solar-Flare-Accelerated Nuclei with the Solar Photosphere and the Isotopic Composition of the Solar Wind

The nuclear interactions of solar-flare-accelerated protons and ions with the solar atmosphere and the deeper layers of the Sun lead to the formation of several stable and radioactive isotopes. This article examines the GEANT4 depth profiles of 2H, 3H, 3He, 6Li, 7Li, 10Be, and 14C. When accelerated particles pass through a layer of 0.1–2 g cm–2, 6Li, 7Li, 10Be, and 14C isotopes form in sufficient amounts to explain their anomalous abundances in lunar soil samples. It is assumed that they escape into interplanetary space with coronal mass ejections immediately after the flare.

Modulation of galactic cosmic rays and its traces in isotopic tracks on the Earth and the moon

The high-altitude track of the rates of production of cosmogenic isotopes 14С, 10Be and 36Cl in the Earth’s atmosphere under the action of galactic cosmic rays is calculated using different intranuclear cascade models in the GEANT4 environment. Inferences based on these models are discussed in comparison to the available experimental data on these isotopes.

Effect of cosmic rays on the isotopic composition of the Martian surface

Results from simulating the rate of formation of 3He, 21Ne and 36Ar isotopes according to the effect cosmic rays have on the surface layer of the soil on Mars are presented. The results are compared to data obtained by the Mars Science Laboratory for samples of the surface layer. It is shown that with a constant spectrum and an average flow of cosmic rays, the exposure required to explain the experimental data could have been accumulated in only 160–220 million years. The existence of a layer of water at least 8–10 meters thick and/or a dense atmosphere in the period of evolution preceding the irradiation of the tested samples is hypothesized.