Large solar event of September 29, 1989: ten years after

Out of the 56 Ground Level Enhancements (GLEs) of solar cosmic rays (SCRs) observed since 1942 until the present, 15 events were recorded in the 22nd cycle of solar activity (1986–1996). Solar proton events (SPEs) in that cycle displayed some peculiarities, which may need an interpretation on a new concept base. The event of September 29, 1989 is of special interest. Since the well-known event of February 23, 1956, it proved to be the most intense in the relativistic range of proton energies. This GLE affords a unique opportunity to study the propagation of SCRs over a wide range of rigidity.In spite of its occurrence behind the western solar limb, the originating major flare could be observed over a wide range of the wavelengths and particle energy spectra – from gamma rays to decametric radio waves, from >2 MeV electrons to multi-GeV protons; there were also measurements of the energy spectra and charge states of solar heavy nuclei. The flare was followed by some energetic solar phenomena (large magnetic loops, coronal eruptions and mass ejections, shocks, etc.). Due to the very hard rigidity spectrum, this was the first GLE recorded by underground muon detectors. The event also has a number of other unusual features, for example, an extended component of gamma-ray emission and the change in direction of the probable particle source during the event's initial stage. In addition, the intensity-time profile of the GLE is notable for its non-classic shape, showing a two-peak structure. The latter implies the possibility of a two-component (or two-source) ejection of accelerated particles from the Sun.The available observational data for the event is described in detail, the main focus of this paper is concentrated on different attempts to interpret the data within the framework of traditional and non-traditional concepts: shock and/or post-eruption acceleration, two-component (dual) ejection, two-source model of particle acceleration in large (extended) coronal structures, etc. None of the models put forward for explaining this event is exhaustive. The rigidity spectrum of ejected protons is estimated and the problem of the maximum rigidity, R _m, of the accelerated particles is discussed. In the relativistic range, this event proved to be by 1–2 orders less intense than the event of February 23, 1956. It is also shown that the event of September 29, 1989 could not have been recorded with the present-day neutrino detectors.     

Can a double component outflow explain the X-ray and optical lightcurves of Swift Gamma-Ray Bursts?

An increasing sample of Gamma-Ray Bursts (GRBs) observed by Swift show evidence of ‘chromatic breaks’, i.e. breaks that are present in the X-ray but not in the optical. We find that in a significant fraction of these GRB afterglows the X-ray and the optical emission cannot be produced by the same component. We propose that these afterglow lightcurves are the result of a two-component jet, in which both components undergo energy injection for the whole observation and the X-ray break is due to a jet break in the narrow outflow. Bursts with chromatic breaks also explain another surprising finding, the paucity of late achromatic breaks. We propose a model that may explain the behaviour of GRB emission in both X-ray and optical bands. This model can be a radical and noteworthy alternative to the current interpretation for the ‘canonical’ XRT and UVOT lightcurves, and it bears fundamental implications for GRB physics.     

Nonlinear development of MHD waves in coronal loops

The solar corona, modelled by a low β, resistive plasma slab sustains MHD wave propagations due to footpoint motions in the photosphere. The numerical simulation presents the evolution of MHD waves and the formation of current sheets. Steep gradients at the slab edges, which are signatures of resonance layers are observed. Singularities are removed by the inclusion of finite resistivity. The fast waves develop kink modes. As the plasma evolves the current sheets which provide heating at the edges fragment into two current sheets at each edge which in turn come closer when the twist is enhanced.     

Photochemical synthesis of citric acid cycle intermediates based on titanium dioxide

The emergence of the citric acid cycle is one of the most remarkable occurrences with regard to understanding the origin and evolution of metabolic pathways. Although the chemical steps of the cycle are preserved intact throughout nature, diverse organisms make wide use of its chemistry, and in some cases organisms use only a selected portion of the cycle. However, the origins of this cycle would have arisen in the more primitive anaerobic organism or even back in the proto-metabolism, which likely arose spontaneously under favorable prebiotic chemical conditions. In this context, we report that UV irradiation of formamide in the presence of titanium dioxide afforded 6 of the 11 carboxylic acid intermediates of the reductive version of the citric acid cycle. Since this cycle is the central metabolic pathway of contemporary biology, this report highlights the role of photochemical processes in the origin of the metabolic apparatus.     

Probabilistic assessment of radiation risk for astronauts in space missions

Accurate estimations of the health risks to astronauts due to space radiation exposure are necessary for future lunar and Mars missions. Space radiation consists of solar particle events (SPEs), comprised largely of medium energy protons (less than several hundred MeV); and galactic cosmic rays (GCR), which include high-energy protons and heavy ions. While the frequency distribution of SPEs depends strongly upon the phase within the solar activity cycle, the individual SPE occurrences themselves are random in nature. A solar modulation model has been developed for the temporal characterization of the GCR environment, which is represented by the deceleration potential, ?. The risk of radiation exposure to astronauts as well as to hardware from SPEs during extra-vehicular activities (EVAs) or in lightly shielded vehicles is a major concern for radiation protection. To support the probabilistic risk assessment for EVAs, which could be up to 15% of crew time² on lunar missions, we estimated the probability of SPE occurrence as a function of solar cycle phase using a non-homogeneous Poisson model [1] to fit the historical database of measurements of protons with energy>30 MeV, Φ₃₀. The resultant organ doses and dose equivalents, as well as effective whole body doses, for acute and cancer risk estimations are analyzed for a conceptual habitat module and for a lunar rover during space missions of defined durations. This probabilistic approach to radiation risk assessment from SPE and GCR is in support of mission design and operational planning for future manned space exploration missions.     

Space Shuttle drops down the SAA doses on ISS

Long-term analysis of data from two radiation detection instruments on the International Space Station (ISS) shows that the docking of the Space Shuttle drops down the measured dose rates in the region of the South Atlantic Anomaly (SAA) by a factor of 1.5–3. Measurements either by the R3DE detector, which is outside the ISS at the EuTEF facility on the Columbus module behind a shielding of less than 0.45 g cm⁻², and by the three detectors of the Liulin-5 particle telescope, which is inside the Russian PEARS module in the spherical tissue equivalent phantom behind much heavier shielding demonstrate that effect. Simultaneously the estimated averaged incident energies of the incoming protons rise up from about 30 to 45 MeV. The effect is explained by the additional shielding against the SAA 30–150 MeV protons, provided by the 78 tons Shuttle to the instruments inside and outside of the ISS. An additional reason is the ISS attitude change (performed for the Shuttle docking) leading to decreasing of dose rates in two of Liulin-5 detectors because of the East–West proton fluxes asymmetry in SAA. The Galactic Cosmic Rays dose rates are practically not affected.     

Radiation analysis for manned missions to the Jupiter system.

An analysis for manned missions targeted to the Jovian system has been performed in the framework of the NASA RASC (Revolutionary Aerospace Systems Concepts) program on Human Exploration beyond Mars. The missions were targeted to the Jupiter satellite Callisto. The mission analysis has been divided into three main phases, namely the interplanetary cruise, the Jupiter orbital insertion, and the surface landing and exploration phases. The interplanetary phase is based on departure from the Earth-Moon L1 point. Interplanetary trajectories based on the use of different propulsion systems have been considered, with resulting overall cruise phase duration varying between two and five years. The Jupiter-approach and the orbital insertion trajectories are considered in detail, with the spacecraft crossing the Jupiter radiation belts and staying around the landing target. In the surface exploration phase the stay on the Callisto surface is considered. The satellite surface composition has been modeled based on the most recent results from the GALILEO spacecraft. In the transport computations the surface backscattering has been duly taken into account. Particle transport has been performed with the HZETRN heavy ion code for hadrons and with an in-house developed transport code for electrons and bremsstrahlung photons. The obtained doses have been compared to dose exposure limits.