Extreme Solar Particle Events Research Articles

Hybrid methods of radiation shielding against deep-space radiation

In the last decade, NASA and other space exploration organizations have focused on making crewed missions to different locations in our solar system a priority. To ensure the crew members’ safety in a harsh radiation environment outside the protection of the geomagnetic field and atmosphere, a robust radiation protection system needs to be in place. Passive shielding methods, which use mass shielding, are insufficient as a standalone means of radiation protection for long-term deep-space missions. Active shielding methods, which use electromagnetic fields to deflect charged particles, have the potential to be a solution that can be used along with passive shielding to make deep-space travel safer and more feasible. Past active shielding studies have demonstrated that substantial technological advances are required for active shielding to be a reality. However, active shielding has shown potential for near-future implementation when used to protect against solar energetic particles, which are less penetrating than galactic cosmic rays (GCRs). This study uses a novel approach to investigate the impacts of passive and active shielding for protection against extreme solar particle events (SPEs) and free-space GCR spectra under solar minimum and solar maximum conditions. Hybrid shielding configuration performance is assessed in terms of effective dose and radiobiological effectiveness (RBE)-weighted dose reduction. A novel electrostatic shielding configuration consisting of multiple charged planes and charged rods was chosen as the base active shielding configuration. After a rigorous optimization process, two hybrid shielding configurations were chosen based on their ability to reduce RBE-weighted dose and effective dose. For protection against the extreme SPE, a hybrid active-passive shielding configuration was chosen, where active shielding was placed outside of passive shielding. In the case of GCRs, to gain additional reduction compared to passive shielding, the passive shielding configuration was placed before the active shielding to intentionally fragment HZE ions to improve shielding performance.

Multiproxy Reconstructions of Integral Energy Spectra for Extreme Solar Particle Events of 7176 BCE, 660 BCE, 775 CE, and 994 CE

AbstractExtreme solar particle events (ESPEs) are rare and the most potent known processes of solar eruptive activity. During ESPEs, a vast amount of cosmogenic isotopes (CIs) 10Be, 36Cl, and 14C can be produced in the Earth's atmosphere and deposited in natural stratified archives. Accordingly, CI measurements in these archives allow us to evaluate particle fluxes during ESPEs. In this work, we present a new method of ESPE fluence (integral flux) reconstruction based on state‐of‐the‐art modeling advances, allowing to fit together different CI data within one model. We represent the ESPE fluence as an ensemble of scaled fluence reconstructions for ground‐level enhancement (GLE) events registered by the neutron monitor network since 1956 coupled with satellite and ionospheric measurements data. Reconstructed ESPE fluences appear softer in its spectral shape than earlier estimates, leading to significantly higher estimates of the low‐energy (E < 100 MeV) fluence. This makes ESPEs even more dangerous for modern technological systems than previously believed. Reconstructed ESPE fluences are fitted with a modified Band function, which eases the use of obtained results in different applications.

Radiation Risks in Cis-Lunar Space for a Solar Particle Event Similar to the February 1956 Event

Solar particle events (SPEs) can pose serious threats for future crewed missions to the Moon. Historically, there have been several extreme SPEs that could have been dangerous for astronauts, and thus analyzing their potential risk on humans is an important step towards space exploration. In this work, we study the effects of a well-known SPE that occurred on 23 February 1956 on a mission in cis-Lunar space. Estimates of the proton fluence spectra of the February 1956 event were obtained from three different parameterized models published within the past 12 years. The studied geometry consists of a female phantom in the center of spherical spacecraft shielded by aluminum area densities ranging from 0.4 to 40 g cm−2. The effective dose, along with lens, skin, blood forming organs, heart, and central nervous system doses, were tallied using the On Line Tool for the Assessment of Radiation In Space (OLTARIS), which utilizes the High Z and Energy TRansport code (HZETRN), a deterministic radiation transport code. Based on the parameterized models, the results herein show that thicknesses comparable to a spacesuit might not protect against severe health consequences from a February 1956 category event. They also show that a minimum aluminum shielding of around 20 g cm−2 is sufficient to keep the effective dose and critical organ doses below NASA’s permissible limits for such event. In addition, except for very thin shielding, the input models produced results that were within good agreement, where the doses obtained from the three proton fluence spectra tended to converge with slight differences as the shielding thickness increases.

Revisited Reference Solar Proton Event of 23 February 1956: Assessment of the Cosmogenic‐Isotope Method Sensitivity to Extreme Solar Events

AbstractOur direct knowledge of solar eruptive events is limited to several decades and does not include extreme events, which can only be studied by the indirect proxy method over millennia, or by a large number of Sun‐like stars. There is a gap, spanning 1–2 orders of magnitude, in the strength of events between directly observed and reconstructed ones. Here, we study the proxy method sensitivity to identify extreme solar particle events (SPEs). First, the strongest directly observed SPE (23 February 1956), used as a reference for proxy‐based reconstructions, was revisited using the newly developed method. Next, sensitivity of the cosmogenic‐isotope method to detect a reference SPE was assessed against the precision and number of individual isotopic records, showing that it is too weak by a factor ≈30 to be reliably identified in a single record. Uncertainties of 10Be and 14C data are shown to be dominated by local/regional patterns and measurement errors, respectively. By combining several proxy records, a SPE 4–5 times stronger than the reference one can be potentially detected, increasing the present‐day sensitivity by an order of magnitude. This will allow filling the observational gap in SPE strength distribution, thus enriching statistics of extreme events from 3–4 presently known ones to several tens. This will provide a solid basis for research in the field of extreme events, both for fundamental science, namely solar and stellar physics, and practical applications, such as the risk assessments of severe space‐based hazards for modern technological society.

Spatial Organization of Seven Extreme Solar Energetic Particle Events

Abstract Emission of relativistic protons and helium responsible for extreme solar particle events (ground level enhancements (GLEs)) is often structured. We investigate its organization depending on the eruption stage characterized by the heliocentric height of associated coronal mass ejections (CMEs). Seven GLEs are considered: events on 1997 November 6, 1998 May 2, 2000 July 14, 2001 December 26, 2003 November 2, 2006 December 13, and 2012 May 17, which are half of the SOlar and Heliospheric Observatory (SOHO )-era GLEs, excluding very weak events. Count-rate profiles of the GLEs plotted as a function of the CME height reveal two types (or two components) of the high-energy particle emission. The first component rises in a step-like manner during the CME transit from 2 R ⊙ to 3 R ⊙, when the CME exits from predominantly closed coronal magnetic structures, irrespective of the CME speed (type H). This component is of coronal origin. The second component of the GLE-producing particles starts to rise when CME is at about 4 R ⊙, achieves its maximum at 6–10 R ⊙, and declines shortly after that (type J). The type J particle injection into the interplanetary space coincides with the decametric–hectometric radio burst complex that includes enhanced emission of type II and concurrent low-frequency type III bursts, indicative of the CME interaction with a streamer-like structure at a few solar radii from the Sun. Those could be delayed particles from the flare region. A possible additional contribution of the CME-bow-shock acceleration in unstructured solar wind is not large in the two considered types of events.

Investigating the Origins of Two Extreme Solar Particle Events: Proton Source Profile and Associated Electromagnetic Emissions

Abstract We analyze the high-energy particle emission from the Sun in two extreme solar particle events in which protons are accelerated to relativistic energies and can cause a significant signal even in the ground-based particle detectors. Analysis of a relativistic proton event is based on modeling of the particle transport and interaction, from a near-Sun source through the solar wind and the Earth’s magnetosphere and atmosphere to a detector on the ground. This allows us to deduce the time profile of the proton source at the Sun and compare it with observed electromagnetic emissions. The 1998 May 2 event is associated with a flare and a coronal mass ejection (CME), which were well observed by the Nançay Radioheliograph, thus the images of the radio sources are available. For the 2003 November 2 event, the low corona images of the CME liftoff obtained at the Mauna Loa Solar Observatory are available. Those complementary data sets are analyzed jointly with the broadband dynamic radio spectra, EUV images, and other data available for both events. We find a common scenario for both eruptions, including the flare’s dual impulsive phase, the CME-launch-associated decimetric-continuum burst, and the late, low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch, then trapped in large-scale magnetic loops and later released by the expanding CME.

Constraints on a potential aerial biosphere on Venus: I. Cosmic rays

While the present-day surface of Venus is certainly incompatible with terrestrial biology, the planet may have possessed oceans in the past and provided conditions suitable for the origin of life. Venusian life may persist today high in the atmosphere where the temperature and pH regime is tolerable to terrestrial extremophile microbes: an aerial habitable zone. Here we argue that on the basis of the combined biological hazard of high temperature and high acidity this habitable zone lies between 51km (65°C) and 62km (−20°C) altitude. Compared to Earth, this potential venusian biosphere may be exposed to substantially more comic ionising radiation: Venus has no protective magnetic field, orbits closer to the Sun, and the entire habitable region lies high in the atmosphere – if this narrow band is sterilised there is no reservoir of deeper life that can recolonise afterwards. Here we model the propagation of particle radiation through the venusian atmosphere, considering both the background flux of high-energy galactic cosmic rays and the transient but exceptionally high-fluence bursts of extreme solar particle events (SPE), such as the Carrington Event of 1859 and that inferred for AD 775. We calculate the altitude profiles of both energy deposition into the atmosphere and the absorbed radiation dose to assess this astrophysical threat to the potential high-altitude venusian biosphere. We find that at the top of the habitable zone (62km altitude; 190g/cm2 shielding depth) the radiation dose from the modelled Carrington Event with a hard spectrum (matched to the February 1956 SPE) is over 18,000 times higher than the background from GCR, and 50,000 times higher for the modelled 775 AD event. However, even though the flux of ionising radiation can be sterilizing high in the atmosphere, the total dose delivered at the top of the habitable zone by a worst-case SPE like the 775 AD event is 0.09Gy, which is not likely to present a significant survival challenge. Nonetheless, the extreme ionisation could force atmospheric chemistry that may perturb a venusian biosphere in other ways. The energy deposition profiles presented here are also applicable to modelling efforts to understand how fundamental planetary atmospheric processes such as atmospheric chemistry, cloud microphysics and atmospheric electrical systems are affected by extreme solar particle events. The companion paper to this study, Constraints on a potential aerial biosphere on Venus: II. Solar ultraviolet radiation (Patel et al., in preparation), considers the threat posed by penetration of solar UV radiation. The results of these twin studies are based on Venus but are also applicable to extrasolar terrestrial planets near the inner edge of the circumstellar habitable zone.

Analysis of radiation induced effects in high-density commercial memories on-board Alsat-1: The impact of extreme solar particle events

This paper presents a long-term study on radiation effects in non-hardened high density memory devices operating within the main on-board computer system of the Algerian microsatellite Alsat-1 in Low Earth Orbit (LEO). A statistical analysis of single-event upset (SEU) activity is presented for commercial SRAM devices, and their response to extreme solar events shows SEU rate significant increases correlated with high-energy protons (E>100MeV). Ground based neutron monitor data are used to illustrate the long-term correlation between galactic cosmic rays and Alsat-1 upsets. The short-term effects of energetic solar particles are illustrated with space environment data from GOES-11. The Alsat-1 observed SEU rates are compared to the predicted rates based on ground test data and environment models. The prediction results are in good agreement with in-flight data.

The magnitude and effects of extreme solar particle events

The solar energetic particle (SEP) radiation environment is an important consideration for spacecraft design, spacecraft mission planning and human spaceflight. Herein is presented an investigation into the likely severity of effects of a very large Solar Particle Event (SPE) on technology and humans in space. Fluences for SPEs derived using statistical models are compared to historical SPEs to verify their appropriateness for use in the analysis which follows. By combining environment tools with tools to model effects behind varying layers of spacecraft shielding it is possible to predict what impact a large SPE would be likely to have on a spacecraft in Near-Earth interplanetary space or geostationary Earth orbit. Also presented is a comparison of results generated using the traditional method of inputting the environment spectra, determined using a statistical model, into effects tools and a new method developed as part of the ESA SEPEM Project allowing for the creation of an effect time series on which statistics, previously applied to the flux data, can be run directly. The SPE environment spectra is determined and presented as energy integrated proton fluence (cm−2 ) as a function of particle energy (in MeV). This is input into the SHIELDOSE-2, MULASSIS, NIEL, GRAS and SEU effects tools to provide the output results. In the case of the new method for analysis, the flux time series is fed directly into the MULASSIS and GEMAT tools integrated into the SEPEM system. The output effect quantities include total ionising dose (in rads), non-ionising energy loss (MeV g−1 ), single event upsets (upsets/bit) and the dose in humans compared to established limits for stochastic (or cancer-causing) effects and tissue reactions (such as acute radiation sickness) in humans given in grey-equivalent and sieverts respectively.

OCCURRENCE OF EXTREME SOLAR PARTICLE EVENTS: ASSESSMENT FROM HISTORICAL PROXY DATA

The probability of occurrence of extreme solar particle events (SPEs) with the fluence of (>30 MeV) protons F30>10^{10} cm^{-2} is evaluated based on data of cosmogenic isotopes 14C and 10Be in terrestrial archives centennial-millennial time scales. Four potential candidates with F30=(1-1.5)x10^{10} cm^{-2} and no events with F30>2x10^{10} cm^{-2} are identified since 1400 AD in the annually resolved 10Be data. A strong SPE related to the Carrington flare of 1859 AD is not supported by the data. For the last 11400 years, 19 SPE candidates with F30=(1-3)x10^{10} cm^{-2} are found and clearly no event with F30>5x10^{10} cm^{-2} (50-fold the SPE of 23-Feb-1956) occurring. This values serve as an observational upper limit for the strength of SPE on the time scale of tens of millennia. Two events, ca. 780 and 1460 AD, appear in different data series making them strong candidates to extreme SPEs. We built a distribution of the occurrence probability of extreme SPEs, providing a new strict observational constraint. Practical limits can be set as F30~1x, 2-3x, and 5x10^{10} cm^{-2} for the occurrence probability ~10^{-2}, 10^{-3} and 10^{-4} year^{-1}, respectively. Because of uncertainties, our results should be interpreted as a conservative upper limit of the SPE occurrence near Earth. The mean SEP flux is evaluated as ~40 (cm2 sec)^{-1} in agreement with estimates from the lunar rocks. On average, extreme SPEs contribute about 10% to the total SEP fluence.

Solar particle event analysis using the standard radiation environment monitors: applying the neutron monitor's experience

The Standard Radiation Environment Monitor (SREM) is a particle detector developed by the European Space Agency for satellite applications with the main pur- pose to provide radiation hazard alarms to the host space- craft. SREM units have been constructed within a radiation hardening concept and therefore are able to register extreme solar particle events (SPEs). Large SPEs are registered at Earth, by ground based detectors as neutron monitors, in the form of Ground Level Enhancements of solar cosmic rays. In this work, a feasibility study of a possible radiation alert, deduced by SREM measurements was implemented for the event of 20 January 2005. Taking advantage of the neutron monitor's experience, the steps of the GLE alert algorithm were put into practice on SREM measurements. The out- come was that SREM units did register the outgoing SPE on-time and that these could serve as indicators of radiation hazards, leading to successful alerts.

Solar proton events in cosmogenic isotope data

A possible contribution of solar energetic particle events to the production of cosmogenic 10Be and 14C in the atmosphere is studied. The solar particle effect is negligible in the 14C data, but extreme events may be detectable in high‐resolution 14C data. Although the overall effect is small in the 10Be data, strong events may contribute notably on the inter‐annual time scale. In combination with the 11‐year solar modulation of galactic cosmic rays, it may lead to an intermittent 5.5‐year periodicity, which is seen in high resolution 10Be data. We have identified ten episodes during 1750–1950 when 10Be may hold signatures of strong solar proton events. This opens a new possibility to study extreme solar particle events in the past using high resolution cosmogenic isotope data.