The Mars Science Laboratory spacecraft, containing the Curiosity rover, was launched to Mars on 26 November 2011, and for most of the 253-day, 560-million-kilometer cruise to Mars, the Radiation ...Assessment Detector made detailed measurements of the energetic particle radiation environment inside the spacecraft. These data provide insights into the radiation hazards that would be associated with a human mission to Mars. We report measurements of the radiation dose, dose equivalent, and linear energy transfer spectra. The dose equivalent for even the shortest round-trip with current propulsion systems and comparable shielding is found to be 0.66 ± 0.12 sievert.
Context.
The launch of Parker Solar Probe (PSP) in 2018, followed by Solar Orbiter (SO) in February 2020, has opened a new window in the exploration of solar magnetic activity and the origin of the ...heliosphere. These missions, together with other space observatories dedicated to solar observations, such as the Solar Dynamics Observatory, Hinode, IRIS, STEREO, and SOHO, with complementary in situ observations from WIND and ACE, and ground based multi-wavelength observations including the DKIST observatory that has just seen first light, promise to revolutionize our understanding of the solar atmosphere and of solar activity, from the generation and emergence of the Sun’s magnetic field to the creation of the solar wind and the acceleration of solar energetic particles.
Aims.
Here we describe the scientific objectives of the PSP and SO missions, and highlight the potential for discovery arising from synergistic observations. Here we put particular emphasis on how the combined remote sensing and in situ observations of SO, that bracket the outer coronal and inner heliospheric observations by PSP, may provide a reconstruction of the solar wind and magnetic field expansion from the Sun out to beyond the orbit of Mercury in the first phases of the mission. In the later, out-of-ecliptic portions of the SO mission, the solar surface magnetic field measurements from SO and the multi-point white-light observations from both PSP and SO will shed light on the dynamic, intermittent solar wind escaping from helmet streamers, pseudo-streamers, and the confined coronal plasma, and on solar energetic particle transport.
Methods.
Joint measurements during PSP–SO alignments, and magnetic connections along the same flux tube complemented by alignments with Earth, dual PSP–Earth, and SO-Earth, as well as with STEREO-A, SOHO, and BepiColumbo will allow a better understanding of the in situ evolution of solar-wind plasma flows and the full three-dimensional distribution of the solar wind from a purely observational point of view. Spectroscopic observations of the corona, and optical and radio observations, combined with direct in situ observations of the accelerating solar wind will provide a new foundation for understanding the fundamental physical processes leading to the energy transformations from solar photospheric flows and magnetic fields into the hot coronal plasma and magnetic fields and finally into the bulk kinetic energy of the solar wind and solar energetic particles.
Results.
We discuss the initial PSP observations, which already provide a compelling rationale for new measurement campaigns by SO, along with ground- and space-based assets within the synergistic context described above.
We present Solar Orbiter energetic particle observations of two 3He-rich events with features more clearly observed than in prior studies. The event of 2022 November 9 observed from 0.59 au contained ...hundreds of ultra-heavy ions (UH, mass >78 amu) whereas previous observations at 1 au have shown only an occasional count or two. The event of 2023 April 8 observed from 0.29 au fortuitously had very low ambient activity, making it possible to observe spectra from the 3He acceleration mechanism without contamination, revealing extremely low H and 4He intensities arriving simultaneously with other ions observed in typical 3He-rich events. Taken together with previous studies we believe these data show that 3He-rich events have a single acceleration mechanism that is responsible for the unique abundance features of 3He, heavy ions, and UH ions. Considering the acceleration model of Roth and Temerin (1997) that heats the ions over a broad range of gyrofrequencies away from those damped by H and 4He, we calculate reasonable fits to the observed abundances O-Fe. A key result is that high values of, e.g., Fe/O typical of such events is not due to preferential Fe heating, but on the contrary is due mainly to the depletion of O which at elevated temperatures has a charge-to-mass ratio in the region of the waves damped by 4He. The model also naturally incorporates features of high ionization states and neutron-rich isotope enhancements that have been long-standing puzzles in observations of this type of flare.
Using improved, self‐consistent analysis techniques, we determine the average solar wind charge state and elemental composition of nearly 40 ion species of He, C, N, O, Ne, Mg, Si, S, and Fe observed ...with the Solar Wind Ion Composition Spectrometer on Ulysses. We compare results obtained during selected time periods, including both slow solar wind and fast streams, concentrating on the quasi‐stationary flows away from recurrent or intermittent disturbances such as corotating interaction regions or coronal mass ejections. In the fast streams the charge state distributions are consistent with a single freezing‐in temperature for each element, whereas in the slow wind these distributions appear to be composed of contributions from a range of temperatures. The elemental composition shows the well‐known first ionization potential (FIP) bias of the solar wind composition with respect to the photosphere. However, it appears that our average enrichment factor of low‐FIP elements in the slow wind, not quite a factor of 3, is smaller than that in previous compilations. In fast streams the FIP bias is found to be yet smaller but still significantly above 1, clearly indicating that the FIP fractionation effect is also active beneath coronal holes from where the fast wind originates. This imposes basic requirements upon FIP fractionation models, which should reproduce the stronger and more variable low‐FIP bias in the slow wind and a weaker (and perhaps conceptually different) low‐FIP bias in fast streams. Taken together, these results firmly establish the fundamental difference between the two quasi‐stationary solar wind types.
The Radiation Assessment Detector (RAD), onboard the Mars Science Laboratory (MSL) rover Curiosity, measures the energetic charged and neutral particles and the radiation dose rate on the surface of ...Mars. An important factor for determining the biological impact of the Martian surface radiation is the specific contribution of neutrons, with their deeper penetration depth and ensuing high biological effectiveness. This is very difficult to measure quantitatively, resulting in considerable uncertainties in the total radiation dose. In contrast to charged particles, neutral particles (neutrons and gamma rays) are generally only measured indirectly. Measured spectra are a complex convolution of the incident particle spectrum with the detector response function and must be unfolded. We apply an inversion method (based on a maximum likelihood estimation) to calculate the neutron and gamma spectra from the RAD neutral particle measurements. Here we show the first spectra on the surface of Mars and compare them to theoretical predictions. The measured neutron spectrum (ranging from 8 to 740 MeV) translates into a radiation dose rate of 14±4μGy/d and a dose equivalent rate of 61±15μSv/d. This corresponds to 7% of the measured total surface dose rate and 10% of the biologically relevant surface dose equivalent rate on Mars. Measuring the Martian neutron and gamma spectra is an essential step for determining the mutagenic influences to past or present life at or beneath the Martian surface as well as the radiation hazard for future human exploration, including the shielding design of a potential habitat.
Key Points
We calculated the Martian neutron and gamma spectra
We compare the results to Planetocosmics simulations
We calculate dose and dose equivalent rate for the neutron spectrum
The 10–12 September Solar Energetic Particle event produced the strongest increase of the radiation environment measured by the Radiation Assessment Detector on the surface of Mars since landing in ...August 2012. We report the details of the measurements of the energetic particle environment from Radiation Assessment Detector in Gale crater during this event. The Solar Energetic Particle event increased the low‐energy proton flux (below 100 MeV) by a factor of 30, and the higher‐energy proton flux by a factor of 4, above preevent levels. The 4He flux (below 100 MeV/nuc) rose by factors up to 10, and neutral particles by a factor of 2 above background. The increase started on 10 September around 19:50 UTC, peak‐level fluxes were reached on the morning of 11 September and prevailed for about 10 hr before decreasing toward background levels. The onset of a Forbush decrease on 13 September decreased the proton flux below preevent intensities.
Plain Language Summary
On 10 September 2017, increased solar activity produced a solar energetic particle (SEP)event. This SEP event arrived at Mars around UTC 20:00 the same day in form of energetic particles accelerated to high enough energies to reach the Martian surface. We report here measurements of the energetic particle environment during the event in Gale crater on Mars, made with the Radiation Assessment Detector on board NASA's Curiosity rover. The SEPs increased the Martian surface proton flux below 100‐MeV energy by a factor of 30, and by a factor of 4 at higher energies. The neutral particle environment doubled during the event, which is of particular interest for the planning of solar storm shelters, as the shielding is less effective against neutrons as it is against charged particles. The increase in proton flux was the highest so far observed by Radiation Assessment Detector since landing on Mars in August 2012. However, stronger SEP events are possible that can increase the Martian radiation environment by orders of magnitude more. This makes monitoring the effect of SEPs crucial as radiation remains one of the major health risks for astronauts on exploration missions.
Key Points
On 11 September 2017, RAD observed the strongest solar particle event on the Martian surface since landing
Proton fluxes at the Martian surface increased by factors of up to 30, helium fluxes by factors up to 10
Doubling of neutral particle counts is important for planning of future storm shelter shielding, which is not as effective against neutrons
We report dosimetric quantities measured by the Mars Science Laboratory Radiation Assessment Detector (RAD) on the surface of Mars during the 10–12 September 2017 solar particle event. Despite ...23 g/cm2 of CO2 shielding provided by the atmosphere above RAD, dose rates rose above background galactic cosmic ray levels by factors of 2 to 3 over the course of several hours and leveled off at sustained peak rates for about 12 hr before declining over the following 36 hr. As the solar particle event flux was gradually declining, a shock front reached Mars and caused a sudden drop of about 15% in instantaneous dose rates. No solar particles followed the shock arrival, and the magnetic shielding of galactic cosmic rays by the shock reduced their intensity to levels below those seen before the start of the event. This event is the largest seen to date by RAD on Mars.
Plain Language Summary
We report the radiation dose rate on the surface of Mars measured by the Radiation Assessment Detector (RAD) aboard the Curiosity rover before, during, and after the solar energetic particle (SEP) event of 10–12 September 2017. Future astronauts exploring Mars will be at risk from SEP events, which occur sporadically and often with little warning, as well as from galactic cosmic rays, which are a continuous source of radiation dose and which generally have higher energies than SEPs. The event described here was the largest so far observed by RAD in more than five years on Mars. Although the atmosphere of Mars is only about 1–2% as thick as Earth's, it provides a measure of shielding against solar particles, most of which are protons with energies insufficient to penetrate Mars' atmosphere and reach the surface. But in this event, RAD saw a clear increase in dose rates; the peak dose rate was nearly three times above galactic cosmic ray levels measured prior to the event. Though the increase was rapid and lasted for three days, it was too small to represent a risk to the health of an astronaut receiving it. Much larger SEP events are possible and could cause problematic doses.
Key Points
Protons accelerated during the large solar particle event of September 2017 reached the surface of Mars and were observed by MSL‐RAD
Dose rates were seen to increase by factors of 2 to 3 above the background level of the galactic cosmic rays
Doses integrated over a 30‐day interval that included the event remained well below NASA radiation exposure limits for astronauts
Context.
The potential field source surface (PFSS) model is an important tool that helps link the solar coronal magnetic field to the solar wind. Due to its simplicity, it allows for predictions to ...be computed rapidly and requires little input data, though at the cost of reduced accuracy compared to more complex models. So far, PFSS models have almost exclusively been computed for a spherical outer boundary or “source surface”. Changing this to an elliptical source surface holds promise to increase its prediction accuracy without the necessity of incorporating complex computations or additional model assumptions.
Aims.
The main goal of this work is to evaluate the merit of adding another parameter, namely the ellipticity of the source surface, to the PFSS model. In addition, the applicability of the PFSS model during different periods of the solar activity cycle as well as the impact of the source surface radius are analyzed.
Methods.
To evaluate the model, in situ spacecraft data are mapped back to the source surface via a ballistic approach. The in situ magnetic field polarity is compared to the magnetic field polarity predicted by the model at the source surface. This method is based on the assumption that better performing models provide better agreements between the prediction and the measured magnetic field polarity. We employ data from the Advanced Composition Explorer and the twin Solar Terrestrial Relations Observatory (STEREO) for this analysis.
Results.
We show that the PFSS model performs slightly better with oblate elliptical source surfaces elongated along the solar equatorial plane, although the best found ellipticity varies for different spacecraft and periods. In addition, it is demonstrated that the performance of the presented analysis degrades during the active times of the solar activity cycle.
ABSTRACT
Important efforts are currently being made to understand the so-called kinetic instabilities, driven by the anisotropy of different species of plasma particles present in the solar wind and ...terrestrial magnetosphere. These instabilities are fast enough to efficiently convert the free energy of plasma particles into enhanced (small-scale) fluctuations, with multiple implications, regulating the anisotropy of plasma particles. In this paper we use both linear and quasi-linear (QL) frameworks to describe complex unstable regimes, which realistically combine different temperature anisotropies of electrons and ions (protons). Thus various instabilities are parametrized, for example the proton and electron firehose, electromagnetic ion cyclotron and whistler instabilities, showing that their main linear properties are markedly altered by the interplay of anisotropic electrons and protons. Linear theory may predict the strong competition of two instabilities of different natures when their growth rates are comparable. In the QL phase, wave fluctuations grow and saturate at different levels and temporal scales, in comparison to results for the individual excitation of the proton or electron instabilities. In addition, the cumulative effects of the combined proton- and electron-induced fluctuations can markedly stimulate the relaxation of their temperature anisotropies. Only whistler fluctuations inhibit the efficiency of proton firehose fluctuations in the relaxation of anisotropic protons. These results offer valuable premises for further investigations in numerical simulations to decode the full spectrum of kinetic instabilities resulting from the interplay of anisotropic electrons and protons in space plasmas.
Galactic cosmic rays (GCRs) are an intrinsic part of the heliospheric radiation environment and an inevitable challenge to long-term space exploration. Here we show solar-cycle-induced GCR modulation ...at Mars in the period 2005–2020, along with GCR radial gradients, by comparing Mars Express and Rosetta engineering parameters to sunspot number time series. The engineering parameters used are the error detection and correction (EDAC) counters, cumulative counters that are triggered by charged energetic particles that cause memory errors in onboard computers. EDAC data provide a new way of gaining insight into the field of particle transport in the heliosphere; these data also allow us to complement dedicated radiation instrumentation as EDAC software is present on all spacecraft. This dataset was used to capture variations in GCRs in both space and time, yielding the same qualitative information as ground-based neutron monitors. Our analysis of the Mars Express EDAC parameter reveals a strong solar cycle GCR modulation, with a time lag of ∼5.5 months. By combining Mars Express with Rosetta data, we calculate a 4.7 ± 0.8% increase in EDAC count rates per astronomical unit, which we attribute to a radial gradient in GCR fluxes in accordance with established literature. The potential of engineering data for scientific purposes remains mostly unexplored. The results obtained from this work demonstrate, for the first time for heliophysics purposes, the usefulness of the EDAC engineering parameter, the usefulness of data mining, and the utility of keeping missions operational for many years, all of which provide complimentary data to nominal science instruments.
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