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NASA NTRS2023

Parker Solar Probe: Four Years of Discoveries at Solar Cycle Minimum

Launched on 12 Aug. 2018, NASA’s Parker Solar Probe had completed 13 of its scheduled 24 orbits around the Sun by Nov. 2022. The mission’s primary science goal is to determine the structure and dynamics of the Sun’s coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what processes accelerate energetic particles. Parker Solar Probe returned a treasure trove of science data that far exceeded quality, significance, and quantity expectations, leading to a significant number of discoveries reported in nearly 700 peer-reviewed publications. The first four years of the 7-year primary mission duration have been mostly during solar minimum conditions with few major solar events. Starting with orbit 8 (i.e., 28 Apr. 2021), Parker flew through the magnetically dominated corona, i.e., sub-Alfvénic solar wind, which is one of the mission’s primary objectives. In this paper, we present an overview of the scientific advances made mainly during the first four years of the Parker Solar Probe mission, which go well beyond the three science objectives that are: (1) Trace the flow of energy that heats and accelerates the solar corona and solar wind; (2) Determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind; and (3) Explore mechanisms that accelerate and transport energetic particles.

Sun↗
NASA NTRS1992

The Charge, Element, and Isotope Analysis System CELIAS on SOHO

The CELIAS instrument is designed to study the composition of the Solar Wind (SW) and of solar and interplanetary accelerated energetic particles on SOHO (Solar and Heliospheric Observatory). It consists of three different sensors with associated electronics, which are optimized each for a particular aspect of ion composition. These aspects are the elemental, isotopic, and ionic charge compostion of SW or energetic ions emanating from the Sun. A fourth sensor, the Solar EUV Monitor (SEM) was included into CELIAS for monitoring the absolute EUV flux from the Sun.

Hovestadt, Dietrich↗
NASA NTRS1983

The ISPM solar-wind ion composition spectrometer

The International Solar Polar Mission (ISPM) Solar-Wind Ion Composition Spectrometer which determines elemental and ionic-charge composition, and the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 145 km/sec (protons) to 1352 km/sec (Fe+8) is described. The instrument, which covers an energy per charge range from 110 eV/q to 66.7 keV/q in 13 min, combines an electrostatic analyzer with postacceleration, followed by a time-of-flight and energy measurement. Conditions and processes in the region of the corona where the solar wind is accelerated; location of the source regions of the solar wind in the corona; coronal heating processes; the extent and causes of variations in the composition of the solar atmosphere; plasma processes in the solar wind; acceleration of energetic particles in the solar wind; the thermalization and acceleration of interstellar ions in the solar wind, and their composition; and the composition and behavior of the plasma in the Jovian magnetosphere are studied.

Gloeckler, G.↗
NASA NTRS1995

Interstellar Pickup Hydrogen Observations from the Pioneer 10 and 11 Plasma Analyzers

The Pioneer 10 and 11 Ames plasma analyzers included off-angle integrating counters used for the first exploration of magnetospheric plasmas at Jupiter and Saturn. When summed over multi-day intervals during interplanetary cruise, at times of relatively constant solar wind speed during 1972 to 1977, the resulting count rates show a dependence on acceptance energies of the plasma analyzer deflection plates. The count rates could be produced by energetic charged particles, solar wind protons moving at a large angle to the bulk flow, and interstellar pickup ions. We interpret the more energetic of two peaks that are sometimes observed as the signature of interstellar pickup hydrogen. This peak is located at just below twice the solar wind speed (V(sub SW)), when near 3 AU heliocentric distance, decreasing to just above V(sub SW) as the heliocentric distance increases. Also, in the 8 to 12 AU range of heliocentric distances, we identify the pickup hydrogen signature as a shelf that ends at an edge located below 2V(sub SW). During these observations, the spacecraft longitude relative to the upstream interstellar flow changes roughly from 25 deg, to 155 deg at the larger heliocentric distance. The peak at the smaller heliocentric distances is most consistent with a velocity distribution that is a shell in phase space, with limited thickening as the pickup ions are assimilated into the solar wind flow.

Mihalov, J. D.↗
NASA NTRS1980

A survey of approximately 1 MeV/nucleon solar flare particle abundances, in the Z ? 1-26 range, during the 1973-1977 solar minimum period

The abundances of the major elements over the range H-Fe in solar flare energetic particles near 1 MeV/nucleon were surveyed for a large number of flares during the period 1973-1977; observations were carried out by the IMP 8 spacecraft in interplanetary space. The survey considered two types of solar flare events: (1) large events from which the average boundaries were deduced, and (2) events which have significant abundance differences from average. In addition, two He-3-rich events with abundance features that are different from previous examples are reported: one case with no enhancements of heavy ions, and a second case in which, compared to O, the heavy-ion enhancements are confined to the charge range Si-Fe rather than the usual case in which all elements Ne-Fe are enriched.

Mason, G. M.↗
NASA NTRS1990

The scientific mission of Ulysses

The major aims of the Ulysses' scientific investigations of the heliosphere at all latitudes are described. Missions goals include the assessment of the global three-dimensional properties of the interplanetary magnetic field and solar wind, the study of the composition of the solar wind plasma at different heliographic latitudes, and the study of the acceleration of energetic particles in solar flares. Waves, shocks and other discontinuities in the solar wind will be investigated through sampling of various plasma conditions, and interplanetary dust and cosmic rays will be analyzed. Other important goals include the search for gamma-ray-burst sources and for low-frequency gravitational waves by using the spacecraft's radio communication link. Achievement of the Ulysses' solar pole trajectory, which will utilize both launch vehicle thrust and gravitational pull, is also described.

Wenzel, K.-P.↗
NASA NTRS2014

Integrated Science Investigation of the Sun (ISIS): Design of the Energetic Particle Investigation

The Integrated Science Investigation of the Sun (ISIS) is a complete science investigation on the Solar Probe Plus (SPP) mission, which flies to within nine solar radii of the Sun's surface. ISIS comprises a two-instrument suite to measure energetic particles over a very broad energy range, as well as coordinated management, science operations, data processing, and scientific analysis. Together, ISIS observations allow us to explore the mechanisms of energetic particles dynamics, including their: (1) Origins-defining the seed populations and physical conditions necessary for energetic particle acceleration; (2) Acceleration-determining the roles of shocks, reconnection, waves, and turbulence in accelerating energetic particles; and (3) Transport-revealing how energetic particles propagate from the corona out into the heliosphere. The two ISIS Energetic Particle Instruments measure lower (EPI-Lo) and higher (EPI-Hi) energy particles. EPI-Lo measures ions and ion composition from approx. 20 keV/nucleon-15 MeV total energy and electrons from approx.25-1000 keV. EPI-Hi measures ions from approx. 1-200 MeV/nucleon and electrons from approx. 0.5-6 MeV. EPI-Lo comprises 80 tiny apertures with fields-of-view (FOVs) that sample over nearly a complete hemisphere, while EPI-Hi combines three telescopes that together provide five large-FOV apertures. ISIS observes continuously inside of 0.25 AU with a high data collection rate and burst data (EPI-Lo) coordinated with the rest of the SPP payload; outside of 0.25 AU, ISIS runs in low-rate science mode whenever feasible to capture as complete a record as possible of the solar energetic particle environment and provide calibration and continuity for measurements closer in to the Sun. The ISIS Science Operations Center plans and executes commanding, receives and analyzes all ISIS data, and coordinates science observations and analyses with the rest of the SPP science investigations. Together, ISIS' unique observations on SPP will enable the discovery, untangling, and understanding of the important physical processes that govern energetic particles in the innermost regions of our heliosphere, for the first time. This paper summarizes the ISIS investigation at the time of the SPP mission Preliminary Design Review in January 2014.

Coronal Mass Ejections↗
NASA NTRS2022

Dependence of Energetic Storm Particle Heavy Ion Peak Intensities and Spectra on Source CME Longitude and Speed

We examine variations in energetic storm particle (ESP) heavy ion peak intensities and energy spectra at CME-driven interplanetary shocks. We focus on their dependence with heliolongitude relative to the source region of their associated CMEs, and with CME speed, for events observed in Solar Cycle 24 at the STEREO-A, STEREO-B, and/or ACE spacecraft. We find that observations of ESP events at 1 au are organized by longitude relative to their CME solar source. The ESP event longitude distribution also showed organization with CME speed. The near-Sun CME speeds (V i ) for these events ranged from ∼560 to 2650 km s −1 while the average CME transit speeds to 1 au were significantly slower. The angular width of the events had a clear threshold at V i of ∼1300 km s −1 , above which events showed significantly larger angular extension compared to events with speeds below. High-speed events also showed larger heavy ion peak intensities near the nose of the shock compared to the flanks while their spectral index was smaller near the nose and larger near the flanks. This organization for events with V i < 1300 km s −1 was not as clear. These ESP events were observed over a narrower range of longitudes though the heavy ion peak intensities still appeared largest near the nose of the shock. Their heavy ion spectra showed no clear organization with longitude. These observations highlight the impact of spacecraft position relative to the CME source longitude and Vi on the properties of ESP events at 1 au.

Solar energetic particles↗
NASA NTRS2015

Solar Flare Track Exposure Ages in Regolith Particles: A Calibration for Transmission Electron Microscope Measurements

Mineral grains in lunar and asteroidal regolith samples provide a unique record of their interaction with the space environment. Space weathering effects result from multiple processes including: exposure to the solar wind, which results in ion damage and implantation effects that are preserved in the rims of grains (typically the outermost 100 nm); cosmic ray and solar flare activity, which result in track formation; and impact processes that result in the accumulation of vapor-deposited elements, impact melts and adhering grains on particle surfaces. Determining the rate at which these effects accumulate in the grains during their space exposure is critical to studies of the surface evolution of airless bodies. Solar flare energetic particles (mainly Fe-group nuclei) have a penetration depth of a few millimeters and leave a trail of ionization damage in insulating materials that is readily observable by transmission electron microscope (TEM) imaging. The density of solar flare particle tracks is used to infer the length of time an object was at or near the regolith surface (i.e., its exposure age). Track measurements by TEM methods are routine, yet track production rate calibrations have only been determined using chemical etching techniques [e.g., 1, and references therein]. We used focused ion beam-scanning electron microscope (FIB-SEM) sample preparation techniques combined with TEM imaging to determine the track density/exposure age relations for lunar rock 64455. The 64455 sample was used earlier by [2] to determine a track production rate by chemical etching of tracks in anorthite. Here, we show that combined FIB/TEM techniques provide a more accurate determination of a track production rate and also allow us to extend the calibration to solar flare tracks in olivine.

Berger, Eve L.↗
NASA NTRS1999

Cosmic Ray Telescope Experiment (CRT), Pioneer 10/11 Program

In May 1996 the electrical power on Pioneer 10 was no longer adequate to support the Cosmic Ray Telescope Experiment (CRT). In March 1997 ground based operations for the mission were terminated. The 25 years of Pioneer 10 were a remarkable voyage of discovery as it ventured into a vast new unexplored region of space. These observations by the Pioneer experiments led in the development of a new discipline of space science - heliospheric physics. For cosmic ray studies it was an incredible era, leading to the identification of new energetic particle populations and processes and initiating the study of the dynamics and large-scale structure and began the study of the dynamics and large-scale structure of the outer heliosphere. A summary of some of the principal scientific findings of the CRT experiment over this period is given in the next section. Even with the cessation of data from the Pioneer 10/11 mission there remained a great deal of scientific analysis and data archiving that required on the order of an additional three years of effort on the part of the CRT team. We have tried to select those tasks where the P10/11 CRT data have an important role to play. Special emphasis is placed on long-term synoptic studies that make use of the extended temporal and spatial coverage of the missions and the full capabilities of the CRT experiment. The major scientific objectives of this study are: (1) A phenomenological study of the modulation process in the heliosphere, thereby laying the foundation for developing a unified model of cosmic ray modulation over a complete 22 year heliomagnetic cycle; (2) These modulation studies and the temporal changes in the cosmic ray intensities also provide information on the large-scale structure and dynamics of the outer heliosphere; (3) use the galactic and anomalous cosmic ray data from Pioneer 10 to obtain a more accurate estimate of the distance to the modulation boundary and to the termination shock; (4) Use the results from (2) and from temporal variations to determine whether significant modulation occurs in the region of the heliosphere; (5)study the acceleration and transport of low energy solar interplanetary energetic particles and their relation to solar activity and interplanetary phenomena.

McDonald, Frank B.↗
NASA NTRS1972

Enrichment of very heavy nuclei in the composition of solar accelerated particles.

Measurement of the abundances of the nuclei C, N, O, Ne, Mg, Si, Ar, and Ca and the group Cr-Co relative to oxygen from seven solar energetic-particle events in the energy range from about 14 to 61 MeV per nucleon with a solid-state detector telescope on the OGO-5 satellite, 1968-1971. The differential energy spectra of O (14 to 29 MeV per nucleon) and Cr-Co (3 to 61 MeV per nucleon) have a spectral index of about (-3) for a power law in kinetic energy. The relative abundances of C, N, O, and Ne are in excellent agreement with emulsion studies. However, when compared with the solar photospheric and coronal abundances, the OGO-5 measurements show a large enhancement of relative abundances beginning with Si, and extending to the Cr-Co group. The enhancement over the solar and universal abundances is in rough agreement with the composition of the galactic cosmic radiation.

Mogro-Campero, A.↗
NASA NTRS1992

Energetic particle observations and the abundances of elements in the solar corona

During the last few years it has become clear that energetic particles in the largest solar events, where abundances are commonly measured, are not accelerated in flares. Rather they are accelerated from the ambient plasma above active regions by shock waves driven by coronal mass ejections. The lowest energy particles from these events have abundances that almost directly reflect those of the source plasma. Residual effects of acceleration, that depend smoothly on the ion's corona Q/A, vanish when abundances are averaged over many events, yielding the characteristic dependence of the average coronal abundances of the First Ionization Potential (FIP) of the elements from H through Fe. In contrast, energetic ions accelerated out of the high speed solar wind from large coronal holes show a reduced FIP effect with a different pattern.

Reames, Donald V.↗
NASA NTRS1981

Interplanetary ions during an energetic storm particle event - The distribution function from solar wind thermal energies to 1.6 MeV

An ion velocity distribution function of the postshock phase of an energetic storm particle (ESP) event is obtained from data from the ISEE 2 and ISEE 3 experiments. The distribution function is roughly isotropic in the solar wind frame from solar wind thermal energies to 1.6 MeV. The ESP event studied (8/27/78) is superposed upon a more energetic particle event which was predominantly field-aligned and which was probably of solar origin. The observations suggest that the ESP population is accelerated directly out of the solar wind thermal population or its quiescent suprathermal tail by a stochastic process associated with shock wave disturbance. The acceleration mechanism is sufficiently efficient so that approximately 1% of the solar wind population is accelerated to suprathermal energies. These suprathermal particles have an energy density of approximately 290 eV cubic centimeters.

Gosling, J. T.↗
NASA NTRS1991

Solar particle abundances at energies of greater than 1 MeV per nucleon and the role of interplanetary shocks

The abundances of elements in large solar energetic-particle events in the energy range of 2-12 MeV per nucleon are examined. It is confirmed that the abundances relative to mean values vary approximately monotonically as a function of mass, except for He-4; some events show a gradual depletion of heavy ions, whereas a small number displays a gradual increase. A further organization of abundance data is shown, which depends on the longitude of the source region. Enhancements in Fe/C and other heavy elements relative to C occur when source regions are near west 60 deg; the enhancements are attributed to the sampling of a flare-heated material. Depletions of these elements are found to be greatest for source regions near central meridian; they are matched by a steepening of the spectrum and can be understood in terms of diffusive shock acceleration.

Cane, H. V.↗
NASA NTRS1992

Particle acceleration in solar flares - Observations

Contrary to our historical understanding, the energetic particles in most major solar proton events do not come from the flare itself. The particle abundances, ionization states, time evolution, and longitude distributions all indicate that the particles are accelerated from the ambient plasma by a shock wave driven by a coronal mass ejection in these events. In contrast, the particles that do come from impulsive solar flares are unique in character. These particles are electron rich, have He-3/He-4 enhancements of up to 10,000, and enhancements in heavy elements such as Fe/C by factors of 10. The high ionization state of Fe, +20 indicates that the material has been heated to temperatures of about 2 x 10 exp 7 K. It is generally believed that preferential heating by selective absorption of plasma waves is combined with stochastic acceleration in these events. Recent studies of the broad gamma-ray lines emitted by energetic particles within the flare loops indicate that they are also Fe-rich, He-3 rich and proton-poor like the particles seen at 1 AU. In large impulsive events, particles from the impulsive phase may be reaccelerated by a coronal blast-wave shock.

Reames, Donald V.↗
NASA NTRS1980

Solar particle fluxes and the ancient sun

The implications of the statistical data on solar flare particle fluxes, for the present and the ancient sun, considering modern data from the past two solar cycles, C-14 data from the past 7000 years, and Al-26 and Mn-53 data in lunar samples for the last 10-million years are reviewed. All of these records suggest that there is a maximum proton fluence (greater than 10 MeV) from a solar flare on the order of 10 to the 10th p/sq cm, above which the size-frequency distribution steepens sharply. From this it is extremely unlikely that energetic particles from solar flares could have contributed to extinction catastrophes in the fossil record.

Lingenfelter, R. E.↗
NASA NTRSDate not supplied

Heliospheric energetic particle transport: Analysis of near-field-aligned particle propagation for SEP events observed by Wind and MAVEN

Magnetic field alignments of spacecraft over large distances in the heliosphere are rare and are usually very limited in duration. Cruise phases of planetary transfers, however, are an exception to this rule, given the Hohmann-Parker effect. The transfer of the MAVEN s/c in 2014 is one such example. Multiple (~10) solar particle events occurred and were detected at both MAVEN and the Wind s/c, originating from solar activity near the foot points of both s/c. We show initial analysis results of the data collected by the solar wind and energetic particle instruments on both s/c while they were more than 0.2 AU apart, but practically Parker field aligned. Using a 1D model, we present initial simulations in qualitative agreement with energetic electron measurements. Next step is to implement the 2D model with approximate particle release from the Sun, and transport durations between Sun, Earth, and MAVEN. We will discuss implications for this data-model comparison, including the possibility to constrain particle scattering inside 1 AU, as well as its radial dependence between Earth and MAVEN.

Solar Energetic Particles↗
NASA NTRS2003

L2 Plasma Environments

The second LaGrange point, 1.5 million miles from the Earth in the anti-solar direction, is becoming an important destination for scientific spacecraft. The quasi-stable gravity field requires little energy resources for station keeping and astronomical missions-infrared and microwave in particular-find the minimal impact from Earth albedo radiation and limited restrictions on viewing directions a tremendous advantage in their mission design. Spacecraft design for L2 missions will have to consider the plasma environments of the ambient solar wind, magnetosheath, and magnetotail from energies of a few 10s of an eV through 10s of keV in addition to enhanced energetic particle populations from 10s to 1000 keV during solar energetic particle events. This presentation will provide a background on the appropriate L2 charged particle environments at L2 and describe modeling efforts at MSFC to develop environment specification tools for the L2 plasma environment.

Minow, Joseph I.↗