The Solar Orbiter mission Müller, D.; St. Cyr, O. C.; Zouganelis, I. ...
Astronomy and astrophysics (Berlin),
10/2020, Volume:
642
Journal Article
Peer reviewed
Open access
Aims.
Solar Orbiter, the first mission of ESA’s Cosmic Vision 2015–2025 programme and a mission of international collaboration between ESA and NASA, will explore the Sun and heliosphere from close up ...and out of the ecliptic plane. It was launched on 10 February 2020 04:03 UTC from Cape Canaveral and aims to address key questions of solar and heliospheric physics pertaining to how the Sun creates and controls the Heliosphere, and why solar activity changes with time. To answer these, the mission carries six remote-sensing instruments to observe the Sun and the solar corona, and four in-situ instruments to measure the solar wind, energetic particles, and electromagnetic fields. In this paper, we describe the science objectives of the mission, and how these will be addressed by the joint observations of the instruments onboard.
Methods.
The paper first summarises the mission-level science objectives, followed by an overview of the spacecraft and payload. We report the observables and performance figures of each instrument, as well as the trajectory design. This is followed by a summary of the science operations concept. The paper concludes with a more detailed description of the science objectives.
Results.
Solar Orbiter will combine in-situ measurements in the heliosphere with high-resolution remote-sensing observations of the Sun to address fundamental questions of solar and heliospheric physics. The performance of the Solar Orbiter payload meets the requirements derived from the mission’s science objectives. Its science return will be augmented further by coordinated observations with other space missions and ground-based observatories.
Geomagnetically trapped oxygen ions of solar and ionospheric origin have previously been observed in the Earth's magnetosphere. Early observations from Active Magnetospheric Particle Tracer ...Explorers/CCE have studied this distribution within a limited spatial range of L shells over all magnetic local times (MLT). This study expands on these early results using observations from the Polar spacecraft. The distributions by charge state show O6+, from the solar wind, charge exchanging into O5+, O4+, and O3+ as the ion populations drift to lower L shells. Meanwhile, ionospheric O+ and O2+ are primarily seen at low L shells and may also play a role in O3+ populations. We also present here the Dst, Vsw∗Bz, and AE dependencies of oxygen charge states (O+ through O6+) in MLT and L shell in the magnetosphere of the Earth. The distributions of these charge states provide insight into the injection and energization of both ionospheric oxygen as well as solar wind ions inside the magnetosphere.
Key Points
The distribution of oxygen charge states are studied in the global magnetosphere using Polar data
These distributions are investigated in both L shell and magnetic local time
Distributions of ionospheric O+ and solar wind O6+ are studied against Dst, Vsw∗Bz, and AE
MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) measurements taken during passes over Mercury's dayside hemisphere indicate that on four occasions the spacecraft remained in ...the magnetosheath even though it reached altitudes below 300 km. During these disappearing dayside magnetosphere (DDM) events, the spacecraft did not encounter the magnetopause until it was at very high magnetic latitudes, ~66 to 80°. These DDM events stand out with respect to their extremely high solar wind dynamic pressures, Psw ~140 to 290 nPa, and intense southward magnetic fields, Bz ~ −100 to −400 nT, measured in the magnetosheath. In addition, the bow shock was observed very close to the surface during these events with a subsolar altitude of ~1,200 km. It is suggested that DDM events, which are closely associated with coronal mass ejections, are due to solar wind compression and/or reconnection‐driven erosion of the dayside magnetosphere. The very low altitude of the bow shock during these events strongly suggests that the solar wind impacts much of Mercury's sunlit hemisphere during these events. More study of these disappearing dayside events is required, but it is likely that solar wind sputtering of neutrals from the surface into the exosphere maximizes during these intervals.
Key Points
The dayside magnetosphere of Mercury is observed to disappear at MESSENGER's orbit during some coronal mass ejection impacts
The cause appears to be extreme solar wind compression and/or reconnection‐driven erosion of Mercury's dayside magnetic field
The low altitude of the bow shock during these events strongly suggests that Mercury's dayside surface experiences direct solar wind impact
Understanding the sources and subsequent evolution of plasma in a magnetosphere holds intrinsic importance for magnetospheric dynamics. Previous studies have investigated the balance of ...ionospheric‐originating heavy ions (low charge state) from those of solar wind origin (high charge state) in the magnetosphere of Earth. These studies have suggested a variety of entry mechanisms for solar wind ions to penetrate into the magnetosphere. Following from recently published distributions for oxygen charge states observed by the Polar spacecraft, this paper investigates oxygen charge state flux distributions versus L shell and magnetic latitude. By showing these distributions in this frame, and binning by various proxies for magnetospheric dynamics (Dst, AE, VSW∗BZ, Pdyn), insight has been gained into the underlying physics at play for oxygen injection. Ionospheric‐originating oxygen is observed to depend predominantly on Dst, whereas solar wind‐originating oxygen is observed to have a strong dependence on solar wind dynamic pressure (Pdyn) at the flanks and on VSW∗BZ at the dayside. This suggests that both Kelvin‐Helmholtz instabilities and reconnection play major roles in solar wind ion penetration into a magnetosphere. Additionally, the near‐Earth magnetotail reconnection site does not seem to be a major injection site of solar wind‐originating plasma in the 1 to 200 keV/e energy range.
Key Points
Several possible entry mechanisms for solar wind‐originating plasma are investigated
Dayside reconnection and Kelvin‐Helmholtz instabilities appear to be important entry mechanisms for solar wind plasma
Magnetotail reconnection, diamagnetic cavities, gradient drift, and impulsive penetration are not observed to be sufficient entry mechanisms
Composition of 1–128 keV Magnetospheric ENAs Valek, P. W.; Delmonico, E.; McComas, D. J. ...
Journal of geophysical research. Space physics,
April 2018, 2018-04-00, 20180401, Volume:
123, Issue:
4
Journal Article
Peer reviewed
The Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) mission has observed the inner magnetosphere since 2008. TWINS flies energetic neutral atom (ENA) cameras aboard two spacecraft in ...separate Molniya orbits. TWINS images the ENA emissions from the inner magnetosphere across a broad range of energies (1 to 128 keV for H, 16 to 128 keV for O, and higher energies for total ENAs). This allows TWINS to observe the evolution, on minute timescales, of the trapped and precipitating particles that dominate storm time dynamics. Presented here are ENA observations over this broad energy range of the large storm of 17 March 2015 (Dst < −223)—the St. Patrick's Day storm. The ENA observations are presented with a 15‐min cadence for improved counting statistics. During the St. Patrick's Day storm the flux of ENAs and the concentration of O+/H+ increased significantly during the main phase. The concentration increased to a value of 1.0 for the 16 keV ions, and the temperature in the inner magnetosphere dropped during the time between the prestorm phase and the main phase. Comparing the results from this storm to a moderate storm on 22 July 2009, and a collection of nine other large storms, we find that the most energetic O+ ions in the ring current occur before the peak of the storm.
Key Points
First composition‐separated ENA images that simultaneously cover the medium and higher energy ranges (1–128 keV)
During large storms the most energetic O+ ions in the ring current occur before the peak of the storm
At lower energies (e.g., 16 keV) the O+/H+ is at 1, indicating major mass loading of the ring current
Recent studies have utilized different charge states of oxygen ions as a tracer for the origins of plasma populations in the magnetosphere of Earth, using O+ as an indicator of ...ionospheric‐originating plasma and O6+ as an indicator of solar wind‐originating plasma. These studies have correlated enhancements in O6+ to various solar wind and geomagnetic conditions to characterize the dominant solar wind injection mechanisms into the magnetosphere but did not include analysis of the temporal evolution of these ions. A sixth‐order Fourier expansion model based empirically on a superposed epoch analysis of geomagnetic storms observed by Polar is presented in this study to provide insight into the evolution of both ionospheric‐originating and solar wind‐originating plasma throughout geomagnetic storms. At high energies (~200 keV) the flux of O+ and O6+ are seen to become comparable in the outer magnetosphere. Moreover, while the density of O+ is far higher than O6+, the two charge states have comparable pressures in the outer magnetosphere. The temperature of O6+ is generally higher than that of O+, because the O6+ is injected from preheated magnetosheath populations before undergoing further heating once in the magnetosphere. A comparison between the model results with O+ observations from the Magnetospheric Multiscale mission and the Van Allen Probes provides a validation of the model. In general, this empirical model agrees qualitatively well with the trends seen in both data sets. Quantitatively, the modeled density, pressure, and temperature almost always agree within a factor of at most 10, 5, and 2, respectively.
Key Points
An empirical model was created for equatorial O+ and O6+ flux during geomagnetic storms and compared to O+ observations from MMS and VAP
While O6+ pressure is sometimes comparable to O+, the O6+ temperatures generally exceeds that of O+
The main regions of O6+ density enhancements are along the dayside and the flanks, consistent with reconnection and KHI‐related injection
Mercury's flux transfer event (FTE) showers are dayside magnetopause crossings accompanied by large numbers (≥10) of magnetic flux ropes (FRs). These shower events are common, occurring during 52% ...(1,953/3,748) of the analyzed crossings. Shower events are observed with magnetic shear angles (θ) from 0° to 180° across the magnetopause and magnetosheath plasma β from 0.1 to 10 but are most prevalent for high θ and low plasma β. Individual FR duration correlates positively, while spacing correlates negatively, with θ and plasma β. FR flux content and core magnetic field intensity correlate negatively with plasma β, but they do not correlate with θ. During shower intervals, FRs carry 60% to 85% of the magnetic flux required to supply Mercury's Dungey cycle. The FTE showers and the large amount of magnetic flux carried by the FTE‐type FRs appear quite different from observations at Earth and other planetary magnetospheres visited thus far.
Plain Language Summary
Any planet with an interior dynamo will interact with the outward streaming stellar wind and likely form a magnetosphere. The magnetopause is a boundary between the shocked solar wind and planetary magnetic field, which can prevent most of the solar wind from directly entering into the magnetosphere. The multiple X‐line reconnection that frequently occurs in the magnetopause creates helical magnetic fields that are termed magnetic flux ropes (FRs) about which open and interplanetary magnetic fields drape. FTE‐type FRs generally have magnetic field lines with one end embedded in the solar wind and the other end connected to the planet through the magnetospheric cusp. The investigation of FTEs in Mercury's magnetosphere is of particular interest because they often occur in large numbers with extremely small temporal spacing, i.e., FTE showers, that are not seen elsewhere. We find that the properties of the FTE‐type flux ropes in these showers depend upon plasma β in the magnetosheath and the magnetic shear angle across the magnetopause. The magnetic flux carried by these flux ropes dominates magnetic flux transfer between Mercury's dayside and nightside magnetosphere. These new results may contribute significantly to our understanding of solar wind‐magnetosphere‐exosphere coupling at Mercury.
Key Points
Flux transfer event (FTE) showers (≥10 flux ropes in a magnetopause crossing) are prevalent when shear angle is large and plasma β is small
FTE‐type flux rope duration, spacing, core field, and flux content during shower events are shown to depend upon shear angle and plasma β
FTE‐type flux ropes in shower events carry between 60% and 85% of the magnetic flux required to supply Mercury's Dungey cycle
The Miniaturized Electron pRoton Telescope, MERiT, is a low‐mass, low‐power, compact instrument using an innovative combination of particle detectors, sensor electronics, and onboard processing. ...MERiT is flying on the Compact Radiation belt Explorer, CeREs, a 3U CubeSat launched into a low earth orbit of 500‐km altitude and inclination of 85° on 16 December 2018. The primary and secondary science goals of CeREs are to investigate electron microbursts and to study solar particles. MERiT comprises a stack of solid state detectors (SSD) behind space facing avalanche photo diodes (APDs) surrounded by W‐Al shielding to reduce side‐penetrating particle background. The APD‐SSD combination enables measurement of electrons from 5 to 200 keV and 1 to 8 MeV; protons from 200–400 keV and 7–100 MeV in differential channels with energy resolution ΔE/E≈30% for both electrons and protons. MERiT measures microbursts with a high time resolution ranging from 4 to 16 ms and solar particles with a cadence of 1 s. MERiT energy channels and cadences are software configurable via algorithms and lookup tables residing on a field‐programmable gate array. The lookup tables can be changed via ground commands. MERiT geometry factor is 31 sq.cm‐sr and optimized to measure microbursts with the instrument viewing the local zenith in orbit. MERiT enables investigation of dynamical processes of radiation belt electron energization and loss, solar electron and proton transport, and their access to the Earth's polar caps. We describe the MERiT sensor design, calibration, operational modes, data products, and science goals.
•Physico-chemical characterization of nanotalcs.•Nanostructuring of new synthetic nanotalc in polyamide 6 and polypropylene matrices.•Improvement of thermal and mechanical properties of ...nanocomposites.
New layered synthetic nanotalc prepared at a lab-scale by a conventional hydrothermal process and commercial natural fine talc were used in order to establish a comparative study in terms of their contributions on the improvement of the final properties of two different polymers: a nonpolar polyolefin matrix and a polyamide. All samples were prepared by melt extrusion in a co-rotating microcompounder. The surface properties of talc – surface energy and isoelectric point – were probed. The particles’ crystalline structure and the distribution/dispersion within the polymer matrix were performed using transmission electron microscopy and X-ray diffraction. The effect of talc particles on the crystallinity, the thermal and mechanical properties was highlighted as a function of the surface properties of talc. In the case of talc-filled PP systems, it seems that the incorporation of both natural and synthetic talc greatly improves the thermal stability of polypropylene matrix. The highest elastic modulus was obtained in presence of highly nucleating natural talc. Oppositely, the best ductility was observed for the synthetic talc-filled PP systems. For PA6/talc nanocomposites, a remarkable improvement in the dispersion of talc layers was shown and a significant increase in Young’s modulus was determined due to the closer affinity between the hydrophilic nanotalc lamellae and the polar PA6 matrix.
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