Parker Solar Probe (PSP) observations of a small dispersive event on 2022 February 27 and 28 indicate scatter-free propagation as the dominant transport mechanism between the low corona and greater ...than 35 solar radii. The event occurred during unique orbital conditions that prevailed along specific flux tubes that PSP encountered repeatedly between 25 and 35 Rs during outbound orbit 11. This segment of the PSP orbit exhibits almost stationary angular motion relative to the rotating solar surface, such that in the rotating frame, PSP’s motion is essentially radial. The time dispersion often observed in impulsive solar energetic particle (SEP) events continues in this case down to velocities including the core solar-wind ion velocities. Especially at the onset of this event, the 3He content is much larger than the usual SEP abundances seen in the energy range from ∼100 keV to several MeV for helium. Later in the event, iron is enhanced. The compositional signatures suggest this to be an example of an acceleration mechanism for generating the seed energetic particles required by shock (or compression) acceleration models in SEP events to account for the enrichment of various species above solar abundances in such events. A preliminary search of similar orbital conditions over the PSP mission has not revealed additional such events, although favorable conditions (isolated impulsive acceleration and well-ordered magnetic field connection with minimal magnetic field fluctuation) that would be required are infrequently realized, given the small fraction of the PSP trajectory that meets these observation conditions.
A detailed overview of the knowledge gaps in our understanding of the heliospheric interaction with the largely unexplored Very Local Interstellar Medium (VLISM) are provided along with predictions ...of with the scientific discoveries that await. The new measurements required to make progress in this expanding frontier of space physics are discussed and include in-situ plasma and pick-up ion measurements throughout the heliosheath, direct sampling of the VLISM properties such as elemental and isotopic composition, densities, flows, and temperatures of neutral gas, dust and plasma, and remote energetic neutral atom (ENA) and Lyman-alpha (LYA) imaging from vantage points that can uniquely discern the heliospheric shape and bring new information on the interaction with interstellar hydrogen. The implementation of a pragmatic Interstellar Probe mission with a nominal design life to reach 375 Astronomical Units (au) with likely operation out to 550 au are reported as a result of a 4-year NASA funded mission study.
The solar wind has been measured directly from 0.3 AU outward, and the Sun's atmosphere has been imaged from the photosphere out through the corona. These observations have significantly advanced our ...understanding of the influence of the Sun's varying magnetic field on the structure and dynamics of the corona and the solar wind. However, how the corona is heated and accelerated to produce the solar wind remains a mystery. Answering these fundamental questions requires in situ observations near the Sun, from a few solar radii (RS) out to ∼20 RS, where the internal, magnetic, and turbulent energy in the coronal plasma is channeled into the bulk energy of the supersonic solar wind. A mission to make such observations has long been a top priority of the solar and space physics community. The recent Solar Probe study has proven that such a mission is technically feasible and can be accomplished within reasonable resources.
Context.
The observation of numerous magnetic switchbacks and associated plasma jets in Parker Solar Probe (PSP) during its first five orbits, particularly near the Sun, has attracted considerable ...attention. Switchbacks have been found to be systematically associated with correlated reversals in the direction of the propagation of Alfvénic fluctuations, as well as similar reversals of the electron strahl.
Aims.
Here we aim to see whether the energetic particles change direction at the magnetic field switchbacks.
Methods.
We use magnetic field data from the MAG suite’s fluxgate magnetometer instrument to identify switchback regions. We examine the radial anisotropy of the energetic particles measured by the EPI-Lo instrument of the IS⊙IS suite.
Results.
We find that energetic particles measured by EPI-Lo generally do not preferentially change their directionality from that of the background magnetic field to that of the switchbacks.
Conclusions.
A reasonable hypothesis is that particles with smaller gyroradii, such as strahl electrons, can reverse direction by following the magnetic field in switchbacks, but that larger gyroradii particles cannot. This provides the possibility of setting a constraint on the radius of the curvature of the magnetic field in switchbacks, a property not otherwise observed by PSP. We expect that particles at higher energies than those detectable by EPI-Lo will also not respond to switchbacks. The observed reversals of radial energetic particle flux are separate phenomena, likely associated with source locations or other propagation effects occurring at greater radial distances.
The Cassini spacecraft passed within 168.2 kilometers of the surface above the southern hemisphere at 19:55:22 universal time coordinated on 14 July 2005 during its closest approach to Enceladus. ...Before and after this time, a substantial atmospheric plume and coma were observed, detectable in the Ion and Neutral Mass Spectrometer (INMS) data set out to a distance of over 4000 kilometers from Enceladus. INMS data indicate that the atmospheric plume and coma are dominated by water, with significant amounts of carbon dioxide, an unidentified species with a mass-to-charge ratio of 28 daltons (either carbon monoxide or molecular nitrogen), and methane. Trace quantities (<1%) of acetylene and propane also appear to be present. Ammonia is present at a level that does not exceed 0.5%. The radial and angular distributions of the gas density near the closest approach, as well as other independent evidence, suggest a significant contribution to the plume from a source centered near the south polar cap, as distinct from a separately measured more uniform and possibly global source observed on the outbound leg of the flyby.
We present an analysis of Parker Solar Probe (PSP) IS IS observations of ∼30-300 keV n−1 ions on 2018 November 11 when PSP was about 0.25 au from the Sun. Five hours before the onset of a solar ...energetic particle (SEP) event, a coronal mass ejection (CME) was observed by STEREO-A/COR2, which crossed PSP about a day later. No shock was observed locally at PSP, but the CME may have driven a weak shock earlier. The SEP event was dispersive, with higher energy ions arriving before the lower energy ones. Timing suggests the particles originated at the CME when it was at ∼7.4R . SEP intensities increased gradually from their onset over a few hours, reaching a peak, and then decreased gradually before the CME arrived at PSP. The event was weak, having a very soft energy spectrum (−4 to −5 spectral index). The earliest arriving particles were anisotropic, moving outward from the Sun, but later, the distribution was observed to be more isotropic. We present numerical solutions of the Parker transport equation for the transport of 30-300 keV n−1 ions assuming a source comoving with the CME. Our model agrees well with the observations. The SEP event is consistent with ion acceleration at a weak shock driven briefly by the CME close to the Sun, which later dissipated before arriving at PSP, followed by the transport of ions in the interplanetary magnetic field.
Jets of water ice from surface fractures near the south pole of Saturn's icy moon Enceladus produce a plume of gas and particles. The source of the jets may be a liquid water region under the ice ...shell-as suggested most recently by the discovery of salts in E-ring particles derived from the plume-or warm ice that is heated, causing dissociation of clathrate hydrates. Here we report that ammonia is present in the plume, along with various organic compounds, deuterium and, very probably, (40)Ar. The presence of ammonia provides strong evidence for the existence of at least some liquid water, given that temperatures in excess of 180K have been measured near the fractures from which the jets emanate. We conclude, from the overall composition of the material, that the plume derives from both a liquid reservoir (or from ice that in recent geological time has been in contact with such a reservoir) as well as from degassing, volatile-charged ice.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Energetic charged particles are pervasive throughout the heliosphere with contributions from solar energetic particle events, stream and corotating interaction regions, galactic cosmic rays, ...anomalous cosmic rays, and suprathermal ions. The Integrated Science Investigation of the Sun (IS⊙IS) on board the Parker Solar Probe is a suite of energetic particle detectors covering the energy range ∼20 keV–200 MeV nuc
−1
. IS⊙IS measures energetic particles closer to the Sun than any instrument suite in history, providing a singular view of the energetic particle population in a previously unexplored region. To enable the global research community to efficiently use IS⊙IS data, we have developed an online living catalog of energetic particle enhancements observed by the IS⊙IS instruments. Event identification methodology, information on accessing the catalog, highlights of several events, and a summary of the overall trends are presented. Also included is a summary Event Catalog showing many of the key event parameters for IS⊙IS events to the time of writing.
Composition of Titan's ionosphere Cravens, T. E.; Robertson, I. P.; Waite, J. H. ...
Geophysical research letters,
April 2006, Letnik:
33, Številka:
7
Journal Article
Recenzirano
Odprti dostop
We present Cassini Ion and Neutral Mass Spectrometer (INMS) measurements of ion densities on the nightside of Titan from April 16, 2005, and show that a substantial ionosphere exists on the nightside ...and that complex ion chemistry is operating there. The total ionospheric densities measured both by the INMS and the Cassini Radio and Plasma Wave (RPWS) experiments on Cassini suggest that precipitation from the magnetosphere into the atmosphere of electrons with energies ranging from 25 eV up to about 2 keV is taking place. The absence of ionospheric composition measurements has been a major obstacle to understanding the ionosphere. Seven “families” of ion species, separated in mass‐to‐charge ratio by 12 Daltons (i.e., the mass of carbon), were observed and establish the importance of hydrocarbon and nitrile chains in the upper atmosphere. Several of the ion species measured by the INMS were predicted by models (e.g., HCNH+ and C2H5+). But the INMS also saw high densities at mass numbers not predicted by models, including mass 18, which we suggest will be ammonium ions (NH4+) produced by reaction of other ion species with neutral ammonia.
The Cassini Ion and Neutral Mass Spectrometer (INMS) investigation will determine the mass composition and number densities of neutral species and low-energy ions in key regions of the Saturn system. ...The primary focus of the INMS investigation is on the composition and structure of Titan's upper atmosphere and its interaction with Saturn's magnetospheric plasma. Of particular interest is the high-altitude region, between 900 and 1000 km, where the methane and nitrogen photochemistry is initiated that leads to the creation of complex hydrocarbons and nitriles that may eventually precipitate onto the moon's surface to form hydrocarbon-nitrile lakes or oceans. The investigation is also focused on the neutral and plasma environments of Saturn's ring system and icy moons and on the identification of positive ions and neutral species in Saturn's inner magnetosphere. Measurement of material sputtered from the satellites and the rings by magnetospheric charged particle and micrometeorite bombardment is expected to provide information about the formation of the giant neutral cloud of water molecules and water products that surrounds Saturn out to a distance of approximately 12 planetary radii and about the genesis and evolution of the rings. The INMS instrument consists of a closed ion source and an open ion source, various focusing lenses, an electrostatic quadrupole switching lens, a radio frequency quadrupole mass analyzer, two secondary electron multiplier detectors, and the associated supporting electronics and power supply systems. The INMS will be operated in three different modes: a closed source neutral mode, for the measurement of non-reactive neutrals such as N2 and CH4; an open source neutral mode, for reactive neutrals such as atomic nitrogen; and an open source ion mode, for positive ions with energies less than 100 eV. Instrument sensitivity is greatest in the first mode, because the ram pressure of the inflowing gas can be used to enhance the density of the sampled non-reactive neutrals in the closed source antechamber. In this mode, neutral species with concentrations on the order of not less than 10 exp 4/cu cm will be detected (compared with not less than 10 exp 5/cu cm in the open source neutral mode). For ions the detection threshold is on the order of 10 exp -2/cu cm at Titan relative velocity (6 km/sec). The INMS instrument has a mass range of 1-99 Daltons and a mass resolution M/Delta-M of 100 at 10 percent of the mass peak height, which will allow detection of heavier hydrocarbon species and of possible cyclic hydrocarbons such as C6H6. The INMS instrument was built by a team of engineers and scientists working at NASA's Goddard Space Flight Center (Planetary Atmospheres Laboratory) and the University of Michigan (Space Physics Research Laboratory). INMS development and fabrication were directed by Dr. Hasso B. Niemann (Goddard Space Flight Center). The instrument is operated by a Science Team, which is also responsible for data analysis and distribution.
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