The Sun moves through the local interstellar medium, continuously emitting ionized, supersonic solar wind plasma and carving out a cavity in interstellar space called the heliosphere. The recently launched Interstellar Boundary Explorer (IBEX) spacecraft has completed its first all-sky maps of the interstellar interaction at the edge of the heliosphere by imaging energetic neutral atoms (ENAs) emanating from this region. We found a bright ribbon of ENA emission, unpredicted by prior models or theories, that may be ordered by the local interstellar magnetic field interacting with the heliosphere. This ribbon is superposed on globally distributed flux variations ordered by both the solar wind structure and the direction of motion through the interstellar medium. Our results indicate that the external galactic environment strongly imprints the heliosphere.

We have assembled a data set of 1821 magnetopause crossings. Separate fits to subsets of this data set determine the magnetopause location as a function of solar wind dynamic pressure and interplanetary magnetic field orientation. Solar wind dynamic pressure variations produce self‐similar magnetopause motion on time scales of one hour or longer. We verify the pressure balance relationship between the solar wind dynamic pressure and the location of the subsolar magnetopause. We quantify the relationship between the IMF Bz, region l Birkeland current strength, the position of the subsolar magnetopause, and the shape of the dayside magnetosphere. Cross sections of the dayside magnetopause in planes perpendicular to the Earth‐Sun line are oblate.

X-ray images of the solar corona, taken on November 24, 1970, showed a magnetically open structure in the low corona which extended from N20W20 to the south pole. Analysis of the measured X-ray intensities shows the density scale heighl within the structure to be typically a factor of two less than that in the surrounding large scale magnetically closed regions. The structure is identified as a coronal hole.Since there have been several predictions that such a region should be the source of a high velocity stream in the solar wind, wind measurements for the appropriate period were traced back to the Sun by the method of instantaneous ideal spirals. A striking agreement was found between the Carrington longitude of the solar source of a recurrent high velocity solar wind stream and the position of the hole. Solar wind bulk velocity and photospheric magnetic field data from the period 1962-1970 indicate the possible extension of the result to the interpretation of long term variations in the wind pattern.

The magnetospheric imaging instrument (MIMI) is a neutral and charged particle detection system on the Cassini orbiter spacecraft designed to perform both global imaging and in-situ measurements to study the overall configuration and dynamics of Saturn's magnetosphere and its interactions with the solar wind, Saturn's atmosphere, Titan, and the icy satellites. The processes responsible for Saturn's aurora will be investigated; a search will be performed for substorms at Saturn; and the origins of magnetospheric hot plasmas will be determined. Further, the Jovian magnetosphere and Io torus will be imaged during Jupiter flyby. The investigative approach is twofold. (1) Perform remote sensing of the magnetospheric energetic (E > 7 keV) ion plasmas by detecting and imaging charge-exchange neutrals, created when magnetospheric ions capture electrons from ambient neutral gas. Such escaping neutrals were detected by the Voyager l spacecraft outside Saturn's magnetosphere and can be used like photons to form images of the emitting regions, as has been demonstrated at Earth. (2) Determine through in-situ measurements the 3-D particle distribution functions including ion composition and charge states (E > 3 keV/e). The combination of in-situ measurements with global images, together with analysis and interpretation techniques that include direct "forward modeling" and deconvolution by tomography, is expected to yield a global assessment of magnetospheric structure and dynamics, including (a) magnetospheric ring currents and hot plasma populations, (b) magnetic field distortions, (c) electric field configuration, (d) particle injection boundaries associated with magnetic storms and substorms, and (e) the connection of the magnetosphere to ionospheric altitudes. Titan and its torus will stand out in energetic neutral images throughout the Cassini orbit, and thus serve as a continuous remote probe of ion flux variations near 20R S (e.g., magnetopause crossings and substorm plasma injections). The Titan exosphere and its cometary interaction with magnetospheric plasmas will be imaged in detail on each flyby. The three principal sensors of MIMI consists of an ion and neutral camera (INCA), a charge-energy-mass-spectrometer (CHEMS) essentially identical to our instrument flown on the ISTP/Geotail spacecraft, and the low energy magnetospheric measurements system (LEMMS), an advanced design of one of our sensors flown on the Galileo spacecraft. The INCA head is a large geometry factor (G ∼ 2.4 cm 2 sr) foil time-of-flight (TOF) 234 S. M. KRIMIGIS ET AL. camera that separately registers the incident direction of either energetic neutral atoms (ENA) or ion species (≥5 • full width half maximum) over the range 7 keV/nuc < E < 3 MeV/nuc. CHEMS uses electrostatic deflection, TOF, and energy measurement to determine ion energy, charge state, mass, and 3-D anisotropy in the range 3 ≤ E ≤ 220 keV/e with good (∼0.05 cm 2 sr) sensitivity. LEMMS is a two-ended telescope that measures ions in the range 0.03 ≤ E ≤ 18 MeV and electrons 0.015 ≤ ...

[1] Spectra, integral moments, and composition (H, He, O, S) of energetic ions (50 keV to 50 MeV) are presented for selected Jupiter magnetospheric positions near the equator between radial distances of $6 to $46 Jupiter radii (R J ), as revealed by analysis of the Galileo Energetic Particle Detector data. These characteristics are then used as the basis of interpreting and modeling reported signatures of energetic ion/neutral gas interactions within Jupiter's inner magnetosphere, particularly energetic neutral atom emissions measured during the Cassini spacecraft flyby of Jupiter. Key findings include the following: (1) sulfur ions significantly dominate the energetic (!50 keV) ion density and pressure at all radial distances >7 R J ; (2) protons dominate integral number and energy intensity planetward of 20-25 R J ; (3) a distinct signature of local, equatorial acceleration of energetic protons is revealed between Io (5.9 R J ) and Europa (9.4 R J ); (4) significant spectral and compositional signatures of neutral gas interactions are also revealed between the orbits of Io and Europa; (5) a previously reported significant depletion of ring current ion populations between Io and Europa during the early-phase operation of Galileo ($1995), as compared with observations obtained during the Voyager epoch (1979), has persisted and probably deepened during later Galileo phases (1999); and (6) detailed energetic neutral atom emission modeling, based on the in situ results reported here, further constrains recent estimates of the contents of the neutral gas torus of Europa.

Voyager 1 (V1) began measuring precursor energetic ions and electrons from the heliospheric termination shock (TS) in July 2002. During the ensuing 2.5 years, average particle intensities rose as V1 penetrated deeper into the energetic particle foreshock of the TS. Throughout 2004, V1 observed even larger, fluctuating intensities of ions from 40 kiloelectron volts (keV) to >/=50 megaelectron volts per nucleon and of electrons from >26 keV to >/=350 keV. On day 350 of 2004 (2004/350), V1 observed an intensity spike of ions and electrons that was followed by a sustained factor of 10 increase at the lowest energies and lesser increases at higher energies, larger than any intensities since V1 was at 15 astronomical units in 1982. The estimated solar wind radial flow speed was positive (outward) at approximately +100 kilometers per second (km s(-1)) from 2004/352 until 2005/018, when the radial flows became predominantly negative (sunward) and fluctuated between approximately -50 and 0 km s(-1) until about 2005/110; they then became more positive, with recent values (2005/179) of approximately +50 km s(-1). The energetic proton spectrum averaged over the postshock period is apparently dominated by strongly heated interstellar pickup ions. We interpret these observations as evidence that V1 was crossed by the TS on 2004/351 (during a tracking gap) at 94.0 astronomical units, evidently as the shock was moving radially inward in response to decreasing solar wind ram pressure, and that V1 has remained in the heliosheath until at least mid-2005.

We present a new method for determining the shape of the magnetopause as a bivariate function of the hourly averaged solar wind dynamic pressure (p) and the north‐south component of the interplanetary magnetic field (IMF) Bz. We represent the magnetopause (for XGSE>−40RE) as an ellipsoid of revolution in solar‐wind‐aberrated coordinates and express the (p, Bz) dependence of each of the three ellipsoid parameters as a second‐order (6‐term) bivariate expansion in lnp and Bz. We define 12 overlapping bins in a normalized dimensionless (p, Bz) “control space” and fit an ellipsoid to those magnetopause crossings having (p, Bz) values within each bin. We also calculate the bivariate (lnp, Bz) moments to second order over each bin in control space. We can then calculate the six control‐space expansion coefficients for each of the three ellipsoid parameters in configuration space. From these coefficients we can derive useful diagnostics of the magnetopause shape as joint functions of p and Bz: the aspect ratio of the ellipsoid's minor‐to‐major axes; the flank distance, radius of curvature, and flaring angle (at XGSE = 0); and the subsolar distance and radius of curvature. We confirm and quantify previous results that during periods of southward Bz the subsolar magnetopause moves inward, while at XGSE = 0 the flank magnetopause moves outward and the flaring angle increases. These changes are most pronounced during periods of low pressure, wherein all have a dependence on Bz that is stronger and functionally different for Bz southward as compared to Bz northward (i.e., the behavior of a “half‐wave rectifier”). In contrast, all these changes are much less sensitive to IMF Bz at the highest pressures. As an application of these new results, we use a pressure balance relationship to estimate the difference between the magnetic field strength just inside the subsolar magnetopause and that of the dipole field, and we find that this difference decreases rapidly as Bz becomes more negative (although it is relatively insensitive to northward changes in Bz). Quantitative comparison shows that Region 1 Birkeland currents could make the dominant contribution to this depression in the inferred magnetic field at the subsolar point.

Simulations of energetic neutral atom (ENA) maps predict flux magnitudes that are, in some cases, similar to those observed by the Interstellar Boundary Explorer (IBEX) spacecraft, but they miss the ribbon. Our model of the heliosphere indicates that the local interstellar medium (LISM) magnetic field (B(LISM)) is transverse to the line of sight (LOS) along the ribbon, suggesting that the ribbon may carry its imprint. The force-per-unit area on the heliopause from field line draping and the LISM ram pressure is comparable with the ribbon pressure if the LOS approximately 30 to 60 astronomical units and B(LISM) approximately 2.5 microgauss. Although various models have advantages in accounting for some of the observations, no model can explain all the dominant features, which probably requires a substantial change in our understanding of the processes that shape our heliosphere.