Measurements by dust detectors on interplanetary spacecraft appear to indicate a substantial flux of interstellar particles with masses exceeding 10^{-12}gram. The reported abundance of these massive grains cannot be typical of interstellar gas: it is incompatible with both interstellar elemental abundances and the observed extinction properties of the interstellar dust population. We discuss the likelihood that the Solar System is by chance located near an unusual concentration of massive grains and conclude that this is unlikely, unless dynamical processes in the ISM are responsible for such concentrations. Radiation pressure might conceivably drive large grains into "magnetic valleys". If the influx direction of interstellar gas and dust is varying on a ~10 yr timescale, as suggested by some observations, this would have dramatic implications for the small-scale structure of the interstellar medium.
High-resolution ultraviolet observations of nearby bright and faint stars are required to evaluate changes in the past and future galactic environments of the Sun, and the possibly impact of these changes on the interplanetary environment at 1 AU (around the Earth). The boundary conditions of the heliosphere and interplanetary environments are constrained by the characteristics of the surrounding interstellar material (ISM), which changes on timescales of 10^3-10^5 years. An increase in the density of the interstellar cloud surrounding the solar system to 10 cm^-3 decreases the heliosphere rad…
Several sets of data show that small interstellar grains captured in interstellar magnetic fields draped over the heliosphere appear to polarize the light of nearby stars. The maximum polarization direction is offset in ecliptic longitude by about +35 from the upwind direction, and the polarization peak is enhanced for stars near the ecliptic plane. A band of weak polarization stretches through the southern ecliptic hemisphere to the downwind direction. The interstellar field at the heliosphere is directed towards l=105 deg, forming an angle of about 75 deg. with the inflowing gas. Grain align…
Tiny interstellar dust grains causing the polarization of light from the nearest stars are deflected sideways in the outer heliosheath regions, along with the interstellar magnetic field. Observations of optical polarization of stars beyond the heliosphere nose, suggest the direction of the upwind interstellar magnetic field is relatively constant. The polarizations of nearby stars and offset angle between HeI and HeI flowing into the heliosphere have position angles in galactic coordinates of 30- 40 deg, indicating a local magnetic field direction inclined by ~55 deg and ~65 deg, respectively…
The properties of the Local Bubble, Local Fluff complex of nearby interstellar clouds, and the heliosphere are mutually constrained by data and theory. Observations and models of the diffuse radiation field, interstellar ionization, pick-up ion and anomalous cosmic-ray populations, and interstellar dust link the physics of these regions. The differences between the one-asymmetric-superbubble and two-superbubble views of the Local Bubble are discussed.
Because of the dynamic nature of the interstellar medium, the Sun should have encountered a variety of different interstellar environments in its lifetime. As the solar wind interacts with the surrounding interstellar medium to form a heliosphere, different heliosphere shapes, sizes, and particle contents result from the different environments. Some of the large possible interstellar parameter space (density, velocity, temperature) is explored here with the help of global heliosphere models, and the features in the resulting heliospheres are compared and discussed. The heliospheric size, expre…
The interstellar cloud surrounding the solar system regulates the galactic environment of the Sun, and determines the boundary conditions of the heliosphere. Both the Sun and interstellar clouds move through space, so these boundary conditions change with time. Data and theoretical models now support densities in the cloud surrounding the solar system of n(HI)=0.22+/-0.06 cm^-3, and n(e-)~0.1 cm-3, with larger values allowed for n(HI) by radiative transfer considerations. Ulysses and Extreme Ultraviolet Explorer satellite HeI data yield a cloud temperature of 6,400 K. Nearby interstellar gas a…
Observations of the weak polarization of light from nearby stars, reported by Tinbergen (1982), are consistent with polarization by small, radius <0.14 microm, interstellar dust grains entrained in the magnetic wall of the heliosphere. The direction of maximum polarization is offset by ~35 deg from the heliosphere nose, and extends to low ecliptic latitudes. An offset is found between the direction of the best aligned dust grains, and the upwind direction of the undeflected large interstellar grains seen by Ulysses and Galileo. In the aligned-grain region, the strength of polarization anti-cor…
The interaction of dust grains originating from the local interstellar cloud with the environment inside the heliosphere is investigated. As a consequence of this interaction the spatial distribution of interstellar dust grains changes with time. Since dust grains are charged in the interplanetary plasma and radiation environment, the interaction of small grains with the heliosphere is dominated by their coupling to the solar wind magnetic field. The change of the field polarity with the solar cycle imposes a temporal variation of the spatial distribution and the flux of small (radius smaller …
Radiative transfer equilibrium models of nearby interstellar matter (ISM) yield the boundary conditions of the heliosphere when constrained with observations of ISM inside and outside of the heliosphere. Filtration factors for interstellar neutrals crossing the heliosheath region, from charge exchange with interstellar plasma, are given for H, He, N, O, Ar, and Ne. The best models predict n(HI)~0.2 /cc, n(e)~0.1 /cc, however if the isotropic 2 kHz emission observed by Voyager (Kurth & Gurnett 2003) is formed in the surrounding ISM, an alternate model with lower electron densities is indicated.…
Many studies of the Loop I magnetic superbubble place the Sun at the edges of the bubble. One recent study models the polarized radio continuum of Loop I as two magnetic shells with the Sun embedded in the rim of the 'S1' shell. If the Sun is in such a shell, it should be apparent in both the local interstellar magnetic field and the distribution of nearby interstellar material. The properties of these subshells are compared to optical polarization data that trace the nearby interstellar magnetic field (ISMF), and the distribution of interstellar FeII and CaII within about 55 pc of the Sun. Th…
Interstellar matter (ISM) sets the boundary conditions of the heliosphere and dominates the interplanetary medium. The heliosphere configuration has varied over recent history, as the Sun emerged from the Local Bubble and entered a turbulent outflow of cloudlets originating from the Scorpius-Centaurus Association direction. Several indicators suggest that the local interstellar magnetic field is weak and parallel to the galactic plane. Observations of the interaction products of the ISM with the heliosphere, such as pickup ions and anomalous cosmic rays, when combined with data on the ISM towa…
The boundary conditions of the heliosphere are set by the ionization, density and composition of inflowing interstellar matter. Constraining the properties of the Local Interstellar Cloud (LIC) at the heliosphere requires radiative transfer ionization models. We model the background interstellar radiation field using observed stellar FUV and EUV emission and the diffuse soft X-ray background. We also model the emission from the boundary between the LIC and the hot Local Bubble (LB) plasma, assuming that the cloud is evaporating because of thermal conduction. We create a grid of models covering…
We study the influence of the non-flat shape of the solar Lyman-alpha line on the distribution of neutral interstellar hydrogen in the inner heliosphere and assess importance of this effect for interpretation of heliospheric in situ measurements. Based on available data, construct a model of evolution of the solar Lyman-alpha line profile with solar activity. Modify an existing test-particle code calculating distribution of neutral interstellar hydrogen in the inner heliosphere to take into account the dependence of radiation pressure on radial velocity. Discrepancies between the classical and…
In the early 1990s, after its Jupiter flyby, the Ulysses spacecraft identified interstellar dust in the solar system. Since then the in-situ dust detector on board Ulysses continuously monitored interstellar grains with masses up to 10e-13 kg, penetrating deep into the solar system. While Ulysses measured the interstellar dust stream at high ecliptic latitudes between 3 and 5 AU, interstellar impactors were also measured with the in-situ dust detectors on board Cassini, Galileo and Helios, covering a heliocentric distance range between 0.3 and 3 AU in the ecliptic plane. The interstellar dust …
With the plethora of detailed results from heliospheric missions and at the advent of the first mission dedicated IBEX, we have entered the era of precision heliospheric studies. Interpretation of these data require precision modeling, with second-order effects quantitatively taken into account. We study the influence of the non-flat shape of the solar Ly-alpha line on the distribution of neutral interstellar H in the inner heliosphere. Based on available data, we (i) construct a model of evolution for the solar Ly-alpha line profile with solar activity, (ii) modify an existing test-particle c…
Galactic interstellar dust (ISD) is the major ingredient in planetary formation. However, information on this important material has been extremely limited. Recently the Ulysses dust detector has identified and measured interstellar dust outside 1.8~AU from the Sun at ecliptic latitudes above $50^{\circ}$. Inside this distance it could not reliably distinguish interstellar from interplanetary dust. Modeling the Ulysses data suggests that up to 30 % of dust flux with masses above $10^{-16}\rm kg$ at 1~AU is of interstellar origin. From the Hiten satellite in high eccentric orbit about the Earth…
The physical properties and kinematics of the partially ionized interstellar material near the Sun are typical of warm diffuse clouds in the solar vicinity. The interstellar magnetic field at the heliosphere and the kinematics of nearby clouds are naturally explained in terms of the S1 superbubble shell. The interstellar radiation field at the Sun appears to be harder than the field ionizing ambient diffuse gas, which may be a consequence of the low opacity of the tiny cloud surrounding the heliosphere. The spatial context of the Local Bubble is consistent with our location in the Orion spur.
We use self-consistent kinetic/hydrodynamic models of the heliosphere to predict H I Lyman-alpha absorption profiles for various lines of sight through the heliosphere. These results are compared with Lyman-alpha absorption lines of six nearby stars observed by the Hubble Space Telescope. The directions of these lines of sight range from nearly upwind (36 Oph) to nearly downwind (Epsilon Eri). Only three of the Lyman-alpha spectra (36 Oph, Alpha Cen, and Sirius) actually show evidence for the presence of heliospheric absorption, which is blended with the ubiquitous interstellar absorption, but…
We study the EUV/soft X-ray emission generated by charge transfer between solar wind heavy ions and interstellar H and He neutral atoms in the inner Heliosphere. We present heliospheric maps and spectra for stationary solar wind, depending on solar cycle phase, solar wind anisotropies and composition, line of sight direction and observer position. A time-dependant simulation of the X-ray intensity variations due to temporary solar wind enhancement is compared to XMM Newton recorded data of the Hubble Deep Field North observation (Snowden et al. 2004). Results show that the heliospheric compone…
Opher et al. 2006 showed that an interstellar magnetic field parallel to the plane defined by the deflection of interstellar hydrogen atoms can produce a north/south asymmetry in the distortion of the solar wind termination shock. This distortion is consistent with Voyager 1 and Voyager 2 observations of the direction of field-aligned streaming of the termination shock particles upstream the shock. The model also indicates that such a distortion will result in a significant north/south asymmetry in the distance to the shock and the thickness of heliosheath. The two Voyager spacecraft should re…
Redshifted L$α$ absorption toward $α$ Cen has been interpreted by Linsky & Wood (1996) and Frisch et al. (1996) as evidence for decelerated interstellar hydrogen piled up on the upstream side of the heliosphere. We utilize newly developed two-dimensional multi-fluid models of the solar wind interaction with the ISM to corroborate this interpretation by synthesizing the L$α$ absorption profile predicted for this ``hydrogen wall''. Both subsonic and supersonic inflow into the heliosphere are considered, corresponding to one-shock and two-shock global morphologies, respectively. It is found that …
The solar system is moving through the partially ionized local interstellar cloud (LIC). The ionized matter of the LIC interacts with the expanding solar wind forming the heliospheric interface. The neutral component (interstellar atoms) penetrates through the heliospheric interface into the heliosphere, where it is measured directly "in situ" as pick-up ions and neutral atoms (and as anomalous cosmic rays) or indirectly through resonant scattering of solar Ly-alpha. When crossing the heliospheric interface, interstellar atoms interact with the plasma component through charge exchange. This in…
Combined heliosphere-astronomical data and models enrich our understanding both of effects the solar galactic environment might have on the inner heliosphere, and of interstellar clouds. Present data suggest that FeII/DI increases toward the upwind direction of the cluster of interstellar clouds (CLIC) flowing past the Sun. Cloud kinematics and abundances suggest an origin related to a supershell around the Scorpius-Centaurus Association. The solar space trajectory indicates the Sun entered the CLIC gas relatively recently.
The heliosphere serves as a probe of interstellar material (ISM) close to the Sun. Measurements of ISM inside and outside of the heliosphere show that we reside in typical warm partially ionized ISM that can be successfully modeled using equilibrium photoionization models. The heliosphere wake leaves a ~200 X 1000 AU trail in space of low density, n<0.05 /cc, cooling plasma comingled with ISM. The closest ISM flows through the solar vicinity at V_LSR ~20 km/s, with an upwind direction towards the Scorpius-Centaurus Association. Clouds in this flow have thicknesses typically <1 pc. The flow is …
Recent results on nearby interstellar gas and interstellar byproducts within the solar system are used to select among the equilibrium radiative transfer models of the nearest interstellar material of Slavin and Frisch (2002). Assuming O/H~400 ppm, Models 2 and 8 are found to yield good fits to available data on local interstellar material, and pickup ions and anomalous cosmic rays inside of the heliosphere, with the exception of Ne. For these models, the density of interstellar gas at the entry point to the heliosphere is n(HI)~0.20 /cc and n(e-)~0.1 /cc. These models suggest the chemical com…
Observations of interstellar gas and dust towards nearby stars and within the solar system show that the Sun is embedded in a warm diffuse partially-ionized cloud. This cloud is the leading edge of a flow of interstellar matter (ISM) through our Galactic neighborhood. Interstellar matter sets the boundary conditions of the heliosphere and astrospheres of extra-solar planetary systems. Moreover, the interplanetary regions in these systems are sensitive to inflowing ISM.
The gas-to-dust mass ratios found for interstellar dust within the Solar System, versus values determined astronomically for the cloud around the Solar System, suggest that large and small interstellar grains have separate histories, and that large interstellar grains preferentially detected by spacecraft are not formed exclusively by mass exchange with nearby interstellar gas. Observations by the Ulysses and Galileo satellites of the mass spectrum and flux rate of interstellar dust within the heliosphere are combined with information about the density, composition, and relative flow speed and…
Most cosmic ray antiprotons observed near the Earth are secondaries produced in collisions of energetic cosmic ray (CR) particles with interstellar gas. The spectrum of secondary antiprotons is expected to peak at ~2 GeV and decrease sharply at lower energies. This leaves a low energy window in which to look for signatures of exotic processes such as evaporation of primordial black holes or dark matter annihilation. In the inner heliosphere, however, modulation of CRs by the solar wind makes analysis difficult. Detecting these antiprotons outside the heliosphere on an interstellar probe remove…
At present, the heliosphere is embedded in a warm low density interstellar cloud that belongs to a cloud system flowing through the local standard of rest with a velocity near ~18 km/s. The velocity structure of the nearest interstellar material (ISM), combined with theoretical models of the local interstellar cloud (LIC), suggest that the Sun passes through cloudlets on timescales of < 10^3 - 10^4 yr, so the heliosphere has been, and will be, exposed to different interstellar environments over time. By means of a multi-fluid model that treats plasma and neutral hydrogen self-consistently, the…
Aims: Investigate/Study de-charging of solar wind C, N, O, Mg, Si and S ions and assess fluxes of resulting ENA in the heliosphere. Methods: The model treats the heavy ions as test particles convected by (and in a particular case also diffusing through) a hydrodynamically calculated background plasma flow, from 1 AU to the termination shock (TS), to heliosheath (HS) and finally to heliospheric tail (HT). The ions undergo radiative and dielectronic recombinations, charge exchanges, photo- and electron impact ionizations with plasma particles, interstellar neutral atoms (calculated on a Monte-Ca…
Modeling of the global heliosphere seeks to investigate the interaction of the solar wind with the partially ionized local interstellar medium. Models that treat neutral hydrogen self-consistently and in great detail, together with the plasma, but that neglect magnetic fields, constitute a sub-category within global heliospheric models. There are several different modeling strategies used for this sub-category in the literature. Differences and commonalities in the modeling results from different strategies are pointed out. Plasma-only models and fully self-consistent models from four research…
The interaction of the heliosphere with interstellar clouds has attracted interest since the late 1920's, both with a view to explaining apparent quasi-periodic climate "catastrophes" as well as periodic mass extinctions. Until recently, however, models describing the solar wind - local interstellar medium (LISM) interaction self-consistently had not been developed. Here, we describe the results of a two-dimensional (2D) simulation of the interaction between the heliosphere and an interstellar cloud with the same properties as currently, except that the neutral H density is increased from the …
The detection of high-energy particles, cosmic rays (CRs), deep inside the heliosphere implies that there are, at least, three distinctly different stages in the lifetime of a CR particle: acceleration, propagation in the interstellar medium (ISM), and propagation in the heliosphere. Gamma rays produced by interactions of CRs with gas, radiation, and magnetic fields can be used to study their spectra in different locations. Still, accurate direct measurements of CR species inside the heliosphere (such as their spectra and abundances) are extremely important for the understanding of their origi…
High-energy collisions of cosmic-ray nuclei with interstellar gas are believed to be the mechanism producing the majority of cosmic ray antiprotons. Due to the kinematics of the process they are created with a nonzero momentum; the characteristic spectral shape with a maximum at ~2 GeV and a sharp decrease towards lower energies makes antiprotons a unique probe of models for particle propagation in the Galaxy and modulation in the heliosphere. On the other hand, accurate calculation of the secondary antiproton flux provides a ``background'' for searches for exotic signals from the annihilation…
