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The recently published Interstellar Probe (ISP) study report describes a pragmatic mission concept with a launch window that starts in 2036 and is expected to reach several hundreds of astronomical units past the heliopause within a time frame of ≥50 years (https://interstellarprobe.jhuapl.edu/Interstellar-Probe-MCR.pdf). Following the ISP report, this paper, that will also be accessible from the Bulletin of the AAS (BAAS) in the framework of the Decadal Survey for Solar and Space Physics (Heliophysics) 2024–2033 (Dialynas et al., A future Interstellar Probe on the dynamic heliosphere and its interaction with the very local interstellar medium: In-situ particle and fields measurements and remotely sensed ENAs, 2022a), aims to highlight the importance of studying the physics of the interactions pertaining to the expanding solar wind that meets the plasma, gas and dust flows of the very local interstellar medium, forming the complex and vast region of our astrosphere. We focus on three fundamental open science questions that reveal the dynamical nature of the heliosphere A) Where are the heliosphere boundaries and how thick is the heliosheath B) Is there a “missing” pressure component towards exploring the dynamics of the global heliosheath and its interaction with the very local interstellar medium C) Why does the shape and size of the global heliosphere appear different in different Energetic Neutral Atom energies? We argue that these questions can only be addressed by exploiting a combination of in-situ charged particle, plasma waves and fields measurements with remotely sensed Energetic Neutral Atoms that can be measured simultaneously from the instruments of a future Interstellar Probe mission, along its trajectory from interplanetary space through the heliosheath and out to the very local interstellar medium.

We study the energy dependence of ~0.5-6 keV energetic neutral atom (ENA) spectra in the southern heliospheric polar region obtained during five six-month sky maps measured by IBEX-Hi. We calculate the spectral slopes in the south pole in four different energy bands, namely, ~0.7-1.1 keV, ~1.1-1.7 keV, ~1.7-2.7 keV, and ~2.7-4.3 keV. We show (1) a persistent flattening of the ENA spectrum between ~1 and 2 keV, (2) significantly different modes (2.31, 1.58, 0.97, and 1.44) for the distributions of the slopes in the four different energy bands, and (3) a general decrease with increasing energy in the widths (FWHM) and mode fluctuations (their spread) of the slope distributions. We also compare the averaged ENA spectra measured at the south pole and at mid-latitudes. We conclude that the flattening between ~1 and 2 keV in the polar spectrum (spectral break) is produced by an enhancement of ENAs created by charge exchange between interstellar neutrals and pick-up ions in the fast solar wind., United States. Dept. of Energy, United States. National Aeronautics and Space Administration

The ecliptic poles are observed continuously by the Interstellar Boundary Explorer (IBEX); thus, it is possible to discern temporal variations in the energetic neutral atoms (ENAs) from the outer heliosphere on timescales much shorter than the time it takes for IBEX to generate a full sky map (six months). Observations indicate that the ENA flux from the polar directions incident at Earth has been steadily decreasing for the two-year period from 2008 December through 2011 February. Over the IBEX-Hi energy range, the decrease in flux is energy dependent, varying at the south ecliptic pole from no drop at 0.71 keV, to 70% at 1.1 keV. At higher energies the drop ranges between 10% and 50%. The decline observed at the north ecliptic pole is as high as 48%, also at 1.1 keV. The trend correlates with the steady decline in solar wind dynamic pressure observed at 1 AU between 2005 and 2009, the likely period when solar wind protons that provide the source for ENAs observed by IBEX would have been outbound from the Sun. We propose a method by which the correlation between the 1 AU solar wind dynamic pressure and the ENA-derived pressure within the inner heliosheath (IHS) can be used to estimate the distance to the termination shock and the thickness of the IHS in the direction of the ecliptic poles. Our new analysis based on IBEX data shows the TS distances to be 110 AU and 134 AU at the south and north poles, respectively, and the corresponding IHS thicknesses to be 55 AU and 82 AU. Our analysis is consistent with the notion that the observed ENA fluxes originate in the IHS and their variations are driven by the solar wind as it evolves through the solar cycle.

A key indicator of the galactic environment of the Sun is provided by the magnetic field in the interstellar medium (ISM), which influences the shape of the heliosphere. The direction of the nearby interstellar magnetic field (ISMF) is determined from starlight polarized in the ISM. The local ISMF direction is found from the ISMF direction that provides the best fit to the polarization position angles of nearby stars, using weighted fits to the data. New polarization observations are included in the analysis. The best-fitting ISMF is close to the magnetic field direction traced by the center of the Ribbon of energetic neutral atoms, discovered by the Interstellar Boundary Explorer spacecraft. Both the magnetic field and kinematics of the local ISM are consistent with a scenario where the local ISM is a fragment of the Loop I superbubble. An ordered component of the local ISMF is found in a region where PlanetPol data show that polarization increases with distance. It extends to within 8 parsecs of the Sun and implies a weak curvature in the nearby ISMF. Variations from the ordered component indicate turbulence of +/-23 deg. The local ISMF is generally uniform in direction over spatial scales of 8-200 parsecs so that it appears similar to interarm magnetic fields. The best-fitting ISMF direction also agrees with the position of tail-in spatial asymmetries in GeV-TeV galactic cosmic rays. The peculiar geometrical relation between the CMB dipole moment, the heliosphere nose, and local ISMF is supported by these new results. Radiative torques are not likely to play a role in grain alignment for these polarizations., Comment: Accepted by the Astrophysical Journal. Changes from version 1 include addition of an appendix and fixing typos

A key indicator of the galactic environment of the Sun is provided by the magnetic field in the interstellar medium (ISM), which influences the shape of the heliosphere. The direction of the nearby interstellar magnetic field (ISMF) is determined from starlight polarized in the ISM. The local ISMF direction is found from the ISMF direction that provides the best fit to the polarization position angles of nearby stars, using weighted fits to the data. New polarization observations are included in the analysis. The best-fitting ISMF is close to the magnetic field direction traced by the center of the Ribbon of energetic neutral atoms, discovered by the Interstellar Boundary Explorer spacecraft. Both the magnetic field and kinematics of the local ISM are consistent with a scenario where the local ISM is a fragment of the Loop I superbubble. An ordered component of the local ISMF is found in a region where PlanetPol data show that polarization increases with distance. It extends to within 8 parsecs of the Sun and implies a weak curvature in the nearby ISMF. Variations from the ordered component indicate turbulence of +/-23 deg. The local ISMF is generally uniform in direction over spatial scales of 8-200 parsecs so that it appears similar to interarm magnetic fields. The best-fitting ISMF direction also agrees with the position of tail-in spatial asymmetries in GeV-TeV galactic cosmic rays. The peculiar geometrical relation between the CMB dipole moment, the heliosphere nose, and local ISMF is supported by these new results. Radiative torques are not likely to play a role in grain alignment for these polarizations., Comment: Accepted by the Astrophysical Journal. Changes from version 1 include addition of an appendix and fixing typos

Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + ClONO2 + 2N2O5 + ...) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self-consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NO2 reservoir are well understood in the lower stratosphere.

Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + ClONO2 + 2N2O5 + ...) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self-consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NO2 reservoir are well understood in the lower stratosphere.

Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + ClONO2 + 2N2O5 + ...) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self-consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NO2 reservoir are well understood in the lower stratosphere.

Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + ClONO2 + 2N2O5 + ...) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self-consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NO2 reservoir are well understood in the lower stratosphere.

Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + ClONO2 + 2N2O5 + ...) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self-consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NO2 reservoir are well understood in the lower stratosphere.

Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + ClONO2 + 2N2O5 + ...) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self-consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO2 measurements, suggesting that the reactions affecting the partitioning of the NO2 reservoir are well understood in the lower stratosphere.