Research relative to the heavy isotope spectrometer telescope experiment

The Heavy Isotope Spectrometer Telescope (HIST) was launched during August 1978 on ISEE-3 (ICE). HIST was designed to measure the isotopic composition of solar, galactic, and interplanetary cosmic ray nuclei for the elements from H to Ni (1 less than or equal to Z less than or equal to 28) in the energy range from approximately 5 to approximately 200 MeV/nucleon. The results of these measurements have been used in studies of the composition of solar matter and galactic cosmic ray sources, the study of nucleosynthesis processes, studies of particle acceleration and propagation, and studies of the life-history of cosmic rays in the heliosphere and in the galaxy. On December 1, 1978, after 110 days in orbit, HIST suffered an electronic failure in its readout system. After that point, only one-half of the telemetry bits associated with the pulse heights measured by HIST were transmitted to Earth. As a result, the resolution of HIST was significantly degraded, and it served as an element rather than an isotope spectrometer. Fortunately, HIST was able to measure the isotopic composition of heavy nuclei in the 9/23/78 solar event (the largest solar energetic particle event since 1972) during the brief period that it operated at full resolution. This grant funded the analysis of data from the HIST instrument over the period from 12/1/85 to 11/30/92. In section 2 of this final report, we summarize the scientific accomplishments that have resulted from HIST measurements during this time period. A bibliography of tasks and papers that resulted is attached

Our heliosphere: The new view from Voyager

Launched in 1977 on a journey to the giant outer planets and beyond, Voyager 1 and 2 have explored the spatial and dynamical properties of the heliosphere that modulates the inward flow of galactic cosmic rays and is the source of anomalous cosmic rays. The two spacecraft are in the heliosheath beyond the termination shock where the supersonic solar wind has slowed as it approaches the boundary of the heliosphere. The shock crossing was 10 AU closer at Voyager 2 in the south than at Voyager 1 in the north, indicating a local interstellar magnetic field pressing inward more strongly on the southern hemisphere. The expected source of anomalous cosmic rays was not observed at the shock, and their intensity has increased deeper in the heliosheath, indicating the source is elsewhere on the shock or in the heliosheath. Voyager 1, now at 121 AU at 35 degrees north, has been in a quasi-stagnation region since 2010 where there is no outward motion of the wind, the magnetic field is enhanced, and the galactic cosmic ray intensity is increasing. In contrast, the heliosheath flow at Voyager 2 at 99 AU and 30 degrees south is faster and increasingly deflected in a non-radial direction as it turns to flow tailward. These observations will be placed in the context of current models of the interaction of the solar and interstellar winds

Voyager 1 in the Vicinity of the Termination Shock: an Overview of Observations beyond 94 AU in the Heliosheath

Voyager 1 has crossed the termination shock, a major milestone in its journey to interstellar space. Since mid-2002, Voyager 1 has been moving outward with the shock, which reached its maximum distance in mid-2004 and starting moving back in as the solar wind pressure declined. On December 15, 2004, the intensity of low energy ions increased rapidly as the termination shock approached Voyager, and plasma waves excited by electrons streaming along the magnetic field indicated the shock was nearby. Voyager 1 crossed the inward moving shock on December 16 at 94 AU, observing the enhanced magnetic field as expected in the subsonic flow in the heliosheath. The lowest energy particles also abruptly increased with a low energy spectral slope of approximately -1.5, corresponding to a shock strength of ~2.5. In distinction to the upstream ions which were highly variable and strongly beamed along the magnetic field, in the heliosheath the energetic ion intensity is much less variable and more nearly isotropic, indicating a stable shock source and steady conditions for diffusive propagation. However, the low energy anomalous cosmic rays were not observed at the shock, indicating that their source region is remote from the location of Voyager 1. Continuing observations should reveal new aspects of this final frontier of the heliosphere

Two Voyagers to Saturn - How Voyager 2 has been reprogrammed

In the past two years, the Pioneer 11 and the Voyager 1 encounters with Saturn have revealed a remarkable richness and diversity of physical phenomena. As a result of these discoveries and of continued Earth-based studies, major changes have been made in the observations planned for Voyager 2, providing additional opportunities for discovery and understanding of the Saturn system. These opportunities are further enhanced by the significantly different path that Voyager 2 must take through the system, passing 101,000 km above Saturn's cloud tops on 26 August as it continues on to Uranus. Of necessity, the most exciting discovery will be unexpected; but some of the opportunities for new observations are described below for each of the four major areas of investigation-the atmosphere, rings, satellites and magnetosphere

Frontiers of space: technology and the search for life elsewhere

LectureIt will take about a decade to develop the technology for a planetfinder telescope. There is a prototype interferometer at the Palomar Observatory in California, and over the next several years a full-scale system will be installed at the Keck Observatory. Experience with these ground-based systems will enable us to design and develop the ultimate space-based observatory that will extend our search for life beyond the solar system

Global Asymmetry of the Heliosphere

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 reveal the nature and degree of the asymmetry in the termination shock and heliosheath.Comment: 6 pages, 5 figures, AIP Proceedings of the 5th IGPP "The Physics of the Inner Heliosheath: Voyager Observations, Theory and Future Prospects

Analysis of energetic proton and electron data in Neptune's magnetosphere

This grant was for the analysis and interpretation of data obtained by the cosmic ray system (CRS) on Voyager 2 in the magnetosphere of Neptune. The research goals included the following: characterize the distribution and intensity of trapped electrons and protons; relate them to theoretical models of particle transport; study the particle absorption signatures of Neptune's moons and rings; develop planetary magnetic field models based on the particle data; and study Neptune's cosmic ray cutoff

Anomalous Cosmic Rays

Anomalous cosmic rays (ACRs) first started showing up in observations 40 years ago. Within a few years a paradigm was developed to explain their origin: they begin their life as interstellar neutral atoms that drift into the heliosphere, become singly ionized by chargeexchange with a solar wind ion or by photoionization, are picked up by the expanding solar wind, and accelerated to the observed energies by diffusive shock acceleration at the solar wind termination shock. This paradigm became widely accepted and withstood the tests of further observations until 16 December 2004, when Voyager 1 crossed the termination shock and didn't find their source. In August 2007, Voyager 2 crossed the termination shock and also did not find the source location of ACRs. Clearly, the source location was not at the termination shock where the two Voyagers crossed. Alternative models have been proposed with acceleration elsewhere on the shock or by other acceleration processes in the heliosheath. We discuss the latest observations of ACRs from the Voyager spacecraft and hopefully shed more light on this ongoing puzzle