Tycho T. von Rosenvinge

The international cometary explorer mission to comet giacobini-zinner.

The International Cometary Explorer (ICE) became the first spacecraft ever to encounter a comet when it passed through the tail of comet Giacobini-Zinner. An overview of this encounter is presented, including highlights of the results.

High-Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission for the next (2000) solar maximum

The primary scientific objective of the High Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission selected by NASA is to investigate the physics of particle acceleration and energy release in solar flares. Observations will be made of x-rays and (gamma) rays from approximately 3 keV to approximately 20 MeV with an unprecedented combination of high resolution imaging and spectroscopy. The HESSI instrument utilizes Fourier- transform imaging with 9 bi-grid rotating modulation collimators and cooled germanium detectors. The instrument is mounted on a Sun-pointed spin-stabilized spacecraft and placed into a 600 km-altitude, 38 degrees inclination orbit.It will provide the first imaging spectroscopy in hard x-rays, with approximately 2 arcsecond angular resolution, time resolution down to tens of ms, and approximately 1 keV energy resolution; the first solar (gamma) ray line spectroscopy with approximately 1-5 keV energy resolution; and the first solar (gamma) -ray line and continuum imaging,with approximately 36-arcsecond angular resolution. HESSI is planned for launch in July 2000, in time to detect the thousands of flares expected during the next solar maximum.

Characterization Of Large-Area Silicon Ionization Detectors For The ACE Mission

We report on extensive tests of large-area (10 cm diameter) high-purity ion-implanted silicon detectors for the solar isotope spectrometer (SIS), and lithium-drifted silicon detectors for the cosmic ray isotope spectrometer (CRIS), which are under development for launch on the advanced composition explorer (ACE) mission. Depletion and breakdown characteristics versus bias were studied, as were long-term current and noise stability in a thermally cycled vacuum. Dead-layer and total thickness maps were obtained using laser interferometry, beams of energetic argon nuclei and radioactive sources of alpha particles. Results, selection criteria, and yields are presented.

Solar Energetic Particles: An Overview

This paper presents an overview of what we know about energetic particles from the sun, discusses where progress still needs to be made, and briefly enumerates what steps need to be taken next in order to better understand how and where solar electrons and ions are accelerated to high energies.

The ICE project

The International Cometary Explorer (ICE) spacecraft passed through the plasma tail of comet Giacobini-Zinner (G/Z) on September 11, 1985 and made in situ measurements of particles, fields, and waves. The preliminary results appear to establish comets and their interaction with the solar wind as a rich source of plasma physics phenomena. Time of closest approach to the comet was approximately 11:02 UT and occurred at a tailward distance of 7,800 km. The spacecraft was in the strong interaction region for roughly 3-12 hours, and spent about 10 minutes in the central tail region. The scientific results indicate: 1. that the magnetic field capture and draping model, originated by Alfven, is correct. Oppositely-polarized magnetic tail lobes, and a current sheet separating them, were observed. 2. that the comet/solar-wind interaction produces energetic ions, probably by the “pick up” process 3. the presence of intense plasma wave activity 4. that the central plasma tail is dense and cold 5. that the principal ions are in the H2O+ - H3O+ group 6. that the bow wave, as seen on the flanks, is not a shock but an extended interaction region 7. that impacts of micron-sized dust particles were detected. The ICE spacecraft survived the encounter with comet G/Z relatively unscathed and made fields and particles measurements upstream of Halleys Comet, actually detecting the comet via plasma wave and energetic particle measurements over the nuclear distance range 28,000,000–35,000,000 km.

Elemental Abundances of Ultra-Heavy GCRs measured by SuperTIGER and ACE-CRIS and the Origin of Galactic Cosmic Rays

The Super Trans-Iron Galactic Element Recorder (SuperTIGER) long-duration balloon instrument and the Cosmic Ray Isotope Spectrometer (CRIS) on the NASA Advanced Composition Explorer (ACE) satellite have measured the abundances of galactic cosmic-ray elements from _(10)Ne to _(40)Zr with high statistics and single-element resolution. SuperTIGER launched from Williams Field, McMurdo Station, Antarctica, on December 8, 2012, flying for a record 55 days. During that flight we detected ∼1,300 nuclei with atomic number Z ≥ 30. The resolution in charge (Z) of SuperTIGER is excellent, with σ_Z ≈ 0.16 c.u. at _(26)Fe. SuperTIGER is sensitive to nuclei with energy at the top of the atmosphere of E > 0.8 GeV/nucleon. The instrument has now been recovered and preparations are underway for its next flight. ACE/CRIS has been taking data in space for more than 17 years since launch in 1997, has collected ∼625 nuclei with atomic number Z ≥ 30, and shows excellent resolution with clear separation between the charges for 30 ≤ Z ≤ 40. ACE/CRIS is sensitive to nuclei in the energy range 150 ≤ E ≤ 600 MeV/nucleon. Preliminary results from the balloon-borne SuperTIGER show good agreement with ACE measurements in space, validating our corrections to SuperTIGER abundances for nuclear interactions in the atmosphere. The results from these experiments will be discussed in the context of the OB association model for the origin of galactic cosmic rays. Future missions to measure elemental abundances to higher Z, the SuperTIGER-II LDB instrument and the orbiting Heavy Nuclei eXplorer (HNX) mission, will also be discussed.

The Properties of Cycle 23 Solar Energetic Proton Events

Around 350 solar energetic proton events with energies >20 MeV were detected by near‐Earth spacecraft during solar cycle 23. Focusing on the 280 events with ∼25 MeV intensity >2×10−4particles/(cm23 sr s MeV), we examine the early stages (∼first 12 hours) of these events including their intensity and composition and the properties of the related solar phenomena such as CMEs, flares and radio bursts. Although we divide the events into 5 representative groups based on particle profiles and relative abundances, we find no single, or set of variables that divides the particle events into clear cut “classes” for example associated with shock and flare acceleration. In particular, there is a continuum of event properties from the smallest, flare‐accelerated events, to the largest events dominated by shock acceleration. This suggests that both flare and shock acceleration can contribute in individual events.

A 360° Survey of Solar Energetic Particle Events and One Extreme Event

We report on a 3-point longitudinal survey of Solar Energetic Particle (SEP) events during 2010-2014 using data from the STEREO and near-Earth spacecraft. During the period from August 2010 through September 2014 a total of 77 SEP events were identified with >10 MeV proton intensities that exceeded the NOAA criterion of >10 protons/(cmsr-s), including 37 events at STEREO-A and 36 each at GOES and STEREO-A. Thirty-seven percent of the events reached this threshold intensity at more than one location. Unexpected solar activity in December 2006 provided an opportunity to cross-calibrate the STEREO and GOES sensors, demonstrating that the >10 MeV response for GOES was ~5%-8% greater than for the STEREOs, while the STEREO A&B responses agreed to within 2%. The July 23, 2012 event observed by STEREO-A was found to be the most intense SEP event in more than 20 years. We present observations of the longitude distribution of SEP events and fluences and compare properties of the July 23, 2012 event with those of the largest events of earlier solar cycles.

Insights Into Particle Transport Obtained from Solar Energetic Particle Anisotropies

Solar energetic particle (SEP) pitch-angle distributions are shaped by the competing effects of magnetic focusing and scattering as the particles travel through interplanetary space. Therefore, measurements of SEP anisotropies provide insight into particle transport and can probe interplanetary conditions at remote locations from the observer. The Low Energy Telescopes (LETs) onboard the twin STEREO spacecraft measure pitch-angle distributions for protons and heavier ions at energies of about 2-12 MeV/nucleon. Using these instruments, we have observed a wide variety of SEP anisotropies, such as bidirectional flows within interplanetary coronal mass ejections, sunward-flowing particles when the spacecraft was magnetically connected to the back side of a distant shock, and loss-cone distributions in which particles with large pitch angles magnetically mirror at an interplanetary field enhancement that is too weak to reflect particles with the smallest pitch angles. One of the more puzzling observations is unusual oscillations on a timescale of several minutes in the width of a beamed distribution at the onset of the very large 23 July 2012 SEP event. We report LET anisotropy observations at both STEREO spacecraft during the extreme event of 23 July 2012, in which a large range of anisotropies were observed at various times during the event, and discuss their implications for SEP transport.

The Longitudinal Distribution of Solar Energetic Particles

Using observations from the High Energy Telescopes (HETs) on STEREO A and B and similar observations from SoHO, near-Earth, we have identified ~250 individual solar energetic particle events that include >14 MeV protons since the beginning of the STEREO mission [1]. Between the end of December 2009, when the STEREO A and B spacecraft were, respectively, ahead and behind Earth by ~ 65° in ecliptic longitude, and the end of December 2013, 43 different events were clearly detected at all three locations. The observed intensities of such an event are usually assumed to be Gaussian distributed as a function of the longitudes of the Parker Spiral footpoints at the Sun for each observer. This neglects the fact that the interplanetary magnetic field may have large deviations from Parker Spirals, e.g. due to coronal mass ejections from prior events. Nonetheless, we have fit Gaussians to the peak intensities observed simultaneously at three spacecraft for all 43 events. The Gaussian peak intensity is poorly correlated with the corresponding CME speed and the FWHM is uncorrelated with the CME speed. Surprisingly, however, there appear to be distinctly non-random variations of the FWHM values from event to event.