Solar-Terrestrial Probes: The Future of Space Science in the New Millenium.

As the International Solar-Terrestrial Physics program enters into an extended mission phase, the next generation of exciting NASA missions are just now being planned or started. With the establishment by Congress of a new line of Solar Terrestrial Probes, NASA has identified several key areas where large-cost, community-consensus missions are required to address outstanding questions in space physics. These include missions to study microphysical processes at thin boundary layers (Magnetospheric MultiScale), to study the instantaneous global configuration of fields and particles at low (Global Electrodynamics) and high altitudes (Magnetospheric Constellation), to study the genesis and 3-D evolution of coronal mass ejections (Solar Stereo), and to study the energetics and dynamics of the thermosphere, ionosphere, and mesosphere (TIMED). Of all these missions, magnetospheric constellation is probably the most technologically challenging as it represents at least one order of magnitude increase in the number of satellites dedicated to one coordinated mission. Herein we define a constellation to be any coordinated suite of satellites, orbiting throughout large volumes of the magnetosphere so as to instantaneously extract fundamental knowledge of macroscale structures and global dynamics. While the notion of constellations has been discussed in the literature since the 1960's, they received scant serious attention owing to past technological limitations. With the advent of miniaturized sensors and spacecraft subsystems, the reality of implementing constellation missions is here. Several constellation mission scenarios have been discussed recently, motivated in part by NASA's New Mission Concept program and the community-wide Roadmap exercise. In this talk, we provide an overview of the fundamental macroscopic problems that are uniquely addressed by constellation missions. We then outline several developing implementation strategies, including the so-called MMM project here at BU, differing in style according to the focus of the investigation. These missions will be compared and contrasted to the Magnetospheric MultiScale mission (formerly known as Grand Tour Cluster). Finally, we will present the feasibilty of launching hundreds of magnetometry nanosatellites to probe, for example, the global development of substorms, using currently available technologies. 

Do we understand the rate of connection? Do we care?

A magnetic field reconnection model generated in the sixties has generally been recognized as providing a mechanism whereby reconnection can be rapid even in a high conductivity medium. While the initial theory derived a specific rate, recent theories suggest that a range of fast rates can exist and that they depend on arbitrary assumptions about the upstream current. It will be shown that even though the original theory did not justify its choice of zero current, the theory is nevertheless correct. Other choices of the upstream current correspond to definable boundary conditions. The fact that many numerical calculations appear to disagree with the theory will also be discussed. Finally it will be observed that occurence rather than rate of reconnection is by far the more interesting question. 

Measurements of Radio Frequency Emissions on the Galileo Probe Mission into Jupiter's Atmosphere.

One of the instruments carried on the Galileo Probe during its descent into the atmosphere of Jupiter was the Lightning and Radio Emissions Detector (LRD). During the descent, the instrument measured radio emissions in Jupiter's atmosphere in the frequency range 100 Hz - 100 kHz. These signals, whose source is in the Jovian atmosphere, show that in a region of some 15,000 to 20,000 km around the probe entry site, the Jovian lightning was more intense by a factor of about 10 than in cloud to ground discharges on earth, but also less frequent in occurrence by a significant amount. 

Oceans Beyond Earth: Evidence from Recent Spacecraft Exploration of Europa and Mars.

Most people think of oceans as being a peculiarly Earth-like phenomenon. However, recent exploration of Europa by the Galileo spacecraft has provided new evidence for a global ocean beneath the very young solid ice crust. In addition, several investigators have proposed that oceans were present in the northern lowlands of Mars in its past history, and new spacecraft data from Mars Global Surveyor are being used to assess the evidence. This talk will focus on how we test ideas for the presence of oceans beyond Earth, what we are learning, and what the implications might be for the history of the planets and the origin and evolution of life." 

Far- and extreme-ultraviolet observations of the Moon.

Recent space-based observations of the Moon in the far- and extreme- ultraviolet wavelength ranges have provided new insights into the nature of the Moon's surface and atmosphere. In particular, FUV spectra of the Moon obtained in December 1996 using the ORFEUS SPAS-II satellite have yielded the first remote detection of argon in the lunar atmosphere and indicate an argon abundance above the lunar dayside that greatly exceeds Apollo-era predictions. More recently, EUV imaging and spectroscopy obtained with the Extreme Ultraviolet Explorer have provided the first EUV albedo map and spectrum of the Moon. The EUV data reveal complexity in the lunar spectral reflectivity that may provide a useful tool for remote compositional studies and may indicate possible surface fluorescence. 

Lunar Prospector results: Water and other finds on the moon.

Maps of epithermal and fast neutron fluxes measured by Lunar Prospector were used to search for enhanced deposits of hydrogen at both lunar poles. Clear depressions in epithermal fluxes are observed in close proximity to permanently-shaded areas at both poles. The peak depression at the north pole is 4.6% below the average epithermal flux intensity at lower latitudes, and that at the south pole is 3.0% below the low-latitude average. No measurable depression in fast neutrons is seen at either pole. These data are consistent with deposits of hydrogen in the form of water ice that are covered by as much as 50 cm of dessicated regolith within permanently-shaded craters near both poles. 

JIM: A Global Model of Jupiter's Ionosphere

The Jupiter Group at University College London have developed one of the first global circulation models of Jupiter's thermosphere and ionosphere. Such models have been a desirable goal for many years in order to model the effects of planetary winds and extended auroral regions on the composition of the planet's ionosphere. A brief introduction to the model is presented. Preliminary studies have shown that the global patterns of ionization are themselves valuable diagnostics of atmospheric chemistry and magnetic field geometry. JIM simulations have also shown the need to invoke an extra energy input to explain the observed levels of high latitude infrared emission from the molecular ion H3+. Finally, we consider the dynamical output of JIM and implications for flows dominated by electrodynamics and gas dynamics in Jupiter's auroral regions. 

Ion Dynamics During Magnetotail Reconnection.

Due to the breakdown of particle adiabaticity in the tail current sheet with it's highly curved magnetic field the application of fluid equations is questionable. Therefore a detailed understanding of magnetotail dynamics during reconnection requires that the particle dynamics is resolved on length scales comparable to the ion inertia length and/or the ion gyroradius. Furthermore, slow mode shocks are expected to occur during magnetotail reconnection. Their structure, length scale and dissipation can only be investigated by kinetic simulations. Recent results obtained from hybrid simulations of magnetotail reconnection will be reported. It will be demonstrated that ion kinetic effects determine not only the small scale structure, but are also of great importance for the large-scale structures during magnetotail reconnection. 

Auroral Radio Emissions Observed at Ground Level.

Active aurora produce several types of high frequency radio waves observed at ground-level. These have colorful names based on their appearances in frequency-time spectrograms: auroral hiss, roar, and MF-burst. These radiations do not represent a large fraction of the auroral energy budget, but they provide a nearby laboratory for studying emissions processes which occur ubiquitously in space plasmas. Also, these emissions may provide a valuable method for remote sensing auroral processes. Auroral roar and MF-burst are least understood. Left-hand polarized auroral roar is relatively narrow band, occurs near two and three times the electron cyclotron frequency at a source altitude of about 275 km, lasts from minutes to yours, and characterizes both pre- and post-substorm conditions. Recent evidence suggests that it is concentrated at the poleward edge of the auroral zone. Left-hand polarized auroral MF-burst consists of broadband impulses with time variations as short as 100 microseconds lasting only a few minutes at the time of substorm onset and strongly correlated with impulsive auroral hiss. Both emissions are believed to result from indirect radiation processes whereby auroral electrons destabilize electrostatic waves which mode convert to escaping O-mode radiation, with auroral roar likely resulting from free energy in the perpendicular component of the electron distribution function while auroral MF-burst results from free energy in the parallel part. Many details of the theory, especially the mode conversion mechanism, need yet to be worked out. 

Magnetospheric Currents determined from Ionospheric Modeling.

This talk surveys the phenomena of electric fields and currents in the ionosphere and their role in the dynamics of the ionosphere/thermosphere/ magnetosphere system. High conductivity along lines of force of the Earth's magnetic field leads to strong electromagnetic coupling throughout the ionosphere and magnetosphere. Within the ionosphere, currents perpendicular to the magnetic field flow mainly between 100 km and 200 km altitude at day, with much weaker currents between 200 km and 400 km both day and night. The dynamics of the neutral thermosphere is strongly influenced by the Ampere force of these currents. One source of the currents is the dynamo effect generated by thermospheric winds that move the conducting medium through the geomagnetic field. Observations of the geomagnetic perturbations produced by the ionospheric currents, and of the polarization electric fields associated with the currents, provide valuable information about the wind system. At high latitudes, interactions with the magnetosphere dominate ionospheric electrodynamics, and supply major sources of momentum and heat to thethermosphere. Thermospheric winds driven by these sources in turn generate their own dynamo effects and thereby feed back into the coupled ionosphere-magnetosphere electrodynamics. Simulation modeling of coupled magnetosphere-thermosphere-ionosphere electrodynamics is starting to become an important area of solar-terrestrial research 

Magnetospheric Imaging Instrument (MINT) on Cassini: A New Approach.

Our view of earth's and other planets magnetospheres has been pieced together by occasional in-situ measurements from different spacecraft at various times. These measurements have been connected through empirical and theoretical models into a synoptic view that may or may not represent a true image of magnetospheric topology and cannot provide an account of dynamical processes that are known to occur in all magnetospheres. The Cassini Magnetospheric Imaging Instrument (MIMI) comprises three sensors, one of which is the Ion and Neutral Camera (INCA) and will be able to obtain images of the magnetosphere, utilizing energetic neutral atoms (ENAs) resulting from charge exchange between trapped ions and various neutral species residing within Saturn's magnetospheric envelope. Further, the interaction between magnetospheric plasma and the exospheres of Titan and the icy satellites will be imaged and such quantities as exospheric density and species will be determined. A description of the relevant magnetospheric science objectives will be given, including simulations of expected images from the INCA sensor, and the principle of operation and hardware implementation of this new imaging device will be described. 

Charged-Particle Acceleration by Magnetic-Field-Aligned Electric Fields.

The Northern lights, a picturesque display that have been worshipped and studied for centuries, may now be giving us insight on charged particle acceleration applicable to astrophysical domains. Particle acceleration in the aurora comes from magnetic-field-aligned electric fields which produce precipitating electrons that create the visible display. The recent uncovering of magnetic-field-aligned potentials in a new plasma regime suggests that they may be fundamental, supplementing the classical mechanisms of Fermi and betatron acceleration. I will discuss observation and theory of magnetic-field-aligned electric fields which were, at one time, believed to be not possible in a collisionless plasma.