ISBN 13: 9783540195993
The purpose of this report is to consider research priorities in the light of the space exploration vision. This sketch is not to scale; for example, in reality the Sun is Earth-diameters across and the Sun-Earth distance is solar-diameters; Mars is half the size of Earth and 1. The commission report considered science in two contexts: enabling science , which is research that provides new knowledge or capability that facilitates exploration, and enabled science , which is research to create new knowledge by means of exploration.
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Finding 7 from the commission report p. The gas in space is a composite of several distinct classes of particles. In the interplanetary environment the dominant class is the solar wind mostly ionized hydrogen, i.
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This high-speed plasma not only fills interplanetary space but also controls the energy that drives aspects of space weather. These aspects include the very energetic and intense radiation belt particles that populate planetary environments, such as that of Earth and Jupiter, and the electrical currents and auroral particle acceleration that also characterize planetary environments. A second important class comprises galactic cosmic rays, moving at close to the speed of light c and infiltrating in through the magnetic fields in the solar wind from the surrounding interstellar space.
They are primarily protons plus a smaller number of heavier nuclei and a few electrons.
An Exploration into Information Physics
Outside the protecting magnetic field and atmosphere of Earth each square centimeter about the area of a fingernail is penetrated once or twice per second by a cosmic-ray proton. The lowest-energy cosmic rays 0. Above 1 GeV the number of cosmic-ray particles, and their reduction by the solar wind, decline rapidly with increasing energy. At 20 GeV 0. The particles above 1 GeV pose a particularly difficult problem for human interplanetary travel, because their enormous energy makes them difficult to shield against. The higher the initial proton energy, the worse this becomes. This provides adequate protection here at the surface of Earth.
Out in space, however, devising a practical means for protecting astronauts remains a major technical challenge. Finally, there are the energetic particles emitted by flares on the Sun, or accelerated in shock fronts near the Sun and in interplanetary space, that are typically referred to as solar energetic particles or solar cosmic rays. These particles mostly protons, a few heavier nuclei, and some electrons are usually at much lower energies 10 MeV to 10 GeV than the galactic cosmic rays. However, their enormous numbers can do fatal damage to exposed electronics and astronauts. The problem is that these solar cosmic rays are highly variable and appear intermittently in unanticipated intense events—solar proton events SPEs —associated with individual flares and coronal mass ejections at the Sun.
It is essential, therefore, to understand the physics of solar activity to know when such an event is likely to occur. Astronauts can then be warned not to stray far from shelter in case a potentially lethal burst occurs. Unfortunately, about once in 20 to 30 years there is an exceptional flare that produces a spectacular burst of particles with energies up to 20 GeV or more, supplying a potentially lethal dose of radiation that cannot be readily shielded against.
The physics of these remarkable events such events occurred in , , and has yet to be properly understood. Thus, current understanding of the production of SPEs is very poor, although gaining the ability to recognize the magnetic configurations on the Sun that creates them would be an important next step. BOX 1.
These dynamical processes are ubiquitous to highly evolved stellar systems, such as our own, but also play important roles in their formation and evolution. Stellar systems are born out of clumpy, rotating, primordial nebulas of gas and dust. Gravitational contraction, sometimes aided by shock waves possibly from supernovas , passage through dense material, and other disruptions, forms condensation centers that eventually become stars, planets, and small bodies. Magnetic fields moderate early-phase contractions and may also play vital roles in generating jets and shedding angular momentum, allowing further contraction.
The densest of the condensation centers become protostars surrounded by accretion disks.
dblp: Tom Stonier
Dynamo action occurs within the protostars as the heat of contraction ionizes their outer gaseous layers, resulting in stellar winds. In similar fashion, rotating solid and gaseous planets form, and many of these also support dynamo action, producing magnetic fields. Ultraviolet and x-ray photons from the central stars partially ionize the upper atmospheres of the planets as well as any interstellar neutral atoms that traverse the systems.
In its present manifestation, the heliosphere—the local cosmos—is a fascinating corner of the universe, challenging our best scientific efforts to understand its diverse machinations. It must be appreciated at the same time that our local cosmos is a laboratory for investigating the complex dynamics of active plasmas and fields that occur throughout the universe from the smallest ionospheric scales to galactic scales.
Close inspection and direct samplings within the heliosphere are essential parts of the investigations that cannot be carried out by a priori theoretical efforts alone. Moreover, SEC exploration contributes to the broader goals of understanding the origin and evolution of planetary and astrophysical systems, as illustrated by the example of exploration of the heliosphere discussed in Box 1. Some of the most exciting basic space research involves the underlying physical processes that are common to plasmas i.
For example, the process of magnetic reconnection in a plasma Box 1. The central contribution of the SEC program to scientific exploration is illustrated by the exploration of the heliosphere.
Gravitational waves detected for the first time
Indeed, the interplanetary medium beyond about 10 AU is dominated, by mass, by neutral atoms of interstellar origin rather than by solar wind. Thus, exploration of the outer heliosphere offers the opportunity to learn about both the interplanetary and the interstellar medium, and the manner in which they interact.
The detailed interaction between the local interstellar medium LISM; i. From physical reasoning, researchers know that boundary regions must separate the solar wind from the LISM. However, these regions are completely unexplored since they are so far out, well beyond the planets of our solar system. The boundary regions are likely separated by several enormous shocks. The innermost shock may be a site where cosmic rays are accelerated, thereby providing a link to supernova shocks thought to accelerate galactic cosmic rays. In the past year scientists working with data from Voyager-1 raised the exciting possibility that Voyager may be in the vicinity of the heliospheric boundary.
There is indirect evidence for a "hydrogen wall" where the flow of neutral hydrogen from the LISM is slowed down, compressed, and heated before it penetrates the solar wind. Obtaining direct observations of the interstellar interaction remains a high priority for scientific discovery at the outer frontier of solar and space physics.
Sending future spacecraft to the boundaries of our heliosphere to begin the exploration of our galactic neighborhood will be one of the great scientific enterprises of the new century—one that will capture the imagination of people everywhere. Interstellar space is a largely unknown frontier that, along with the Sun as the source of the solar wind, determines the size, shape, and variability of the heliosphere, the first and outermost shield against the influence of high-energy cosmic rays.
The interstellar medium is the cradle of the stars and planets, and its physical state and composition hold clues to understanding the evolution of matter in our galaxy and the universe. With plentiful bodies of all sizes and dust in the Edgewood-Kuiper Belt and in the Oort Cloud, the outer heliosphere is a repository of frozen and pristine material from the formation of the solar system. After the contents of our solar system, which is 4. Last but not least, the heliosphere is the only example of an asterosphere that is accessible to detailed study.
These perspectives provide a natural bridge and synergism between in situ space physics, the astronomical search for the origins of life, and astrophysics. These explosions are the driver of space weather, and the penetrating radiation from these events poses significant hazards to unprotected spacecraft and their human and technological assets. The mechanisms for particle energization and what determines the onset of the explosive energy release—critical for space weather forecasting—remain less fully understood. The broad importance of this topic is reflected in the high priority given in the decadal survey report 1 to the Magnetospheric Multiscale MMS mission, a four-satellite mission designed to explore the fundamentals of reconnection.
The first of a planned trilogy, this book examines the proposition that "Information" is as much a part of the physical universe as energy and matter. The acceptance of such a proposition has profound implications for the physical sciences it also lays the foundations for a general theory of information. See details. See all 2 brand new listings. Buy It Now. Add to cart. Be the first to write a review About this product.
About this product Product Information The first of a planned trilogy, this book examines the proposition that "Information" is as much a part of the physical universe as energy and matter. The acceptance of such a proposition has profound implications for the physical sciences; it also lays the foundations for a general theory of information. This book is directed firstly at researchers in information theory and scientists in other disciplines.
However, its relatively non-mathematical nature and accessible writing style place it at the "scientific" end of the spectrum of popular science books. A general theory of information will emerge in the second volume; the third will examine the mechanism and evolution of human and machine intelligence.
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