is produced in region A (see Figure III.7). The central body acts as a unipolar inductor and the e. ![]() Hannes Alfven argued that since a conductor rotating in a magnetic field produces an electric current, then the Sun behaves as a unipolar inductor: Magnetohydrodynamic (MHD) theory predicts that the motion of a conducting fluid (e.g., the interplanetary medium) in a magnetic field, induces electric currents which in turn generates magnetic fields, and in this respect it behaves like an MHD dynamo. But satellite observations show that it is about 100 times greater at around 10 -9 tesla. If space were a vacuum, then the Sun’s 10 -4 tesla magnetic dipole field would reduce with the cube of the distance to about 10-11 tesla. The plasma in the interplanetary medium is also responsible for the strength of the Sun’s magnetic field at the orbit of the Earth. ![]() The influence of the Sun’s rotating magnetic field on the plasma in the interplanetary medium creates the heliospheric current sheet, which separates regions with magnetic fields pointing in different directions. In this case, the plasma consists of hydrogen and helium ions, together with the electrons that were liberated when those ions were produced.” Magnetic field So, although it is common to see the Sun referred to as a gaseous body, a more specific description is that it is made of plasma. Such a highly ionized gas is called a plasma. This is particularly true in the hot, dense interior, where essentially all the hydrogen and helium atoms are completely ionized. “Most of the atoms in the Sun are ionized. These ions are quite different to the gaseous atoms, and behave quite differently. Because the temperatures are so high, the atoms are nearly completely ionized into hydrogen ions and helium ions, ie. The Sun and stars consist of very little actual hydrogen and helium gas. The structure of our Sun is thought to include (from inside to out), the core, the radiative zone, the convection zone, the photosphere (visible surface), and its atmosphere comprising of five main zones: the temperature minimum, the chromosphere, the transition region, the corona, and the heliosphere.Īlso associated with the Sun are sun spots, solar flares, coronal mass ejections. The movement of the plasma produces strong magnetic fields and corresponding electric currents. The TRACE findings may also help astronomers better predict the behavior of coronas surrounding other stars, says Aschwanden.A Star and hence our Sun, is an almost entirely ionized ball of plasma, consisting of electrons and ions, in which there is hardly any gas (neutral atoms). although we still don’t know the mechanism of energy release,” says Lockheed’s Alan M. The magnetic carpet “is the most likely source of the energy. Like thousands of pilot lights, this energy could heat the corona’s base. Each bundle is composed of pairs of oppositely directed field lines that merge and annihilate each other, releasing vast reserves of energy every 40 hours or so. The craft found that tens of thousands of magnetic field bundles carpet the sun’s surface and loop up into the corona (SN: 11/08/97, p. Any mechanism now proposed to heat the corona “had better be able to dissipate all of its energy within the first 10,000 km or so ,” he notes.Įarlier observations by the Solar and Heliospheric Observatory (SOHO) spacecraft suggest such a mechanism, several solar physicists told Science News. Antiochus of the Naval Research Laboratory in Washington, D.C. “I’m hoping these observations will lead to a breakthrough,” says Spiro K. ![]() That can only occur if some energy source is continually reheating the corona’s base, which leaks heat quickly to higher regions, the Lockheed team asserts. Instead, TRACE found that the temperature is uniform from the top of the corona to the bottom. If that theory were correct, the tops of the arches would be hottest, because the gas there is thinnest and can’t dissipate the heat it absorbs as quickly as can the denser gas at the corona’s base. As these waves travel along the arches, they would gradually transfer their energy. 10 Astrophysical Journal.Ī popular theory had assumed that the arches were heated throughout their height by waves generated by the turbulent ocean of gases at the solar surface. Schrijver, and David Alexander, describe their work in the Oct. He and his Lockheed colleagues, Carolus J. Aschwanden of the Lockheed Martin Advanced Technology Center in Palo Alto, Calif. “The mysterious energy source that makes the sun’s atmosphere so incredibly hot has been an enigma for more than 70 years, and before we discover what it is, we needed to learn where it is,” notes Markus J. The TRACE measurements indicate that the heating occurs near the bottom of these arches, about 16,000 kilometers above the sun’s surface. The corona consists of millions of giant arches of gas-some high enough to span 30 Earths-that move along looping magnetic field lines.
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