用戶:JazzyJimmy/IPMSB
The interplanetary medium is the material which fills the solar system and through which all the larger solar system bodies such as planets, asteroids and comets move. 行星際物質泛指充滿太陽系空間的物質，而其他較大的太陽系天體如行星，小行星，及彗星在太陽系中運動時皆穿越這些物質。
組成及物理性質
The interplanetary medium includes interplanetary dust, cosmic rays and hot plasma from the solar wind. The temperature of the interplanetary medium is approximately 10,000 K, and its density is very low at about 5 particles per cubic centimeter in the vicinity of the Earth; it decreases with increasing distance from the sun, in proportion with the inverse square of the distance.
行星際物質由行星際塵埃，宇宙射線，及等離子所構成。塵埃的大小約...？宇宙射線則泛指各種高能粒子（微中子，質子，電子及其他離子），可能由太陽產生，也可能來自太陽系外的其他事件（如超新星爆發）。等離子由太陽風吹出，溫度可達絕對溫度一萬度，但是密度卻是非常的低：在地球附近只有每立方厘米五個粒子，而且隨着與太陽距離成平方反比遞減。但是這些等離子的密度也會隨着磁場大小的變化與太陽風的強度驟變（如日冕物質噴發）而改變，當太陽風強度增強時其密度甚至可達每立方厘米一百個粒子。
The density is variable, and may be affected by magnetic fields and events such as coronal mass ejections. It may rise to as high as 100 particles/cm³.
（以下所說似乎假設行星際物質大部分是等離子？或是只描述等離子部份？-> 移至可觀測之現象）
Since the interplanetary medium is a plasma, it has the characteristics of a plasma, rather than a simple gas; for example, it carries with it the Sun's magnetic field, is highly electrically conductive (resulting in the Heliospheric current sheet), forms plasma double layers where it comes into contact with a planetary magnetosphere or at the heliopause, and exhibits filamentation (such as in aurora).
The plasma in the interplanetary medium is also responsible for the strength of the Sun's magenetic field at the orbit of the Earth being over 100 times greater than originally anticipated. 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. But satellite observations show that it is about 100 times greater at around 10-9 tesla. 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 a MHD dynamo.
行星際物質的等離子性質也導致了一些有趣的現象。
最遠可及之處
The outer edge of the solar system is the boundary between the flow of the solar wind and the interstellar medium. This boundary is known as the heliopause and is believed to be a fairly sharp transition of the order of 110 to 160 astronomical units from the sun. The interplanetary medium thus fills the roughly spherical volume contained within the heliopause.
行星際物質充滿整個太陽系，一直到太陽系的邊界——太陽風最遠可及，被稱為「太陽系頂」的位置。太陽系頂約位於距太陽110至160天文單位之處，定義為行星際物質與系外星際物質的交界。
與行星的交互影響
How the interplanetary medium interacts with planets depends on whether they have magnetic fields or not. Bodies such as the Moon have no magnetic field and the solar wind can impact directly on their surface. Over many billions of years, the lunar regolith has acted as a collector for solar wind particles, and so studies of rocks from the moon's surface can be valuable in studies of the solar wind.
High energy particles from the solar wind impacting on the Moon's surface also cause it to emit faintly at X-ray wavelengths.
Planets with their own magnetic field, such as the Earth and Jupiter, are surrounded by a magnetosphere within which their magnetic field is dominant over the sun's. This disrupts the flow of the solar wind, which is channelled around the magnetosphere. Material from the solar wind can 'leak' into the magnetosphere, causing aurorae and also populating the Van Allen Belts with ionised material.
觀測上之現象
The interplanetary medium is responsible for several effects which can be seen from earth. The 黃道光 is a broad band of faint light sometimes seen after sunset and before sunrise, stretched along the ecliptic and brightest near the horizon. It is caused by sunlight scattering off dust particles in the interplanetary medium between the Earth and the Sun.
A similar effect is the 對日照, which is seen directly opposite to the sun's position in the sky. It is much fainter than the Zodiacal light, and is caused by sunlight reflecting off dust particles outside the earth's orbit.
歷史沿革
Originally, astronomers thought that space was an empty vacuum. In 1913, Norwegian explorer and physicist Kristian Birkeland may have been the first to predict that space is not only a plasma, but also contains "dark matter". He wrote: "It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. We have assumed that each stellar system in evolutions throws off electric corpuscles into space. It does not seem unreasonable therefore to think that the greater part of the material masses in the universe is found, not in the solar systems or nebulae, but in "empty" space. (See "Polar Magnetic Phenomena and Terrella Experiments", in The Norwegian Aurora Polaris Expedition 1902-1903 (publ. 1913, p.720)
參考書目
Bill Arnett's Nine Planets page about the interplanetary medium