Interplanetary medium
The interplanetary medium ( IPM ) is the medium that fills interplanetary space , i.e. space in the solar system . All larger celestial bodies such as planets , dwarf planets , asteroids and comets move through this medium.
composition
The interplanetary medium consists of interplanetary dust , the hot plasma of the solar wind and other particles of cosmic radiation , some of which also come from the interstellar medium outside the solar system. The particle density of the solar wind can fluctuate strongly locally, but generally decreases with the square of the distance from the sun. At a distance of about 1 AU from the sun (radius of the earth's orbit) it averages about 5 particles / cm³. It is influenced by magnetic fields and events such as coronal mass ejections and can reach up to 100 particles / cm³.
Since the interplanetary medium hardly contains electrically neutral atoms , but is a highly conductive plasma of ions (especially protons ) and electrons , it has the typical properties of plasmas. It carries the sun's magnetic field with it, forms an electric current layer shaped like a ballerina skirt , the heliospherical current layer , interacts with planetary magnetospheres and forms filaments, for example in prominences and polar lights .
The temperature of the interplanetary medium decreases with distance from the sun. Dust in the asteroid belt has temperatures of around 200 K (−73 ° C) at 2.2 AU; at 3.2 AU the temperature is 165 K (−108 ° C).
expansion
The space filled by the interplanetary medium is the heliosphere . In its outer area, the helio envelope , the interplanetary medium begins to mix with the interstellar medium , and at the heliopause the space that is exclusively filled by the interstellar medium begins.
Interaction with celestial bodies
How the interplanetary medium interacts with celestial bodies depends heavily on whether or not they have a magnetic field.
Bodies like the Earth's moon have no magnetic field worth mentioning and the solar wind hits them unhindered. For example, the lunar regolith has undergone severe space weathering over several billion years . The investigation of the lunar regolith therefore allows conclusions to be drawn about the solar wind.
Bodies with their own magnetic field, such as the earth or Jupiter , are surrounded by magnetospheres in which their own magnetic field is dominant over the solar magnetic field. Most of the solar wind is deflected around these bodies and does not hit them. Small amounts of particles cause auroras and provide the material for radiation belts such as the Van Allen Belt .
Depending on its size, interplanetary dust migrates either outwards (smallest particles) or inwards towards the sun (larger particles). It hits planets, dwarf planets and moons in the form of micrometeorites .
The zodiacal cloud
An interplanetary dust and gas cloud surrounds the sun in a ring in the planetary plane as a thin disk. It is visible as zodiacal light on very clear nights and is therefore also known as the zodiacal cloud . This optical phenomenon also includes the counter- light near the sun's counterpoint .
Research history
Historically, it was initially believed that the space between the planets was a perfect vacuum . At the end of the 17th century this was modified to the effect that this vacuum was filled with ether in order to explain the propagation of light through this space.
The German physicist Ludwig Biermann suggested in 1951 and 1953, based on the direction of cometary tails , that the sun should emit “solar particle radiation” in all directions. His idea was not taken seriously, but was confirmed by the American astrophysicist Eugene N. Parker in 1959 . Today it is known that interplanetary space is filled with a medium, just like interstellar space ( interstellar medium ) and even intergalactic space ( intergalactic medium ).
Individual evidence
- ^ FJ Low: Infrared cirrus - New components of the extended infrared emission . In: Astrophysical Journal Letters . tape 278 , 1984, pp. L19-L22 , doi : 10.1086 / 184213 .