Interplanetary medium

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The Zodiacal Light is over the Faulkes Telescope, Haleakala, Maui. Credit: 808caver.

Our local 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.


Main sources: Astronomy/Mediums and Mediums

Def. the nature of the surrounding environment is called a medium.


Daf. existing or occurring between planets is called interplanetary.

Def. that part of outer space between the planets of a solar system and its star is called interplanetary space.

The interplanetary medium includes interplanetary dust, cosmic rays and hot plasma from the solar wind. The temperature of the interplanetary medium varies. For dust particles within the asteroid belt, typical temperatures range from 200 K (−73 °C) at 2.2 AU down to 165 K (−108 °C) at 3.2 AU[1] The density of the interplanetary medium is very low, about 5 particles per cubic centimeter in the vicinity of the Earth; it decreases with increasing distance from the sun, in inverse proportion to the square of the distance. It 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.

Planetary sciences[edit]

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 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.

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.


Main source: Minerals

"A new cosmogony proposed by author bases on idea that formation of planets takes place on pre-solar stage of evolution of proto-stellar/proto-planetary nebula. [...] The hypothesis predicts that all particles in one stream are of the same mineral composition and of the same density."[2]

Theoretical interplanetary medium[edit]

Def. any collection of heavenly bodies including a star or binary star, and any lighter stars, brown dwarfs, planets, and other objects in orbit is called a solar system.

Usage notes

As Sol is the name of our star, this phrase is usually used to refer specifically to our own sun and planets (the Sol system), in which case it is used with the and generally capitalised (as the Solar system or the Solar System). Other systems are then known as star systems or planetary systems, or specified by the name of the individual star (the Alpha Centauri system).

Entity astronomy[edit]

A Double Layer Formation Summary is shown. Credit: Ian Tresman.

A double layer is a structure in a plasma and consists of two parallel layers with opposite electrical charge. The sheets of charge cause a strong electric field and a correspondingly sharp change in voltage (electrical potential) across the double layer. Ions and electrons which enter the double layer are accelerated, decelerated, or reflected by the electric field. In general, double layers (which may be curved rather than flat) separate regions of plasma with quite different characteristics. Double layers are found in a wide variety of plasmas, from discharge tubes to space plasmas to the Birkeland currents supplying the Earth's aurora, and are especially common in current-carrying plasmas. Compared to the sizes of the plasmas which contain them, double layers are very thin (typically ten Debye lengths), with widths ranging from a few millimeters for laboratory plasmas to thousands of kilometres for astrophysical plasmas.

Double layers are formed in four main ways[3]

Double layers are associated with (filamentary) currents.[4]

Other names for a double layer are electrostatic double layer, electric double layer, plasma double layers, electrostatic shock (a type of double layer which is oriented at an oblique angle to the magnetic field in such a way that the perpendicular electric field is much stronger than the parallel electric field),[5] space charge layer.[6] In laser physics, a double layer is sometimes called an ambipolar electric field.[7]

If there is a net current present, then the DL is oriented with the base of the L in line with direction of current.[8]

The details of the formation mechanism depend on the environment of the plasma (e.g. double layers in the laboratory, ionosphere, solar wind, fusion, etc.).

  1. Between plasmas of different temperatures[9]
  2. By pinches in cosmic plasma regions[10]
  3. By an electrical discharge[11]

The production of a double layer requires regions with a significant excess of positive or negative charge, that is, where quasi-neutrality is violated.[12][13] In general, quasi-neutrality can only be violated on scales of the order of the Debye length. The thickness of a double layer is of the order of ten Debye lengths, which is a few centimeters in the ionosphere, a few tens of meters in the interplanetary medium, and tens of kilometers in the intergalactic medium.

"Since the double layer acts as a load, there has to be an external source maintaining the potential difference and driving the current. In the laboratory this source is usually an electrical power supply, whereas in space it may be the magnetic energy stored in an extended current system, which responds to a change in current with an inductive voltage".[14]

Strong forces[edit]

"Due to the very low energy of the colliding protons in the Sun, only states with no angular momentum (s-waves) contribute significantly. One can consider it as a head-on collision, so that angular momentum plays no role. Consequently, the total angular momentum is the sum of the spins, and the spins alone control the reaction. Because of Pauli's exclusion principle, the incoming protons must have opposite spins. On the other hand, in the only bound state of deuterium, the spins of the neutron and proton are aligned. Hence a spin flip must take place [...] The strength of the nuclear force which holds the neutron and the proton together depends on the spin of the particles. The force between an aligned proton and neutron is sufficient to give a bound state, but the interaction between two protons does not yield a bound state under any circumstances. Deuterium has only one bound state."[15]

The "force acting between the protons and the neutrons [is] the strong force".[15]

"A potential of 36 MeV is needed to get just one energy state."[15]

The width of a bound proton and neutron is "2.02 x 10-13 cm".[15]


"The first systematic attempt to base a theory of the origin of the solar system on electromagnetic or hydromagnetic effects was made in Alfvén (1942). The reason for doing so was that a basic difficulty with the old Laplacian hypothesis: how can a central body (Sun or planet) transfer angular momentum to the secondary bodies (planets or satellites) orbiting around it? It was demonstrated that this could be done by electromagnetic effects. No other acceptable mechanism has yet been worked out. [...] the electromagnetic transfer mechanism has been confirmed by observations, as described in the monograph Cosmic Plasma (Alfvén, 1981, pp. 28, 52, 53 0."[16]

"If charged particles (electrons, ions or charged grains) move in a magnetic dipole field - strong enough to dominate their motion - under the action of gravitation and the centrifugal force, they will find an equilibrium in a circular orbit if their centrifugal force is 2/3 of the gravitational force [...] The consequence of this is that if they become neutralized, so that electromagnetic forces disappear, the centrifugal force is too small to balance the gravitation. Their circular orbit changes to an elliptical orbit with the semi-major axis a = 3/4a0 and e = 1/3 (where a0 is the central distance where the neutralization takes place [...] Collisional (viscous) interaction between the condensed particles will eventually change the orbit into a new circular orbit with a = 2/3a0 and e = 0."[16]

"If [...] there is plasma in the region [collisional interaction results in] matter in the 2/3-[region]. [...] matter in the region [...] will produce a [cosmogonic] shadow in the region".[16]


"The hydromagnetic approach led to the discovery of two important observational regularities in the solar system: (1) the band structure [such as in the rings of Saturn and in the asteroid belt], and (2) the cosmogonic shadow effect (the two-thirds fall down effect)."[16]


This picture is of the Alpha-Monocerotid meteor outburst in 1995. It is a timed exposure where the meteors have actually occurred several seconds to several minutes apart. Credit: NASA Ames Research Center/S. Molau and P. Jenniskens.

Some wanderers are meteors.

A meteor is the visible path of a meteoroid that has entered the Earth's atmosphere. Meteors typically occur in the mesosphere, and most range in altitude from 75 km to 100 km.[17] Millions of meteors occur in the Earth's atmosphere every day. Most meteoroids that cause meteors are about the size of a pebble.

The Perseid meteor shower, usually the richest meteor shower of the year, peaks in August. Over the course of an hour, a person watching a clear sky from a dark location might see as many as 50-100 meteors. Most meteors are actually pieces of rock that have broken off a comet and continue to orbit the Sun. The Earth travels through the comet debris in its orbit. As the small pieces enter the Earth's atmosphere, friction causes them to burn up.

Def. "[a]ll other objects [not a planet or dwarf planet], except satellites, orbiting the Sun" are called collectively Small Solar-System Bodies.[18]

"Coronal mass ejections (CMEs) are large‐scale expulsions of plasma and magnetic field from the solar corona to the interplanetary space. During a large CME event, ∼1016 g of coronal material with energies of ∼1032 ergs are ejected from the Sun [Hundhausen, 1997; Vourlidas et al., 2002]. While accelerating away from the Sun, CMEs present speeds between few tens up to ∼2500 km/s. CMEs with speeds exceeding the magnetosonic speed can drive fast shocks ahead of them. CME‐driven fast shocks are able to accelerate charged particles up to very high energies (∼GeV/nucleon) [Wang and Wang, 2006]."[19]

Current "knowledge of the orbital structure of the outer solar system, [is] mostly slanted towards that information which has been learned from the Canada-France-Ecliptic Plane Survey (CFEPS: Based on our current datasets (inside and outside CFEPS) outer solar system modeling is now entering the erra of precission cosmogony."[20]

"Since the discovery of the first members of the Kuiper belt (Jewitt and Luu, 1993) the growth in knowledge of the outer solar system has been marked (perhaps driven) by the discovery of individual objects whose dynamics pointed at previously unknown reserviours; for example: 1993 RO and the plutinos, 1996 TL66 and the ‘scattering disk’, 2003 CR103 and the detectatch disk, 90377 Sedna and the Inner Oort Cloud."[20]

The "‘main Kuiper belt’ is populated by dynamically ‘hot’ and ‘cold’ subcomponents (Brown 2001), the dyncamically ‘cold’ component is further sub-divided into a ‘stirred’ and ‘kernel’ component (Petit et al., 2011). The plane of the Ecliptic does not match the ecliptic or invariable planes of the solar sytem (Elliot et al., 2005). Collisional families exists, Haumea (Brown et al., 2007)."[20]


"The abundance ratios of stable isotopes of the light elements in comets may provide clues of cosmogonical significance."[21]

"In 1997 we observed comet Hale-Bopp with the 2.6 m Nordic Optical Telescope on La Palma, Canary Islands, with a view to estimating the 12C/13C abundance ratio. About twenty high-resolution (λ /Δ λ ~ 70000) spectra of the strong CN Violet (0,0) band were secured with the SOFIN spectrograph from 7 to 13 April. The heliocentric and geocentric distances of the comet were then close to 0.9 AU and 1.4 AU, respectively. While the data do show the expected lines of the 13C14N isotopic molecule, we have been surprised to find in addition a number of very weak features, which are real and turn out to be positioned very near to the theoretical wavelengths of lines pertaining to the R branch of 12C15N."[21]


"The ices of Callisto do not seem to have exploded at all."[22]

If the age of the Galilean satellites is "cosmogonic ( ≈ 4 x 109 yr) [...] it is clear that there are no grounds for postulating a cosmogonic crater age [...] "[22]

"The comet data suggest [...] that there should be released simultaneously [...] about two orders of magnitude less (QCN/QH2O ≈ 10-3 by Schloerb et al. (1987)) of cyan compounds, ≈ 2 x 1015 g."[22]


"There the deceased states that “I have strewed green stones",8 most likely with the intention of identifying himself with the [...] time when Amun became the supreme god of the Egyptian pantheon, the creation [...] “He (Amun) created the heaven and made it luminous through the stars."11 In the myths and mythologems discussed above, the stars came into being in a later phase of cosmogony. However, we also know of myths reflecting different views. [...] stage of the birth of the universe.12"[23]


"Then, as that long period was drawing to a close, these Gods directed the orange colored force of life into the smaller matrices of Divine Mind and brought into physical being the lichens and the mussels and all the lowest forms of life on land and sea."[24]


Hubble's Wide Field Planetary Camera 2 to snapped this new image of Vesta on May 14 and 16, 2007. Credit: NASA; ESA; L. McFadden and J.Y. Li (University of Maryland, College Park); M. Mutchler and Z. Levay (Space Telescope Science Institute, Baltimore); P. Thomas (Cornell University); J. Parker and E.F. Young (Southwest Research Institute); and C.T. Russell and B. Schmidt (University of California, Los Angeles).

"To prepare for the Dawn spacecraft's visit to Vesta, astronomers used Hubble's Wide Field Planetary Camera 2 to snap new images of the asteroid. The image at right was taken on May 14 and 16, 2007. Using Hubble, astronomers mapped Vesta's southern hemisphere, a region dominated by a giant impact crater formed by a collision billions of years ago. The crater is 285 miles (456 kilometers) across, which is nearly equal to Vesta's 330-mile (530-kilometer) diameter. If Earth had a crater of proportional size, it would fill the Pacific Ocean basin. The impact broke off chunks of rock, producing more than 50 smaller asteroids that astronomers have nicknamed "vestoids." The collision also may have blasted through Vesta's crust. Vesta is about the size of Arizona."[25]

"Previous Hubble images of Vesta's southern hemisphere were taken in 1994 and 1996 with the wide-field camera. In this new set of images, Hubble's sharp "eye" can see features as small as about 37 miles (60 kilometers) across. The image shows the difference in brightness and color on the asteroid's surface. These characteristics hint at the large-scale features that the Dawn spacecraft [sees] when it arrives at Vesta."[25]

"Hubble's view reveals extensive global features stretching longitudinally from the northern hemisphere to the southern hemisphere. The image also shows widespread differences in brightness in the east and west, which probably reflects compositional changes. Both of these characteristics could reveal volcanic activity throughout Vesta. The size of these different regions varies. Some are hundreds of miles across."[25]

"The brightness differences could be similar to the effect seen on the Moon, where smooth, dark regions are more iron-rich than the brighter highlands that contain minerals richer in calcium and aluminum. When Vesta was forming 4.5 billion years ago, it was heated to the melting temperatures of rock. This heating allowed heavier material to sink to Vesta's center and lighter minerals to rise to the surface."[25]

"Astronomers combined images of Vesta in two colors to study the variations in iron-bearing minerals. From these minerals, they hope to learn more about Vesta's surface structure and composition."[25]

"The simplest model for the genesis of the HED meteorites involves a series of partial melting and crystallization events [1] of a small parent body whose bulk composition is more or less consistent with cosmic abundances but is depleted in the moderately volatile elements Na and K [2]."[26]

"Why should both Vesta and the Moon be rich in oxidized Fe but depleted in Na and K?"[26]

"How did the HEDs get here from Vesta? The discovery of a string of Vesta-like asteroids in orbits linking Vesta to nearby orbital resonances [5] has shown that [...] arguments [...] for material originating at Vesta to reach Earth-crossing orbits are [...] valid."[26]

"An alternative theory is based on electromagnetic heating during an episode of strong solar wind from the early proto-Sun when our star experienced a T Tauri phase, as predicted by modern stellar astrophysics."[27]


"The deuterium enrichment of cometary water is one of the most important cosmogonic indicators in comets. The (D/H)H2O ratio preserves information about the conditions under which comet material formed, and tests the possible contribution of comets in delivering water for Earth's oceans. Water (H2O) and HDO were sampled in comet 8P/Tuttle from 2008 January 27 to 2008 February 3 using the new IR spectrometer (Cryogenic Infrared Echelle Spectrograph) at the 8.2 m Antu telescope of the Very Large Telescope Observatory atop Cerro Paranal, Chile."[28]


Stars "believed to have circumstellar disks similar to the primitive solar nebula [are] based on the criteria [...]:

  1. high far-infrared optical depths around visible stars,
  2. shallow spectral energy densities longward of 5 µm, and
  3. large millimeter-wave flux densities indicative of ≳ 0.01 M of H2."[29]

"Evidence for changes in particle composition, size, or shape, reflected in the emissivity index, could therefore be relevant to theories of cosmogony."[29]

"The observations were carried out at the Caltech Submillimeter Observatory (CSO) in Hawaii during 1989 November through December 4, and 1990 December 4 through 9. The detector was a silicon composite bolometer fed by a Winston cone and cooled to a few tenths of a degree with a 3He refrigerator. The filtering employed standard techniques: a scattering filter of black polyethylene fused to fluorogold at 77 K blocked wavelengths in the far-infrared; a crystal quartz filter coated with black polyethylene at 4 K eliminated all near-infrared radiation; and bandpass filters made of metal mesh on nylon or polyethylene, defined the actual wavebands (e.g., Whitcomb & Keene 1980; Cunningham 1982). Different Winston cones were used with each filter to match the diffraction limit of the 10 m telescope, giving different beam sizes on the sky."[29]


"Very low values of the radio brightness temperatures of the rings of Saturn indicate that their high radar reflectivity is not simply due to a gain effect in the backscatter direction. These two sets of observations are consistent with the ring particles having a very high single scattering albedo at radio wavelengths with multiple scattering effects being important. Comparison of scattering calculations for ice and silicate particles with radio and radar observations imply a mean particle radius of ~ 1 cm. [...] The inferred mean size is consistent with a model in which meteoroid impacts have caused a substantial reduction in the mean particle size from its initial value."[30]


Interplanetary scintillation refers to random fluctuations in the intensity of radio waves of celestial origin, on the timescale of a few seconds. It is analogous to the twinkling one sees looking at stars in the sky at night, but in the radio part of the electromagnetic spectrum rather than the visible one. Interplanetary scintillation is the result of radio waves traveling through fluctuations in the density of the electron and protons that make up the solar wind.

Scintillation occurs as a result of variations in the refractive index of the medium through which waves are traveling. The solar wind is a plasma, composed primarily of electrons and lone protons, and the variations in the index of refraction are caused by variations in the density of the plasma.[31] Different indices of refraction result in phase changes between waves traveling through different locations, which results in interference. As the waves interfere, both the frequency of the wave and its angular size are broadened, and the intensity varies.[32]

"Comets provide important clues to the physical and chemical processes that occurred during the formation and early evolution of the Solar System [...] Comparing abundances and cosmogonic values (isotope and ortho:para (o/p) ratios) of cometary parent volatiles to those found in the interstellar medium, in disks around young stars, and between cometary families, is vital to understanding planetary system formation and the processing history experienced by organic matter in the so-called interstellar-comet connection [2]. [...] ground-based radio observations towards comets C/2009 P1 (Garradd) and C/2012 F6 (Lemmon) [...] constrain the chemical history of these bodies."[33]

Plasma objects[edit]

Because "of the huge spatiotemporal scales of plasma objects in space, the basic accepted views about the theory of plasma stability, which is now better suited for laboratory applications, are already in need of revision."[34]

Gaseous objects[edit]

"In accord with modern cosmogonic concepts that are discussed later, three basic materials have been used to construct interior models of the giant planets: a solar mixture of elements dominated by hydrogen and helium ("gas"); water, methane, and ammonia with O, C, and N in solar proportions ("ice")2; and magnesium- and iron-containing silicates and metallic iron, with Mg, Fe, and Si in cosmic proportions ("rock"). [...] Gaseous objects, such as stars, are the end products of one or several successive gravitational instabilities that occur in dense molecular clouds."[35]

Liquid objects[edit]

"For specific cosmogonic details the most important piece of Mesopotamian literature is the Babylonian epic story of creation, Enuma Elish (ibid., 60–72). Here, as in Genesis, the priority of water is taken for granted, i.e., the primeval chaos consisted of a watery abyss. The name for this watery abyss, part of which is personified by the goddess Tiamat, is the etymological equivalent of the Hebrew tehom (Gen. 1:2), a proper name that always appears in the Bible without the definite article. (It should be noted, however, that whereas "Tiamat" is the name of a primal generative force, tehom is merely a poetic term for a lifeless mass of water.) In both Genesis (1:6–7) and Enuma Elish (4:137–40) the creation of heaven and earth resulted from the separation of the waters by a firmament. The existence of day and night precedes the creation of the luminous bodies (Gen. 1:5, 8, 13, and 14ff.; Enuma Elish 1:38)."[36]

"Apart from the scientific interest for fluid sciences and material sciences in space, the rotating liquid drops have high interest for cosmogony, geophysics and nuclear physics as well."[37]

Rocky objects[edit]

""Foam-born" Aphrodite is linked to the Moon through her epithet Pasiphaessa, the 'All-shinig One'. In Hesiod's Theogony, Aphrodite was conceived in the lap of the waves which were fertilized by semen from the severed genitals of Ouranos, Heaven, and was 'born in soft foam', as the Homeric Hymn to Aphrodite puts it.71"[38]

"An aspect of current cosmogonic models is reviewed which until a few years ago had received little consideration: the transformation by accretion of kilometer-size objects into bodies comparable in size to the earth."[39]

"The generally accepted model for terrestrial-planet formation describes their hierarchical accumulation from smaller rocky objects. [...] Developing scenarios that predict the formation of large terrestrial-type planets with low eccentricities represents a significant and as yet unsolved problem of cosmogony."[40]


Main sources: Chemicals/Oxygens and Oxygens
The earliest dust and rocks are forming in the solar nebula by this artist's impression. Credit: NASA.

An oxygen isotope "discrepancy was noted forty years ago in a stony meteorite that exploded over Pueblito de Allende, Mexico. It has since been confirmed in other meteorites, which are asteroids that fall to Earth. These meteorites are some of the oldest objects in the Solar System, believed to have formed nearly 4.6 billion years ago within the solar nebula’s first million years. The mix of oxygen-16 (the most abundant form with one neutron for each proton) and variants with an extra neutron or two is markedly different in the meteorites than that seen on terrestrial Earth, the moon or Mars."[41]

“Oxygen isotopes in meteorites are hugely different from those of the terrestrial planets, ... With oxygen being the third most abundant element in the universe and one of the major rock forming elements, this variation among different solar system bodies is a puzzle that must be solved to understand how the solar system formed and evolved.”[42]

"In most instances, oxygen isotopes sort out according to mass. Oxygen-17, for example, has just one extra neutron and is incorporated into molecules half as often as oxygen-18, which has two extra neutrons. In these meteorites, however, the rate at which they were incorporated was independent of their masses."[41]

"One theory proposes that the mix of oxygen isotopes was different back when the earliest solid matter in the Solar System formed, perhaps enriched by matter blasted in from a nearby supernova. Another suggests a photochemical effect called self-shielding, which this team had previously ruled out. The final surviving theory was that a physical chemical principle called symmetry could account for the observed patterns of oxygen isotopes."[41]

The final surviving theory was tested "by filling a hockey puck sized chamber with pure oxygen, varying amounts of pure hydrogen and a little black nugget of solid silicon monoxide. A laser was used to vaporize a plume of silicon monoxide gas into the mix. This mixture of ingredients is observed by radiotelescopes in interstellar clouds, the starting point for our Solar System."[41]

"The oxygen and nitrogen reacted with the silicon monoxide gas to form silicon dioxide. This solid, which is the basis of silicate minerals like quartz that are so prevalent in the crust of the Earth, settled as dust in the chamber. The earliest solid materials in the Solar System were formed by these reactions of gases."[41]

After [collecting and analyzing the dust] a mix of oxygen isotopes [was found] that matched the anomalous pattern found in stony meteorites. The fact that the degree of the anomaly scaled with the percentage of the atmosphere that was hydrogen points to a reaction governed by symmetry."[41]

“No mattter what else happened early on in the nebula, this is the last step in making the first rocks from scratch, ... We’ve shown that you don’t need a magic recipe to generate this oxygen anomaly. It’s just a simple feature of physical chemistry.”[43]


Main sources: Plasmas/Ions and Ions

"[F]luxes of ions should be measurable from a detector in a 100 km lunar orbit."[44]


Into the exosphere or outer space, temperature rises from around 1,500°C (centigrade) to upwards of 100,000 K (kelvin).


Main sources: Rocks/Meteorites and Meteorites
The Williamette Meteorite is on display at the American Museum of Natural History in New York City. Credit: Dante Alighieri.
This image is a cross-section of the Laguna Manantiales meteorite showing Widmanstätten patterns. Credit: Aram Dulyan.
This is a micrometerorite collected from the antarctic snow. Credit: NASA.

Def. a metallic or stony object that is the remains of a meteor is called a meteorite.

Many of the meteorites that are found on Earth turn out to be from other solar system objects: the Moon and Mars, for example.

Widmanstätten patterns, also called Thomson structures, are unique figures of long nickel-iron crystals, found in the octahedrite iron meteorites and some pallasites. They consist of a fine interleaving of kamacite and taenite bands or ribbons called lamellæ. Commonly, in gaps between the lamellæ, a fine-grained mixture of kamacite and taenite called plessite can be found.

Micrometeorite is often abbreviated as MM. Most MMs are broadly chondritic in composition, meaning "that major elemental abundance ratios are within about 50% of those observed in carbonaceous chondrites."[45] Some MMs are chondrites, (basaltic) howardite, eucrite, and diogenite (HED) meteorites or Martian basalts, but not lunar samples.[45] "[T]he comparative mechanical weakness of carbonaceous precursor materials tends to encourage spherule formation."[45] From the number of different asteroidal precursors, the approximate fraction in MMs is 70 % carbonaceous.[45] "[T]he carbonaceous material [is] known from observation to dominate the terrestrial MM flux."[45] The "H, L, and E chondritic compositions" are "dominant among meteorites but rare among micrometeorites."[45]

"Ureilites occur about half as often as eucrites (Krot et al. 2003), are relatively friable, have less a wide range of cosmic-ray exposure ages including two less than 1 Myr, and, like the dominant group of MM precursors, contain carbon."[45]


Main sources: Stars/Sun and Sun (star)

From model calculations based on data from Ulysses and Skylab, “[i]nside 2 Rʘ the [interplanetary medium] temperature is a minimum over the poles, with values Teff ~106 K, while farther from the Sun the temperature is a maximum over the poles with Teff ~3 x 106 K at its maximum value [at about 5 Rʘ out to 7 Rʘ].”[46] Teff is estimated to be ~2 x 105 K at 1 AU over the poles and ~1.5 x 105 in the equatorial region out at 1 AU, which compare well with spacecraft observations.[46]

"A persistent problem of solar cosmic-ray research has been the lack of observations bearing on the timing and conditions in which protons that escape to the interplanetary medium are first accelerated in the corona."[47]

The heliospheric current sheet[48] is the surface within the Solar System where the polarity of the Sun's magnetic field changes from north to south. This field extends throughout the Sun's equatorial plane in the heliosphere.[49][50] The shape of the current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium (solar wind).[51] A small electrical current flows within the sheet, about 10−10 A/m². The thickness of the current sheet is about 10,000 km near the orbit of the Earth.

The underlying magnetic field is called the interplanetary magnetic field, and the resulting electric current forms part of the heliospheric current circuit.[52] The heliospheric current sheet is also sometimes called the interplanetary current sheet.

Coronal clouds[edit]

"Lynch et al. [2010], for example, observed plasma pileup structures around magnetic clouds."[19]

"A [plasma depletion layer] PDL was observed in the sheath by Liu et al. [2006] in front of a fast moving and expanding magnetic cloud, in the region where the magnetic field lines change around it."[19]

Solar winds[edit]

The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV.

"Energetic photons, ions and electrons from the solar wind, together with galactic and extragalactic cosmic rays, constantly bombard surfaces of planets, planetary satellites, dust particles, comets and asteroids."[44]

The solar wind is divided into two components, respectively termed the slow solar wind and the fast solar wind. The slow solar wind has a velocity of about 400 km/s, a temperature of 1.4–1.6×106 K and a composition that is a close match to the corona. By contrast, the fast solar wind has a typical velocity of 750 km/s, a temperature of 8×105 K and it nearly matches the composition of the Sun's photosphere.[53] The slow solar wind is twice as dense and more variable in intensity than the fast solar wind. The slow wind also has a more complex structure, with turbulent regions and large-scale structures.[54][55]

The slow solar wind appears to originate from a region around the Sun's equatorial belt that is known as the "streamer belt". Coronal streamers extend outward from this region, carrying plasma from the interior along closed magnetic loops.[56][57] Observations of the Sun between 1996 and 2001 showed that emission of the slow solar wind occurred between latitudes of 30–35° around the equator during the solar minimum (the period of lowest solar activity), then expanded toward the poles as the minimum waned. By the time of the solar maximum, the poles were also emitting a slow solar wind.[58]

The fast solar wind is thought to originate from coronal holes, which are funnel-like regions of open field lines in the Sun's magnetic field.[59] Such open lines are particularly prevalent around the Sun's magnetic poles. The plasma source is small magnetic fields created by convection cells in the solar atmosphere. These fields confine the plasma and transport it into the narrow necks of the coronal funnels, which are located only 20,000 kilometers above the photosphere. The plasma is released into the funnel when these magnetic field lines reconnect.[60]


Main sources: Wanderers/Mercury and Mercury

"[T]he Mercury encounter (M I) by Mariner 10 on 29 March 1974 occurred during the height of a Jovian electron increase in the interplanetary medium."[61]

During its second flyby of the planet on October 6, 2008, MESSENGER discovered that Mercury's magnetic field can be extremely "leaky." The spacecraft encountered magnetic "tornadoes" – twisted bundles of magnetic fields connecting the planetary magnetic field to interplanetary space – that were up to 800 km wide or a third of the radius of the planet. These 'tornadoes' form when magnetic fields carried by the solar wind connect to Mercury's magnetic field. As the solar wind blows past Mercury's field, these joined magnetic fields are carried with it and twist up into vortex-like structures. These twisted magnetic flux tubes, technically known as flux transfer events, form open windows in the planet's magnetic shield through which the solar wind may enter and directly impact Mercury's surface.[62]

The process of linking interplanetary and planetary magnetic fields, called magnetic reconnection, is common throughout the cosmos. It occurs in Earth's magnetic field, where it generates magnetic tornadoes as well. The MESSENGER observations show the reconnection rate is ten times higher at Mercury. Mercury's proximity to the Sun only accounts for about a third of the reconnection rate observed by MESSENGER.[62]


Main sources: Wanderers/Venus and Venus

"During a rare period of very low density solar outflow, the ionosphere of Venus was observed to become elongated downstream, rather like a long-tailed comet. ... Under normal conditions, the solar wind has a density of 5 - 10 particles per cubic cm at Earth's orbit, but occasionally the solar wind almost disappears, as happened in May 1999. ... A rare opportunity to examine what happens when a tenuous solar wind arrives at Venus came 3 - 4 August 2010, following a series of large coronal mass ejections on the Sun. NASA's STEREO-B spacecraft, orbiting downstream from Venus, observed that the solar wind density at Earth's orbit dropped to the remarkably low figure of 0.1 particles per cubic cm and persisted at this value for an entire day."[63]

"The observations show that the night side ionosphere moved outward to at least 15 000 km from Venus' centre over a period of only a few hours," said Markus Fraenz, also from the Max Planck Institute for Solar System Research, who was the team leader and a co-author of the paper.[63] "It may possibly have extended for millions of kilometres, like an enormous tail."[63]

"Although we cannot determine the full length of the night-side ionosphere, since the orbit of Venus Express provides limited coverage, our results suggest that Venus' ionosphere resembled the teardrop-shaped ionosphere found around comets, rather than the more symmetrical, spherical shape which usually exists."[63]

"The side of Venus' ionosphere that faces away from the sun can billow outward like the tail of a comet, while the side facing the star remains tightly compacted, researchers said. ... "As this significantly reduced solar wind hit Venus, Venus Express saw the planet’s ionosphere balloon outwards on the planet’s ‘downwind’ nightside, much like the shape of the ion tail seen streaming from a comet under similar conditions," ESA officials said in a statement today (Jan. 29). It only takes 30 to 60 minutes for the planet's comet-like tail to form after the solar wind dies down. Researchers observed the ionosphere stretch to at least 7,521 miles (12,104 kilometers) from the planet, said Yong Wei, a scientist at the Max Planck Institute in Katlenburg, Germany who worked on this research."[64]


Main source: Earth

The Gegenschein 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.

The Zodiacal light is a faint, roughly triangular, diffuse white glow seen in the night sky that appears to extend up from the vicinity of the Sun along the ecliptic or zodiac.[65] It is best seen just after sunset and before sunrise in spring and autumn when the zodiac is at a steep angle to the horizon. Caused by sunlight scattered by space dust in the zodiacal cloud, it is so faint that either moonlight or light pollution renders it invisible. The zodiacal light decreases in intensity with distance from the Sun, but on very dark nights it has been observed in a band completely around the ecliptic. In fact, the zodiacal light covers the entire sky, being responsible for major part[66] of the total skylight on a moonless night. There is also a very faint, but still slightly increased, oval glow directly opposite the Sun which is known as the gegenschein. The dust forms a thick pancake-shaped cloud in the Solar System collectively known as the zodiacal cloud, which occupies the same plane as the ecliptic. The dust particles are between 10 and 300 micrometres in diameter, with most mass around 150 micrometres.[67]

The Van Allen radiation belt is split into two distinct belts, with energetic electrons forming the outer belt and a combination of protons and electrons forming the inner belts. In addition, the radiation belts contain lesser amounts of other nuclei, such as alpha particles.

The large outer radiation belt extends from an altitude of about three to ten Earth radii (RE) or 13,000 to 60,000 kilometres above the Earth's surface. Its greatest intensity is usually around 4–5 RE. The outer electron radiation belt is mostly produced by the inward radial diffusion[68][69] and local acceleration[70] due to transfer of energy from whistler mode plasma waves to radiation belt electrons. Radiation belt electrons are also constantly removed by collisions with atmospheric neutrals,[70] losses to magnetopause, and the outward radial diffusion. The outer belt consists mainly of high energy (0.1–10 MeV) electrons trapped by the Earth's magnetosphere. The gyroradii for energetic protons would be large enough to bring them into contact with the Earth's atmosphere. The electrons here have a high flux and at the outer edge (close to the magnetopause), where geomagnetic field lines open into the geomagnetic "tail", fluxes of energetic electrons can drop to the low interplanetary levels within about 100 km (a decrease by a factor of 1,000).

"Current theories for the origin of Earth’s ocean require a contribution from both asteroids and comets, although the relative importances of the asteroidal and cometary fractions is still under investigation (Delsemme, 2000; Morbidelli et al., 2000)."[71]


Main sources: Wanderers/Moon and Moon
The Moon is where a prediction of a lunar double layer was confirmed in 2003. Credit: Mdf.

The Moon is where a prediction of a lunar double layer[72] was confirmed in 2003.[73] In the shadows, the Moon charges negatively in the interplanetary medium.[74]


Main sources: Wanderers/Mars and Mars

"At the end of the eighth century and the beginning of the seventh century before the present era, when every fifteen years Mars was approaching dangerously close to the Earth, Isaiah prophesied “the day of the Lord’s vengeance,” in which day “the streams [of Idumea] shall be turned into pitch, and the dust thereof into brimstone, and the land thereof shall become burning pitch.” (8) [Isaiah 34:9] A curse upon man and his land was that “brimstone shall be scattered upon his habitation.” (9) [Job 18:15] “Upon the wicked he shall rain pitch, fire and brimstone, and a horrible tempest.” (10) [Psalm 11:6] This eschatological vision was alive with Ezekiel in the days of the Babylonian Exile. He spoke about “an overflowing rain, and great hailstones [meteorites], fire and brimstone.” (11) [Ezekiel 38:22]"[75]


This color picture is made from images taken by the imaging system on the Galileo spacecraft about 14 minutes before its closest approach to asteroid 243 Ida on August 28, 1993. Credit: NASA/JPL. Derivative work: Chzz.
The asteroid belt is shown in (white) and the Trojan asteroids (green). Credit: Mdf.

The majority of known asteroids orbit within the asteroid belt between the orbits of Mars and Jupiter ... This belt is now estimated to contain between 1.1 and 1.9 million asteroids larger than 1 km in diameter,[76] and millions of smaller ones.[77]

"The recent investigation of the orbital distribution of Centaurs (Emel’yanenko et al., 2005) showed that there are two dynamically distinct classes of Centaurs, a dominant group with semimajor axes a > 60 AU and a minority group with a < 60 AU."[78] "[T]he intrinsic number of such objects is roughly an order of magnitude greater than that for a<60 AU"

"From the dominant group, the asteroids evolve to intersect the Earth's orbit on a median time scale of about 60 Myr."[79] "The MB group is the most numerous group of MCs. ... 50 % of the MB Mars-crossers [MCs] become ECs within 59.9 Myr and [this] contribution ... dominates the production of ECs"[79]. MB denotes the main belt of asteroids.[79] EC denotes Earth-crossing.[79]

"Asteroids ... are space weathered by radiation."[44]

At right is an image of asteroid 243 Ida and its moon which is visible to the right of the asteroid. This picture is made from images through the 410.0-nm (violet), 756.0 nm (infrared) and 968.0 nm (infrared) filters. The color is 'enhanced' in the sense that the CCD camera is sensitive to near infrared wavelengths of light beyond human vision; a 'natural' color picture of this asteroid would appear mostly gray. Shadings in the image indicate changes in illumination angle on the many steep slopes of this irregular body as well as subtle color variations due to differences in the physical state and composition of the soil (regolith). There are brighter areas, appearing bluish in the picture, around craters on the upper left end of Ida, around the small bright crater near the center of the asteroid, and near the upper right-hand edge (the limb). This is a combination of more reflected blue light and greater absorption of near infrared light, suggesting a difference in the abundance or composition of iron-bearing minerals in these areas. Ida's moon also has a deeper near-infrared absorption and a different color in the violet than any area on this side of Ida. The moon is not identical in spectral properties to any area of Ida in view here, though its overall similarity in reflectance and general spectral type suggests that it is made of the same rock types basically.


Main sources: Wanderers/Jupiter and Jupiter

"Jovian electrons, both at Jupiter and in the interplanetary medium near Earth, have a very hard spectrum that varies as a power law with energy (see, e.g., Mewaldt et al. 1976). This spectral character is sufficiently distinct from the much softer solar and magnetospheric electron spectra that it has been used as a spectral filter to separate Jovian electrons from other sources ... A second Jovian electron characteristic is that such electrons in the interplanetary medium tend to consist of flux increases of several days duration which recur with 27 day periodicities ... A third feature of Jovian electrons at 1 AU is that the flux increases exhibit a long-term modulation of 13 months which is the synodic period of Jupiter as viewed from Earth".[61]

Jovian electrons propagate "along the spiral magnetic field of the interplanetary medium [from Jupiter and its magnetosphere to the Sun]".[61]


Main sources: Wanderers/Saturn and Saturn

Powered by the Saturnian equivalent of (filamentary) Birkeland currents, streams of charged particles from the interplanetary medium interact with the planet's magnetic field and funnel down to the poles.[80] Double layers are associated with (filamentary) currents,[4][81] and their electric fields accelerate ions and electrons.[82]


Main source: Comets
This is a photograph taken in 1910 during the passage of Halley's comet. Credit: The Yerkes Observatory.

The 1910 approach [of Halley's comet], which came into naked-eye view around 10 April[83] and came to perihelion on 20 April,[83] was notable for several reasons: it was the first approach of which photographs exist, and the first for which spectroscopic data were obtained.[84] Furthermore, the comet made a relatively close approach of 0.15AU,[83] making it a spectacular sight. Indeed, on 19 May, the Earth actually passed through the tail of the comet.[85][86] One of the substances discovered in the tail by spectroscopic analysis was the toxic gas cyanogen,[87] which led astronomer Camille Flammarion to claim that, when Earth passed through the tail, the gas "would impregnate the atmosphere and possibly snuff out all life on the planet."[48] His pronouncement led to panicked buying of gas masks and quack "anti-comet pills" and "anti-comet umbrellas" by the public.[88] In reality, as other astronomers were quick to point out, the gas is so diffuse that the world suffered no ill effects from the passage through the tail.[89]

"It is quite possible that [faint streamers preceding the main tail and lying nearly in the prolonged radius vector] may have touched the Earth, probably between May 19.0 and May 19.5, [1910,] but the Earth must have passed considerably to the south of the main portion of the tail [of Halley's comet]."[90]

A magnetohydrodynamics (MHD) and chemical comet-coma model is applied to describe and analyze the plasma flow, magnetic field, and ion abundances in Comet Halley.[91] A comparison of model results is made with the data from the Giotto mission.[91]

"In the second dominant group of ions we generally see more discrepancies in the model and the HIS data".[91]

The principal application of the dominant group concept is to the ion density measurements at or within 1500 km of the comet nucleus, where "the model abundances for the light ions, up to 21 amu, are in very good agreement with the 1500 km observations."[91]

The comparison between model and measurements "generally becomes worse as one considers higher molecular masses and greater distance from the [comet] nucleus."[91]

For elongated dust particles in cometary comas an investigation is performed at 535.0 nm (green) and 627.4 nm (red) peak transmission wavelengths of the Rosetta spacecraft's OSIRIS Wide Angle Camera broadband green and red filters, respectively.[92] "In the green, the polarization of the pure silicate composition qualitatively appears a better fit to the shape of the observed polarization curves".[92] "[B]ut they are characterized by a high albedo."[92] The silicates used to model the cometary coma dust are olivene (Mg-rich is green) and the pyroxene, enstatite.[92]

"It is found that near 1 AU, the dominant group of the local geometrical cross section changes."[93] Approximately 80 % of interplanetary dust is cometary at R ~ 0.8 AU.

Kuiper belts[edit]

Main source: Kuiper belts
Known objects in the Kuiper belt, are derived from data from the Minor Planet Center. Credit: WilyD.

In the image at right, objects in the main part of the Kuiper belt are coloured green, while scattered objects are coloured orange. The four outer planets are blue. Neptune's few known trojans are yellow, while Jupiter's are pink. The scattered objects between Jupiter's orbit and the Kuiper belt are known as centaurs. The scale is in astronomical units. The pronounced gap at the bottom is due to difficulties in detection against the background of the plane of the Milky Way.

The Kuiper belt is a region of the solar system extending from the orbit of Neptune (at 30 AU to approximately 60 AU from the Sun.[94] It consists mainly of small bodies.

Protoplanetary disks[edit]

The dwarf planet Eris is the largest known scattered-disc object (center), with its moon Dysnomia (left of object). Credit: NASA, ESA, and Michael E. Brown.

The scattered disc (or scattered disk) is a distant region of the solar system that is sparsely populated by icy minor planets, a subset of the broader family of trans-Neptunian objects. The scattered-disc objects (SDOs) have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater than 30 astronomical units (4.5 x 109 km; 2.8 x 109 mi.). While the nearest distance to the Sun approached by scattered objects is about 30–35 AU, their orbits can extend well beyond 100 AU. This makes scattered objects "among the most distant and cold objects in the Solar System".[95]

Oort clouds[edit]

Main source: Oort clouds
Here, the presumed distance of the Oort cloud is compared to the rest of the Solar System using the orbit of Sedna. Credit: NASA / JPL-Caltech / R. Hurt.
Sedna, a possible inner Oort cloud object, is a discovery in 2003. Credit: NASA.

The Oort cloud or the Öpik–Oort cloud[96] is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun.[97] This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the region of the Sun's gravitational dominance.[98]


Def. the region of space where interstellar medium is blown away by solar wind; the boundary, heliopause, is often considered the edge of the Solar System is called the heliosphere.

The heliosphere is a bubble in space "blown" into the interstellar medium (the hydrogen and helium gas that permeates the galaxy) by the solar wind. Although electrically neutral atoms from interstellar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself.

The point where the solar wind slows down is the termination shock". Further out "is the heliosheath area. As of June 2011, the heliosheath area is thought to be filled with magnetic bubbles (each about 1 AU wide), creating a "foamy zone".[99]

Electron winds[edit]

As of December 5, 2011, "Voyager 1 is about ... 18 billion kilometers ... from the [S]un [but] the direction of the magnetic field lines has not changed, indicating Voyager is still within the heliosphere ... the outward speed of the solar wind had diminished to zero in April 2010 ... inward pressure from interstellar space is compacting [the magnetic field] ... Voyager has detected a 100-fold increase in the intensity of high-energy electrons from elsewhere in the galaxy diffusing into our solar system from outside ... [while] the [solar] wind even blows back at us."[100]


The point where the interstellar medium and solar wind pressures balance is called the heliopause.

The point where the interstellar medium, traveling in the opposite direction, slows down as it collides with the heliosphere is the bow shock.

Interstellar mediums[edit]

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.

The interstellar medium begins where the interplanetary medium of the Solar System ends. The solar wind slows to subsonic velocities at the termination shock, 90—100 astronomical units from the Sun. In the region beyond the termination shock, called the heliosheath, interstellar matter interacts with the solar wind. Voyager 1, the farthest human-made object from the Earth (after 1998[101]), crossed the termination shock December 16, 2004 and later entered interstellar space when it crossed the heliopause on August 25, 2012, providing the first direct probe of conditions in the ISM[102].


Main source: Astrochemistry

Chemical ions above the Earth's atmosphere, moving at very high speeds and at concentrations up to 100 particles per cm3 (centimeter cubed, a unit of volume) constitute the interplanetary medium.


Main source: Astrophysics
This is an optical image of U Camelopardalis from the Hubble Space Telescope. Credit: ESA/Hubble, NASA and H. Olofsson (Onsala Space Observatory).

"The accretion disk can become thermally stable in systems with high mass-transfer rates (Ṁ).[103] Such systems are called nova-like (NL) stars, because they lack outbursts characteristic of dwarf novae.[104]"[105]

"A bright star [in the image at left] is surrounded by a tenuous shell of gas in this unusual image from the NASA/ESA Hubble Space Telescope. U Camelopardalis, or U Cam for short, is a star nearing the end of its life. As it begins to run low on fuel, it is becoming unstable. Every few thousand years, it coughs out a nearly spherical shell of gas as a layer of helium around its core begins to fuse. The gas ejected in the star’s latest eruption is clearly visible in this picture as a faint bubble of gas surrounding the star."[106]

"U Cam is an example of a carbon star. This is a rare type of star whose atmosphere contains more carbon than oxygen. Due to its low surface gravity, typically as much as half of the total mass of a carbon star may be lost by way of powerful stellar winds."[106]

"Located in the constellation of Camelopardalis (The Giraffe), near the North Celestial Pole, U Cam itself is actually much smaller than it appears in Hubble’s picture. In fact, the star would easily fit within a single pixel at the centre of the image. Its brightness, however, is enough to overwhelm the capability of Hubble’s Advanced Camera for Surveys making the star look much bigger than it really is. The shell of gas, which is both much larger and much fainter than its parent star, is visible in intricate detail in Hubble’s portrait. While phenomena that occur at the ends of stars’ lives are often quite irregular and unstable (see for example Hubble’s images of Eta Carinae, potw1208a), the shell of gas expelled from U Cam is almost perfectly spherical."[106]

"The image was produced with the High Resolution Channel of the Advanced Camera for Surveys [using the 606 nm and 814 nm filters]."[106]

Voyager 1[edit]

The plot shows a dramatic increase in the rate of cosmic ray particle detection by the Voyager 1 spacecraft (October 2012). Credit: NASA.

The Voyager 1 spacecraft is a 722 kg (1,592 lb) space probe launched by NASA on September 5, 1977 to study the outer Solar System and interstellar medium.

The Cosmic Ray System (CRS) determines the origin and acceleration process, life history, and dynamic contribution of interstellar cosmic rays, the nucleosynthesis of elements in cosmic-ray sources, the behavior of cosmic rays in the interplanetary medium, and the trapped planetary energetic-particle environment.

Mariner 10[edit]

The Energetic Particles Experiment aboard Mariner 10 "was designed to measure energetic ... protons ... in the interplanetary medium and in the vicinities of Venus and Mercury. The instrumentation consisted of a main telescope and a low-energy telescope. The main telescope consisted of six co-linear sensors (five silicon detectors and one CsI scintillator) surrounded by a plastic scintillator anti-coincidence cup. One pulse height analysis was performed every 0.33 s, and counts accumulated in each coincidence/anti-coincidence mode were measured every 0.6 s. Particles stopping in the first sensor were protons ... in the range 0.62--10.3 MeV/nucleon ... . The aperture half angle for this mode was 47 degrees, and the geometric [factor was] 7.4 sq cm-sr for protons ... . The telescope aperture half-angle decreased to 32 degrees for coincident counts in the first and third sensors. The low-energy telescope, a two-element (plus anti-coincidence) detector with a 38 degree half angle aperture and a 0.49 sq cm sr geometrical factor, was designed to measure 0.53--1.9 MeV and 1.9--8.9 MeV protons without responding to electrons over a wide range of electron energies and intensities."[107]

Aboard Mariner 10, "[t]he extreme ultraviolet spectrometer consisted of two instruments: an occultation spectrometer that was body-fixed to the spacecraft and an airglow spectrometer that was mounted on the scan platform. When the sun was obscured by the limbs of the planet, the occultation spectrometer measured the extinction properties of the atmosphere. The occultation spectrometer had a plane grating which operated at grazing incidence. The fluxes were measured at 47.0, 74.0, 81.0, and 89.0 nm using channel electron multipliers. Pinholes defined the effective field of view of the instrument which was 0.15 degree full width at half maximum (FWHM). Isolated spectral bands at approximately 75 nm (FWHM) were also measured. The objective grating airglow spectrometer was flown to measure airglow radiation from Venus and Mercury in the spectral range from 20.0--170.0 nm. With a spectral resolution of 2.0 nm, the instrument measured radiation at the following wavelengths: 30.4, 43.0, 58.4, 74.0, 86.9, 104.8, 121.6, 130.4, 148.0, and 165.7 nm. In addition, to provide a check on the total incident extreme UV flux to the spectrometer, two zero-order channels were flown. The effective field of view of the instrument was 0.13 by 3.6 degree. Data also include the interplanetary region."[108]

Orbiting Astronomical Observatory[edit]

This is an image of the Orbiting Astronomical Observatory (OAO 1) 1966-031A. Credit: NASA.

"OAO 1 was a solar-cell-powered satellite instrumented to make precision astronomical observations and to measure the absorption and emission characteristics of the stars, planets, nebulae, and the interplanetary and interstellar media from visible to gamma-ray regions. The stabilization system permitted three axes a pointing accuracy of 1 arc minute after the star tracker acquired a guide star. The control system permitted an ultimate pointing accuracy of 0.1 arc second."[109]


Main source: Hypotheses
  1. The interplanetary medium demonstrates that there is no such thing as empty space.


  1. "an axisymmetric, spherical toroidal flux rope is distorted into a teardrop shape, a configuration that gives the flux rope system sufficient free energy for an eruption [... and]
  2. a flux rope (above the surface) is prescribed by a given toroidal current and is in equilibrium with a background field generated by an infinite line current and two point charges underneath the photosphere [... are used] as a “proof of concept” to explore how different initialization mechanisms can be distinguishable in the lower corona."[19]

See also[edit]


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