Interplanetary Matter Research Articles

The Distribution of Asteroidal Dust in the Inner Solar System

In this paper we demonstrate how the action of secular resonances near the inner edge of the asteroid belt strongly effects the inclinations and eccentricities of asteroidal dust particles, such that they lose the orbital characteristics of their parent body and are dispersed into the zodiacal background. As a consequence, it may not be possible to relate the distribution of interplanetary material at 1 AU to given asteroidal or cometary sources with the level of confidence previously imagined.

The origin of organic matter in the solar system: evidence from the interplanetary dust particles

The detailed examination of meteorites and interplanetary dust particles provides an opportunity to infer the origin of the organic matter found in primitive Solar System materials. If this organic matter were produced by aqueous alteration of elemental (graphitic or amorphous) carbon on an asteroid, then we would expect to see the organic matter occurring preferentially in interplanetary materials that exhibit evidence of aqueous activity, such as the presence of hydrated silicates. On the other hand, if the organic matter were produced either during the nebula phase of Solar System evolution or in the interstellar medium, we might expect this organic matter to be incorporated into the dust as it formed. In that case pre-biotic organic matter would be present in both the anhydrous and the hydrated interplanetary materials. We have performed carbon X-ray absorption near-edge structure spectroscopy and infrared spectroscopy on primitive anhydrous and hydrated interplanetary dust particles (IDPs) collected by NASA from the Earth's stratosphere. We find that organic matter is present in similar types and abundances in both the anhydrous and the hydrated IDPs, and, in the anhydrous IDPs some of this organic matter is the “glue” that holds grains together. These measurements provide the first direct, experimental evidence from the comparison of extraterrestrial samples that the bulk of the pre-biotic organic matter occurs in similar types and abundances in both hydrated and anhydrous samples. This indicates that the bulk of the pre-biotic organic matter in the Solar System did not form by aqueous processing, but, instead, had already formed at the time that primitive, anhydrous dust was being assembled. Thus, the bulk of the pre-biotic organic matter in the Solar System was formed by non-aqueous processing, occurring in either the Solar nebula or in an interstellar environment. Aqueous processing on asteroids may have altered this pre-existing organic matter, but such processing did not affect in any substantial way the C=O content of the organic matter, the aliphatic C-H abundance, or the mean aliphatic chain length.

Current status and scientific capabilities of the Rosetta lander payload

ESA's cornerstone mission “ROSETTA” to comet 46P/Wirtanen will bring a 100 kg Lander (provided by an international European consortium) with a scientific payload of about 27 kg to the surface of the comet's nucleus. After a first scientific sequence it will operate for a considerable fraction of the cometary orbit around the sun (between 3 AU and 2 AU). The Lander is an autonomous spacecraft, powered with solar cells and using the ROSETTA Orbiter as a telemetry relais to Earth. The main scientific objectives are the in-situ investigation of the chemical, elemental, isotopic and mineralogical composition of the comet, study of the physical properties of the surface material, analyze the internal structure of the nucleus, observe temporal variations (day/night cycle, approach to sun), study the relationship between the comet and the interplanetary matter and provide ground reference data for Orbiter instruments. Ten experiments with a number of sub-experiments are foreseen to fulfil these objectives. In this paper we present the current status of the instrumental development and the scientific capabilities of each of the experiments.

Leonid fluxes: 1994–1998 activity patterns

Abstract— The Leonid meteor shower was observed worldwide in 1998 November in an intensive campaign without precedent. During this international effort ∼35 500 meteors were reported by members and collaborators of the International Meteor Organization (IMO) using a standard methodology. Despite the absence of a meteor storm in 1998, the rich observational data allow us to obtain a detailed unprecedented knowledge of the stream structure between 1994 and 1998.

REE-bearing sulfide in Bishunpur (LL3.1), a highly unequilibrated ordinary chondrite

This is a report of the first unambiguous discovery of rare earth elements (REE) in iron sulfide (FeS) in an ordinary chondrite. The content and the pattern of REE as well as the reduced state of the chondrules with the REE-containing sulfide suggest that the sulfide inside the Bishunpur (LL3.1) chondrules is of igneous origin, formed during crystallization of the chondrule melts. The similarities in the content and the pattern of REE between chondrule sulfide and matrix sulfide in Bishunpur indicate a genetic relationship. The presence of igneous sulfide inside chondrules provides constraints on the ambient nebular temperature and the duration of chondrule formation. The results of this study allow, on the basis of REE content and pattern, discrimination of igneous sulfide from condensate and secondary sulfide in chondrites and other interplanetary materials.

Detection of a high density meteoroid on cometary orbit

AbstractWe report a detection of a unique fireball photographed at three Czech stations of the European Fireball Network on June 1, 1997. The main exceptionality of this fireball is given by its retrograde heliocentric orbit (i= 138°) typical for comets and, at the same time, a behavior in the Earth’s atmosphere typical for the hardest component of the interplanetary matter. The spectrum of the fireball is unique by the absence of the sodium line. With the entry velocity of 65 km s−1, the meteoroid of an estimated initial mass of 0.2 kg (diameter of several centimeters) penetrated down the altitude 65 km, i.e. significantly deeper (about 25 km) than cometary meteoroids of a comparable velocity and mass. A comparison with a typical cometary meteoroid is demonstrated on anηAquarid fireball photographed one month before.The event reported is unique in decades-long records of the fireball networks. The origin of the meteoroid in the asteroid belt is highly improbable owing to the orbit. The possibility that comets contain centimeter sized compact stones is therefore suggested.

Prospects for the evolution of life on Mars: Viking 20 years later

During the summer of 1976 the two Viking spacecraft arrived at Mars. Their primary objective was to determine if there was life on Mars. The results of the three life detection experiments aboard the two landers, while not definitive, did not show the presence of extant life. In addition, the GC-MS analyses did not find any organic matter in the Martian regolith at either landing site. Although Viking found no life, it provided data to help explain why no extant life was found at the Martian surface: The surface of Mars is an oxidizing, desiccated environment devoid of liquid water. However, data from the chemical analyses of the regolith conducted during the Viking mission as well as recent analyses of SNC meteorites suggests that all of the chemical elements necessary for life to arise occur on Mars. Further, Mars and Earth accreted from the same interplanetary material suggesting that the early chemical and physical environments of the two planets may have been similar. If this is true then the prospects for the evolution of life on Mars rests on the degree and the duration of similarity between Earth and Mars. Data gathered to date suggests that if liquid water existed on the surface of Mars for sufficient time the probability for life to have arisen is quite reasonable.

On the fragmentation processes in the meteoroid streams

Radar observations of the main meteor showers in 1993–1995 carried out by a forward-scatter radiosystem Bologna-Lecce in Italy are analysed and discussed in terms of fragmentation effects even in the orbit of the streams of interplanetary matter. The existence of very small particles in all meteoroid streams is revealed by counts of echoes of durationT≤0.05 s. A progressive fragmentation is observed to procede in any meteoric complex, likely as a possible consequence of the disintegration of larger bodies in the stream. This disintegration appears to be more significant in some meteoric complexes (Geminids, Leonids and δ-Aquarids), in connection with their differentiated structure and composition.

The local interstellar medium

The local interstellar medium can be probed in different ways: by analyzing low energy X-ray data in the range 0.1–0.4 keV, where the radiation is absorbed by the interstellar gas at column densities in excess of about 1020 cm-2 — and can therefore be regarded as ‘local’, by determining the absorption of stellar emission spectra from nearby stars along their lines of sight by intervening gas and by directin situ measurements of those components which penetrate the heliosphere sufficiently far, provided they can be distinguished from interplanetary material. The current status of these different investigations gives the following picture: the solar system is surrounded by a ‘bubble’ of hot gas (density 0.005cm-3, temperature 106 K) out to several tens of parsecs. More locally it is embedded in a small warm cloud of density 0.07cm-3, temperature 7000 K, column density ∼ 5 × 1017 cm-2 — which gives a mass of about 0.1M⊙. The transition to the heliosphere is governed by solar UV ionization, snowploughing of the interstellar gas by the outwardly expanding solar wind and the bow shock. The heliosphere is the region inside the solar wind terminal shock. Classically it would be regarded as not yet affected by (or aware of) the obstacle ahead. Practically, the existence of the interstellar medium makes itself felt even far inside the heliosphere by the penetration of neutral gas, dust, plasma waves, shock accelerated particles and cosmic rays. These are the local ‘probes’ of the interstellar medium.

A General Formulation for the Distribution of Impacts and Ejecta from Small Planetary Satellites

Small planetary satellites and ring moons are the source of dust rings around each of the giant planets, and presumably Mars, by cratering impacts from interplanetary material. The relative velocities of planetary satellites and interplanetary impactors lead to an anisotropic flux of impactors onto planetary satellites. The anistropy in the impactor flux seen from the frame of the satellite results in an anisotropic production of dust from the surface of the satellite. This anisotropy can have observable consequences for the distribution of material in dust rings. In this paper, an expression for the angular distribution of meteoroid ejecta from impacts onto a single moon or ring particle orbiting a planet with arbitrary obliquity is derived. I allow for any distribution of orbits of the impactors by using a Monte Carlo approach for the micrometeoroid orbits. Ejecta distributions are prograde due to the enhanced impact velocity on the leading face of the target. Ejecta orbits are therefore concentrated in the region exterior to the source satellite. Orbitally averaged ejecta distributions are weakly dependent on the planetary obliquity. Ejecta distributions vary with orbital season for planets with a significant obliquity. The orbitally averaged ejecta distribution is weakly dependent on the orbital distribution of the impactor population, largely due to the smearing effect of the assumed ejects "phase function." The impact velocity of micrometeoroids in the frame of the satellite is correlated with the orbital element distribution of the micrometeoroid population, allowing the orbital elements of interplanetary dust to be inferred from dust impact experiments, such as those on Galileo and Cassini. Dust rings derived from micrometeoroid ejecta from small planetary satellites may show seasonal variations in the vertical distribution of dust as the planet orbits the Sun.

Silicon carbide in laboratory, in interstellar space and in the solar system

Using theoretical models and our laboratory data on different dust mixtures containing silicon carbide grains, we obtained the best fit of several infrared emission spectra of carbon stars and comets. The results suggest that silicon carbide formed in the envelopes around carbon stars and also present in our solar system may provide an important link between interstellar and interplanetary solid material.

Cosmoids: Solution to the pioneer 10 and 11 meteoroid measurement enigma

A theory characterizing interplanetary matter and the zodiacal light has been derived from the dust experiments on the Pioneer 10 and 11 spacecraft to explain the extremely disparate results of the distribution of particles and the zodiacal light measurements. The theory based on these measurements requires a population in the inner solar system of cold meteoroids, cosmoids, composed mainly of volatile molecules, moving in highly eccentric orbits and seldom surviving a single perihelion passage. Impulsive or bursty disruptions from solar heating appears necessary to explain the measured rapid orders of magnitude increases in optical cross section. The integrated scattering from the dispersed material appears to account for nearly all the zodiacal light, with polarization from scattering by micron sized particles. The sublimation time in sunlight opposes the gravitational flux increase expected in approaching the sun. The three Pioneer 10/11 dust experiments were: the Imaging Photopolarimeter (IPP) for the zodiacal light (ZL), the Meteoroid Detection Experiment (MDE) that measured penetrations of 25 (Pioneer 10) and 50 (Pioneer 11) /smm thick walls of pressurized gas cells, and the Asteroid/Meteoroid Experiment or “Sisyphus” that remotely measured meteoroids from reflected sunlight and ZL between meteoroid “events”. No two investigations agreed on the dust distribution and only the IPP could be fitted to the prevailing model of dust spiraling inward from the asteroid belt. MDE data showed a nearly constant flux from 1 to 18 AU! The IPP showed the ZL decreasing between an inverse square and cube rate from 1 to 3.3 AU where it was no longer detectable. The prevailing model has the ZL decrease one power faster than the dust. Sisyphus showed small radial variations from 1 to 3.5 AU where measurements ceased abruptly with the instrument still operating. Sisyphus results were questioned because meteoroid orbits could not be calculated as intended and the ZL as computed from individual meteoroids did not agree with values determined from the ZL mode and from the IPP. Reexamination of the Sisyphus data shows that the instrument measured a population of long period meteoroids, cosmoids, composed primarily of water which dominates the dust distribution. Once the prevailing short period dust model is discounted, the three instruments, measuring cosmoids, are shown to agree. The subsequent measurements from Helios also show evidence of “fluffy” particles with eccentric orbits. This cosmoid population may interact with the outer planets, effecting rings, radial spoke formation and perhaps impulsive radio signatures.

Spatial Distribution and Orbital Properties of Zodiacal Dust

AbstractWithin the recent years the spatial distribution of Zodiacal dust has been subject to a variety of modelling approaches. Whereas models derived from observations in the visual range tend to demand for an increase of interplanetary matter above the solar poles (bulges), models based on infrared measurements and extended to small r seem to favor a decrease there (holes). The models are reviewed, and the dynamical structure implicated in the models is outlined.

The height distribution of radio meteors: observations at 2 MHz

Conventional meteor radars, operating at wavelengths of around 5–15 m, are unable to detect high-altitude meteors due to the wavelength-dependent echo ceiling. It is suggested that the ‘missing mass’ in the 10 −6–10 −2 g range of interplanetary material is in fact a high-velocity component which is normally undetected since it ablates at high altitude. This contention is supported by previous work. In this paper we describe measurements of the heights of radio meteors (limiting magnitude about +7) at a wavelength of 150 m (frequency 2 MHz), for which the echo ceiling is above 140 km. The resultant true height distribution is found to peak at ~ 104 km, about 10 km above the peak found by conventional meteor radars. The majority of meteors are detected at or above this peak, and substantial numbers are seen right up to 140 km. It is therefore concluded that the ‘missing mass’, comprising the vast majority of the meteoric input to the atmosphere, ablates well above 100 km.

Interplanetary material as a guide to the composition of interstellar grains

Interplanetary material as a guide to the composition of interstellar grains

Plans for Release of Simulated Interplanetary Materials into Low Earth Orbit

AbstractA number of experimental releases into low earth orbit of small, but detectable, quantities of very fine particulates are planned for the next several years. The principal materials are chemically and physically similar to those generally assumed to be the major constituents of interplanetary and circumstellar dusts (silicates, silicon carbide, graphitic materials). Later releases will include multi-phase releases of non-volatile particulates and volatile ices, simulating cometary material. Both ground-based and Space-Shuttle-based observations will be made in the visible and infra-red to study particle-plasma interactions, cometary physics and cloud dynamics in orbit.Since opportunities for observing the behavior of such well-characterized materials in space are likely to be rare, and the effective duration of significant concentrations will be very short, we wish to have early input from the scientific community so as to maximize the scientific return. We will be receptive to all suggestions including collaborations in making the observations.

Evidence for the Phi-Dependent Rotation-Oscillation of the Sun (and for the Driving Mechanism of the Asymmetric Dynamo)

AbstractLongitude-dependent oscillations of the solar rotation are derived from the 27-day averages of the photospheric velocity data. Two pairs of prominent periods are obtained. Their harmonic means correspond to a semiannual variation and to the first harmonic of the latter. To explain the origin of the oscillation the corona and the interplanetary material are supposed to rotate parallel to the planetary plane with an inclination to the solar equator. The non-uniform shearing around the equator is assumed to result in oscillation with a period of half of a year.

Progress in defining the solar wind sputter rate on protoplanets and interplanetary matter

Solar wind sputtering of exposed surfaces in heliocentric orbits is considered for bodies ranging in size from planets down to micrometeoroids. Erosion rates derived from APOLLO sample lunar regolith studies are presented together with the results of computer modelling of surface topographical alteration in order to characterize the sputter erosion process on Solar System bodies bombarded by the solar wind. The consensus of recent measurements leads to a rate of between 0.025 to 0.045 Å yr −1 near the lunar equator.

γand X rays from the zodiacal dust

γ-RAY lines can be produced by MeV protons in interactions with interstellar1–4 and solar coronal matter5–7. Here I show that, in favourable conditions, solar flare protons can produce both observable γ-ray lines and characteristic X-ray lines, when interacting with the material of the zodiacal dust cloud. Of particular interest are narrow γ-ray lines without kinematical broadening (ΔE <1 keV), which are produced by long-lived nuclear excited states (τ ≳; 10−12 s) in solids. A typical zodiacal dust grain is sufficiently large for such narrow line production, and modern germanium detectors can detect and identify these lines. Observation of X rays and γ rays together would yield information on the average interplanetary dust density, grain size, material density, and chemical composition. This might help to determine whether the dust is of Solar System (for example, cometary) or of interstellar origin. Protons ≳ 10 MeV form a probe for which the dust grains are transparent, so that the measured quantity does not depend on grain size and surface properties, in contrast to the zodiacal light.

The characterization of lunar surface impact erosion and solar wind sputter processes on the lunar surface

A wide variety of processes have been instrumental in the evolutionary progression of the lunar surface towards its present state. During the early history of the Moon, chemical differentiation, volcanism and, particularly for the mare areas, infilling by magma flow have been major mass transport factors but, since further cooling some 3 x 10 to the power of 9 years ago, the development of surface features has been primarily determined by impact erosion from remnants of the primeval stellar condensation and matter associated with asteroids and comets. As a result of the evolutionary decrement of interplanetary matter impact erosion is time dependent but even so at a particular epoch the relative importance of impact erosion to solar wind sputter erosion in the determination of the topology of a feature will be dependent on the scale of the feature examined. An impact crater formed on the lunar surface is normally exposed to the 400 km s-1 solar wind spectrum which will result in sputter erosion of surface atoms. Under varying angles of incidence during the lunar cycle, features exposed to the solar wind will be gradually smoothed and will eventually disappear. A similar erosion effect is the abrasion of large craters due to the formation within them of much smaller craters, i.e. a process similar to sand blasting. We also have the possibility during these quasi-continuous processes of single and complete obliteration by an impacting particle at least as large as that which caused the original crater. Thus we may characterize any particular crater with three erosion lifetimes: (1) the sputter lifetime, (2) the (small particle) abrasion lifetime, and (3) the (large particle) erasure lifetime.