Collision Of Comet Research Articles

The proximities of asteroids and critical points of the distance function

The proximities are important for different purposes, for example to evaluate the risk of collisions of asteroids or comets with the Solar-System planets. We describe a simple and efficient method for finding the asteroid proximities in the case of elliptical orbits with a common focus. In several examples we have compared our method with the recent excellent algebraic and polynomial solutions of Gronchi (2002, 2005).

Shocked quartz grains in the polymict breccia of the Granby structure, Sweden–‐Verification of an impact

Abstract— The Middle Ordovician Granby structure in Sweden is generally considered the result of an asteroidal or cometary collision with Earth, although no hard evidence, i.e., shock metamorphic features or traces of the impactor, have been presented to date. In this study, drill core samples of a sedimentary breccia from the Granby structure have been investigated for microscopic shock metamorphic evidence in an attempt to verify the impact genesis of the structure. The finding of multiple sets of decorated planar deformation features (PDFs) in quartz grains in these samples provides unambiguous evidence that the structure is impact derived. Furthermore, the orientation of the PDFs, e.g., ω {101 }, π {101 } and r, z {101 }, is characteristic for impact deformation. The fact that a majority of the PDFs are decorated implies a water‐bearing target. The shocked quartz grains can be divided into two groups; rounded grains found in the breccia matrix likely originated from mature sandstone, and angular grains in fragments from crystalline target rocks. The absence of melt particles provides an estimated maximum shock pressure for the sedimentary derived quartz of 15–20 GPa and the frequency distribution of PDF orientations in the bedrock quartz implies pressures of the order of 10 GPa.

Astrochemistry: from astronomy to astrobiology

Preface. 1. The molecular universe. 1.1 The Standard Model Big Bang Theory. 1.2 Galaxies, stars and planets. 1.3 Origins of life. 1.4 Other intelligent life. 1.5 Theories of the origin of life. Concepts and calculations. 2. Starlight, galaxies and clusters. 2.1 Simple stellar models-black body radiation. 2.2 2.726 K-cosmic microwave background radiation. 2.3 Stellar classification. 2.4 Constellations. 2.5 Galaxies. 2.6 Cosmology. Concepts and calculations. Problems. 3. Atomic and molecular astronomy. 3.1 Spectroscopy and the structure of matter. 3.2 Line shape. 3.3 Telescopes. 3.4 Atomic spectroscopy. 3.5 Molecular astronomy. 3.6 Molecular masers. 3.7 Detection of hydrogen. 3.8 Diffuse interstellar bands. 3.9 Spectral mapping. Concepts and calculations. Problems. 4. Stellar chemistry. 4.1 Classes of stars. 4.2 Herzprung-Russell diagram. 4.3 Stellar evolution. 4.4 Stellar spectra. 4.5 Exotic stars. 4.6 Cycle of star formation. Concepts and calculations Problems. 5. The interstellar medium. 5.1 Mapping clouds of molecules. 5.2 Molecules in the interstellar and circumstellar medium. 5.3 Physical conditions in the interstellar medium. 5.4 Rates of chemical reactions. 5.5 Chemical reactions in the interstellar medium. 5.6 Photochemistry. 5.7 Charged particle chemistry. 5.8 Polycyclic aromatic hydrocarbons. 5.9 Dust grains. 5.10 Kinetic models of molecular clouds. 5.11 Prebiotic molecules in the interstellar medium. Concepts and calculations. Problems. 6. Meteorite and comet chemistry. 6.1 Formation of the solar system. 6.2 Classification of meteorites. 6.3 Meteorite mineralogy. 6.4 Geological time. 6.5 Chemical analysis of meteorites by L2MS. 6.6 The Murchison meteorite-kerogen. 6.7 Meteorite ALH84001. 6.8 Comet chemistry. 6.9 Structure of a comet. 6.10 Physicochemical conditions in a cometary coma. 6.11 Chemical composition of comets. 6.12 Cometary collisions. 6.13 The Rosetta mission-origin of the solar system. Concepts and calculations. Problems. 7. Planetary chemistry. 7.1 Structure of a star-planet system. 7.2 Surface gravity. 7.3 Formation of the Earth. 7.4 Earth-Moon system. 7.5 Geological time. 7.6 Radiative heating. 7.7 The habitable zone. 7.8 Extrasolar planets. 7.9 Planetary atmospheres. 7.10 Atmospheric photochemistry. 7.11 Biomarkers in the atmosphere. Concepts and calculations. Problems. 8. Prebiotic chemistry. 8.1 Carbon- and water-based life forms. 8.2 Spontaneous chemical reactions. 8.3 Rates of chemical reactions. 8.4 Endogenous production of organic molecules. 8.5 Exogenous delivery of organic molecules. 8.6 Homochirality. 8.7 Surface metabolism-'clay organisms'. 8.8 Geothermal vents-'black smokers'. 8.9 RNA World hypothesis. Concepts and calculations. Problems. 9. Primitive life forms. 9.1 Self-assembly and encapsulation. 9.2 Protocells. 9.3 Universal tree of life. 9.4 Astrobiology. 9.5 Microbial Mars. Concepts and calculations. Problems. 10. Titan. 10.1 Physical properties. 10.2 The atmosphere. 10.3 Temperature-dependent chemistry. 10.4 Energy balance and the greenhouse effect. 10.5 Atmospheric chemistry. 10.6 Astrobiology on Titan. Concepts and calculations. Problems. Glossary of terms and abbreviations. Appendix A: constants and units. Appendix B: astronomical data. Appendix C: thermodynamic properties of selected compounds. Answers to problems. Bibliography. Index.

An Algebraic Method to Compute the Critical Points of the Distance Function Between Two Keplerian Orbits

We describe an efficient algorithm to compute all the critical points of the distance function between two Keplerian orbits (either bounded or unbounded) with a common focus. The critical values of this function are important for different purposes, for example to evaluate the risk of collisions of asteroids or comets with the Solar system planets. Our algorithm is based on the algebraic elimination theory: through the computation of the resultant of two bivariate polynomials, we find a 16th degree univariate polynomial whose real roots give us one component of the critical points. We discuss also some degenerate cases and show several examples, involving the orbits of the known asteroids and comets.

Structure in the ε Eridani Debris Disk

New submillimeter images have been obtained of the dust disk around the nearby K2 V star e Eridani, with the total data set now spanning 5 yr. These images show the distribution of dusty debris generated by comet collisions, reflecting clearing and perturbations by planets, and may give insights to early conditions in the solar system. The structure seen around e Eri at 850 mm and published in 1998 is confirmed in the new observations, and the same structure is also seen in an image obtained for the first time at 450 mm. The disk is inclined by ≈25 to the sky plane, with emission peaking at 65 AU, a 105 AU radius outer edge, and an inner cavity fainter by a factor of ≈2. The structure within the dust ring suggests perturbations by a planet orbiting at tens of AU, and long-term tracking of these features will constrain its mass and location. A preliminary analysis shows that two clumps and one arc appear to follow the stellar motion (i.e., are not background objects) and have tentative evidence of counterclockwise rotation of ∼1 yr 1 . Within the ring, the mass of colliding comets is estimated at 5–9 M, similar to the primordial Kuiper Belt, and so any inner terrestrial planets may be undergoing an epoch of heavy bombardment. Subject headings: circumstellar matter — planetary systems: formation — stars: individual (e Eridani)

Some anomalies in the occurrence of debris discs around main-sequence A and G stars

Debris discs consist of large dust grains that are generated by collisions of comets or asteroids around main-sequence stars, and the quantity and distribution of debris may be used to detect the presence of perturbing planets akin to Neptune. We use stellar and disc surveys to compare the material seen around A- and G-type main-sequence stars. Debris is detected much more commonly towards A stars, even when a comparison is made only with G stars of comparable age. Detection rates are consistent with disc durations of ∼0.5 Gyr, which may occur at any time during the main sequence. The higher detection rate for A stars can result from this duration being a larger fraction of the main-sequence lifetime, possibly boosted by a globally slightly larger disc mass than for the G-type counterparts. The disc mass range at any given age is a factor of at least ∼100 and any systematic decline with time is slow, with a power law estimated to not be steeper than t −1/2 . Comparison with models shows that dust can be expected as late as a few Gyr when perturbing planetesimals form slowly at large orbital radii. Currently, the Solar system has little dust because the radius of the Kuiper Belt is small and hence the time-scale to produce planetesimals was less than 1 Gyr. However, the apparently constant duration of ∼0.5 Gyr when dust is visible is not predicted by the models.

The Jovian Stratosphere after Comet Shoemaker‐Levy/9: Unusual Isotopic Ratios in Molecular Trace Constituents

Since the collision of comet Shoemaker-Levy/9 with Jupiter in 1994 July, a number of minor molecular species have been observed to persist in the stratosphere of the planet. Here we report observations acquired in 1998 September at frequencies near 350 GHz (wavelength 850 μm) of HCN and CS and their respective isotopomers H13CN, HC15N, and C34S. Through radiative transfer modeling of the observed lines, we find that the isotopic abundance ratios 12C/13C, 14N/15N, and 32S/34S are considerably elevated with respect to their terrestrial values. We speculate that this result indicates an unusual composition for comet Shoemaker-Levy/9, or that cometary grains evaporated in the collisions significantly modified the isotope ratios.

Secondary Fragmentation of the [ITAL]Solar and Heliospheric Observatory[/ITAL] Sungrazing Comets at Very Large Heliocentric Distance

The temporal distribution of the Kreutz group of sungrazing comets has been known to have an episodic character on timescales from weeks to tens of years. With the large number of minor members of this group being nowadays discovered in images taken with the Solar and Heliospheric Observatory coronagraphs, it has become apparent that the distribution of these faint comets is episodic on a much shorter timescale, with objects arriving in pairs during a small fraction of a day. It is shown that the rate of these pairs is much too high for a random sample. Their existence is readily explained as a result of secondary, low-velocity, nontidal fragmentation episodes, which occur virtually spontaneously at very large heliocentric distances and involve the products of near-perihelion splitting of progenitor fragments during their previous return to the Sun. In fact, the pairs are merely extreme manifestations of larger clusters of such subnuclei, with a complex hierarchy of fragments. Each cluster is an outcome of a sequence of nontidal fragmentation events, which begins—after the initial tidal breakup—at some point along the outbound leg of the orbit and then continues episodically to and past aphelion. A similar scenario of posttidal progressive disintegration was firmly established for comet Shoemaker-Levy 9, based on extensive observations of its secondary and tertiary nuclei during many months preceding the comet's collision with Jupiter. Also, there are similarities with the mechanism proposed recently for the formation of striations in the dust tail of comet Hale-Bopp, and a logical extension of this process is the evolution of comet dust trails.

Evaluation of Light Flashes Caused by Impacts of Small Comets on the Surface of the Moon

Images of the dayglow of the Earth's atmosphere in the ultraviolet wavelength region obtained by the photometer of the spacecraft Dynamics Explorer revealed dark spots of the order of 50 km in diameter. These “atmospheric holes” were interpreted by the American physicist Frank as concentrations of water vapor formed as a result of the disintegration and vaporization of so-called small comets at high altitudes. An analysis of the same images showed that their explanation requires a frequency of comet collisions with the Earth as high as 20 events a minute! This sensational hypothesis evoked a heated scientific debate. The paper below contains an analysis of the possibility of observing Frank's hypothetical comets during their collisions with the Moon. By solving a two-dimensional radiative–gasdynamic problem, the authors demonstrate that the flashes occurring during such impacts can be observed from the Earth with ordinary telescopes.

Infrared Kuiper Belt Constraints

We compute the temperature and IR signal of particles of radius a and albedo α at heliocentric distance R, taking into account the emissivity effect, and give an interpolating formula for the result. We compare with analyses of COBE DIRBE data by others (including recent detection of the cosmic IR background) for various values of heliocentric distance R, particle radius a, and particle albedo α. We then apply these results to a recently developed picture of the Kuiper belt as a two-sector disk with a nearby, low-density sector (40<R<50-90 AU) and a more distant sector with a higher density. We consider the case in which passage through a molecular cloud essentially cleans the solar system of dust. We apply a simple model of dust production by comet collisions and removal by the Poynting-Robertson effect to find limits on total and dust masses in the near and far sectors as a function of time since such a passage. Finally, we compare Kuiper belt IR spectra for various parameter values. Results of this work include: (1) numerical limits on Kuiper belt dust as a function of (R, a, α) on the basis of four alternative sets of constraints, including those following from recent discovery of the cosmic IR background by Hauser et al.; (2) application to the two-sector Kuiper belt model, finding mass limits and spectrum shape for different values of relevant parameters including dependence on time elapsed since last passage through a molecular cloud cleared the outer solar system of dust; and (3) potential use of spectral information to determine time since last passage of the Sun through a giant molecular cloud.

On the probability that a comet that has escaped from another solar system will collide with the Earth

Stars pass the Sun all the time, and many of these stars may have their own planetary systems and their own `Oort cloud' of comets. We consider a straightforward problem in which the planetary system of the passing star is identical to the planetary system of the Sun, and also the cloud of comets is identical to the Oort cloud of the Solar system. We calculate (1) the rate of loss of comets from this other planetary system, (2) the frequency of passage of other stars at a minimum distance r0 and at a constant velocity v0 relative to the Sun, (3) the number and velocity distribution of comets coming from the passing star and impacting our planetary system, and finally (4) the number of cometary collisions with the Earth resulting from this process.

Jupiter's Synchrotron Emission Induced by the Collision of Comet Shoemaker-Levy 9

From July 13 to August 21, 1994, we observed Jupiter at 1420 MHz using one of the 30-m single dishes of the Instituto Argentino de Radioastronomia. After the impact of fragment G, we detected a rapid increase of the 21cm-continuum flux, which reached the maximum (≈ 20% of Jupiter's flux) at the end of the impact period. The nature of this radiation is clearly synchrotron. We interpret it in terms of a new population of relativistic electrons (≈ 2 × 1029) injected into the Jovian magnetosphere as a consequence of the impact explosions. The proposed mechanism is that the relativistic plasma was blown as magnetic clouds that flowed along the magnetic lines of force towards the jovimagnetic equator. We constructed a model in which the energies of the fresh electrons, generated within the magnetized clouds with a power law energy spectrum, were highly degraded by the comet dust grains attached to the magnetized plasma. The model can account for the spectral shape based on observations at several frequencies (de Pater et al., 1995, Science 268, 1879; Venturi et al., 1996, Astron. Astrophys. 316, 243). The energy released by the explosions under the form of relativistic electrons is of ≈ 2 × 1025 erg, which represents a fraction of about 1–3 per cent of the explosion energy. The efficiency in converting the explosion energy into the relativistic electron energy is, therefore, of the same order of magnitude as that of supernova explosions. An alternative model is considered. This gives figures for the total energy and number of relativistic electrons that are similar to the corresponding ones of the favoured model. Finally, we suggest that the behavior of the flux decay in the various observed frequencies is the result of the diffusion of electrons into the loss-cone due to the resonant scattering of the electrons by Alfven waves.

The Evolution of Debris from Comet D/Shoemaker–Levy 9 on Jupiter

We present low-resolution photometric spectra in the wavelength range 407–907 μm of impact sites G, H, E, C, K, L, Q1, and W plus K together, arising from the collision of Comet D/Shoemaker–Levy 9 with Jupiter. The spectra were obtained from narrow band CCD images taken between July 15th and July 22nd using the 1-m Jacobus Kapteyn Telescope on La Palma. Our results indicate the impact debris to have low overall optical depths (τ < 1) which decrease with increasing wavelength for all individual sites observed. Our results also imply that mass absorption of sunlight is the dominant process occurring in the impact debris and that a decrease in optical depth with time is due to the material dissipating in the jovian atmosphere.

The Collision of Comet Shoemaker-Levy 9 with Jupiter

The discovery of Comet Shoemaker-Levy 9 in March 1993 opened an extraordinary few years in the study of the history of impacts in the solar system. This review paper offers a background that attempts to set the events of 1993 and 1994 into a historical context, and describes events leading to the discovery and the mounting of a unique and unprecedented international effort to observe the comet's collision with Jupiter. A selection of the results is presented to explore how the fate of Comet Shoemaker-Levy 9 has affected scientific and popular understanding of impacts in the solar system.

Dust ablation during the Shoemaker‐Levy 9 impacts

Because of the complexity of the physical and chemical processes that occurred during the collision of Comet Shoemaker‐Levy 9 with Jupiter, our understanding of the observed phenomena is not complete. In this paper, models of the ablation of small particles from both the incoming cometary comae and the refalling impact plumes are used to better define the physics and chemistry of the impacts. The incomplete ablation of small refractory plume grains can explain both the timing and relative strengths of the metal emission lines (e.g., Mg and Na) that were observed many minutes after the impacts. Model‐data comparisons show that silicate dust was present in the fastest moving portions of the plume and that some of the plume material (at least during the L impact) was ejected at velocities in excess of 22 km s−1 (for a 45° ejection angle). The models also show that the plume dust is not completely ablated at typical plume reentry velocities; therefore, a good estimate for the maximum size of the plume grains is the final observed radius of the high‐altitude dust (e.g., &lt;0.15 μm), and abundances inferred from the metallic emission features observed after the impacts do not provide a good measure of the amount of silicate material in the plume. Other implications for the physical and chemical properties of the comet/impact plume and for the timing and other features of the observations are discussed in detail.

Erratum to: Dissolution-collapse breccias and paleokarst resulting from dissolution of evaporite rocks, especially sulfates

The lithological trinity of dolostone, limestone, and sulfates (anhydrite and/or gypsum) is subject to rapid dissolution of the sulfates and leads to the development of dissolution-collapse breccias resulting from the withdrawal of the sulfates. The resultant features commonly include spectacular dissolution-collapse breccias. Owing to their mobility and chemical instability evaporite rocks, such as gypsum and anhydrite, are highly soluble and can be dissolved rapidly to form karstic features. When anhydrite and/or gypsum are dissolved the overlying continuous strata of carbonate rocks collapse, generating dissolution-collapse breccia composed of carbonate clasts. Such dissolution-collapse breccias as a result of dissolution of gypsum and/or anhydrite are more common worldwide than the literature suggests. Evaporite karst interferes with human activity, including highways, buildings, canals, and agriculture. A Cretaceous deposit composed of dolostone, limestone, and anhydrite breccia set in a carbonate matrix has been interpreted as the result of asteroid- or comet collision. An origin as evaporite paleokarst could explain the formation of this same breccia. In the Williston Basin of Montana anhydrites form the caps of basin-wide peritidal cycles in successions which brine upward. The supratidal cycle caps are zones of anhydrite leaching and creation of dissolution-collapse breccia. Cambro-Lower Ordovician (Sauk) platform cycles in the Appalachian Basin are composed of peritidal upward-shallowing carbonate facies which show evidence of ultimate emergence. The sulfates in the cycle caps have entirely dissolved out and the paleokarst serves as testament to their former presence.

Shoemaker‐Levy 9 and Plume‐forming Collisions on Eartha

ABSTRACT: Computational models for the July, 1994 collision of comet Shoemaker‐Levy 9 with Jupiter have provided a framework for interpreting the observational data. Imaging, photometry, and spectroscopy data from ground‐based, Hubble Space Telescope, and Galileo spacecraft instruments are consistent with phenomena that were dominated by the generation of incandescent fireballs that were ballistically ejected to high altitudes, where they formed plumes that subsequently collapsed over large areas of Jupiter's atmosphere. Applications of similar computational models to collisions into Earth's atmosphere show that a very similar sequence of events should take place for NEO impacts with energies as low as 3 megatons, recurring on 100 year timescales or less. This result suggests that the 1908 Tunguska event was a plume‐forming atmospheric explosion, and that some of the phenomena associated with it might be related to the ejection and collapse of a high plume. Hazards associated with plume growth and collapse should be included in the evaluation of the impact threat to Earth, and opportunities should be sought for observational validation of atmospheric impact models by exploiting data already being collected from the natural flux of multikiloton to megaton sized objects that constantly enter Earth's atmosphere on annual to decadal timescales.

The impact of comet D/Shoemaker-Levy 9 with Jupiter

The collision of comet D/Shoemaker-Levy 9 with Jupiter in July 1994 was an unprecedented opportunity to witness a phenomenon that was ubiquitous in the early solar system and which continues to shape its evolution. The tidal breakup of the comet, and the subsequent evolution of its fragments, have provided important insights into the nature of cometary nuclei, although conclusions regarding the comet's fundamental properties remain controversial. Detailed models describing the passage of the fragments through the jovian atmosphere have been fairly successful in explaining many aspects of the observations, including the appearance of giant plumes extending &gt;3000 km above Jupiter's limb, the huge infrared signals following the splashback of material into the jovian atmosphere, and the formation of dark impact scars over large regions at mid-southern jovian latitudes. New chemical species (e.g., CO, H2O, S2, CS2, CS, OCS, HCN, C2H4, and possibly H2S) were created in Jupiter's atmosphere due to the shock heating of the mixture of cometary and jovian gases. The large NH3 enhancement in the jovian stratosphere was apparently caused by heating of the ambient NH3 cloud followed by upwelling. The presence of metal atoms and ions in the jovian atmosphere was an unmistakable signature of the comet. Photochemistry may have played an important role in the temporal evolution of the newly-created species. The appearance of expanding rings emanating from the impact sites was originally explained as the propagation of gravity waves, but this required an oxygen abundance in the deep jovian atmosphere that was ∼10 times solar, an hypothesis that has been apparently contradicted by recent results from the Galileo probe. Although the impacts clearly produced dramatic effects in Jupiter's atmosphere, most traces of the trauma were barely discernible one year later.

An analytical model of the Comet's collision with Jupiter

An important feature observed in the wake of the Jupiter-comet clash was the appearance of the ring structure axisymmetrically positioned around the center of the impact. The persistent expansion of the dark rings and its speed indicated an outward propagating gravity wave (Benka, 1995). We employ an analytical model of constant density, uniform finite depth and inviscid fluid layer to investigate the wave motion produced by the impact of Comet Shoemaker-Levy 9 on the Jovian atmosphere. The relevant thermal effects are neglected and an explosion resulting from the collision is then described by an initial impulsive pressure at the surface of the Jovian atmosphere. Under the assumption that all the kinetic energy of a comet fragment is completely converted into the energy of wave motions in the Jovian atmosphere, an analytical formula describing the relationship between the resulting wave motion in the atmosphere and the parameters of a comet fragment (the radius, density and speed) is derived. Results from the present simple analytical model give a qualitative agreement with observations regarding the distance and speed of the waves.

Столкновение кометы Шумейкер—Леви 9 с Юпитером: что мы увидели

Столкновение кометы Шумейкер—Леви 9 с Юпитером: что мы увидели