Comet Impact Research Articles

Research Spotlight: New study casts doubt on evidence for Younger Dryas impact theory

A new study challenges a previous hypothesis that a comet explosion or impact about 12,900 years ago caused devastating fires over much of North America and Europe and triggered an abrupt global cold period known as the Younger Dryas. Proponents of the impact theory claim that carbonaceous spherules and nanodiamonds found in deposits from the Younger Dryas formed through intense heat following a comet impact. The new study, however, finds that the carbon spherules are actually fossilized balls of fungus, charcoal, and fecal pellets created by low‐intensity wildfires.

A hydrocode calculation coupled with reaction kinetics of carbon compounds within an impact vapor plume and its implications for cometary impacts on Galilean satellites

The synthesis of organic molecules via chemical reactions within impact vapor plumes has been proposed as a mechanism to supply organics on a planet. However, the kinetics of chemical reactions within a rapidly expanding vapor plume or quenching process of the reactions has not been studied extensively. In this study, we constructed a new numerical model that calculates kinetics of the entire chemical reactions within an impact vapor plume. Numerical results revealed that the semi-analytical models proposed so far, in which the final amount of a chemical species was given by the equilibrium abundance at the quenching temperature of the fastest reaction path involving the species, underestimates the yield of organic molecules, such as HCN, by up to a factor of 10. This is because the previously used assumption that a species can achieve equilibrium with the rest of the reaction system via the fastest reaction path involving the species is not necessarily valid. Our analysis of the high-temperature H/C/N/O reaction system suggests that the quenching of slow reactions divides the reaction network into smaller reaction sub-systems isolated from the rest of the reaction system. Then, the fastest reaction path cannot equilibrate an isolated reaction sub-system with the rest of the reaction system. Simulation of this actual disequilibrium mechanism requires a simultaneous numerical calculation of the entire reaction network, which is equivalent to conducting a full kinetic model calculation, such as our model. Our numerical code makes it possible to discuss quantitatively the impact chemistry for various situations, such as the Galilean satellites. In this study, our numerical model is applied to the delivery of organic molecules via cometary impact on the Galilean satellites. Our numerical results indicate that small-particle impacts would produce HCN efficiently. Resulting HCN may freeze out immediately and be deposited on satellite surfaces, where it may be eventually converted into complex organics via irradiation of charged particle. On the other hand, large-size impacts may form transient CH 4–N 2 atmospheres, in which complex organics (tholin) may be formed via energy deposition of UV and/or charged particle. Resulting complex organics may subsequently precipitate on the satellite surfaces without clear correlation with the locations of impact craters. Such distribution of complex organics created by chemical reactions within vapor plumes due to cometary impacts may explain an absorption (4.57 μm) on Galilean satellites nonassociated with observable (moderate- and large-size) impact craters.

Complex aromatic hydrocarbons in Stardust samples collected from comet 81P/Wild 2

Abstract– The successful return of the Stardust spacecraft provides a unique opportunity to investigate the nature and distribution of organic matter in cometary dust particles collected from comet 81P/Wild 2. Analysis of individual cometary impact tracks in silica aerogel using the technique of two‐step laser mass spectrometry demonstrates the presence of complex aromatic organic matter. While concerns remain as to the organic purity of the aerogel collection medium and the thermal effects associated with hypervelocity capture, the majority of the observed organic species appear indigenous to the impacting particles and are hence of cometary origin. While the aromatic fraction of the total organic matter present is believed to be small, it is notable in that it appears to be N rich. Spectral analysis in combination with instrumental detection sensitivies suggest that N is incorporated predominantly in the form of aromatic nitriles (R–C≡N). While organic species in the Stardust samples do share some similarities with those present in the matrices of carbonaceous chondrites, the closest match is found with stratospherically collected interplanetary dust particles. These findings are consistent with the notion that a fraction of interplanetary dust is of cometary origin. The presence of complex organic N containing species in comets has astrobiological implications as comets are likely to have contributed to the prebiotic chemical inventory of both the Earth and Mars.

Cometary airbursts and atmospheric chemistry: Tunguska and a candidate Younger Dryas event

Research Article| April 01, 2010 Cometary airbursts and atmospheric chemistry: Tunguska and a candidate Younger Dryas event Adrian L. Melott; Adrian L. Melott 1Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA Search for other works by this author on: GSW Google Scholar Brian C. Thomas; Brian C. Thomas 2Department of Physics and Astronomy, Washburn University, Topeka, Kansas 66621, USA Search for other works by this author on: GSW Google Scholar Gisela Dreschhoff; Gisela Dreschhoff 1Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA Search for other works by this author on: GSW Google Scholar Carey K. Johnson Carey K. Johnson 3Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Adrian L. Melott 1Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA Brian C. Thomas 2Department of Physics and Astronomy, Washburn University, Topeka, Kansas 66621, USA Gisela Dreschhoff 1Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA Carey K. Johnson 3Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, USA Publisher: Geological Society of America Received: 07 Jul 2009 Revision Received: 28 Oct 2009 Accepted: 04 Nov 2009 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2010 Geological Society of America Geology (2010) 38 (4): 355–358. https://doi.org/10.1130/G30508.1 Article history Received: 07 Jul 2009 Revision Received: 28 Oct 2009 Accepted: 04 Nov 2009 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Adrian L. Melott, Brian C. Thomas, Gisela Dreschhoff, Carey K. Johnson; Cometary airbursts and atmospheric chemistry: Tunguska and a candidate Younger Dryas event. Geology 2010;; 38 (4): 355–358. doi: https://doi.org/10.1130/G30508.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We find agreement between models of atmospheric chemistry changes from ionization for the A.D. 1908 Tunguska (Siberia region, Russia) airburst event and nitrate enhancement in Greenland Ice Sheet Project 2 (GISP2H and GISP2) ice cores, plus an unexplained ammonium spike. We then consider a candidate cometary impact at the Younger Dryas onset (YD). The large estimated NOx production and O3 depletion are beyond accurate extrapolation, but the ice core peak is much lower, possibly because of insufficient sampling resolution. Ammonium and nitrate spikes in both Greenland Ice Core Project (GRIP) and GISP2 ice cores have been attributed to biomass burning at the onset of the YD. A similar result is well resolved in Tunguska ice core data, but that forest fire was far too small to account for this. Direct input of ammonia from a comet into the atmosphere is adequate for YD ice core data, but not for the Tunguska data. An analog of the Haber process with hydrogen contributed by cometary or surface water, atmospheric nitrogen, high pressures, and possibly catalytic iron from a comet could in principle produce ammonia, accounting for the peaks in both data sets. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Debris discs and comet populations around Sun-like stars: the Solar system in context

Numerous nearby FGK dwarfs possess discs of debris generated by collisions among comets. Here we fit the levels of dusty excess observed by Spitzer at 70$\umu$m and show that they form a rather smooth distribution. Taking into account the transition of the dust removal process from collisional to Poynting-Robertson drag, all the stars may be empirically fitted by a single population with many low-excess members. Within this ensemble, the Kuiper Belt is inferred to be such a low-dust example, among the last 10% of stars, with a small cometary population. Analogue systems hosting gas giant planets and a modest comet belt should occur for only a few per cent of Sun-like stars, and so terrestrial planets with a comparable cometary impact rate to the Earth may be uncommon. The nearest such analogue system presently known is HD154345 at 18pc, but accounting for survey completeness, a closer example should lie at around 10pc.

Volatile retention from cometary impacts on the Moon

Impacts of comets and asteroids play an important role in volatile delivery on the Moon. We use a novel method for tracking vapor masses that reach escape velocity in hydrocode simulations of cometary impacts to explore the effects of volatile retention. We model impacts on the Moon to find the mass of vapor plume gravitationally trapped on the Moon as a function of impact velocity. We apply this result to the impactor velocity distribution and find that the total impactor mass retained on the Moon is approximately 6.5% of the impactor mass flux. Making reasonable assumptions about water content of comets and the comet size–frequency distribution, we derive a water flux for the Moon. After accounting for migration and stability of water ice at the poles, we estimate a total 1.3 × 10 8 – 4.3 × 10 9 metric tons of water is delivered to the Moon and remains stable at the poles over 1 Ga. A factor of 30 uncertainty in the estimated cometary impact flux is primarily responsible for this large range of values. The calculated mass of water is sufficient to account for the neutron fluxes poleward of 75° observed by Lunar Prospector. A similar analysis for water delivery to the Moon via asteroid impacts shows that asteroids provide six times more water mass via impacts than comets.

Radiation-induced amorphization of crystalline ice

We study radiation-induced amorphization of crystalline ice, analyzing the results of three decades of experiments with a variety of projectiles, irradiation energy, and ice temperature, finding a similar trend of increasing resistance of amorphization with temperature and inconsistencies in results from different laboratories. We discuss the temperature dependence of amorphization in terms of the ‘thermal spike’ model. We then discuss the common use of the 1.65 μm infrared absorption band of water as a measure of degree of crystallinity, an increasingly common procedure to analyze remote sensing data of astronomical icy bodies. The discussion is based on new, high quality near-infrared reflectance absorption spectra measured between 1.4 and 2.2 μm for amorphous and crystalline ices irradiated with 225 keV protons at 80 K. We found that, after irradiation with 10 15 protons cm −2, crystalline ice films thinner than the ion range become fully amorphous, and that the infrared absorption spectra show no significant changes upon further irradiation. The complete amorphization suggests that crystalline ice observed in the outer Solar System, including trans-neptunian objects, may results from heat from internal sources or from the impact of icy meteorites or comets.

Asteroid-comet impact hazard: New approaches

Comet and asteroid impact hazards are a very popular topic, discussed by scientists, politicians, state officials, journalists, military personnel, amateurs, and ordinary people. This popularity is justified: new knowledge, obtained in recent years, has shown that the problem of asteroid-comet danger is much more significant for humankind than was thought ten to fifteen years ago. Programs on studying asteroid-comet impact hazards and preparing our country for this threat are being discussed in Russia.

First observation of CO at 345 GHz in the atmosphere of Saturn with the JCMT: New constraints on its origin

We have performed the first observation of the CO(3-2) spectral line in the atmosphere of Saturn with the James Clerk Maxwell Telescope. We have used a transport model of the atmosphere of Saturn to constrain the origin of the observed CO. The CO line is best-fit when the CO is located at pressures less than ( 15 ± 2 ) mbar with a mixing ratio of ( 2.5 ± 0.6 ) × 10 - 8 implying an external origin. By modeling the transport in Saturn’s atmosphere, we find that a cometary impact origin with an impact 200–350 years ago is more likely than continuous deposition by interplanetary dust particles (IDP) or local sources (rings/satellites). This result would confirm that comet impacts are relatively frequent and efficient providers of CO to the atmospheres of the outer planets. However, a diffuse and/or local source cannot be rejected, because we did not account for photochemistry of oxygen compounds. Finally, we have derived an upper limit of ∼ 1 × 10 - 9 on the tropospheric CO mixing ratio.

Wildfire responses to abrupt climate change in North America

It is widely accepted, based on data from the last few decades and on model simulations, that anthropogenic climate change will cause increased fire activity. However, less attention has been paid to the relationship between abrupt climate changes and heightened fire activity in the paleorecord. We use 35 charcoal and pollen records to assess how fire regimes in North America changed during the last glacial-interglacial transition (15 to 10 ka), a time of large and rapid climate changes. We also test the hypothesis that a comet impact initiated continental-scale wildfires at 12.9 ka; the data do not support this idea, nor are continent-wide fires indicated at any time during deglaciation. There are, however, clear links between large climate changes and fire activity. Biomass burning gradually increased from the glacial period to the beginning of the Younger Dryas. Although there are changes in biomass burning during the Younger Dryas, there is no systematic trend. There is a further increase in biomass burning after the Younger Dryas. Intervals of rapid climate change at 13.9, 13.2, and 11.7 ka are marked by large increases in fire activity. The timing of changes in fire is not coincident with changes in human population density or the timing of the extinction of the megafauna. Although these factors could have contributed to fire-regime changes at individual sites or at specific times, the charcoal data indicate an important role for climate, and particularly rapid climate change, in determining broad-scale levels of fire activity.

The worldwide impact of Donati's comet on art and society in the mid-19th century

AbstractDonati's comet was one of the most spectacular astronomical events of the nineteenth century. Its extended sword-like tail was a spectacular sight that inspired several literary and artistic representations. Traces of Donati's comet are found in popular magazines, children's books, collection cards, and household objects through the beginning of the twentieth century.

The riddle of the clays

Rising carbon levels contributed to profound climate change 55 million years ago. Where did that extra carbon come from? One proposal — a cometary impact — is rebuffed by two analyses of magnetic particles in clay sediment cores from New Jersey.

The Contributions of Comets to Planets, Atmospheres, and Life: Insights from Cassini-Huygens, Galileo, Giotto, and Inner Planet Missions

Comets belong to a group of small bodies generally known as icy planetesimals. Today the most primitive icy planetesimals are the Kuiper Belt objects (KBOs) occupying a roughly planar domain beyond Neptune. KBOs may be scattered inward, allowing them to collide with planets. Others may move outward, some all the way into the Oort cloud. This is a spherical distribution of comet nuclei at a mean distance of ∼50,000 AU. These nuclei are occasionally perturbed into orbits that intersect the paths of the planets, again allowing collisions. The composition of the atmosphere of Jupiter—and thus possibly all outer planets—shows the effects of massive early contributions from extremely primitive icy bodies that must have been close relatives of the KBOs. Titan may itself have a composition similar to that of Oort cloud comets. The origin and early evolution of its atmosphere invites comparison with that of the early Earth. Impacts of comets must have brought water and other volatile compounds to the Earth and the other inner planets, contributing to the reservoir of key ingredients for the origin of life. The magnitude of these contributions remains unknown but should be accessible to measurements by instruments on spacecraft.

Investigating the origins of the Jovian decimetric emission's variability

The long‐term variability of the Jovian radiation observed at 13‐cm wavelength over 30 years is investigated using a physical model of the radiation belts. The model enables us to quantify the effect of the geometric parameter DE on the synchrotron emission. When a full Jupiter rotation is taken into account in the computations, the variability of the total radio flux with DE is only ≃1% of that measured. Such a dependence is not detectable. In contrast, radio fluctuations observed at a central meridian longitude (CML) and caused by DE changes can be very important, up to 10% of that measured. This strong dependence of the total radio flux on the geometric factor can result in difficulties for examining the origins of the Jovian synchrotron emission's fluctuations during periods where times of observation are not covering large CML range values. The numerical computations reveal that the variability either of the populations injected near the outer boundary of our simulations (Io's orbit) or the inward radial transport can, independently or in combined action, conduct variability in the decimetric emission. The theoretical fluctuations required in our computations for reproducing the radio measurements do not confirm any direct correlation between the long‐term changes in the radio data and the radial transport driven by solar wind conditions or solar radio fluxes. Nevertheless, a linear relationship between the total radio flux and solar wind ram pressure for the period of 1970 to 2002 is established. The maximum correlation is reached when the Psw data are shifted by ≃2.7 years prior to the radio observations. Using this time‐lag in the computations, the simulation results show that (Psw)γ can be associated with the variations of the particle injections and the radial transport. The correlation coefficient, associated with the fit between radio data and simulated radio flux densities, is 0.59 for the period of 1971–2002, 0.93 for the period of 1971–1972, and 0.83 for the periods of 1975–1989 and 1992–1995. The index γ is set to 0.35 when only particle injections are fluctuating with time, to 0.50 when temporal variations are driving the radial transport, and to 0.15–0.20 when the particles injected in the inner magnetosphere and their transport are simultaneously following the variations of the solar wind ram pressure. The model suggests that the solar wind ram pressure fluctuations can be related to variations of the Jovian decimetric emission on timescales of months, particularly to the enhancements in total radio flux observed in 1987, 1988, 1990 and 1994. Our results thus support the idea that the increase in radio emission in July 1994 was due to the impact of Comet Shoemaker‐Levy 9 into Jupiter, in addition to the response of the Jovian magnetosphere to steep changes in solar wind conditions. The divergence between observations and simulations indicates that mechanisms other than those discussed in the modeling must govern the radiation belts dynamics for the periods of 1972–1975 and 1996–2002.

Structure of the South Pole-Aitken lunar basin

The hypsometric map and the basin height profiles, for the first time relying upon a spherical daturence surface, have been constructed based on the generalization of the heights measured within the hemisphere including the ring structure of the South Pole-Aitken basin. The distribution of the major chemical elements (Fe and Th), depending upon the structure height levels, has been obtained. The relationship between these lunar rock indicators and the height levels of the rock preferential distribution has been revealed. The outer basin ring has been distinguished and the ring structure of the central basin depression has been revealed against a combined hypsometric and geochemical background. A total basin diameter of about 3500 km has been reliably determined for the first time. A unique feature of the basin structure consists in that the arrangement of the basin inner rings does not show a central circular symmetry, which can indicate that a hypothetical impactor moved along the trajectory (or orbit) oriented almost normally to the ecliptic plane. In combination with the revealed very small depth-diameter ratio in the initial basin structure, this circumstance makes it possible to put forward the hypothesis that a comet impact produced the South Pole-Aitken basin.

Magnetofossil spike during the Paleocene‐Eocene thermal maximum: Ferromagnetic resonance, rock magnetic, and electron microscopy evidence from Ancora, New Jersey, United States

Previous workers identified a magnetically anomalous clay layer deposited on the northern United States Atlantic Coastal Plain during the Paleocene‐Eocene thermal maximum (PETM). The finding inspired the highly controversial hypothesis that a cometary impact triggered the PETM. Here we present ferromagnetic resonance (FMR), isothermal and anhysteretic remanent magnetization, first‐order reversal curve, and transmission electron microscopy analyses of late Paleocene and early Eocene sediments in drill core from Ancora, New Jersey. A novel paleogeographic analysis applying a recent paleomagnetic pole from the Faeroe Islands indicates that New Jersey during the initial Eocene had a ∼6°–9° lower paleolatitude (∼27.3° for Ancora) and a more zonal shoreline trace than in conventional reconstructions. Our investigations of the PETM clay from Ancora reveal abundant magnetite nanoparticles bearing signature traits of crystals produced by magnetotactic bacteria. This result, the first identification of ancient biogenic magnetite using FMR, argues that the anomalous magnetic properties of the PETM sediments are not produced by an impact. They instead reflect environmental changes along the eastern margin of North America during the PETM that led to enhanced production and/or preservation of magnetofossils.

Transfer of mass from Io to Europa and beyond due to cometary impacts

We simulate the production and orbital evolution of escaping ejecta due to cometary impacts on Io. The model includes the four Galilean satellites, Amalthea, Thebe, Jupiter's gravitational moments, Saturn and the Sun. Five scenarios are examined: an impact at the apex, the sub-jovian point, the anti-jovian point, the antapex, and at the south pole of Io. We estimate that on average a cometary impact injects thrice its mass (in the form of Io surface material) into jovicentric orbit. The majority of the escaping debris comes back to Io, but a sizeable fraction (between 5.0 and 8.7%) manages to reach Europa, and a smaller fraction Ganymede (between 1.5 and 4.6%). Smaller fractions reached Amalthea Thebe, Callisto, and Jupiter itself. For million year time scales, the mass transfer to Europa is estimated as 1.8 – 3.1 × 10 14 g / Myr . The median time for transfer of ejecta from Io to Europa is ∼56 years.

Joint IODP/ICDP Scientific Drilling of the Chicxulub Impact Crator

Impacts of asteroids and comets on planets are fundamental processes in the solar system. Relatively few pristine craters are preserved on the Earth because of the vigorous endogenic geologic processes that affect its surface. Nonetheless, only terrestrial craters can provide us with direct observations on the subsurface structure of impact craters, the dynamics of crater formation, and the effect on the planetary environment as preserved in the geological record.

Subsurface migration of H2O at lunar cold traps

Permanently shaded areas near the poles of the Moon and Mercury may harbor water ice. We develop a physical model for migration of water molecules in the regolith and discover two pathways that can lead to accumulation of H2O in the subsurface. A small fraction of water molecules delivered, either continuously or abruptly, to permanently cold areas diffuses into the regolith and can remain there longer than on the surface. Higher temperatures lead to deeper burial. At constant temperature, this diffusive migration produces less than one molecular layer of volatile H2O on grains, because it is driven by differences in surface concentrations. The water is therefore expected to be in adsorbed form, and the amount stored in this fashion could be at most a few hundred ppm of H2O. A second pathway is pumping by diurnal temperature oscillations from a transient ice cover that may have formed during a large comet impact. It can lead to high ground ice densities, but the ground ice layer lasts not long beyond the disappearance of the ice cover. Both types of subsurface charging mechanism work best for temperatures typical of permanently shaded areas with sunlit surfaces in their field of view.

The impact and rotational light curves of Comet 9P/Tempel 1

UVES and HIRES high-resolution spectra of Comet 9P/Tempel 1 are used to investigate the impact and rotational light curves of various species with a view toward building a simple model of the distribution and activity of the sources. The emission by OH, NH, CN, C 3, CH, C 2, NH 2, and OI, are analyzed, as well as the light scattered by the dust. It is found that a simple model reproduces fairly well the impact light curves of all species combining the production of the observed molecules and the expansion of the material throughout the slit. The impact light curves are consistent with velocities of 400–600 m/s. Their modeling requires a three-step dissociation sequence “Grand-Parent → Parent → Daughter” to produce the observed molecules. The rotational light curve for each species is explained in terms of a single model with three sources. The dust component can however not easily be explained that way.