— Within the very last years, results of the stardust mission and new exciting telescope camera observations have led astronomers and experts from the NASA space missions to speak of necessary paradigm changes especially with regard to the origin and composition of comets, shedding some light on the possible impactor to have produced the Chiemgau meteorite crater strewn field. The gist of what NASA experts even claim is that “out there” ALL can gad about.
In the light of this development it is curious to note that only a short while ago (in 2006) a noted planetologist with regard to the Chiemgau impact publicly declared that “we know ALL about comets”.
Astronomical aspects and relations (original contribution)
From the shape and location of the strewnfield as well as from the size and the distribution of the craters very rough figures for the size, composition, density and velocity of the cosmic body penetrating the earth’s atmosphere may be deduced. This holds true also for the probable trajectory.
First, a certain “grading” of the hitherto documented craters (diameters: 3 – ~500 m; depths 0.4 – ~40 (70 ?) m) in an elliptical field sized about 58 x 27 km² (~ 1,200 km², between 47,8° – 48,4° N and 12,3° – 13,0° E) is striking: the small craters are located predominantly in the northern part, and the larger ones are predominantly accumulated in the southern part of the strewn ellipse.
Fig. 1. On penetrating the earth’s atmosphere, the celestial body disintegrates into cascades of fragments of various sizes producing an elliptical strewnfield with increasingly larger craters along the trajectory.
Such a distribution is related with the different kinetic energy corresponding with the different masses of the fragments of a disintegrated cosmic body, the original entry velocities being identical. Because of their larger momentum, fragments rich in masses brake less in the atmosphere compared with the smaller fragments. Consequently, the smaller projectiles get to the point of maximum braking and crash earlier than the larger ones, and, additionally, they describe steeper trajectories (about 20° from the vertical) than do the larger masses (about 30° from the vertical). Depending on density, strength, shape and material, the explosive fragmentation may occur in multiple stages, which in the end leads to the gradation of the crater sizes as described.
Applied to the Chiemgau strewnfield and the hitherto documented craters, the entry trajectory of the impactor must have had an orientation more or less from northeast to southwest. From preliminary model calculations we have deduced a very low-density object (< 1.3 g/cm³), sized roughly 1100 m and having entered the atmosphere at a velocity of about 12 km/s on a low-oblique (~ 7°) trajectory. A first fragmentation occurred at an altitude of 70 km. The modeled scenario applies for a meteoroid that was intact on entering the denser layers of the atmosphere.
Alternatively, the cosmic body could have disintegrated in space by tidal forces at an altitude of about 22,200 km (Roche limit for a 1.3 g/cm³-density object) enabling the fragments to penetrate the atmosphere like a string of beads implying further cascadic fragmentation and a multiple impact.
Fig. 2. Comet Shoemaker-Levy 9 (D1993/F2). Images taken with Hubble Space Telescope (HST), Wide Field Planetary Camera 2. Beads of fragments (upper) and details near the brightest object (lower). Copyright: Dr. H.A. Weaver & T.E. Smith STScI (STScI-PRC1994-13), NASA.
An example for tidal disintegration is comet Shoemaker-Levy 9 (D1993/F2) and its crash with Jupiter in July 1994 (Fig. 2). In succession, 21 fragments of the original 10 km-diameter celestial body entered Jupiter’s atmosphere causing gigantic turbulences to be observed on earth even with small telescopes.
Possibly, the meteoroid that caused the Chiemgau impact disintegrated in the near-earth space into several larger fragments with the consequence that the observed strewn field in fact is an accumulation of several smaller ellipses. This idea is substantiated by the unusual width of the strewnfield (27 km, with regard to the length of 58 km) that could have resulted from the earth’s rotation during a multiple impact.
We emphasize that these considerations and model calculations are preliminary only due to the current and so far limited knowledge of the impact field pattern.
Fig. 3. Sketch of the different types of meteoroids and meteorites and of produced craters and crater strewnfields. [to be improved and translated soon].
Where did the cosmic body come from that caused the Chiemgau crater field? A hint is given by the low (12 – 14 km/s) entry velocity. Such a “slow” object, progradely orbiting the sun, should originate rather from the inner solar system, that is from the Planetoid Belt between Mars and Jupiter, or from a near-earth orbit. In this case, the object was the fragment of a very low-density planetoid or a non-active comet nucleus (short-period comet) of similarly low density. Possibly, the impactor originated from the Kuiper belt or from the Oort comet cloud and was forced by the gravity of the large Jupiter and Saturn planets on a path into the inner solar system (Fig. 8). The comets Lexell (D/1770 L1) in the year 1776, or P/ Shoemaker-Levy 9 (D1993/F2) in the year 1994 are characteristic examples.
Fig. 4. The exceptionally dark planetoid (253) Mathilde (albedo 0,04; type C asteroid) has a size of 66 × 48 × 46 km3 and a very low density of below 1.3 g/cm3. Probably it is not a solid body but an agglomeration of debris remnants from collisions with other planetoids or meteoroids. The image shows an area of 59 km x 47 km. The crater in the foreground has a diameter of 10 km. (253) Mathilde orbits the sun every 4.31 years (distance about 398 Mill. km) and rotates once every 17d 9h 30m. A fragment of such a celestial object could possibly have been the Chiemgau impactor. Copyright: NEAR Spacecraft Team, JHUAPL, NASA.
Fig. 5. Comet Machholz C/2004 Q2 near the Pleiades Open Cluster in the Taurus constellation. Photograph: Thorsten Böckl, Astrogilde Fürstenfeldbruck & Gilching, 8.1.2005, Sudlfeld, Canon EOS 20 D, Nikon 300 mm f 1:2,8, Bel. 3 x 120 s, ASA 800
Fig. 6. The very dark nucleus of comet Halley (16 km x 7.5 km x 8 km). Photograph taken with the Halley Multicolor Camera, ESA Giotto mission, on March 13, 1986, at a distance of 20,160 km. The density of the nucleus is about 0.1 g/cm3. The regions of degassing are clearly visible. About 10% of the comet’s nucleus were active. Halley orbits the sun every 76-79.3 years. Copyright: ESA (Giotto, HMC 01814).
Fig. 7. August 5, 2000: Comet Linear (C/1999 S4) disintegrates into a swarm of “cometesimals”, fragments up to the size of 30 m. It is assumed that the impactor that formed the Lake Tüttensee crater had a size of roughly 25 – 30 m. Copyright: NASA, Harold Weaver (the Johns Hopkins University), HST Comet LINEAR Investigation Team, University of Hawaii.
Fig. 8. By the gravity of large planets, comets may be deflected from their original long-period path to turn to a short-period orbit or to an impact trajectory aimed at a planet, planetoid or moon. In this way, more primitive celestial bodies from a distant region in the solar system may be “shipped” to near-earth regions. [to be improved and translated soon]
The so far known terrestrial meteorite crater strewnfields are related with the “usual” meteoritical matter that depending on the type contains iron, nickel, carbon and other elements in a defined ratio of a mixture. In the Chiemgau crater field extending from the town of Altötting to the Lake Chiemsee region, a comparable situation does not exist according to our current knowledge. The hitherto performed minerological analyses (Raeymaekers & Schryvers 2004, Schryvers & Raeymaekers 2005, Schüssler 2005) instead establish ferrosilicides of various compositions, in particular ferromonosilicides but also the extremely rare minerals gupeiite (Fe3Si) und xifengite (Fe5Si3) in combination with titanium carbide (TiC), alpha-Fe and other compounds that need further analyses. Since an origin of the peculiar matter from human activities (e.g., industry) and from geologic processes can practically be excluded (see Discussion of alternate models), two possibilities remain:
- a production in the course of the impact process with the contribution of earth materials and/or
- a delivery as primary matter contained in the impactor.
There are a few meteorites that contain ferrosilicides. In 2001, the Dhofar meteorite was sampled near Oman (Dhofar 280) that according to its chemical composition is suggested to be a Moon meteorite. One year later, analyses revealed ferrosilicides FeSi and FeSi2 and the new mineral hapkeite, Fe2Si, in Dhofar 280 obviously having originated from a special process of formation on the Moon. Gupeiite (Fe3Si) itself is contained in the meteorite FRO 90036 sampled in the Frontier Mountains in Antarctica.
In another individual find, the minerals gupeiite and xifengite are the main constituents of a meteorite that was discovered in 1984 in the Yanshan mountains in the Hebei province, China. It is important to note that like in the Chiemgau matter the nickel content in the Yanshan meteorite is very low. The central part of the small meteorite spherules is mainly composed of cubic gupeiite (Fe3Si) and hexagonal xifengite (Fe5Si3). Hongquite, originally said to be TiO, in fact is titanium carbide (TiC) together with gupeiite contributing to the core of the spherules. Compared to the peculiar matter from the Chiemgau strewnfield, a significant similarity is obvious.
Provided the unusual, “exotic” Chiemgau matter can actually be derived from the impacting meteoroid, this would imply a hint to the origin of the celestial object having carried this matter: it could originate from the accumulations in the dust and gas nebulas (Fig. 9) that were the “cradle” of the sun and our planetary system (Fig. 10) new-born some 4.6 billion years ago.
Fig. 9. Dust and gas nebulas (here the Trifid nebula (M 29) in the Sagittarius constellation, 9,000 light years away) are the “cradles” of stars and planetary systems. Copyright: NASA, Jeff Hester (Arizona State University), StScI-1999-42.
Fig. 10. Evolving planetary systems in the Orion nebula (M42), Orion constellation, about 1,500 light years away. Collage of images from the Hubble Space Telescope. Copyright: John Bally, Dave Devine, and Ralph Sutherland (CITA).
Fig. 11.Stellar “residuals” in the final stages of evolution (e.g., post-AGB stars, novae, supernovae) are repelled as shell material being the source material for new stars and planetary systems. Within the shells, apart from other elements and molecules, titanium carbide, microdiamonds and ferrosilicides are produced found also in the Chiemgau peculiar matter. Copyright: NASA, ESA, R. Sankrit und W. Blair (Johns Hopkins University), STScI-PRC04-29b.
Fig. 12. In the reflection nebula NGC 7023 (“Iris nebula” in the Kepheus constellation), a ferrosilicide, alpha- FeSi2, was established in 2002. The gas and dust nebula surrounds a star that is in its initial stage of evolution. There is spectral evidence of iron silicides (FeSi) also in the shell around the post-AGB star AFGL 4106 (a binary star). Copyright: Jim Misti und Robert Gendler, 2004.
According to recent research, metallic iron (alpha-Fe) as well as ferro-monosilicides together with titanium carbide (TiC) may be produced in very dense dust shells that are formed by the stellar winds of so-called AGB stars (Asymptotic Giant Branch, stars having a mass > 8 sun masses) in the final stage of their evolution. In fact, tiny particles of an iron-silicide, a-FeSi2, were established in the gas and dust nebula NGC 7023 (Iris nebula) as in proof of the contribution of ferrosilicides to interstellar matter.
Moreover, in the Murchison meteorite (Murchison, Victoria, Australia, 1962), graphite (elemental carbon) spherules were discovered that contained metallic iron taken up by titanium carbide (TiC). It is assumed that the minute dust grains originate from a supernova burst. These observations may be a hint that the peculiar matter finely distributed in the Chiemgau impact strewnfield could possibly be “presolar” that is primary matter from the birthplace of the solar system.
Investigations by Hoffmann et al. (2005), Rösler et al. (2005) and B. Raeymaekers (pers. comm., November 2005) have established mono- and polycrystalline nanodiamonds embedded in millimeter-sized carbon spherules that are found in the Chiemgau crater strewnfield but are distributed also over large areas in Europe. The composition reveals high percentages of carbon together with considerable amounts of oxigen.
CIRT could establish materials of quite similar elemental composition at various locations in the strewnfield. Associated with the occurrences of ferrosilicides, brittle and dull black particles (up to the size of 1 cm, but normally much smaller) are regularly found, practically made up of carbon and oxigen only, the latter up to 20% content.
In addition, structures were found resembling fullerenes. Hoffmann et al. (2005) favor an origin of the peculiar carbon matter from an impact process, and they discuss a primary source (the extraterrestrial object implying degassing and recondensation) as well as a secondary formation during the passage of the impactor through the atmosphere (Boudouard reacting in the shock front).
In the melt crust of rocks from a 20 m-diameter crater, Rösler et al. (2005) could again establish the ferrosilicides gupeiite and xifengite, Fe3Si and Fe5Si3 , but also nanodiamonds were detected (Hoffmann et al., 2005).
In October 2005, CIRT was able to discover an exotic layer at a depth of about 80 cm in the immediate vicinity of the Lake Tüttensee crater. The layer interpreted as an impact horizon is composed of brecciated rocks, extremely corroded cobbles, and cobbles coated with a black matter containing graphite. In addition, planar deformation features (PDFs) as indicative of shock were seen in thin sections. A more detailed description can be read in the chapter An impact layer near Grabenstätt.
Various modifications of carbon in the form of graphite, nanodiamonds and fullerenes have been shown to exist in interstellar and circumstellar matter as well as in meteorites (e.g., in the Allende and Antarctic meteorites) (Bernatowicz et al., Constraints on grain formation around carbon stars from laboratory studies of presolar graphite. The Astrophysical Journal, 631:988–1000; Nittler, L.R., Presolar stardust in meteorites: recent advances and scientific frontiers. Earth and Planetary Science Letters 209, 2003: 259-273; Th. Henning und F. Salama, Carbon in the Universe, Science 282, 1998: 2204-2210; Lodders, K., und Amari, S., Presolar grains from meteorites: Remnants from the early times of the solar system, Chemie der Erde (Geochemistry) 65, 2005: 93-166; Verchovsky et al. , Nanometre-sized diamonds from AGB stars? Lunar and Planetary Science XXXVI (2005), 2285; Huss, G. R., Meteoritic Nanodiamonds: Messengers from the Stars. Elements 1, 2005: 97-100; Harris, et al., Fullerene-like carbon nanostructures in the Allende meteorite, Earth and Planetary Science Letters 183, 2000: 355-359; Becker et al., Higher fullerenes in the Allende meteorite. Nature 400, 1999: 227-228; Rietmeijer, F.J.M: et al. Revisiting C60 Fullerene in carbonaceous chondrites and interplanetary dust particles: HRTEM and RAMAN microspectroscopy. Lunar and Planetary Science XXXVI (2005), 1225; Akai et al., Nano to micro minerals/materials in Antarctic carbonaceous chondrites. Goldschmidt Conference Abstracts 2003, A10.).
The matter may yet originate from the presolar gas and dust nebula that about 4.6 billion years ago was the cradle of the sun, planets, moons, planetoids and comets. There are indications though that nanodiamonds can form also in the inner solar system (Bradley et al., Possible in situ formation of meteoritic nanodiamonds in the early Solar System Nature 418: 157-159, 2002). In this case they were not presolar but nonetheless extraterrestrial.
The formation of graphite, nanodiamonds and fullerenes at high temperatures and pressures in the course of the impact process has also to be discussed considering a possible reaction of primary extraterrestrial matter in the nucleus of the proposed comet with the earth’s atmosphere.
We conclude: Since the nanodiamonds, the fullerenes, the graphite and the ferrosilicides gupeiite and xifengite are with a very high degree of probability neither anthropogenic nor geogenic, an extraterrestrial origin must be assumed, and quite a few things speak in favor of a presolar origin.