Jörg Fritz

Microbial rock inhabitants survive hypervelocity impacts on Mars-like host planets: First phase of lithopanspermia experimentally tested

The scenario of lithopanspermia describes the viable transport of microorganisms via meteorites. To test the first step of lithopanspermia, i.e., the impact ejection from a planet, systematic shock recovery experiments within a pressure range observed in martian meteorites (5-50 GPa) were performed with dry layers of microorganisms (spores of Bacillus subtilis, cells of the endolithic cyanobacterium Chroococcidiopsis, and thalli and ascocarps of the lichen Xanthoria elegans) sandwiched between gabbro discs (martian analogue rock). Actual shock pressures were determined by refractive index measurements and Raman spectroscopy, and shock temperature profiles were calculated. Pressure-effect curves were constructed for survival of B. subtilis spores and Chroococcidiopsis cells from the number of colony-forming units, and for vitality of the photobiont and mycobiont of Xanthoria elegans from confocal laser scanning microscopy after live/dead staining (FUN-I). A vital launch window for the transport of rock-colonizing microorganisms from a Mars-like planet was inferred, which encompasses shock pressures in the range of 5 to about 40 GPa for the bacterial endospores and the lichens, and a more limited shock pressure range for the cyanobacterium (from 5-10 GPa). The results support concepts of viable impact ejections from Mars-like planets and the possibility of reseeding early Earth after asteroid cataclysms.

Earth-like habitats in planetary systems

Understanding the concept of habitability is clearly related to an evolutionary knowledge of the particular planet-in-question. However, additional indications so-called “systemic aspects” of the planetary system as a whole governs a particular planet׳s claim on habitability. In this paper we focus on such systemic aspects and discuss their relevance to the formation of an “Earth-like” habitable planet. This contribution summarizes our results obtained by lunar sample work and numerical models within the framework of the Research Alliance “Planetary Evolution and Life”. We consider various scenarios which simulate the dynamical evolution of the Solar System and discuss the consequences for the likelihood of forming an Earth-like world orbiting another star. Our model approach is constrained by observations of the modern Solar System and the knowledge of its history. Results suggest that on the one hand the long-term presence of terrestrial planets is jeopardized due to gravitational interactions if giant planets are present. On the other hand the habitability of inner rocky planets may be supported in those planetary systems hosting giant planets. Gravitational interactions within a complex multiple-body structure including giant planets may supply terrestrial planets with materials which formed in the colder region of the proto-planetary disk. During these processes, water, the prime requisite for habitability, is delivered to the inner system. This may occur either during the main accretion phase of terrestrial planets or via impacts during a post-accretion bombardment. Results for both processes are summarized and discussed with reference to the lunar crater record. Starting from a scenario involving migration of the giant planets this contribution discusses the delivery of water to Earth, the modification of atmospheres by impacts in a planetary system context and the likelihood of the existence of extrasolar Earth-like habitable worlds.

Discovery of extraterrestrial component carrier phases in Archean spherule layers: Implications for estimation of Archean bolide sizes

In the Barberton greenstone belt (BGB) of South Africa, four distinct spherule horizons (S1–S4) with ages between ca. 3.5 and 3.2 Ga are among the oldest records of large asteroid impacts on Earth. Spherules in these layers are interpreted as molten impact ejecta, condensation products from impact plumes, or impact ejecta melted during atmospheric reentry. Past research has shown that some spherule layer samples from the BGB carry ultrahigh abundances of siderophile elements, including platinum group elements (PGEs), in some cases as much as four times the chondritic abundances. Inferences for very large projectile sizes responsible for these impact layers have been made on the strength of these data. Drilling by the International Continental Scientific Drilling Program has yielded 4 new spherule layer intersections in a 22-cm-long core segment. Scanning electron microscopy–energy dispersive X-ray spectrometry at high spatial resolution identified local areas of PGE enrichment with Ni-rich chromium spinel (Ni-Cr spinel) clusters. They are associated with PGE-rich metal alloy and sulfarsenide phases 600–1400 nm in size. The metal alloys are interpreted as primary objects that formed during the impact process. PGE sulfarsenides are the result of secondary alteration by S- and As-rich fluids. Thus, a micronugget effect caused by PGE phases and Ni-Cr spinel is responsible for the anomalously high extraterrestrial component in some spherule layer samples. This heterogeneous incorporation of meteoritic components due to primary heterogeneous fallout from the vapor plume must be taken into consideration in any attempt to estimate the global fallout of extraterrestrial components and, thus, to constrain projectile sizes.

Shock‐induced deformation phenomena in magnetite and their consequences on magnetic properties

This study investigates the effects of shock waves on magnetic and microstructural behavior of multidomain magnetite from a magnetite-bearing ore, experimentally shocked to pressures of 5, 10, 20, and 30 GPa. Changes in apparent crystallite size and lattice parameter were determined by X-ray diffraction, and grain fragmentation and defect accumulation were studied by scanning and transmission electron microscopy. Magnetic properties were characterized by low-temperature saturation isothermal remanent magnetization (SIRM), susceptibility measurements around the Verwey transition as well as by hysteresis parameters at room temperature. It is established that the shock-induced refinement of magnetic domains from MD to SD-PSD range is a result of cooperative processes including brittle fragmentation of magnetite grains, plastic deformation with shear bands and twins as well as structural disordering in form of molten grains and amorphous nanoclusters. Up to 10 GPa, a decrease of coherent crystallite size, lattice parameter, saturation magnetization (Ms), and magnetic susceptibility and an increase in coercivity, SIRM, and width of Verwey transition are mostly associated with brittle grain fragmentation. Starting from 20 GPa, a slight recovery is documented in all magnetic and nonmagnetic parameters. In particular, the recovery in SIRM is correlated with an increase of the lattice constant. The recovery effect is associated with the increasing influence of shock heating/annealing at high shock pressures. The strong decrease of Ms at 30 GPa is interpreted as a result of strong lattice damage and distortion. Our results unravel the microstructural mechanisms behind the loss of magnetization and the modification of magnetic properties of magnetite and contribute to our understanding of shock-induced magnetic phenomena in impacted rocks on earth and in meteorites.

Application of Raman Spectroscopy as in situ Technology for the search for life

In preparation to future space missions it is necessary to study the circumstances when faced with performing Raman measurements in a non-Earth like environment. The differences and difficulties compared to the established measurement approaches on Earth need to be recognized and solutions must be found. As an example for extraterrestrial application Raman spectroscopy with the same specifications as those onboard the future ExoMars mission are conducted to test their potential of identifying biological material on martian analogue samples. Appropriate measurement parameters for the detection of biological material as well as for the determination of the mineral composition are derived.