RECENT SCIENTIFIC PUBLICATIONS
CHARACTERIZATION OF MUKUNDPURA CARBONACEOUS CHONDRITE
Two meteorite fragments collected from the Mukundpura impactsite, Rajasthan, India have been analysed using scanning electron microscopy, energy dispersive X-ray spectroscopy, Mössbauer spectroscopy, thermogravimetric analysis (TGA) and Raman spectroscopy. High Fe (22.65 wt%), Ni (1.53%) and S (3.69%) and concentrations of other elements obtained by X-ray analysis indicate that it is a carbonaceous chondrite. Mössbauer spectra show similarity with those obtained from Cold Bokkeveld and Murchison carbonaceous chondrites, and this analogy allows us to classify it as belonging to CM group of carbonaceous chondrites. TGA shows large weight loss, implying presence of significant amount of volatiles in this meteorite and Raman spectroscopy shows the presence of abundant organic matter consisting of disordered and aromatic (graphitic or polyaromatic) carbon. These results indicate that Mukundpura meteorite is a rare type of extraterrestrial object deserving further in-depth Raman spectroscopy shows the presence of abundant organic matter consisting of disordered and aromatic(graphitic or polyaromatic) carbon. These results indicate that Mukundpura meteorite is a rare type ofextraterrestrial object deserving further in-depth studies.
LONG-TERM HELIOMAGNETIC FIELD VARIATION BASED ON COSMOGENIC 44TI IN METEORITES
Summary. — Reconstructions of the heliospheric magnetic field (HMF) in the past centuries are mainly based on the analysis of sunspot activity, geomagnetic data or on measurement of cosmogenic radioisotopes stored in terrestrial reservoirs (tree rings and ice cores). There are, however, significant discrepancies among the results obtained by various techniques using different proxies of solar magnetic activity. In this work, new results obtained from a unique approach based on the measurement of the cosmogenic 44Ti activity detected in meteorites are presented and compared with the most recent reconstructions of the near-Earth HMF strength. The very low level of 44Ti activity in several meteorites fallen in the last 250 years was determined by using gamma-ray spectrometers (HPGe+NaI) located in the underground laboratory of Monte dei Cappuccini (INAF-OATo) in Torino, Italy. This approach, specifically designed to overcome the main problems affecting other methods, yields a powerful independent tool to reconstruct the long-term evolution of the HMF through the last two and a half centuries.
GLASSY MAGNETIC CRONSTEDTITE SIGNATURES IN MUKUNDPURA CM2 CHONDRITE BASED ON
MAGNETIC AND M€OSSBAUER STUDIES
Abstract: We have studied the Mukundpura CM2 meteorite for magnetic properties as a function of temperature and magnetic field, as well as its M€ossauer spectrum, at room and low temperatures (up to 5 K). We find that the high temperature paramagnetic phase is followed by two magnetic transitions: a weak transition near 125 K and a strong transition at 8 K. The weak (125 K) magnetic phase can be attributed to complex Fe2+–Fe3+ constituents present in the meteorite. The absence of the characteristic sextet corresponding to magnetite in Mossbauer spectrum indicates that this magnetic phase is not magnetite, which, if present, must be in insignificant amount. The 8 K magnetic ordering is superimposed with weak ferromagnetic ordering, showing spin-glass transition. The M€ossbauer spectrum taken at 5 K substantiates the observed spin-glassy nature, as very large hyperfine field ~32 T is recorded, causing localized subordering leading to spin-glass behavior. The M€ossbauer spectra also confirm that iron is mainly present in serpentine-group minerals, both in ferrous and ferric states. The complete serpentinization of basic silicates indicates aggressive hydrous alteration.
These results show that the observed spin-glass signature is a characteristic feature of the cronstedtite phase in CM meteorites. This feature is unique to carbonaceous CM chondrites and could be used for nondestructive, quick, and independent classification of this rare class of meteorites. Furthermore, the absence of olivine and the presence of cronstedtite in Mossbauer spectra show that the degree of aqueous alteration observed is the most severe in Mukundpura CM2 meteorite, as compared to many other CM2 meteorites. The degree of aqueous alteration in CM2 carbonaceous chondrites increases in the sequence: Paris, Murchison, Murray, Mighei, Nogoya, Cold Bokkeveld, and Mukundpura.
COSMIC RAY EFFECTS IN THE IRON METEORITE GEBEL KAMIL AND ITS ASYMMETRIC ABLATION
Abstract: We have measured gamma rays emanating from radionuclides produced by cosmic ray interactions in two fragments of Gebel Kamil iron meteorite. Based on the cosmogenic 26Al activity, it is deduced that one fragment, taken from the narrow edge of the mace-shaped main mass, was exposed close to the surface and the other fragment was located about 73 cm deep inside the meteoroid. No signal due to 44Ti was detected indicating that it has totally decayed on the Earth after fall of the meteorite and the terrestrial age of the meteorite must be longer than a few centuries. The ablation is shown to be asymmetric around the centre of the meteoroid and the pre-atmospheric mass of the meteoroid has been estimated to be between 30 and 60 tons, consistent with other estimates.
ACTIVE MOON: EVIDENCES FROM CHANDRAYAAN-1 AND THE PROPOSED INDIAN MISSIONS
Chandrayaan-1, the polar Lunar orbiter mission of Indian Space Research Organization, successfully carried out study of Moon’s environment and surface processes for a period of about nine months during 2008–2009. The results obtained by the mission established (i) A tenuous but active hydrosphere (ii) Volcanically active and geologically dynamic Moon and (iii) Global melting of Moon’s surface regions and formation of magma ocean early in the history of Moon. Chandrayaan-1 was equipped with a dozen instruments, including an impact probe, which housed three additional instruments. The results obtained by four instruments viz. Chandra’s Altitudinal Composition Explorer, Moon Mineral Mapper (M3), Solar Wind Monitor and Synthetic Aperture Radar gave an insight into an active hydrosphere, with several complex processes operating between lunar surface and its environment. These inferences are based on identification of H, OH, H2O, CO2, Ar etc. in the lunar atmosphere. There are indications that several young (~2 to100 Ma) volcanic regions are present on the Moon as shown by integrated studies using Terrain Mapping Camera and M3 of Chandrayaan-1 and data from other contemporary missions i.e. Kaguya and Lunar Reconnaissance Orbiter. These data establish that Moon has a dynamic and probably still active interior, in contrast to the generally accepted concept of dormant and quiet Moon. Discovery of Mg spinel anorthosites and finding of kilometer sized crystalline anorthosite exposures by M3 support the formation of global magma ocean on Moon and differentiation early in its evolutionary history. Furthermore, X-ray Spectrometer data showed anorthositic terrain with composition, high in Al, poor in Ca and low in Mg, Fe and Ti in a nearside southern highland region.
This mission provided excellent opportunity for multilateral international cooperation and collaboration in instrumentation and observation in which a dozen countries participated and contributed to the success of the mission. The Mars Orbiter Mission, for study of Martian atmosphere and ionosphere was launched on 5th November, 2013 and is already on its way to Mars. This will be followed by Chandrayaan-2, a well equipped Orbiter-Lander-Rover mission. This article summarizes a few results obtained by Chandrayaan-1, which changed some of the concepts about Moon's evolutionary history.
EARLY 18TH CENTURY COSMIC RAY FLUX INFERRED FROM 44TI IN AGEN METEORITE
Abstract: We report the measurement of radioactivity of cosmogenic44Ti in Agen meteorite, a H5 chondrite that fell in 1814. The 44Ti activity in meteorites is related to centennial-scale changes in cosmic ray intensity caused by heliospheric magnetic field modulation in the interplanetary space between heliocentric distances of 1 and 3 AU. The measured low 44Ti activity in Agen suggests a strong modulation of galactic cosmic rays at the turn of the 18th century, resulting in a low cosmic ray flux and is consistent with the linearly decreasing trend of GCR flux, modulated by the Gleissberg solar cycle during the past 250 years, as previously suggested by us.