排序方式: 共有22条查询结果,搜索用时 15 毫秒
1.
H. Lammer J. H. Bredehöft A. Coustenis M. L. Khodachenko L. Kaltenegger O. Grasset D. Prieur F. Raulin P. Ehrenfreund M. Yamauchi J.-E. Wahlund J.-M. Grießmeier G. Stangl C. S. Cockell Yu. N. Kulikov J. L. Grenfell H. Rauer 《Astronomy and Astrophysics Review》2009,17(2):181-249
This work reviews factors which are important for the evolution of habitable Earth-like planets such as the effects of the
host star dependent radiation and particle fluxes on the evolution of atmospheres and initial water inventories. We discuss
the geodynamical and geophysical environments which are necessary for planets where plate tectonics remain active over geological
time scales and for planets which evolve to one-plate planets. The discoveries of methane–ethane surface lakes on Saturn’s
large moon Titan, subsurface water oceans or reservoirs inside the moons of Solar System gas giants such as Europa, Ganymede,
Titan and Enceladus and more than 335 exoplanets, indicate that the classical definition of the habitable zone concept neglects
more exotic habitats and may fail to be adequate for stars which are different from our Sun. A classification of four habitat
types is proposed. Class I habitats represent bodies on which stellar and geophysical conditions allow Earth-analog planets
to evolve so that complex multi-cellular life forms may originate. Class II habitats includes bodies on which life may evolve
but due to stellar and geophysical conditions that are different from the class I habitats, the planets rather evolve toward
Venus- or Mars-type worlds where complex life-forms may not develop. Class III habitats are planetary bodies where subsurface
water oceans exist which interact directly with a silicate-rich core, while class IV habitats have liquid water layers between
two ice layers, or liquids above ice. Furthermore, we discuss from the present viewpoint how life may have originated on early
Earth, the possibilities that life may evolve on such Earth-like bodies and how future space missions may discover manifestations
of extraterrestrial life. 相似文献
2.
G. A. Galazutdinov J. Kreowski F. A. Musaev P. Ehrenfreund B. H. Foing 《Monthly notices of the Royal Astronomical Society》2000,317(4):750-758
The identity of the carriers of the diffuse interstellar bands (DIBs) is one of the most fascinating puzzles of modern spectroscopy. Over the last few years the number of known DIBs has grown substantially. In this paper we discuss the two recently discovered near-infrared weak interstellar features which have already been proposed as fingerprints of the buckminsterfullerene We present and discuss measurements of the two related DIBs within a larger sample of reddened targets, observed with different spectrometers, telescopes and site conditions. We provide additional arguments in favour of the interstellar origin of the two bands. We find evidence around the 9577-Å DIB of far-wing structures, which may affect broad-band measurements. We estimate corrections and errors for telluric and stellar blends, and show that the cores of the two DIBs are well correlated with a ratio near unity within 20 per cent. Finally, we discuss their relation to the laboratory spectra of and the search for two expected weaker transitions. 相似文献
3.
We have performed field experiments to further develop and validate the Mars Oxidation Instrument (MOI) as well as measurement strategies for the in situ characterization of oxidation mechanisms, kinetics, and carbon cycling on Mars. Using the Atacama Desert as a test site for the current dry conditions on Mars, we characterized the chemical reactivity of surface and near-surface atmosphere in the dry core of the Atacama. MOI is a chemiresistor-based sensor array that measures the reaction rates of chemical films that are sensitive to particular types of oxidants or that mimic chemical characteristics of pre-biotic and biotic materials. With these sensors, the chemical reactivity of a planetary environment is characterized by monitoring the resistance of the film as a function of time. Our instrumental approach correlates reaction rates with dust abundance, UV flux, humidity, and temperature, allowing discrimination between competing hypotheses of oxidant formation and organic decomposition. The sensor responses in the Atacama are consistent with an oxidative attack by strong acids triggered by dust accumulation, followed by transient wetting due to an increase in relative humidity during the night. We conclude that in the Atacama Desert, and perhaps on Mars, low pH resulting from acid accumulation, combined with limited water availability and high oxidation potential, can result in oxidizing acid reactions on dust and soil surfaces during low-moisture transient wetting events (i.e. thin films of water). These soil acids are expected to play a significant role in the oxidizing nature of the soils, the formation of mineral surface coatings, and the chemical modification of organics in the surface material. 相似文献
4.
Charnley S. B. Rodgers S. D. Butner H. M. Ehrenfreund P. 《Earth, Moon, and Planets》2002,90(1-4):349-360
Recent developments in the chemical modelling of cometary comae aredescribed. We discuss the cyanide chemistry and present
new HCNobservations of the recent comet C/2002 C1 (Ikeya–Zhang). Theconnection between interstellar and cometary organic molecules
isdiscussed from the perspective of recent theories of interstellargas-grain chemistry. 相似文献
5.
James R. C. Garry Inge Loes ten Kate Zita Martins Per Nrnberg Pascale Ehrenfreund 《Meteoritics & planetary science》2006,41(3):391-405
Abstract— We have investigated the native amino acid composition of two analogs of Martian soil, JSC Mars‐1 and Salten Skov. A Mars simulation chamber has been built and used to expose samples of these analogs to temperature and lighting conditions similar to those found at low latitudes on the Martian surface. The effects of the simulated conditions have been examined using high‐performance liquid chromatography (HPLC). Exposure to energetic ultraviolet (UV) light in vacuum appears to cause a modest increase in the concentration of certain amino acids within the materials, which is interpreted as resulting from the degradation of microorganisms. The influence of low temperatures shows that the accretion of condensed water on the soils leads to the destruction of amino acids, supporting the idea that reactive chemical processes involving H2O are at work within the Martian soil. We discuss the influence of UV radiation, low temperatures, and gaseous CO2 on the intrinsic amino acid composition of Martian soil analogs and describe, with the help of a simple model, how these studies fit within the framework of life detection on Mars and the practical tasks of choosing and using Martian regolith analogs in planetary research. 相似文献
6.
R. Ruiterkamp S. B. Charnley H. M. Butner H.-C. Huang S. D. Rodgers Y.-J. Kuan P. Ehrenfreund 《Astrophysics and Space Science》2007,310(3-4):181-188
We have observed emission from both ortho and para spin states of ketene (CH2CO) towards several deeply-embedded protostars. The low CH2CO fractional abundances (∼10−10) and the rotation temperatures (∼20 K) are consistent with emission from the cooler envelope. We compare our results with
previous studies and discuss possible production pathways to interstellar ketene. We suggest that, if low observed excitation
temperatures of CH2CO, CH3CHO and H2CO are indicative of their absence from the hot core region, then this may be due to the extensive hydrogenation of pre-existing
grain mantles prior to evaporation into the inner envelope, leading to lower abundances of these compounds and to mantles
rich in alcohols. 相似文献
7.
Z. Martins B. A. Hofmann E. Gnos R. C. Greenwood A. Verchovsky I. A. Franchi A. J. T. Jull O. Botta D. P. Glavin J. P. Dworkin P. Ehrenfreund 《Meteoritics & planetary science》2007,42(9):1581-1595
Abstract— We have analyzed Shi?r 033, a CR chondrite from the Omani desert, using several different analytical techniques designed to study the degree of terrestrial alteration of this meteorite and also its petrologic classification. Bulk chemical analyses (including organic carbon and mean total H2O content) are consistent with a CR classification. Additionally, oxygen isotope analysis on a bulk sample indicates that Shi?r 033 is of type CR2. Amino acid analysis using liquid chromatography with UV fluorescence detection (HPLC‐FD) and liquid chromatography‐time of flight‐mass spectrometry (LC‐ToF‐MS) show that the absolute and the relative amino acid content of Shi?r 033 is distinct from other carbonaceous chondrites. Oxygen isotope analysis of a phyllosilicate‐rich dark inclusion shows that this inclusion is closer to CV3 or CO3 chondrites. The effects of terrestrial weathering in Shi?r 033 are evident from the dark inclusion carbon isotopic data, bulk chemistry (through the elevated concentrations of Sr and Ba), and amino acid data, which suggests extensive amino acid contamination of the meteorite from the fall site soil. Nevertheless, Shi?r 033 contains a small fraction of indigenous components, as indicated by the presence of the extraterrestrial amino acid α‐aminoisobutyric acid (AIB) that was not detected in the Shi?r soils. Finally, the terrestrial age of Shi?r 033 was determined and is discussed in the context of high levels of contamination. 相似文献
8.
Simulating Martian regolith in the laboratory 总被引:1,自引:0,他引:1
Karsten Seiferlin Pascale Ehrenfreund Kurt Gunderson Günter Kargl Jonathan Peter Merrison 《Planetary and Space Science》2008,56(15):2009-2025
Regolith and dust cover the surfaces of the Solar Systems solid bodies, and thus constitute the visible surface of these objects. The topmost layers also interact with space or the atmosphere in the case of Mars, Venus and Titan. Surface probes have been proposed, studied and flown to some of these worlds. Landers and some of the mechanisms they carry, e.g. sampling devices, drills and subsurface probes (“moles”) will interact with the porous surface layer. The absence of true extraterrestrial test materials in ample quantities restricts experiments to the use of soil or regolith analogue materials. Several standardized soil simulants have been developed and produced and are commonly used for a variety of laboratory experiments. In this paper we intend to give an overview of some of the most important soil simulants, and describe experiments (penetrometry, thermal conductivity, aeolian transport, goniometry, spectroscopy and exobiology) made in various European laboratory facilities. 相似文献
9.
P. Ehrenfreund E.F. Van Dishoeck M. Burgdorf J. Cami P. Van Hoof A.G.G.M. Tielens W.A. Schutte W.F. Thi 《Astrophysics and Space Science》1997,255(1-2):83-89
We present ISO observations of bright, high-mass southern starforming regions with the Short Wavelength Spectrometer (SWS)
and Long Wavelength Spectrometer (LWS). The selected targets show a range of pre-main sequence evolutionary phases. Whereas
some objects still show interstellar ice features, the most evolved objects are coincident with ultra-compact HII regions
and show strong emission lines from atomic species and polycyclic aromatic hydrocarbons (PAHs). We discuss the ISO spectra
between 2.5 - 200 μm of selected southern star-forming regions in the context of their evolution.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
Jeffrey L Bada Mark A Sephton Pascale Ehrenfreund Richard A Mathies Allison M Skelley Frank J Grunthaner Aaron P Zent Richard C Quinn Jean-Luc Josset François Robert Oliver Botta Daniel P Glavin 《Astronomy& Geophysics》2005,46(6):6.26-6.27
If we are to find unequivocal evidence for life on Mars, we will need new ways to search for it. Jeff L Bada and the MOD team describe the innovative strategy developed for the ExoMars mission. 相似文献