Amino acids are the essential molecular components of living organisms on Earth, but the proposed mechanisms for their spontaneous generation have been unable to account for their presence in Earth's ...early history. The delivery of extraterrestrial organic compounds has been proposed as an alternative to generation on Earth, and some amino acids have been found in several meteorites. Here we report the detection of amino acids in the room-temperature residue of an interstellar ice analogue that was ultraviolet-irradiated in a high vacuum at 12 K. We identified 16 amino acids; the chiral ones showed enantiomeric separation. Some of the identified amino acids are also found in meteorites. Our results demonstrate that the spontaneous generation of amino acids in the interstellar medium is possible, supporting the suggestion that prebiotic molecules could have been delivered to the early Earth by cometary dust, meteorites or interplanetary dust particles.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The paper describes the Rosetta Lander named Philae and introduces its complement of scientific instruments. Philae was launched aboard the European Space Agency Rosetta spacecraft on 02 March 2004 ...and is expected to land and operate on the nucleus of 67P/Churyumov-Gerasimenko at a distance of about 3 AU from the Sun. Its overall mass is ~98 kg (plus the support systems remaining on the Orbiter), including its scientific payload of ~27 kg. It will operate autonomously, using the Rosetta Orbiter as a communication relay to Earth. The scientific goals of its experiments focus on elemental, isotopic, molecular and mineralogical composition of the cometary material, the characterization of physical properties of the surface and subsurface material, the large-scale structure and the magnetic and plasma environment of the nucleus. In particular, surface and sub-surface samples will be acquired and sequentially analyzed by a suite of instruments. Measurements will be performed primarily during descent and along the first five days following touch-down. Philae is designed to also operate on a long time-scale, to monitor the evolution of the nucleus properties. Philae is a very integrated project at system, science and management levels, provided by an international consortium. The Philae experiments have the potential of providing unique scientific outcomes, complementing by in situ ground truth the Rosetta Orbiter investigations.
Velocity and direction of the flow of the interstellar helium and its temperature and density have been determined from the measurements of the ULYSSES/GAS experiment for two different epochs: during ...the in-ecliptic path of ULYSSES, representing solar maximum conditions, and during the south-to-north pole transition (11/94-6/95), close to the solar minimum conditions. The determination of the density of the interstellar helium at the heliospheric boundary from observations in the inner solar system requires knowledge about the loss processes experienced by the particles on their way to the observer. The simultaneous observation of the helium particles arriving on 'direct' and 'indirect' orbits at the observer provides a tool to directly determine the effects of the loss processes assumed to be predominantly photoionization and (for particles travelling close to the sun) electron impact ionization by high-energy solar wind electrons. Such observations were obtained with the ULYSSES/GAS instrument in February 1995, before the probe passed its perihelion. From these measurements values for the loss rates and the interstellar density could be derived. (Author)
The GAS-instrument onboard the space probe ULYSSES (ULS) is designed to measure the local angular distribution of the flow of interstellar neutral He-atoms within ≈3 AU distance from the sun; it ...allows to infer the kinetic parameters (velocity vector, temperature and density) of these particles outside the heliosphere (“at infinity”). Around the second fast latitude scan of ULYSSES, from 9/2000 to 9/2002 more than 200 new observations were obtained. The average values derived from these observations together with the results of all previous observations, which were recalculated with a refined pointing calibration, are velocity (
v
∞=26.3±0.4 km/s), flow direction (ecliptic longitude
l
∞=74.7°±0.5°, ecliptic latitude
b
∞=−5.2°±0.2°) and temperature (
T
∞=6300±340 K). From 1990 to 2002, covering a complete solar cycle, no significant temporal variations of these parameters were observed nor variations with solar latitude. In contrast to that, variations in the density
n
∞ values derived from the local observations were obvious and are interpreted to be due to variations in the loss processes, predominantly photo ionization, the particles experience on their way to the observer. While the
temporal variations of the ionization rate can be taken into account from instantaneous values of solar EUV-irradiances, which became available from the CELIAS/SEM instrument on SOHO, the residual variations can be explained by
latitudinal variations of the solar irradiance. As a result of a simple model a density
n
∞ in the range (1.2–1.6
×
10
−2 cm
−3) is deduced.
The scientific objectives, design and capabilities of the Rosetta Lander's ROMAP instrument are presented. ROMAP's main scientific goals are longterm magnetic field and plasma measurements of the ...surface of Comet 67P/Churyumov-Gerasimenko in order to study cometary activity as a function of heliocentric distance, and measurements during the Lander's descent to investigate the structure of the comet's remanent magnetisation. The ROMAP fluxgate magnetometer, electrostatic analyser and Faraday cup measure the magnetic field from 0 to 32 Hz, ions of up to 8000 keV and electrons of up to 4200 keV. Additional two types of pressure sensors - Penning and Minipirani - cover a pressure range from 10 super(-8) to 10 super(1) mbar. ROMAP's sensors and electronics are highly integrated, as required by a combined field/plasma instrument with less than 1 W power consumption and 1 kg mass.
“Rosetta” is a Cornerstone Mission of the Horizon 2000 ESA Programme. Its goal is to rendezvous with a comet and to study its nucleus and coma using an orbiting spacecraft and a landed platform. The ...latter is called Philae; the Rosetta Lander has been designed to land softly on the comet nucleus and is equipped with 10 scientific instruments to perform in situ studies of cometary material.
The Lander system is provided by international consortium with the participation of Germany, France, Italy, United Kingdom, Finland, Ireland, Hungary and Austria.
The original Rosetta mission was planned to launch in January 2003 to reach comet 47P/Wirtanen in 2011 at a heliocentric distance of about 3
AU. Due to uncertainties regarding the reliability of the Ariane 5 launcher (after a catastrophic failure in December 2002) the Rosetta launch was postponed and a new mission studied.
Changed mission characteristics (e.g. in launcher capacity; no swing-by at Venus) strongly limited the number of possible alternatives. After careful investigation, a decision was taken for a mission to comet 67/P Churyumov-Gerasimenko with a launch date in February 2004 and rendezvous in 2014.
This new mission scenario has significant consequences for the Rosetta Lander, because the nucleus of P/Churyumov-Gerasimenko is expected to be considerably larger than that of P/Wirtanen. Current best estimates assume a radius of about 2.0
km and, thus, a mass which is about two orders of magnitude larger than that of the original target comet. This impacts strongly on the Lander separation, descent and landing scenario. Analysis of the increased landing risk on P/Churyumov-Gerasimenko has led to modifications of the landing gear to cope with the increased impact velocities expected.
UBF is a DNA binding protein which interacts with both the promoter and the enhancer of various vertebrate ribosomal RNA genes and functions as a transcription initiation factor for RNA polymerase I ...(pol I). We have purified murine UBF to apparent molecular homogeneity and demonstrate that its transactivating potential, but not its DNA binding activity, is modulated in response to cell growth. In vivo labelling experiments demonstrate that UBF is a phosphoprotein and that the phosphorylation state is different in growing and quiescent cells. We show that UBF is phosphorylated in vitro by a cellular protein kinase which by several criteria closely resembles casein kinase II (CKII). A major modification involves serine phosphoesterifications in the carboxy terminal hyperacidic tail of UBF. Deletions of this C‐terminal domain severely decreases the UBF directed activation of transcription. The data suggest that phosphorylation of UBF by CKII may play an important role in growth dependent control of rRNA synthesis.
The Cometary Sampling and Composition (COSAC) experiment is a combined gas chromatograph–mass spectrometer onboard the Philae cometary surface probe of the Rosetta mission. Its goal is to analyse, ...directly at the surface of a comet, the molecular and elemental compositions of the cometary nucleus samples collected by the probe. The present article describes the results of the first calibration campaign done with the whole instrumental suite, in order to evaluate and to improve its analytical performance.
This calibration campaign enabled us: (i) to optimize the operations of the gas chromatograph and thus to improve the chromatographic analytical power; (ii) to confirm the analytical performance of the COSAC chromatograph, by comparison with tests performed at the instrumental component level, excepted a little loss of the chromatographic resolution; (iii) to validate and to evaluate the performance of the different chromatographic analytical modes, i.e. mainly single and multi columns separation modes, and the gas chromatograph–mass spectrometer coupling mode.
This series of tests therefore confirms the potential for the COSAC experiment to provide the first insight of the main molecular composition of a cometary nucleus, and thus to improve our knowledge of these bodies and their history.
Being successfully launched on March 2, 2004, ESA’s cornerstone mission “ROSETTA” (originally planned to be launched in January 2003 to comet Wirtanen) is en route. It will also bring the 100
kg ...Lander “Philae” with a scientific payload of 26.7
kg to the surface of comet 67P/Churyumov-Gerasimenko. After a first scientific sequence in 2014 it will operate for a considerable fraction of the cometary orbit around the sun (between 3 AU and at least 2 AU).
The Lander, after separation, is an autonomous spacecraft powered with solar cells and using the ROSETTA Orbiter as a telemetry relais to Earth. The main scientific objectives are the in situ investigation of the chemical, elemental, isotopic and mineralogical composition of the comet, study of the physical properties of the surface material, analyze the internal structure of the nucleus, observe temporal variations (day/night cycle, approach to sun), study the relationship between the comet and the interplanetary matter and provide ground truth data for the Orbiter instruments. Ten experiments with a number of sub-experiments are foreseen to fulfil these objectives.
Philae is operated (via ESOC) by the Lander Control Centre (LCC) at DLR and the Science Operations and Navigation Centre (SONC) at CNES. In this paper we present the flight status of the scientific instruments as it is known after in-orbit commissioning.
Comets are probably the most primitive bodies of the solar system, and they participated in the early bombardment of the primitive planets. Consequently, the knowledge of their composition can play a ...key role in our understanding of the solar system formation, the origin of the planetary volatile constituents, and the origin of the organics implied in terrestrial prebiotic chemistry. However, we still do not have any direct information about the molecular composition of the cometary nucleus. This is why the COmetary SAmpling and Composition experiment (COSAC), onboard the surface landing probe of the Rosetta cometary mission, is specifically devoted to the molecular and enantiomeric analysis of a cometary nucleus. This experiment includes a gas chromatograph instrument dedicated to the specific identification and quantification of the general molecular species present in samples collected at the nucleus surface. In order to evaluate the performances of the integrated chromatographic system which was selected for the flight model instrument, experiments were carried out with a laboratory set up that reproduced the flight configuration and mimicked the in situ operating conditions. The obtained results demonstrate the ability for the gas chromatograph to identify a wide range of organic and inorganic volatile compounds, even those present at trace level, within the constrained space operating conditions. The aim of this paper is to present, for the first time, the performances of this system and to discuss the potential role of in situ gas chromatographic measurements in the future cometary, planetological and prebiotic chemistry studies.
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