共查询到20条相似文献，搜索用时 968 毫秒
1.
2.
It is shown that phosphorus availability is in close balance with the phosphorus requirement of the bacterial grain model.
This correspondence, which would be fortuitous if the interstellar grains were of inorganic origin, points to the correctness
of the biological model.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Rodney S. Gomes Tabaré Gallardo Julio A. Fernández Adrián Brunini 《Celestial Mechanics and Dynamical Astronomy》2005,91(1-2):109-129
We study the transfer process from the scattered disk (SD) to the high-perihelion scattered disk (HPSD) (defined as the population
with perihelion distances q > 40 AU and semimajor axes a>50 AU) by means of two different models. One model (Model 1) assumes
that SD objects (SDOs) were formed closer to the Sun and driven outwards by resonant coupling with the accreting Neptune during
the stage of outward migration (Gomes 2003b, Earth, Moon, Planets 92, 29–42.). The other model (Model 2) considers the observed population of SDOs plus clones that try to compensate for observational
discovery bias (Fernández et al. 2004, Icarus , in press). We find that the Kozai mechanism (coupling between the argument of perihelion, eccentricity, and inclination),
associated with a mean motion resonance (MMR), is the main responsible for raising both the perihelion distance and the inclination
of SDOs. The highest perihelion distance for a body of our samples was found to be q = 69.2 AU. This shows that bodies can
be temporarily detached from the planetary region by dynamical interactions with the planets. This phenomenon is temporary
since the same coupling of Kozai with a MMR will at some point bring the bodies back to states of lower-q values. However,
the dynamical time scale in high-q states may be very long, up to several Gyr. For Model 1, about 10% of the bodies driven
away by Neptune get trapped into the HPSD when the resonant coupling Kozai-MMR is disrupted by Neptune’s migration. Therefore,
Model 1 also supplies a fossil HPSD, whose bodies remain in non-resonant orbits and thus stable for the age of the solar system,
in addition to the HPSD formed by temporary captures of SDOs after the giant planets reached their current orbits. We find
that about 12 – 15% of the surviving bodies of our samples are incorporated into the HPSD after about 4 – 5 Gyr, and that
a large fraction of the captures occur for up to the 1:8 MMR (a ⋍ 120 AU), although we record captures up to the 1:24 MMR
(a ≃ 260 AU). Because of the Kozai mechanism, HPSD objects have on average inclinations about 25°–50°, which are higher than
those of the classical Edgeworth–Kuiper (EK) belt or the SD. Our results suggest that Sedna belongs to a dynamically distinct
population from the HPSD, possibly being a member of the inner core of the Oort cloud. As regards to 2000 CR105 , it is marginally within the region occupied by HPSD objects in the parametric planes (q,a) and (a,i), so it is not ruled
out that it might be a member of the HPSD, though it might as well belong to the inner core. 相似文献
5.
6.
V. A. Kotov 《Bulletin of the Crimean Astrophysical Observatory》2012,108(1):30-35
Solar pulsations with a period of P 0 = 9600.606(12) were discovered in 1974. A more recent discovery is that planetary distances in the solar system are subject to spatial resonance with the parameter L 0 ?? cP 0 ?? 9600 ls and that the P 0 pulsation itself has cosmological significance (coherent cosmic oscillation, or the pace of absolute time of the universe; c is the speed of light). As of June 2011, 552 extrasolar planets have been discovered. Statistical analysis shows that the distribution of the semimajor axes of alien planets does not have L 0 resonance. Moreover, it appears to have no resonance at all. This frustrates the 20th-century hopes for the existence of extraterrestrial civilizations and possible contact with them. They are simply not there. This explanation of the Fermi paradox, or the Great Silence, appears to rest on the triumph of the anthropic principle, which has been successfully implemented by nature within our planetary system. This leads to a vision whereby the cosmos seems to be created specially for us. The scale L 0 indicates that the sun is a special quantum object, where L 0 is a wave function parameter that is not subject to the rational principles of the classical world, but rather follows a peculiar, quantum logic. 相似文献
7.
J. A. BARRAT J. BLICHERT‐TOFT PH. GILLET F. KELLER 《Meteoritics & planetary science》2000,35(5):1087-1100
Abstract— We report on major and trace element analyses of 17 eucrites, including three cumulate eucrites (Binda, Moore County, and Serra de Magé), determined by, respectively, inductively‐coupled plasma atomic emission spectrometry and inductively‐coupled plasma mass spectrometry. The results obtained for Binda and Moore County are consistent with the model of Treiman (1997) for the formation of cumulate eucrites, which holds that these meteorites were produced from a eucritic melt. Our sample of Serra de Magé contains unusually large amounts of pyroxene and probably an accessory phase rich in heavy rare earth elements and is therefore not representative of this eucrite as known from literature data. Our results for the noncumulate eucrites Bereba, Bouvante, Cachari, Caldera, Camel Donga, Ibitira, Jonzac, Juvinas, Lakangaon, Millbillillie, Padvarninkai, Pasamonte, Sioux County, and Stannern are in good agreement with literature data. The observed decoupling between major and trace elements for noncumulate eucrites can be explained by in situ crystallization during the differentiation of an asteroidal magma ocean. This model can further account for both the Nuevo Laredo and the Stannern trends but has as a consequence that none of the analyzed eucrites represents a primary melt. 相似文献
8.
The Shape of The Sunspot Cycle: A One-Parameter Fit 总被引：1，自引：0，他引：1
D. M. Volobuev 《Solar physics》2009,258(2):319-330
9.
Stuart P. D. Gill Alexander Knebe Brad K. Gibson 《Monthly notices of the Royal Astronomical Society》2005,356(4):1327-1332
We present an investigation of satellite galaxies in the outskirts of galaxy clusters taken from a series of high-resolution N -body simulations. We focus on the so-called backsplash population, i.e. satellite galaxies that once were inside the virial radius of the host but now reside beyond it. We find that this population is significant in number and needs to be appreciated when interpreting the various galaxy morphology environmental relationships and decoupling the degeneracy between nature and nurture. Specifically, we find that approximately half of the galaxies with current cluster-centric distance in the interval 1–2 virial radii of the host are backsplash galaxies that once penetrated deep into the cluster potential, with 90 per cent of these entering to within 50 per cent of the virial radius. These galaxies have undergone significant tidal disruption, losing on average 40 per cent of their mass. This results in a mass function for the backsplash population different from those galaxies infalling for the first time. We further show that these two populations are kinematically distinct and should be observable within existent spectroscopic surveys. 相似文献
10.
Magnetars, neutron stars with ultrastrong magnetic fields ( B ∼ 1014 −1015 G) , manifest their exotic nature in the form of soft gamma-ray repeaters and anomalous X-ray pulsars. This study estimates the birthrate of magnetars to be ∼0.22 per century with a Galactic population comprising ∼17 objects. A population synthesis was carried out based on the five anomalous X-ray pulsars detected in the ROSAT All Sky Survey by comparing their number to that of massive OB stars in a well-defined volume. Additionally, the group of seven X-ray dim isolated neutron stars detected in the same survey were found to have a birthrate of ∼2 per century with a Galactic population of ∼22 000 objects. 相似文献
11.
Pluto's obliquity (the angle between its spin axis and orbit normal) varies between ～102 and ～126° over a period of about 3 million years. These oscillations are nearly sinusoidal and quite stable, leading to only modest changes in the insolation regime. Thus, Pluto's rotation has been slightly retrograde ever since its current orbit and rotation rate were established. 相似文献
12.
Peter H. Stone 《Icarus》1975,24(3):292-298
Current knowledge of the atmosphere of Uranus is reviewed and specific objectives are suggested for satellite missions to Uranus. The anomalous composition of Uranus makes determinations of its atmospheric composition particularly valuable for testing theories of solar system evolution. The weakness of its atmospheric heating makes the determination of its atmospheric structure and dynamics particularly valuable for testing theories of atmospheric behavior. The large axial inclination of Uranus implies an anomalous latitudinal variation of temperature and dynamics different from that of the other planets. 相似文献
13.
Carl Sagan 《Icarus》1973,18(4):649-656
Both non-gray radiative equilibrium and gray convective equilibrium calculations for Titan indicate that the discrepancy between the equilibrium temperature of an atmosphereless Titan and the observed infrared temperatures can be explained by a massive molecular hydrogen greenhouse effect. The convective calculations indicate a probable minimum optical depth of 14, corresponding to many tens of km-atm of H2, and total pressures of ～0.1 bar. The tropopause is several hundred km above the Titanian surface and at a temperature of about 90°K. Methane condensation is likely at this level. Such an atmosphere is unstable against atmospheric blow-off unless typical mesosphere scale heights are < 25km, an unlikely situation. Blow-off can also be circumvented by exospheric temperatures near the freezing point of hydrogen. It is considered more plausible that the present atmosphere is in equilibrium between outgassing and blow-off of the one hand and accretion from protons trapped in a hypothetical Saturnian magnetic field on the other; or exhibits uncompensated blow-off of outgassing products. To maintain the present blow-off rate without compensation for all of geological time requires an outgassing equivalent to the volatilization of a few km of subsurface ices. Photo-dissociation of these volatilized ices produces the observed high abundance of H2 as well as large quantities of complex organic chromophores which may explain the reddish coloration of the Titanian cloud deck. An extensive circum-Titanian hydrogen corona is postulated. Surface temperatures as high as 200°K are not excluded. Because of its high temperatures and pressures and the probable large abundance of organic compounds, Titan is a prime target for spacecraft exploration in the outer solar system. 相似文献
14.
Abstract— Due to their small size, the mineralogical and chemical properties of micrometeorites (MMs) are not representative of their parent bodies on the centimeter to meter scales that are used to define parent body groups through the petrological study of meteorites. Identifying which groups of MM are derived from the same type of parent body is problematic and requires particles to be rigorously grouped on the basis of mineralogical, textural, and chemical properties that reflect the fundamental genetic differences between meteorite parent bodies, albeit with minimal bias towards preconceived genetic models. Specifically, the interpretation of MMs requires a rigorous and meaningful classification scheme. At present the classification of MMs is, however, at best ambiguous. A unified petrological‐chemical classification scheme is proposed in the current study and is based on observations of several thousand MMs collected from Antarctic ice. 相似文献
15.
L. A. L. Da Silva 《Astrophysics and Space Science》1993,202(2):215-236
The present status of the Minkowski-Zwicky supernova classification is reviewed. Some very recent theoretical and observational results are mentioned, and their direct impact in our knowledge of the physics of supernovae and their classification are discussed. We also examine the possibility of imagine an alternative based taxonomy for supernovae, derived mainly from what we know about the physical processes involved in those stars, trying to correlate these physical types to the observational evidences available, in order to see if such a scheme would be useful, in practical terms. 相似文献
16.
D. I. Steel 《Earth, Moon, and Planets》1996,72(1-3):279-292
The geological and biological sciences have gradually dispensed with the nineteenth-century concept of substantive uniformitarianism - or gradualism - whereby the physical and biological features of our planet are assumed to have been brought about by the long-term accumulation of small changes. The catastrophist alternative sees the changes as being wrought largely by discrete, exceptional events; one such type of event is an impact by a substantial asteroid or comet. It is argued here that scientists working on small solar system bodies generally still labour under a form of this gradualism, in that a conventional starting point is to presume a steady-state, and what is seen now is assumed to be diagnostic of the long-term average conditions. This is here termed NEO-uniformitarianism, the NEO referring to Near-Earth Objects. It is maintained herein that this area of science needs to revise its philosophical basis by allowing catastrophist principles to be entertained; that is, the presumption of a steady-state needs to be rejected until such time as evidence to support it is revealed. It is argued that the weight of evidence favours the contrary. For example, evidence is outlined for (a) Variations in the terrestrial cratering rate, disallowing any equating of the crater record with the presently-observed large impactor population; (b) The presence of significant NEO complexes which may be due to giant comet disintegrations within the last 20 kyr, hence solving the problem of the supply of short-period comets; (c) A misbalance between the present supply of meteoroids, there being too many to be supplied by presently-observed comets and also a surplus above the population needed to maintain the interplanetary dust complex; and (d) A substantial variation in the interplanetary dust flux in the past 20 kyr, as might be expected from (b and c). 相似文献
17.
O. S. Shalygina V. V. Korokhin L. V. Starukhina E. V. Shalygin G. P. Marchenko Yu. I. Velikodsky O. M. Starodubtseva L. A. Akimov 《Solar System Research》2008,42(1):8-17
We present new results obtained from the analysis of the seasonal variations in the asymmetry of polarization of light reflected by Jupiter. From the 23-year set of observations, the anticorrelation between the asymmetries of polarization and insolation has been revealed. The mechanism explaining the observed seasonal variations of polarization has been proposed. The core of this mechanism is the effect of temperature changes in the planetary stratosphere on the processes of the stratospheric aerosol haze formation. Additional irregular factors that may influence the observed polarization asymmetry are considered. 相似文献
18.
Jesús Gallego 《Astrophysics and Space Science》1998,263(1-4):1-14
The evolution of the Star Formation Rate (SFR) density of the Universe as a function of look-back time is a fundamental parameter
in order to understand the formation and evolution of galaxies. The current picture, only outlined in the last years, is that
the global SFR density has dropped by about an order of magnitude from a redshift of z∼1.5 to the current value at z=0. Because
these SFR density studies are now extended to the whole range in redshift, it becomes mandatory to combine data from different
SFR tracers. At low redshifts, optical emission lines are the most widely used. Using Hα as current-SFR tracer, the Universidad
Complutense de Madrid (UCM) Survey provided the first estimation of the global SFR density in the Local Universe. The Hα flux
in emission is directly related to the number of ionizing photons and, modulo IMF, to the total mass of stars formed. Metallic
lines like [OII]λ3727 and [OIII]λ5007 are affected by metallicity and excitation. Beyond redshifts z∼0.4, Hα is not observable
in the optical and [OII]λ3727 or UV luminosities have to be used. The UCM galaxy sample has been used to obtain a calibration
between [OII]λ3727 luminosity and SFR specially suitable for the different types of star-forming galaxies found by deep spectroscopic
surveys in redshifts up to z∼1.5. These calibrations, when applied to recent deep redshift surveys confirm the drop of the
SFR density of the Universe since z∼1 previously infered in the UV. However, the fundamental parameter that determines galactic
evolution is mass, not luminosity. The mass function for local star-forming galaxies is critical for any future comparison
with other galaxy populations of different evolutionary status. Hα velocity-widths for UCM galaxies indicate that besides
a small fraction of 1010-1011 M⊙ starburst nuclei spirals, the majority have dynamical masses in the ∼109 M⊙ range. A comparison with published data for faint blue galaxies suggests that star-forming galaxies at z∼1 would have SFR
per unit mass and burst strengths similar to those at z=0, but being intrinsically more massive.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Richard Greenberg Gregory V. Hoppa Paul Geissler Alyssa Sarid B.R. Tufts 《Celestial Mechanics and Dynamical Astronomy》2002,83(1-4):35-47
Theoretical predictions of non-synchronous rotation and of polar wander on Europa have been tested by comparing tectonic features observed in Voyager and Galileo spacecraft images with tidal stresses. Evidence for non-synchronous rotation comes from studying changes in global scale lineaments formed over time, from the character of strike-slip faults, and from comparison of distinctively shaped cycloidal cracks with the longitudes at which such shapes should have formed, in theory. The study of cycloids constrains the rotation period (relative to the direction of Jupiter) to less than 250 000 years, while direct comparison of the orientation of Europa in Voyager and Galileo images shows the rotation is slow, with a period of >12 000 years. Comparison of strike-slip faults with their theoretical locations of formation provides evidence for substantial polar wander, supported by the distribution of various thermally produced features. 相似文献