首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 218 毫秒
1.
Analyses of the data from the Meteoroid Detection Experiment (MDE) and the Imaging Photopolarimeter (IPP) aboard Pioneer 10 and Pioneer 11 have led to contradictory conclusions. While the MDE indicates a significant particle environment in the outer solar system (out to at least 5 AU), the IPP sees no zodiacal light (therefore implying no small particles) past 3.3 AU. We reconcile the two results by noting that the spectral index, p [relating particle radius, s, and particle concentration, n(s), i.e., dn(s) = Cs?pds], is not a constant in the solar system, but changes from p < 2 near 1 AU to p > 2.5 at 5 AU for particles in the range of 10 μm. The MDE value of p = 1.8 at 1 AU is in agreement with previous satellite measurements, while our earlier analysis of the Pioneer 10 Jovian encounter data indicated p > 2.5 at 5 AU. A joint analysis of the Pioneer 10 and Pioneer 11 MDE data also indicates that p > 2.5 in the outer solar system. We show that a varying spectral index violates a major assumption used in the interpretation of the IPP data, which in turn had led to the conclusion that zodiacal dust is absent beyond 3.3 AU. With p a function of solar distance, the MDE data is now consistent with the IPP data, thus indicating a significant particle concentration in the outer solar system.  相似文献   

2.
《New Astronomy》2007,12(2):142-145
We consider a generic minimal modification of the Newtonian potential, that is a modification that introduces only one additional dimensional parameter. The modified potential depends on a function whose behavior for large and small distances can be fixed in order to obtain: (i) galactic flat rotational curves and (ii) a universal constant acceleration independent of the masses of the interacting bodies (Pioneer anomaly). Then using a dimensional argument we show that the Tully–Fisher relation for the maximal rotational velocity of spiral galaxies follows without any further assumptions. This result suggests that the Pioneer anomalous acceleration and the flat rotational curves of galaxies could have a common origin in a modified gravitational theory. The relation of these results with the Modified Newtonian Dynamics (MOND) is discussed.  相似文献   

3.
This paper proposes an explanation for the Pioneer anomaly: an unexplained Sunward acceleration of 8.74 ± 1.33 × 10−10 m s−2 seen in the behaviour of the Pioneer probes. Two hypotheses are made. (1) Inertia is a reaction to Unruh radiation and (2) this reaction is weaker for low accelerations because some wavelengths in the Unruh spectrum do not fit within a limiting scale (twice the Hubble distance) and are disallowed: a process similar to the Casimir effect. When these ideas are used to model the Pioneer crafts' trajectories, there is a slight reduction in their inertial mass, causing an anomalous Sunward acceleration of 6.9 ± 3.5 × 10−10 m s−2 which agrees within error bars with the observed Pioneer anomaly beyond 10 au from the Sun. This new scheme is appealingly simple and does not require adjustable parameters. However, it also predicts an anomaly within 10 au of the Sun, which has not been observed. Various observational tests for the idea are proposed.  相似文献   

4.
By telescopic tracking, we have established that the transneptunian object (TNO) 2000 CR105 has a semimajor axis of 220±1 AU and perihelion distance of 44.14±0.02 AU, beyond the domain which has heretofore been associated with the “scattered disk” of Kuiper Belt objects interacting via gravitational encounters with Neptune. We have also firmly established that the TNO 1995 TL8 has a high perihelion (of 40.08±0.02 AU). These objects, and two other recent discoveries which appear to have perihelia outside 40 AU, have probably been placed on these orbits by a gravitational interaction which is not strong gravitational scattering off of any of the giant planets on their current orbits. Their existence may thus have profound cosmogonic implications for our understanding of the formation of the outer Solar System. We discuss some viable scenarios which could have produced these objects, including long-term diffusive chaos and scattering off of other massive bodies in the outer Solar System. This discovery implies that there must be a large population of TNOs in an “extended scattered disk” with perihelia above the previously suggested 38 AU boundary. The total population is difficult to estimate due to the ease with which such objects would have been lost. This illustrates the great value of frequent and well time-sampled recovery observations of trans-neptunian objects within their discovery opposition.  相似文献   

5.
The Pioneer anomaly is one of the most important problems in modern physics. The observed blueshift of the Doppler signals coming back from the space probes Pioneer 10 and 11 is interpreted as being due to an anomalous acceleration ap = (8.74 ± 1.33) × 10–8 cm s–2 towards the Sun. In this paper the blueshift is explained by the frequency shifts of the receivers. These frequency shifts result from an increase in elementary particle masses in time, the rate of increase being tied up with the present‐day Hubble parameter H0. The result is that the seeming acceleration ap is the product of H0 and the velocity of light. Taking new physics into consideration, this paper presents a new explanation of the Pioneer anomaly based on the assumption that the Universe is eternal and infinite without expansion or contraction (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
All proposed gravitational explanations of the Pioneer anomaly must crucially face the Equivalence Principle. Thus, if Pioneers 10 and 11 were influenced by anomalous gravitational effects in regions containing other Solar System bodies, then those bodies should likewise be influenced, irrespective of their shape, composition or mass. Although the lack of any observed influence upon planetary orbits severely constrains such explanations, here we aim to construct by computer modeling, hypothetical gravitating annuli having no gravitational impact on planetary orbits from Mercury to Neptune. One model has a central zone, free of radial gravitation in the annular plane, and an ‘onset’ beyond Saturn’s orbit, where sunward annular gravitation increases to match the Pioneer anomaly data. Sharp nulls are included so that Uranus and Neptune escape this influence. Such models can be proportionately reduced in mass: a 1 % contribution to the anomaly requires an annulus of approximately 1 Earth mass. It is thus possible to comply with the JPL assessment of newly recovered data attributing 80 %, or more, of the anomaly to spacecraft heat, which appears to allow small contributions from other causes. Following the possibility of an increasing Kuiper belt density at great ranges, another model makes an outward small anomalous gravitation in the TNO region, tallying with an observed slight indication of such an effect, suggesting that New Horizons may slightly accelerate in this region.  相似文献   

7.
We argue that the so-called “Pioneer Anomaly” is related to the quantum vacuum fluctuations. Our approach is based on the hypothesis of the gravitational repulsion between matter and antimatter, what allows considering, the virtual particle–antiparticle pairs in the physical vacuum, as gravitational dipoles. Our simplified calculations indicate that the anomalous deceleration of the Pioneer spacecrafts could be a consequence of the vacuum polarization in the gravitational field of the Sun. At the large distances, the vacuum polarization by baryonic matter could mimic dark matter what opens possibility that dark matter do not exist, as advocated by the Modified Newtonian Dynamics (MOND).  相似文献   

8.
John Chambers 《Icarus》2006,180(2):496-513
A new semi-analytic model for the oligarchic growth phase of planetary accretion is developed. The model explicitly calculates damping and excitation of planetesimal eccentricities e and inclinations i due to gas drag and perturbations from embryos. The effects of planetesimal fragmentation, enhanced embryo capture cross sections due to atmospheres, inward planetesimal drift, and embryo-embryo collisions are also incorporated. In the early stages of oligarchic growth, embryos grow rapidly as e and i fall below their equilibrium values. The formation of planetesimal collision fragments also speeds up embryo growth as fragments have low-e, low-i orbits, thereby optimizing gravitational focussing. At later times, the presence of thick atmospheres captured from the nebula aids embryo growth by increasing their capture cross sections. Planetesimal drift due to gas drag can lead to substantial inward transport of solid material. However, inward drift is greatly reduced when embryo atmospheres are present, as the drift timescale is no longer short compared to the accretion timescale. Embryo-embryo collisions increase embryo growth rates by 50% compared to the case where growth is solely due to accretion of planetesimals. Formation of 0.1-Earth-mass protoplanets at 1 AU and 10-Earth-mass cores at 5 AU requires roughly 0.1 and 1 million years respectively, in a nebula where the local solid surface density is 7 g cm−2 at each of these locations.  相似文献   

9.
We investigate the method by which nearby supernovae – within a few tens of pc of the solar system – can penetrate the solar system and deposit live radioactivities on earth. The radioactive isotopic signatures that could potentially leave an observable geological imprint are in the form of refractory metals; consequently, it is likely they would arrive in the form of supernova-produced dust grains. Such grains can penetrate into the solar system more easily than the bulk supernova plasma, which gets stalled and deflected near the solar system due to the solar wind plasma pressure. We therefore examine the motion of charged grains as they decouple from the supernova plasma and are influenced by the solar magnetic, radiation, and gravitational fields. We characterize the dust trajectories with analytical approximations which display the roles of grain size, initial velocity, and surface voltage. These results are verified with full numerical simulations for wide ranges of dust properties. We find that supernova dust grains traverse the inner solar system nearly undeflected, if the incoming grain velocity – which we take to be that of the incident supernova remnant – is comparable to the solar wind speeds and much larger than the escape velocity at 1 AU. Consequently, the dust penetration to 1 AU has essentially 100% transmission probability and the dust capture onto the earth should have a geometric cross section. Our results cast in a new light the terrestrial deposition of radioisotopes from nearby supernovae in the geological past. For explosions beyond ～10 pc from earth, dust grains can still deliver supernova ejecta to earth, and thus the amount of supernova material deposited is set by the efficiency of dust condensation and survival in supernovae. Turning the problem around, we use observations of live 60Fe in both deep-ocean and lunar samples to infer a conservative lower bound iron condensation efficiency of Mdust,Fe/Mtot,Fe ? 4  × 10?4 for the supernova which apparently produced these species 2–3 Myr ago.  相似文献   

10.
An overview of the results of the search for small solar transient events, in association with muon enhancements (deficits) registered at ground-level by the Tupi muon telescopes, is presented. Among the events, there are three interplanetary shocks and two solar flares of small scale whose X-ray emission flux is much smaller than 10???5 W m?2 at 1 AU (GOES-Tupi connection). Two of the interplanetary shocks are cataloged as corotating interaction region and the third shock is due to the passage of a CME (coronal mass ejection) ejecta (ACE and SOHO-Tupi connection) in the Earth’s proximities. In most cases, the particles excess (deficit) coming from these events have only been observed with spacecraft instruments. However, the Tupi telescopes are located at sea level and within the South Atlantic Anomaly (SAA), a region where the shielding effect of the magnetosphere is not perfectly spherical and shows a ‘dip’. This fact enables the muon telescopes to achieve a low rigidity of response to primary and secondary charged particles (≥?0.1 GV). Muon excesses (deficits) with significances above 4σ have been found. These events observed at ground admit a temporal correlation with solar transient events observed by spacecrafts, which suggests strongly a real connection between them. Details of these observations are reported.  相似文献   

11.
Numerical integration of particle trajectories is performed to evaluate the statistical acceleration coefficients D TT for 1 to 100 MeV protons in a solar wind corotating interaction region (CIR) seen at 2.5 and 5.0 AU. Acceleration is followed in the solar wind reference frame and is due to random wave-particle interactions and to random drift motion in moderate scale field gradients. D TT due to the first effect reaches a peak value of 4 × 10 –7 MeV2 s–1 post shock at 10 MeV at 2.5 AU consistent with estimates based both upon cyclotron resonance and transit time damping theory. D TT from the second effect is less well established but is of the order of 10–7 MeV2 s–1 at 10 MeV, 5 AU. A comparison is made between the time constant for statistical acceleration within this CIR and estimates for diffuse shock acceleration and adiabatic deceleration. All three time constants are of the same order, but deceleration is faster than shock acceleration which in turn is faster than statistical acceleration.  相似文献   

12.
An analytical 3-D magnetohydrodynamic (MHD) solution of a magnetic-flux rope (FR) is presented. This FR solution may explain the uniform propagation, beyond ～?0.05 AU, of coronal mass ejections (CMEs) commonly observed by today’s missions like The Solar Mass Ejection Imager (SMEI), Solar and Heliospheric Observatory (SOHO) and Solar Terrestrial Relations Observatory (STEREO), tracked to tens of times the radius of the Sun, and in some cases up to 1 AU, and/or beyond. Once a CME occurs, we present arguments regarding its evolution based on its mass and linear momentum conservation. Here, we require that the gravitational and magnetic forces balance each other in the framework of the MHD theory for a simple model of the evolution of a CME, assuming it interacts weakly with the steady solar wind. When satisfying these ansätze we identify a relation between the transported mechanical mass of the interplanetary CME with its geometrical parameters and the intensity of the magnetic field carried by the structure. In this way we are able to estimate the mass of the interplanetary CME (ICME) for a list of cases, from the Wind mission records of ICME encountered near Earth, at 1 AU. We obtain a range for masses of ～?109 to 1013 kg, or assuming a uniform distribution, of ～?0.5 to 500 cm?3 for the hadron density of these structures, a result that appears to be consistent with observations.  相似文献   

13.
We study the velocity-space quasi-linear diffusion of the solar wind protons driven by oblique Alfvén turbulence at proton kinetic scales. Turbulent fluctuations at these scales possess the properties of kinetic Alfvén waves (KAWs) that are efficient in Cherenkov-resonant interactions. The proton diffusion proceeds via Cherenkov kicks and forms a quasi-linear plateau – the nonthermal proton tail in the velocity distribution function (VDF). The tails extend in velocity space along the mean magnetic field from 1 to (1.5?–?3) V A, depending on the spectral break position, on the turbulence amplitude at the spectral break, and on the spectral slope after the break. The most favorable conditions for the tail generation occur in the regions where the proton thermal and Alfvén velocities are about equal, V Tp/V A≈1. The estimated formation times are within 1?–?2 h for typical tails at 1 AU, which is much shorter than the solar wind expansion time. Our results suggest that the nonthermal proton tails, observed in situ at all heliocentric distances >?0.3 AU, are formed locally in the solar wind by the KAW turbulence. We also suggest that the bump-on-tail features – proton beams, often seen in the proton VDFs, can be formed at a later evolutional stage of the nonthermal tails by the time-of-flight effects.  相似文献   

14.
In this paper, we investigate the effects that an anomalous acceleration as that experienced by the Pioneer spacecraft after they passed the 20 AU threshold would induce on the orbital motions of the Solar System planets placed at heliocentric distances of 20 AU or larger as Uranus, Neptune and Pluto. It turns out that such an acceleration, with a magnitude of 8.74 × 10−10 m s−2, would affect their orbits with secular and short-period signals large enough to be detected according to the latest published results by E.V. Pitjeva, even by considering errors up to 30 times larger than those released. The absence of such anomalous signatures in the latest data rules out the possibility that in the region 20–40 AU of the Solar System an anomalous force field inducing a constant and radial acceleration with those characteristics affects the motion of the major planets.  相似文献   

15.
《New Astronomy》2007,12(5):383-397
We illustrate the energy transfer during planetary flybys as a function of time using a number of flight mission examples. The energy transfer process is rather more complicated than a monotonic increase (or decrease) of energy with time. It exhibits temporary maxima and minima with time which then partially moderate before the asymptotic condition is obtained. The energy transfer to angular momentum is exhibited by an approximate Jacobi constant for the system.We demonstrate this with flybys that have shown unexplained behaviors: (i) the possible onset of the “Pioneer anomaly” with the gravity assist of Pioneer 11 by Saturn to hyperbolic orbit (as well as the Pioneer 10 hyperbolic gravity assist by Jupiter) and (ii) the Earth flyby anomalies of small increases in energy in the geocentric system (Galileo-I, NEAR, and Rosetta, in addition discussing the Cassini and Messenger flybys). Perhaps some small, as yet unrecognized effect in the energy-transfer process can shed light on these anomalies.  相似文献   

16.
Energetic particle (0.1 to 100 MeV protons) acceleration is studied by using high resolution interplanetary magnetic field and plasma measurements at 1 AU (HEOS-2) and at 5 AU (Pioneer 10). Energy changes of a particle population are followed by computing test particle trajectories and the energy changes through the particle interaction with the time varying magnetic field. The results show that considerable particle acceleration takes place throughout the interplanetary medium, both in the corotating interaction regions (CIR) (5 AU), and in quiet regions (1 AU). Although shocks may contribute to acceleration we suggest statistical acceleration within the CIRs is sufficient to explain most energetic particle observations (e.g., McDonaldet al., 1975; Barnes and Simpson, 1976).The first and second order statistical acceleration coefficients which include transit time damping and Alfvén resonance interactions, are found to be well represented byD T 8.5×10–6 T 0.5 MeV s–1 andD TT 4×10–6 T 1.5 MeV2 s–1 at 5 AU.By comparison, Fisk's estimates (1976), based on quasi-linear theory for transit-time damping, gaveD TT 5×10–7 T MeV2 s–1 at 1 AU.  相似文献   

17.
A.F. Cook 《Icarus》1978,33(2):349-360
Comparison is made between the run of number density of meteoroids from penetration detectors aboard Helios A (masses below 10?8 g) and Pioneer 10 (masses near and above 3 × 10?9 g), the source function of the zodiacal light deduced from photometric observations aboard Helios A and Pioneer 10, counts versus brightness of objects passing by Pioneer 10 from the Sisyphus experiment and the distribution of meteoroids deduced from radar and optical meteors at the Earth. The Sisyphus experiment on Pioneer 10 observed reflecting glints on meteoroids rather than the meteoroids themselves and the counting statistics refer not to the effective radii of the meteoroids but to the effective radii of curvature of the reflecting glints on the meteoroids. The penetration detectors appear to find some increase in number density toward the Sun and a flat distribution outward to 5.2 AU. The overall behavior of the zodiacal light is that the relative distribution over direction is unchanged while the source scattering function diminishes as the inverse 1.4 power of distance from the Sun. The fit to the brightness of the zodiacal light obtained from these statistics can be combined with the mass distribution results from the optical meteors to deduce a mean geometric albedo of meteoroids of 0.006 at 1 AU from the Sun. Combination of the space distribution from radar meteors with the scattering source function of the zodiacal light yields geometric albedos for meteoroids running from 0.07 at 0.1 AU, from the Sun through 0.006 at 1 AU down to about 0.0001 at 3.3 AU which may run flat thence outward. This result is imposed by the indicated modest increase in density of meteoroids very near the Sun, a minimum between the Sun and the Earth near 0.4 AU and rising density outward to somewhere beyond 3.3 AU which is very different from the inverse 1.4 power of the distance shown for scatterers (product of number density and albedo) by the zodiacal light. A check on the distribution at very large sizes is possible if a search is made for fireballs in Jupiter's atmosphere by the Mariner Jupiter Saturn 1977 television cameras during the two encounters with Jupiter in 1979. An easy detection of such activity would put the maximum in the meteoroid distribution out near Jupiter and lend further confirmation to the indicated drop in albedo.  相似文献   

18.
During past years high angular (<1″) resolution imaging has provided useful information about the propagation of “real” jets. Recently, in addition, the spectrograph Hubble's Space Telescope Imaging spectrograph (STIS) on board the Hubble Space Telescope (HST) has finally allowed us to test the magneto-centrifugal paradigm for the jet launching. I present results from HST/STIS spectra at 0.″1 resolution of small-scale jets from T Tauri stars in their initial 140 AU (1″). The jet morphology, kinematics and excitation in different velocity intervals are derived, from which we calculate mass and momentum fluxes. Even more interestingly, we find indications for rotation around the symmetry axis in the peripheral regions of the flow. The investigated component of the wind appears to originate in the disk at a distance of 0.5-2 AU from the star, and it extracts at least 60% of the inner disk angular momentum. These results confirm for the first time the validity of the magneto-centrifugal approach for the jet launching, and constitute a benchmark to test models and simulations. In the near future, near-infrared (NIR) interferometry with AMBER/VLTI and with the LBTI will permit to observe the jet engine down to 0.1 AU from the source, where the acceleration of the jet takes place.  相似文献   

19.
The period of the β Cephei variable, BW Vulpeculae, is increasing all the time at a rate of (14.24±0.20) × 10?10d/d. Also, the residual in the time of light maximum shows a quasi-sinusoidal variation with a period of about 26.3 years and an amplitude of 0.022 – 0.024 days. If this is interpreted as the light-time effect in a binary orbit, then the orbit will have a size a sin i = 1.91 – 2.08 AU and an eccentricity e = 0.52.  相似文献   

20.
This note discusses the stability of collinear equilibrium points around a rotating system composed of two masses rigidly connected by a massless rod in the case, where the centripetal force outweighs the gravitational force. It is found that a stable region appears at L1 when the ratio of gravitational to centripetal acceleration is less than 0.125, and that there is always no stable area at L2 and L3; the result is applied to the fast rotating Asteroid 2000EB14.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号