共查询到20条相似文献，搜索用时 234 毫秒
1.
Slava G. Turyshev William Farr William M. Folkner André R. Girerd Hamid Hemmati Thomas W. Murphy Jr James G. Williams John J. Degnan 《Experimental Astronomy》2010,28(2-3):209-249
Phobos Laser Ranging (PLR) is a concept for a space mission designed to advance tests of relativistic gravity in the solar system. PLR’s primary objective is to measure the curvature of space around the Sun, represented by the Eddington parameter γ, with an accuracy of two parts in 107, thereby improving today’s best result by two orders of magnitude. Other mission goals include measurements of the time-rate-of-change of the gravitational constant, G and of the gravitational inverse square law at 1.5-AU distances—with up to two orders-of-magnitude improvement for each. The science parameters will be estimated using laser ranging measurements of the distance between an Earth station and an active laser transponder on Phobos capable of reaching mm-level range resolution. A transponder on Phobos sending 0.25-mJ, 10-ps pulses at 1 kHz, and receiving asynchronous 1-kHz pulses from earth via a 12-cm aperture will permit links that even at maximum range will exceed a photon per second. A total measurement precision of 50 ps demands a few hundred photons to average to 1-mm (3.3 ps) range precision. Existing satellite laser ranging (SLR) facilities—with appropriate augmentation—may be able to participate in PLR. Since Phobos’ orbital period is about 8 h, each observatory is guaranteed visibility of the Phobos instrument every Earth day. Given the current technology readiness level, PLR could be started in 2011 for launch in 2016 for 3 yr of science operations. We discuss the PLR’s science objectives, instrument, and mission design. We also present the details of science simulations performed to support the mission’s primary objectives. 相似文献
2.
This article provides the main scientific objectives and characteristics of the Phobos-Soil project, intended to fly to the Martian satellite Phobos, deliver its soil samples to the Earth, as well as explore Phobos,
Mars, and the Martian environment with onboard scientific instruments. We give the basic parameters of the ballistic scenario
of the mission, spacecraft, and some scientific problems to be solved with the help of the scientific instruments installed
on the spacecraft. 相似文献
3.
Several of the most fundamental and feasible geophysical problems partially related to the Phobos-Grunt mission have been analyzed based on the available works. The assumed results will form the informational basis for the development
of the cosmogony of planets’ small satellites and asteroids. Correspondingly, the aims of the experiment are to study the
internal structure and energy state of Phobos; to analyze the manifestation of pulsed effects and fields, including the registration
of seismic signals and wave fields of Phobos; and to measure the long-period oscillations on the surface of Phobos in the
range of 10−5–10 Hz. Studying Phobos gives an example of specific problems peculiar to small bodies of the Solar System: specific features
of cratering, grooves, and morphological structures. The registration of gas-dust streams extends the knowledge of the space-time
structure of the Solar System and its objects and processes and will confirm that stellar systems can constantly interact.
The physical principles of the registration of seismic fields and signals are briefly described, and the instrumental basis
for cosmogonic seismology is comparatively presented. It has been indicated that the piezoelectric and electrodynamic systems
of the desired signal registration complete each other, and it is desirable to use both systems if 2- and 3-D registration
systems are applied. The seismometric instrumentation of the Phobos spacecraft has been considered. The device’s physical characteristics, block diagrams, energy consumption, and information
content are presented. The seismoacoustic (HF) device unit and its advantages during the registration of very weak signals
owing to the use of the mechanical transformer effect are described in more detail. The seismic system created can ensure
the solution of the scientific problems of the mission to Phobos, including the study of the internal structure, origin, depth
structures, and external impacts of the field, corpuscular, and micrometeorite types. 相似文献
4.
5.
Peter Thomas 《Icarus》1979,40(2):223-243
Viking Orbiter images have provided nearly complete coverage of the two satellites of Mars and have been used to construct maps of the surface features of Phobos and Deimos. The satellites have radically different appearances although nearly all features on both objects were formed directly or indirectly by impact cratering. Phobos has an extensive network of linear depressions (grooves) that probably were formed indirectly by the largest impact recorded on Phobos. Deimos lacks grooves as well as the large number of ridges that occur on Phobos. Craters on Deimos have substantial sediment fill; those on Phobos have none. Evidence of downslope movement of debris is prominent on Deimos but is rare on Phobos. Many of the differences between Phobos and Deimos may be caused by modest differences in mechanical properties. However, the lack of a very large crater on Deimos may be responsible for its lack of grooves. 相似文献
6.
The Viking Orbiters have obtained several images of Phobos at large phase angles in which the portion of the satellite not directly illuminated by the Sun is faintly visible. A photometric analysis of one such image is presented to prove that the phenomenon is real and can be explained by Marsshine (i.e., the illumination of Phobos by sunlight reflected from Mars). Such images provide cross sections of Phobos and are useful in determining the true shape and size of the satellite. The cross section observed in Picture 111A03 agrees closely with that predicted by triaxial ellipsoid model of Phobos developed by Duxbury (1974). 相似文献
7.
M. Giuranna T.L. Roush T. Duxbury R.C. Hogan C. Carli A. Geminale V. Formisano 《Planetary and Space Science》2011,59(13):1308-1325
The origin of the Martian satellites presents a puzzle of long standing. Addressing the composition of Phobos will help constrain theories of its formation. Visible and near-infrared spectra of Phobos lack deep absorption features, making the compositional interpretation a tricky task. PFS/MEx and TES/MGS observations in the thermal infrared show several spectral features that can be used to investigate the composition of the surface. Our results show that the majority of the spectra are consistent with the presence of phyllosilicates, particularly in the area northeast of Stickney. This area corresponds to the “blue” region as defined by Murchie et al. (1999). Analysis of PFS and TES observations in the “red” region defined by Murchie et al. (1999) are consistent with tectosilicates, especially feldspars/feldspathoids. We discuss several physical and chemical mechanisms that can act to eliminate or reduce the strength of bands in the VIS/NIR spectra, with possibly little or no effect in the mid-IR. Comparison of the TES and PFS data to the meteorites shows that no class of chondritic meteorites provide significant agreement with the spectral features observed. The lack of consistency of the PFS and TES spectra to analogs of ultraprimitive materials (organic residues) suggests that an origin via capture of a transneptunian object is not supported by these observations, although it cannot be completely ruled out. Derived surface temperatures from PFS and TES data are in very good agreement with brightness temperatures derived from Viking orbiter measurements, Earth-based observations, and values predicted by numerical models. Our results show that the surface temperature of Phobos varies with solar incidence angle and heliocentric distance, reconciling the different results.We collect and summarize the compositional clues for the origin of Phobos discussed in this paper, including our results. Currently, the most likely scenario is the in-situ formation of Phobos, although a capture of achrondrite-like meteorites is not ruled out. 相似文献
8.
This work studies the evolution of several Distant Retrograde Orbits (DROs) of varying size in the Earth-Moon system over durations up to tens of millennia. This analysis is relevant for missions requiring a completely hands off, long duration quarantine orbit, such as a Mars Sample Return mission or the Asteroid Redirect Mission. Four DROs are selected from four stable size regions and are propagated for up to 30,000 years with an integrator that uses extended precision arithmetic techniques and a high fidelity dynamical model. The evolution of the orbit’s size, shape, orientation, period, out-of-plane amplitude, and Jacobi constant are tracked. It has been found that small DROs, with minor axis amplitudes of approximately 45,000 km or less decay in size and period largely due to the Moon’s solid tides. Larger DROs (62,000 km and up) are more influenced by the gravity of bodies external to the Earth-Moon system, and remain bound to the Moon for significantly less time. 相似文献
9.
10.
Analysis of disk resolved images of Phobos obtained by the Phobos 2 spacecraft allows us to study the surface scattering law and albedo variations. From low phase angle images we find variations in local geometric albedo approximately 10%, with a correlation length approximately 1km. The scattering law is reasonably well matched by the recent proposed LPI (Lumme et al. 1990a) model, which allows us to deduce a small scale (approximately 1 mm) surface roughness (approximately 0.5), defined here as the rms. tangent of the local surface normal relative to the mean surface normal in the Duxbury (1991) model of Phobos. This value is very close to what has been found for Mercury and the Moon. 相似文献
11.
E. M. Galimov 《Solar System Research》2010,44(1):5-14
The goals and the main scientific objectives of the Phobos-Grunt space mission are considered. The content of the investigations of the main task of the mission—to return a sample of Phobos
material to the Earth in order to answer the question about the origin of this satellite of Mars and to reconstruct its history—is
discussed. 相似文献
12.
At least three large areas on the surface of Phobos are covered by a dark material of complex texture which scatters light according to the Hapke-Irvine Law. The average 20° to 80° intrinsic and disc-integrated phase coefficients of this material are βi = 0.020 ± 0.001 mag/deg and β = 0.033 mag/deg, respectively. These values are slightly greater than the values found for Deimos in Paper II (preceding article). On the largest scale the surface of Phobos is rougher than the surface of Deimos, perhaps accounting for the slightly greater phase coefficients. Contrary to the situation on Deimos, no definite regions of intrinsically brighter material are apparent on Phobos. This difference could account for the slightly lower average reflectance of Phobos relative to Deimos. No evidence for large exposures of solid rock has been found in the three areas studied. 相似文献
13.
Thomas C. Duxbury 《Icarus》1974,23(2):290-299
Initial analysis of the Mariner 9 high resolution pictures of Phobos surface features has been completed. A control network of 38 landmarks has been established and used to determine the physical size, shape, orientation, libration, and topography properties of Phobos. The results verified the synchronous rotation of Phobos and revealed a libration of approximately 5° in the orbit plane of Phobos. A preliminary map of Phobos, based on the control network analysis, is given. 相似文献
14.
Using Mariner 9 results on the shapes, rotation periods and photometric functions of Phobos and Deimos we calculate approximate orbital lightcurves for the two Martian satellites. The prediction is that both Phobos and Deimos should show orbital brightness fluctuations detectable from Earth. For Phobos the detectable amplitude is predicted to be about 0.1 mag; for Deimos, 0.2 mag. 相似文献
15.
A. V. Zakharov N. A. Eismont V. M. Gotlib V. M. Smirnov O. V. Yushkova V. N. Marchuk 《Solar System Research》2017,51(5):386-399
The opportunities to study Phobos’ internal structure provided by radio methods are considered in this paper. The necessity of these studies is related to solution of the problem of the origin of the Martian moons. Radiosounding is one of the most efficient methods of analyzing the internal structure of small space objects and, in particular, that of Phobos. The new Boomerang project planned according to the Federal Space Program of Russia for 2016—2025 within the Expedition-M program aimed at the exploration of Phobos and delivery of soil samples from its surface to the Earth, as well as the specifics of a ballistic scenario of this expedition, provide a unique opportunity to carry out radioscopy of this space object to discover the internal structure Phobos and to solve the key problem of its origin. The model of Phobos’ internal structure, radiosounding ballistic conditions, analysis of optimum frequency range of sounding, and key parameters of the device required for the experiment are considered in this paper. The significance of proposed studies and opportunities for their implementation are discussed. 相似文献
16.
H. Rickman E. Słaby J. Gurgurewicz M. Śmigielski M. Banaszkiewicz J. Grygorczuk M. Morawski K. Seweryn R. Wawrzaszek 《Solar System Research》2014,48(4):279-286
CHOMIK is the name of a penetrator constructed for sampling and retrieval of Phobos surface material. It formed an integral part of the Phobos Sample Return Mission. In this paper we present its construction and intended mode of operation, since the concept is still viable for future missions either to Phobos or to other small bodies of similar dimensions. We take Phobos as an example to describe the science case for such an instrument and how it might be utilized to resolve important open issues regarding the origin of the Martian moons. Concerning the latter, we place emphasis on measurement techniques and analysis tools for mapping trace element concentrations in returned sample. 相似文献
17.
This paper considers morphologic signatures of mass-wasting processes on the surface of Phobos. Two types of downslope movement of material are distinguished: (i) intracrater volume landslides inside impact craters and (ii) downslope near-surface movement of material. Crater statistics for the Stickney area (based on new images of Phobos) showed that the landslide in the crater Stickney could have been formed after resurfacing of the outer rim of the crater in the process of meteorite bombardment. An estimate of the volume of the landslide in Stickney (1–2 km3) and simulation of its movement allowed us to classify the landslide as a long-runout one. The possibility of forming a hummocky topographic relief to the east of Stickney due to the crater ejecta and the emplacement of the frontal part of the long-runout landslide is discussed. 相似文献
18.
We have observed the leading and trailing hemispheres of Phobos from 1.65 to 3.5 μm and Deimos from 1.65 to 3.12 μm near opposition. We find the trailing hemisphere of Phobos to be brighter than its leading hemisphere by 0.24±0.06 magnitude at 1.65 μm and brighter than Deimos by 0.98±0.07 magnitude at 1.65 μm. We see no difference larger than observational uncertainties in spectral slope between the leading and trailing hemispheres when the spectra are normalized to 1.65 μm. We find no 3-μm absorption feature due to hydrated minerals on either hemisphere to a level of ∼5-10% on Phobos and ∼20% on Deimos. When the infrared data are joined to visible and near-IR data obtained by previous workers, our data suggest the leading (Stickney-dominated) side of Phobos is best matched by T-class asteroids. The spectral slope of the trailing side of Phobos and leading side of Deimos are bracketed by the D-class asteroids. The best laboratory spectral matches to these parts of Phobos are mature lunar soils and heated carbonaceous chondrites. The lack of 3-μm absorption features on either side of Phobos argues against the presence of a large interior reservoir of water ice according to current models of Phobos' interior (F. P. Fanale and J. R. Salvail 1989, Geophys. Res. Lett.16, 287-290; Icarus88, 380-395). 相似文献
19.
The shape of a close planetary satellite is distorted from a self-gravitating sphere into a triaxial ellipsoid maintained by tidal and centrifugal forces. Using the family of Roche ellipsoids calculated by Chandrasekhar, it should be possible in some cases to determine the density of an inner satellite by an accurate measurement of its shape alone. The equilibrium figure of Phobos is expected to be the most extreme of any satellite. The shape of Phobos as observed by Mariner 9 approaches but appears not to be a Roche ellipsoid, although the uncertainties of measurement remain too large to exclude the possibility. In any case, Phobos is so small that even the low mechanical strength of an impact-compressed regolith is sufficient to maintain substantial departures from the equipotential figure. If larger close satellites, particularly Amalthea, are found to be Roche ellipsoids, their densities can be estimated immediately from the data presented.Asteroids of size comparable to Phobos and Deimos appear to have more irregular shapes than the Martian satellites. This may reflect the absence of a deep regolith on those asteroids due to the low effective escape velocity for impact ejecta. For Phobos and Deimos, on the other hand, ejecta will tend to remain in orbit about Mars until swept up again by the satellite, contributing to a deeper equilibrium layer of debris. 相似文献
20.
Tadashi Yokoyama 《Planetary and Space Science》2002,50(1):63-77
Due to the tides, the orbits of Phobos and Triton are contracting. While their semi major axes are decreasing, several possibilities of secular resonances involving node, argument of the pericenter and mean motion of the Sun will take place. In the case of Mars, if the obliquity (ε), during the passage through some resonances, is not so small, very significant variations of the inclination will appear. In one case, capture is almost certain provided that ε?20°. For Triton there are also similar situations, but capture seems to be not possible, mainly because in S1 state, Triton's orbit is sufficiently inclined (far) with respect to the Neptune's equator. Following Chyba et al. (Astron. Astrophys. 219 (1989) 123), a simplified equation that gives the evolution of the inclination versus the semi major axis, is derived. The time needed for Triton crash onto Neptune is longer than that one obtained by these authors, but the main difference is due to the new data used here. In general, even in the case of non-capture passages, some significant jumps in inclination and in eccentricities are possible. 相似文献