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Using Mariner 9 results on the shapes, rotation periods, and photometric functions of Phobos and Deimos, approximate orbital light curves are calculated 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.
Images of Phobos and Deimos acquired by the Viking orbiter television system have been used to determine the photometric functions of the Martian moons. Data covering wavelengths from 445 nm to 593 nm and solar phase angles between 0.5 deg and 122 deg were used. Normal reflectances of 0.066 + or - 0.006 for Phobos and 0.069 + or - 0.006 for Deimos were determined. No variations in either photometric function or average normal albedo were observed over the wavelength range studied. The photometric functions demonstrate that the surface of Phobos and Deimos are intricate in texture brightness surges near opposition that are more pronounced than that of the moon.
Ejecta block characteristics observed on Phobos, Deimos, and the moon are examined. The analyzed source craters on Deimos are 0.8-2.3 km in diameter, those on Phobos are 1.5-10 km, and the lunar craters are between 0.2-3.5 km in diameter. The size and radial distribution of the ejecta blocks for the three bodies are compared. It is observed that the size distribution of the ejecta blocks surrounding craters on the three objects are basically similar, and the radial distribution of the blocks for Phobos and the moon are the same (within 2 radii of the crater center); however, the ejecta on Deimos are more dispersed (greater than or equal to 2 radii from the crater center).
The values obtained for brightness ratios between contiguous bright and dark areas on Deimos from Viking Orbiter images, together with the lack of a significant wavelength dependence of these ratios in the 0.4-0.6-micron range, are presently noted to be consistent with particle size fraction measurements of the Murchison CM meteorite. These data, and a near-coincidence of Deimos absolute reflectances with those of laboratory samples, render the present data consistent with both brighter and darker materials on Deimos being akin to carbonaceous chondrites; the material with smaller average particle size is associated with the brighter patches.
This article describes the reduced astrometric observations of Phobos and Deimos as derived from the Phobos Mission imaging data. These astrometric data span 2 months in 1989, contain 37 sets of spacecraft-centered, right ascension and declination observations of Phobos and 8 sets of Deimos. The phobos observations have an orbital position accuracy of about 2 km while the Deimos observations have an accuracy of about 10 km. The details of observation formulation and use for ephemeris improvement are given.
We have estimated the mass of Phobos, Deimos, and Mars using the Viking Orbiter and Mariner 9 tracking data. We divided the data into 282 arcs and sorted the data by periapse height, by inclination, and by satellite. The data were processed with the GEODYN/SOLVE orbit determination programs, which have previously been used to analyze planetary tracking data. The a priori Mars gravity field applied in this study was the 50th degree and order GMM-1 (Goddard Mars Model-1) model. The subsets of data were carefully edited to remove any arcs with close encounters of less than 500 km with either Phobos or Deimos. Whereas previous investigators have used close flybys (less than 500 km) to estimate the satellite masses, we have attempted to estimate the masses of Phobos and Deimos from multiday arcs which only included more distant encounters. The subsets of data were further edited to eliminate spurious data near solar conjunction (Nov.-Dec. 1976 and January 1979). In addition, the Viking-1 data from Oct. through Dec. 1978 were also excluded because of the low periapse altitude (as low as 232 km) and thus high sensitivity to atmospheric drag.
Compositional interpretations of new spectral measurements of Phobos and Deimos from Mars Express/OMEGA and MRO/CRISM and density measurements from encounters by multiple spacecraft support refined estimates of the moons' porosity and internal structure. Phobos' estimated macroporosity of 12-20% is consistent with a fractured but coherent interior; Deimos' estimated macroporosity of 23-44% is more consistent with a loosely consolidated interior. These internal differences are reflected in differences in surface morphology: Phobos exhibits a globally coherent pattern of grooves, whereas Deimos has a surface dominated instead by fragmental debris. Comparison with other asteroids .110 km in diameter shows that this correspondence between landforms and inferred internal structure is part of a pervasive pattern: asteroids interpreted to have coherent interiors exhibit pervasive, organized ridge or groove systems, whereas loosely consolidated asteroids have landforms dominated by fragmental debris and/or retain craters >1.3 body radii in diameter suggesting a porous, compressible interior.
One of the deep-space human exploration activities proposed for the post-Shuttle era is a mission to one of the moons of Mars, Phobos or Deimos. There are several options available to the mission architect for operations around these bodies. These options include distant retrograde orbits (DROs), Lagrange-point orbits such as halos and Lyapunov orbits, and fixed-point stationkeeping or "hovering." These three orbit options are discussed in the context of the idealized circular restricted three body problem, full-dynamics propagations, and a concept of operations. The discussion is focused on Phobos, but all results hold for Deimos
The origin of the martian moons Phobos and Deimos is obscure and enigmatic. Hypotheses include the capture of small bodies originally from the outer main belt or beyond, residual material left over from Mars' formation, and accreted ejecta from a large impact on Mars, among others. Measurements of reflectance spectra indicate a similarity to low-albedo, red D-type asteroids, but could indicate a highly space-weathered veneer. Here we suggest a way of constraining the near-surface composition of the two moons, for comparison with known meteoritic compositions. Neutron spectroscopy, particularly the thermal and epithermal neutron flux, distinguishes clearly between various classes of meteorites and varying hydrogen (water) abundances. Perhaps most surprising of all, a rendezvous with Phobos or Deimos is not necessary to achieve this. Multiple flybys suffice.
The presented trajectory design and analysis was performed for the Phobos and Deimos & Mars Environment (PADME) mission concept as part of a NASA proposal submission managed by NASA Ames Research Center in the 2014-2015 timeframe. The PADME spacecraft would be a derivative of the successfully flown Lunar Atmosphere & Dust Environment Explorer (LADEE) spacecraft. While LADEE was designed to enter low-lunar orbit, the PADME spacecraft would instead enter an elliptical Mars orbit of 2-week period. This Mars orbit would pass by Phobos near periapsis on successive orbits and then raise periapsis to yield close approaches of Deimos every orbit thereafter.
The orbital properties of the two small Martian satellites, Phobos and Deimos, are discussed, as well as those dynamical constants of Mars that can be determined from the satellite orbits. The secular acceleration of the mean motion of Phobos is shown to be very small. Of mechanisms that could cause any such acceleration, only tidal friction appears to be important. From the orbital evolution of the Martian satellites under tidal forces, Phobos and Deimos seem to have originated in nearly circular orbits of low inclination fairly close to the distance at which a satellite's orbital period is the planet's rotation period. It is proposed that the Martian satellites were born at the same time as Mars from equatorial dust clouds. The satellites are predicted to be locked in synchronous rotation, with their axes of minimum moment of inertia pointing on the average toward Mars, whereas their maximum axes are approximately normal to their orbit planes.
The problem was investigated of estimating the masses of Phobos and Deimos from Doppler and onboard optical measurements during the Viking extended mission. A Kalman filter was used to analyze the effects of gravitational uncertainties and nongravitational accelerations. These accelerations destroy the dynamical integrity of the orbit, and multibatch or limited memory filtering is preferred to single batch processing. Optical tracking is essential to improve the relative orbit geometry. The masses can be determined to about 10% and 25% respectively for Phobos and Deimos, assuming satellite densities of about 3 gr/cu cm.
This paper addresses the problem of estimating the masses of Phobos and Deimos from Doppler and onboard optical measurements during the Viking extended mission. A Kalman filter is used to analyze the effects of gravitational uncertainties and nongravitational accelerations. These accelerations destroy the dynamical integrity of the orbit and multi-batch or limited memory filtering is preferred to single batch processing. Optical tracking is essential to improve the relative orbit geometry. The masses can be determined to about 10% and 25% respectively for Phobos and Deimos, assuming satellite densities of about 3 g per cu cm.
Results of geodesy studies of Phobos and Deimos based on Mariner 9 imaging data are presented. This analysis includes a review of the surface coverage and high resolution pictures obtained and the determined sizes, shapes, topographies, and librations of the two Martian satellites. Also, exploration of Phobos and Deimos by missions such as Viking is discussed.
A series of lower- and higher-resolution pictures of Phobos and Deimos taken from Viking spacecraft is presented. The imaging data imply that the two asteroid-size bodies may indeed have originated in the asteroid belt and may be composed of primordial material from the solar nebula. There is now sufficient knowledge on Phobos and Deimos to consider them as candidate targets for future sample/return missions or for locating bases to monitor Mars.
Knowledge acquired from spacecraft observations of the surfaces of Phobos and Deimos is reviewed. Consideration is given to: the first spacecraft data - Mariner 7; the first systematic exploration - Mariner 9; surface texture and composition from Mariner 9 data; surface morphology from Mariner 9; and Viking results. A series of Viking photographs of Phobos and Deimos is presented.
Viking Orbiter images have shown downslope movement of loose material to be an important surface process on Deimos. Loose surface material moves downslope from prominent ridges and accumulates in topographic lows. In some areas, up to 10 m of surface material have been removed; in others, craters up to 200 m in diameter have been filled completely by material moving downslope. Brighter material associated with, and probably derived from crater rims, also moves downslope and forms tapered streamers up to 3 km in length which appear as prominent features on the satellite. The mechanism for downslope movement is uncertain, but thermal creep, micrometeroroid bombardment and impact-related seismic shaking may be involved. Certain craters show conspicuous infilling even though their prominent rims should prevent material moving downslope from reaching their interiors. Such fill must have been emplaced ballistically - the amounts of sediment suggest that over half of all ejecta produced on Deimos are retained on the satellite. Phobos appears to retain little ejecta and shows little evidence of downslope movement of debris.
Small scale surface features of the moons Deimos and Phobos were studied using star tracker observations made by the Mariner 9 and Viking orbiters. The whole-disk brightness/solar phase angle phase curves were developed out to a phase angle of 125 deg. An analysis was undertaken according to Lumme-Bowell theory to obtain accurate phase integrals zero-phase geometric albedos, and Bond albedos. The microstructural and particulate surface properties of the two moons were found to be very similar, as were the whole-body densities and the microphysical makeup, thereby suggesting a common origin. However, the presence of streamers on Deimos and the relatively smooth surfaces of both moons indicates a long-term influence of Mars producing surface morphologies different from what would occur with asteroids.