DI-aries panoramic energy-mass spectrometer of ions for the Phobos-Grunt project

One of the main goals of the Phobos-Grunt project is to analyze the surface composition of Phobos. Plasma methods of the studies make it possible to complete direct surface studies with measurements of the minor components of the solar wind, which are produced when a material sputtered from the surface of Phobos is ionized. The surface of Phobos is sputtered under the action of solar wind protons, energetic ions, hard solar radiation, and meteorites. In addition to the studies of Phobos, the experiment also includes the study of the interaction between the solar wind and Mars. An energy-mass spectrometer, which makes it possible to measure instantaneously complete unobscured distribution of the flux of different ions in the hemisphere, has been designed based on the new CAMERA analyzer of charged particles proposed previously (Vaisberg et al., 2001, 2005; Vaisberg, 2003). The instrument’s electro-optics model and the results of the numerical and laboratory tests are described in this paper. Such an instrument can be used in magnetospheric studies and to study different objects of the Solar System.     

AOST: Fourier spectrometer for studying mars and phobos

An AOST Fourier spectrometer of the Phobos-Soil project is intended for studying Mars and Phobos by means of measurements of IR radiation spectra of the Martian surface and atmosphere, the Phobos surface, and the spectrum of solar radiation passing through the Martian atmosphere on its limb. The main scientific problems to be solved with the spectrometer on Mars are measurements of methane content, search for minor constituents, and study of diurnal variations in the temperature and atmospheric aerosol. The spectrometer will also study the Martian and Phobos surface both remotely and after landing. The spectral range of the instrument is 2.5?C25 ??m, the best spectral resolution (without apodization) is 0.6 cm^?1, and the instantaneous field of view is 2.5°. The recording time of one spectrum is equal to 5 s in solar observations and 50 s in observations of Mars and Phobos. The instrument has self-thermal stabilization and two-axis pointing systems, as well as a built-in radiation source for flight calibration. The spectrometer mass is 4 kg, and power consumption is up to 13 W. Scientific problems, measurement modes, and, briefly, engineering implementation of the experiment are discussed in this work.     

Primeval substance delivery from Phobos to the Earth—the Phobos-Soil project: Ballistics,navigation, and flight control

This paper is concerned with the problems of ballistics, navigation, and flight control of the space craft (SC) in the Phobos-Grunt mission. We consider an insertion into the Earth-Mars transfer trajectory, the Earth-Mars transfer, the strategy of corrections, and the accuracy of the insertion of the SC into Martian orbit. During the orbital maneuvering stage in the sphere of influence of Mars, we set up a scheme that allows for the insertion of the SC, with the prescribed accuracy, into a point 80-km above the Phobos surface over the theoretical landing area. We specify the sequence for a controlled landing and provide methods for solving the problems of navigation and control during a self-c ontained landing. We also consider the liftoff from Phobos, insertion into the parking orbit, and the Mars-Earth transfer.     

Orbital history of the Martian satellites with inferences on their origin

Recent Viking results indicate the Martian satellites are composed of carbonaceous chondritic material, suggesting that Phobos and Deimos were once asteroids captured by Mars. On the other hand, the low eccentricities and inclinations of their orbits on the equator of Mars argue against that hypothesis. This paper presents detailed calculations of the tidal evolution of Phobos and Deimos, considering dissipation in both Mars and its satellites simultaneously and using a new method applicable for any value of the eccentricity. In particular, including precession of the satellites' orbits indicates that they have always remained close to their Laplacian plane, so that the orbital planes of Phobos and Deimos switched from near the Martian orbital plane to the Martian equator once the perturbations due to the planetary oblateness dominated the solar perturbations, as they do presently. The results show that Deimos has been little affected by tides, but several billion (10⁹) years ago, Phobos was in a highly eccentric orbit lying near the common plane of the solar system. This outcome is obtained for very reasonable values of dissipation inside Mars and inside Phobos. Implications for the origin of the Martian satellites are discussed.     

Ballistic capture into distant retrograde orbits around Phobos: an approach to entering orbit around Phobos without a critical maneuver near the moon

This paper discusses an approach for designing missions to Phobos that do not require a critical maneuver in proximity of the moon. A low-energy transfer is designed that utilizes the aspherical mass distribution of Phobos to capture a spacecraft into a distant retrograde orbit (DRO) for the mission duration. The process for generating stable DROs in the Mars–Phobos system is discussed along with the method for generating and surveying a set of ballistic capture trajectories (BCTs) for DROs with altitudes between 0.5 and 14 km above Phobos. Statistical analysis of the BCT set reveals options for designing a mission to the desired DRO. This approach can be used in any three-body system when a significant perturbation is present, such as Phobos’ aspherical co-rotating gravity field.     

The UV environment of the Beagle 2 landing site: detailed investigations and detection of atmospheric state

December 25th 2003 will see the Beagle 2 lander arrive at the surface of Mars in the Isidis region, allowing for the first time in situ measurements of ultraviolet (UV) flux directly from the surface of Mars through the use of a sensor designed as part of a miniaturised environmental package. The expected conditions the sensor will experience are studied here, and the detection signatures for phenomenon such as dust devils, H₂O clouds ands near-surface fogs are presented. The beginning and end of mission surface fluxes show little variation, though the period towards mid-nominal mission does experience a maximum in total daily dose levels. Diurnal profiles are calculated highlighting the effects of increased scattering towards shorter wavelengths. A possible dust storm scenario is presented, and the effect upon component UV fluxes is shown to reverse the relative contributions of direct and diffuse components of the total UV flux. The presence of cloud formation above the landing site will be detectable though the observation of elevated diffuse/direct flux ratios. Near-surface morning fogs show a characteristic ‘dip’ in the morning profile when compared to clear mornings, allowing their detection on cloud-free mornings through post-event analysis of long term data. Predicted Phobos eclipses are investigated at each of the sensor centre wavelengths, and show greatest reduction in relative intensity at short wavelengths. Observations of near-miss eclipse events will also be possible, through monitoring of the diffuse UV flux. Dust devil encounters are shown to create a double minima lightcurve, with the depth of the minima dependent upon the total dust loading of the vortex. The effects of these changing conditions on DNA-weighted irradiances are investigated. Possible dust storms provide the greatest increase in biological protection, whereas expected cloud formations at the Beagle 2 site are found to offer negligible protection. Within just five minutes of landing >95% of any Bacillus subtilis-like bacteria present on the surface of the craft will have lost viability.     

Internal stresses in phobos and other triaxial bodies

The unusual dynamical behavior of Phobos, its strange appearance, and its mysterious network of grooves all make it an intriguing object. Geophysical studies, though, have been hampered by the lack of suitable theories applicable to nonspherical bodies. In this paper the Martian satellites are modeled as homogeneous, elastic triaxial ellipsoids subject to tidal, rotational, and self-gravitational stresses. A novel semianalytical treatment then gives the stress and strain fields throughout their interiors. Yield phenomena and their possible surface expressions are also investigated. The results indicate that Phobos and Deimos have always been stable with respect to tidal fracture or disruption, but that Phobos will probably break up before colliding with Mars. Applications of the new formulation to other nonspherical bodies in the solar system are also discussed.     

GETEMME—a mission to explore the Martian satellites and the fundamentals of solar system physics

GETEMME (Gravity, Einstein??s Theory, and Exploration of the Martian Moons?? Environment), a mission which is being proposed in ESA??s Cosmic Vision program, shall be launched for Mars on a Soyuz Fregat in 2020. The spacecraft will initially rendezvous with Phobos and Deimos in order to carry out a comprehensive mapping and characterization of the two satellites and to deploy passive Laser retro-reflectors on their surfaces. In the second stage of the mission, the spacecraft will be transferred into a lower 1500-km Mars orbit, to carry out routine Laser range measurements to the reflectors on Phobos and Deimos. Also, asynchronous two-way Laser ranging measurements between the spacecraft and stations of the ILRS (International Laser Ranging Service) on Earth are foreseen. An onboard accelerometer will ensure a high accuracy for the spacecraft orbit determination. The inversion of all range and accelerometer data will allow us to determine or improve dramatically on a host of dynamic parameters of the Martian satellite system. From the complex motion and rotation of Phobos and Deimos we will obtain clues on internal structures and the origins of the satellites. Also, crucial data on the time-varying gravity field of Mars related to climate variation and internal structure will be obtained. Ranging measurements will also be essential to improve on several parameters in fundamental physics, such as the Post-Newtonian parameter ?? as well as time-rate changes of the gravitational constant and the Lense-Thirring effect. Measurements by GETEMME will firmly embed Mars and its satellites into the Solar System reference frame.     

Dynamics of Mars-orbiting dust: Effects of light pressure and planetary oblateness

This paper deals with dynamics of impact ejecta from Phobos and Deimos initially on near-circular equatorial orbits around Mars. For particles emitted in a wide size regime of 1 micron and greater, and taking into account the typical particle lifetimes to be less than 100 years, the motion is governed by two perturbing forces: solar radiation pressure and influence of Mars' oblateness. The equations of motion of particles in Lagrangian non-singular elements are deduced and solved, both analytically and numerically, for different-sized ejecta. We state that the coupled effect of both forces above is essential so that on no account can the oblateness of Mars are be neglected. The dynamics of grains prove to be quite different for the ejecta of Phobos and Deimos. For Deimos, the qualitative results are relatively simple and imply oscillations of eccentricity and long-term variations of orbital inclination, with amplitudes and periods both depending on grain size. For Phobos, the dynamics are shown to be much more complicated, and we discuss it in detail. We have found an intriguous peculiar behavior of debris near 300 µm in size. Another finding is that almost all the Phobos ejecta with radii less than 30 µm (against the values of 5 to 20 µm adopted earlier by many authors) should be rapidly lost by collisions with martian surface. The results of the paper may be the base for constructing an improved model of dust belts that presumably exist around Mars.     

Photometric modelling of the Martian dust rings

There are reasons to expect that Mars is surrounded by a region of dust, similar to rings, originating from the bombardment of Phobos and Deimos by meteroids. Using a simple radiative transfer model, we have investigated the angular distribution and the absolute values of the solar radiance scattered by such a dust region, to the purpose of assessing the possibilities and limitations of future photometric searches after the circummartian dust. Our model values of the number density of the dust grains in the space around Mars and of their size distribution have been derived from the results obtained by other authors. The single-scattering albedo of the dust grains has been deduced from the reflectance spectra of Phobos, taken by the spacecraft Phobos 2. Calculations, carried out for a few phenomenological phase functions, have shown that in the visible the radiance scattered by the rings is well within the detectability range of a modern sensible photometer, so that the prospectives for photometric search for the Martian dust rings are optimistic. Furthermore, our results confirm that the dust region could not be observed by the Viking cameras and this supports o our assumptions regarding the optical properties of the circummartian grains.     

Capture of Phobos and Deimos by photoatmospheric drag

It is suggested that Phobos and Deimos are carbonaceous asteroids captured by drag in an extended protoatmosphere of solar composition. The time scales for regularization of the orbital parameters are estimated, and found to be of the order of a few years. The atmosphere is modeled as a slowly-rotating condensation in the solar nebula; the surface pressure should be a few tenths of a bar. Capture and evolution by such an atmosphere are found to be improbable. The odds are greatly improved if the atmosphere is rapidly rotating or if the pressure is 1 to 2 orders of magnitude greater. Escape of the atmosphere, after removal of the nebular pressure, takes a few years, depending on the solar heat input. But it relaxes much more quickly to a state with negligible density at satellite altitudes. This relaxation is taken as the event that leaves the satellites in stable orbits. Previous candidates presumably were added to the solid body of Mars, and later ones were not captured.     

Search for Phobos and Deimos gas/dust tori using in situ observations from Mars Global Surveyor MAG/ER

More than 490 elliptical aerobraking and science phasing orbits made by Mars Global Surveyor (MGS) in 1997 and 1998 provide unprecedented coverage of the solar wind in the vicinity of the orbits of the martian moons Phobos and Deimos. We have performed a comprehensive survey of magnetic field perturbations in the solar wind to search for possible signatures of solar wind interaction with dust or gas escaping from the moons. A total of 1246 solar wind disturbance events were identified and their distribution was examined relative to Phobos, the Phobos orbit, and the Deimos orbit. We find that the spatial distribution of solar wind perturbations does not increase near or downstream of Phobos, Phobos’ orbit, or Deimos’ orbit, which would have been expected if there is significant outgassing or dust escape from the martian moons. Of the 1246 magnetic field perturbation events found in the MGS data set, 11 events were found within 2000 km of the Phobos orbit, while three events were found within 2000 km of the Deimos orbit. These events were analyzed in detail and found to likely have other causes than outgassing/dust escape from the martian moons. Thus we conclude that the amount of gas/dust escaping the martian moons is not significant enough to induce detectable magnetic field perturbations in the solar wind. In essence we have not found any clear evidence in the MGS magnetic field data for outgassing or dust escape from the martian moons.     

TV system for navigation and guidance

A TV system for navigation and guidance (TVSNG) has been designed for solving the navigation and scientific tasks of the Phobos-Grunt mission. It consists of two narrow-angle and two wide-angle television cameras. Each camera has a built-in processor for the real-time processing of received images. The program of TVSNG observations includes three modes: Imaging of Stars, Sequential Imaging, and Landing. The first two modes will be used to calibrate the TVSNG against the stars, to take images of Phobos and Mars, and to detect the dust rings of Mars. In the Landing mode, the height and velocity components of the spacecraft during the landing on Phobos will be measured, and an autonomous selection of the landing site will be made.     

“Bumerang” Must Return to Earth

Solar System Research - The “Bumerang” space mission to the satellites of Mars is discussed. The purpose of the mission is to study the satellites and return of soil samples from Phobos...     

Towards a more habitable Mars — or — the coming martian spring

Two schemes are presented in which matter is moved closer to Mars so as to increase the equinoctal precession period of Mars. In such a way the Martian springs, during which Mars is habitable in the long winter model of Sagan (1971), could be extended and, in fact, prolonged indefinitely. The schemes involve using solar energy to move the satellite Phobos and/or material from the asteroid belt. Difficulties exist with the proposals but they are presented to stimulate discussion.     

Upper limits for the Martian exospheric number density during the Planet B/Nozomi mission

Dissociative recombination (DR) of ionospheric O₂⁺ ions is an important source of suprathermal atomic oxygen in the exosphere as previous studies about the Martian upper atmosphere have shown. Because of the weaker gravitational attraction a hot oxygen corona on Mars should be denser than that observed on Venus. Since the most important mechanism for the production of the hot oxygen atoms in the Martian exosphere is DR, we investigated the variability of this production mechanism depending of solar activity. The Japanese Nozomi spacecraft will have the possibility to detect with the neutral mass spectrometer (NMS) for the first time in-situ the theoretically predicted hot oxygen corona on Mars, if the corona number density above the cold background atmosphere is of the order of 10,000 cm⁻³. Due to a problem in the propulsion system Nozomi failed its planned arrival rendevouzs with Mars in October 1999 and will, therefore, arrive at the red planet not before January 2004. Solar activity will reach its maximum in 2001, so the related production rate of hot oxygen atoms will be in the medium range during the new arrival date of Nozomi. We used the ionospheric profiles from the Viking mission for low solar activity conditions (F_10.7≈70) and the Mariner 9 mission with a solar activity of about 120 for medium solar wind activity. The latter is comparable to the level we expect for the Mars arrival of Nozomi. The resulting influence of the hot oxygen corona number density distribution was calculated with a Monte Carlo technique. This technique is used to compute a hot particle density distribution function. We studied the atomic diffusion process in the Martian atmosphere by simulating the collision probability, particle direction and energy loss after collisions by generating random numbers. Compared to previous studies we have improved the Monte Carlo model by using more and smaller altitude steps and more detailed treatment of particles with a temporary downward motion. This has resulted in an increased amount of collisions and a shift to lower energies in the energy spectrum. Our results show that the hot oxygen component should begin to dominate above the cold background atmosphere at an altitude of about 500 km above the Martian surface. The NMS instrument on board of Nozomi should detect the hot oxygen component after its arrival at Mars in January 2004, at an altitude of about 600 km above the Martian surface. Since the solar activity will decrease during the mission the measurements during the first orbits will be the most significant ones. The first in-situ measurements of the hot oxygen number density would be very important for adjusting atmospheric escape models by separating ballistic, satellite and escape trajectories of the hot oxygen atoms, which are significant for studies of the evolution and solar wind interaction of the Martian atmosphere.     

Motion of blocks on the surface of Phobos: New constraints for the formation of grooves

Although grooves are common on asteroids, on Phobos the grooves have been the subject of various formation hypotheses for two reasons: the fact that Phobos is orbiting around Mars close to the Roche limit, implies an unusual gravity environment as well as the presence of the huge crater impact, Stickney, which seems to be related at least to a family of grooves. Among many hypotheses, it has been suggested that the grooves could have been dug by rolling Stickney ejecta, but this hypothesis was questioned using two main arguments: no block was observed at the end of the grooves, nor do they run downslope. Thus, the study of surface and near surface dynamics on Phobos can clarify the soundness of these controversial arguments.The present study explores this idea by computing the trajectory of a test mass gliding on the surface of Phobos for any initial position and velocity. An ellipsoidal model of Phobos is used for both the gravity and surface geometry, and several orbiting distances from Mars are considered. It is shown that, due to the Phobos rotation, the trajectories generally do not run downslope even for velocities as low as ∼1 m/s. In consequence the corresponding argument against the rolling blocks hypothesis is not applicable. This hypothesis, however, is clearly ruled out for the sets of parallel grooves in the polar regions because of the curvature of the computed trajectories. On the contrary the trajectories issued from the rim of Stickney close to the equator, with velocities of a few m/s, show similitude with the corresponding groove patterns, in particular for the east–west asymmetry. In some conditions the trajectories leave the surface, which may account for regions free of grooves and for trails without blocks at the end. Consequently, the rolling block hypothesis cannot be rejected outright until further analysis is carried out. Damping of the motion on the regolith is simulated introducing a solid damping coefficient in the equations. A relatively small but not unrealistic coefficient of ∼0.1 accounts for the length of the long main western hypothetic block trails. The simulations with damping confirm that the trajectories turn downslope only at the very end for velocities ?1 m/s, but valuable comparison with the observations requires a better model.     

Tidally induced surface displacements, external potential variations, and gravity variations on Mars

We have used and extended Roosbeek’s tidal potential for Mars to calculate tidal displacements, gravity variations, and external gravitational potential variations. The tides on Mars are caused by the Sun, and to a lesser degree by the natural satellites Phobos (8%, relative to the Sun) and Deimos (0.08%, relative to the Sun). To determine the reaction of Mars to the tidal forcing, the Love numbers h, l, and k and the gravimetric factor δ were calculated for interior models of Mars with different state, density, and radius of the core and for models which include mantle anelasticity. The latitude dependence and frequency dependence of the Love numbers have been taken explicitly into account. The Love numbers are about three times smaller than those for the Earth and are very sensitive to core changes; e.g., a difference of about 30% is found between a model with a liquid core and an otherwise similar model with a solid core. Tidal displacements on Mars are much smaller than on Earth due to the smaller tidal potential, but also due to the smaller reaction of Mars (smaller Love numbers). For both the tidal diplacement and the tidal external potential perturbations, the tidal signal is at the limit of detection and is too small to permit properties of Mars’s interior to be inferred. On the other hand, the Phobos tidally induced gravity changes, which are subdiurnal with typical periods shorter than 12 h, can be measured very precisely by the very broad band seismometer with thermal control of the seismological experiment SEIS of the upcoming NetLander mission. It is shown that the Phobos-induced gravity tides could be used to study the Martian core.     

Accurate Mars Express orbits to improve the determination of the mass and ephemeris of the Martian moons

The determination of the ephemeris of the Martian moons has benefited from observations of their plane-of-sky positions derived from images taken by cameras onboard spacecraft orbiting Mars. Images obtained by the Super Resolution Camera (SRC) onboard Mars Express (MEX) have been used to derive moon positions relative to Mars on the basis of a fit of a complete dynamical model of their motion around Mars. Since, these positions are computed from the relative position of the spacecraft when the images are taken, those positions need to be known as accurately as possible. An accurate MEX orbit is obtained by fitting two years of tracking data of the Mars Express Radio Science (MaRS) experiment onboard MEX. The average accuracy of the orbits has been estimated to be around 20–25 m. From these orbits, we have re-derived the positions of Phobos and Deimos at the epoch of the SRC observations and compared them with the positions derived by using the MEX orbits provided by the ESOC navigation team. After fit of the orbital model of Phobos and Deimos, the gain in precision in the Phobos position is roughly 30 m, corresponding to the estimated gain of accuracy of the MEX orbits. A new solution of the GM of the Martian moons has also been obtained from the accurate MEX orbits, which is consistent with previous solutions and, for Phobos, is more precise than the solution from the Mars Global Surveyor (MGS) and Mars Odyssey (ODY) tracking data. It will be further improved with data from MEX-Phobos closer encounters (at a distance less than 300 km). This study also demonstrates the advantage of combining observations of the moon positions from a spacecraft and from the Earth to assess the real accuracy of the spacecraft orbit. In turn, the natural satellite ephemerides can be improved and participate to a better knowledge of the origin and evolution of the Martian moons.     

Principal moments of inertia and secular love number of Phobos

A dynamic homogeneous model of Phobos is used: its boundary is an equipotential surface specified by the second zonal and the second sectorial harmonics plus the constant part of the tidal potential due to Mars. The principal moments of inertia, the hydrostatic second zonal harmonic and the secular Love number of Phobos have been estimated. They support the hypothesis that Phobos is formed out of primordial matter by accretion in orbit.