Secular Acceleration Of Phobos Research Articles

Determination of spacecraft and phobos parameters of motion in the Phobos-Grunt project

For the needs of the upcoming flight to Phobos within the framework of the project Phobos-Grunt, a dynamical numerical theory of the motion of Phobos is developed on the basis of Earth-based and spacecraft (SC) optical measurements and Earth-based radio observations of the SC motion. The theory uses the most reliable astronomical constants. Within the framework of a unified dynamical model, an algorithm is proposed for the joint correction of Phobos and the spacecraft parameters of motion, among which are the secular acceleration of Phobos and its gravitational constant. The accuracy of the obtained ephemeris is estimated for the time of the SC arrival to Phobos.

On the dissipative factor of the Martian interiors

An estimate of the dissipative factor Q μ of the interior of Mars for models with liquid and solid cores is the main result of this paper. The secular acceleration of Phobos was used for this purpose. Weighting factors were calculated for the second-order tides, whose convolutions with the model dissipative factor for the Martian interior Q μ ( r) determine the dissipative factor for Mars Q μ for a fixed value of the period T 2 = 2 × 10 4 s. The weighting functions are small near the surface and large in the middle and lower mantle of Mars. The noted property of the weighting functions enables one to fairly reliably determine the mean value of the dissipative factor for the interior of Mars. These values for the most preferable models of Mars (with liquid and solid cores) are appreciably different: Q μ = 59–68 for the model with the liquid core and Q μ = 40–45 for the model with the solid core. These values are very small for solid silicate planets. It is explained by the fact that they correspond to the long periods, T 2 ∼ 2 × 10 4 s. This result leads us to the conclusion that the model with the liquid core is much more actual than the model with the solid core.

Commission 20: Positions and Motions of Minor Planets, Comets and Satellites (Positions et Mouvements des Petites Planetes, des Cometes et des Satellites)

The past triennium was characterized by important advances in several directions within the broad field of this Commission. Among the most exciting events were the Phobos 2 and Voyager 2 missions to Mars/Phobos and Neptune/Triton; their navigation was critically dependent on precise space- and ground-based observations as well as refined theoretical models of the motions in the solar system. Among many other achievements, the secular acceleration of Phobos was accurately measured and the dynamical analysis of the ring-like arcs at Neptune has just begun.

A possible servomechanism for matter distribution yielding flat rotation curves in spiral galaxies

A dynamic model of gravitational interaction was proposed earlier which results in a velocity-dependent drag. This drag can quantitatively explain the cosmological red shift in a stationary universe, the secular acceleration of Phobos, the secular retardation of the Earth's rotation without any problem of the controversial close approach of the Moon and the extra red shift at the solar limb. In the present paper it has been shown that such a velocity dependent inertial induction can act as a servomechanism for distributing matter in rotating spiral galaxies in such a way that flat rotation curves are obtained. A truncated thin disc model has been assumed, but the results are strongly in favour of the proposition.

Note on the paper by G. F. Schilling, ‘On exospheric drag as the cause of the supposed secular accelerations of phobos’

In his recent paper, Schilling [1964] postulated that the exosphere of Mars may exert a drag on Phobos of sufficient magnitude to account for the secular acceleration in longitude of this satellite as given by Sharpless [1945]. In his examination of the problem, Schilling cited the results of Kerr and Whipple [1954], which indicated that the tide in the mantle of Mars would be about 800 times too small to account for Phobos' secular acceleration. Schilling, consequently, did not consider the tidal effect as a significant contributor to the secular acceleration. F. F. Fish and I [Redmond and Fish, 1964] have re-examined the possibility of a tidal effect being responsible for Phobos' secular acceleration. We have calculated the minimum and the maximum values for the lunitidal interval in Mars that are required to account for the secular acceleration of Phobos; these are 1.1° and 4.4°, respectively. The uncertainty of the result is due to the uncertainties in the physical constants involved in the Mars-Phobos system.

The luni-tidal interval in Mars and the secular acceleration of Phobos

Phobos, the inner satellite of Mars, appears to perform a secular acceleration in longitude. The cause of this acceleration has not, as yet, been satisfactorily explained. The possibility of tidal friction in the solid body of Mars appears to be the most reasonable process; however, some authors dispute this contention. In this paper, a range of the luni-tidal interval required to account for the observed acceleration is calculated and found to be 1.1 to 4.4 degrees.