Comparison of masses of asteroids derived by dynamical methods (mainly from mutual perturbations of asteroids with close encounters) with ones obtained by astrophysical methods is carried out. It is shown that the asteroids with masses >10^-12·M markedly affect the orbit of Mars on the level of accuracy of ranging measurements to the martian landers Viking-1,2 and Pathfinder. The dynamical and astrophysical methods seem to be complimentary. An attempt is undertaken to extent the list of 300 perturbing asteroids accounted in the DE405 ephemerides. Several tests were tried in which the different sets of perturbing asteroids and their masses (up to 351 simultaneously integrating asteroids) varied when processing the observations of the landers. Overall perturbing effect of remaining asteroids (the 300 biggest ones are excluded) has been modeled as being caused by a ring in the ecliptic plane. Mass M and radius R of the ring are estimated as M518*10^-12 ·M