INTERPLANETARY DUST AND NEAR-EARTH OBJECTS: A SOURCE OF NOISE FOR LISA?

The space-borne detector LISA (Laser Interferometer Space Antenna) will perform observations in the gravitational wave low frequency band (from some tenths of mHz to about 0.1 Hz), thus providing information complementary to those attained by ground-based detectors, limited at low frequencies by gravitational gradient fluctuations. Together with known instrumental noises, the space environment in which LISA will operate could be a source of further disturbances. Interplanetary dust grains, in particular, could introduce an additional phase noise due to the scattering of laser light by particles intercepted by laser beams. Large particles and minor bodies in the Solar System, in turn, could disturb the instrument, by partially or totally obscuring one of the laser beams or by gravitationally perturbing one of the spacecraft. The gravitational disturbance has been only partly discussed in the literature, while an analysis of the above phase noise has not yet been performed. The analysis of these potential sources of noise is the main goal of this thesis. After an introductory part about gravitational waves, detection strategies, LISA and sources expected to emit in the low frequency band, also providing some details about the "verification binaries", whose signal could be detected by LISA within one month of scientific operations, we introduce the background needed for the above analysis. Namely, we discuss the dust cloud properties, with emphasis on distributions and meteoroid flux models that will be adopted, and a NEO model, together with some spin-offs. Based on the retrieved results, we estimate the flux of sub-km sized bodies in the LISA region and the probability of a close approach between these objects and one of the spacecraft. Some events per year leading to a partial or total beam obscuration have been found to potentially perturb the apparatus. Concerning the gravitational disturbance, the dust contribution is negligible, while a negligible to significant event rate has been found for large particles and minor bodies, depending on details of modelling. An update of NEO statistics has also been performed to estimate the number of NEOs potentially contributing to the gravitational disturbance. The phase noise due to interplanetary dust has been discussed in the framework of the Mie theory of scattering. To perform a quantitative estimate, the publicly available miex scattering code (upgraded to fix a bug discovered during preliminary tests) has been used together with an IDL code written by the author. The noise spectrum, its dependence on particle bulk density, chemical composition, particle size distribution, dust number density and possible fluctuations in the number density distribution have been discussed. Results show that the investigated source of noise is negligible in all the analyzed cases. To summarize, the presence of dust in the LISA region has been found to be negligible, while large particles and minor bodies could play some role in the context of the investigated noise sources