The interpretation of in situ plasma measurements in space dusty plasmas

In situ plasma measurements are critical in the study of dusty plasmas in space. Diagnostic information on the charge state of embedded dust grains can be obtained by plasma instruments, such as Langmuir probes and plasma spectrometers. For technical reasons, plasma instruments are frequently placed on short booms, and remain close to the surface of the spacecraft, making the interpretation of these measurements difficult. For example, photoelectrons emitted from the spacecraft, and the probes themselves, can contaminate or even dominate the signals of low-energy electrons. We will discuss three effects relevant for dusty plasma studies: 1) spacecraft charging; 2) the possible formation of a plasma wake structure; and 3) the production of dust impact-generated plasmas. These effects depend on the ambient plasma and dust conditions, as well as the orientation of the instruments. We will provide quantitative estimates of these effects on the Cassini measurements near Enceladus.