We report on initial observations made by the Langmuir Probe and Waves relaxation soundingexperiment on board the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. These measurements yield the ionospheric thermal plasma density, and we use these data here for an initial survey of its variability. Studying orbit‐to‐orbit variations, we show that the relative variability of the ionospheric plasma density is lowest at low altitudes near the photochemical peak, steadily increases toward higher altitudes and sharply increases as the spacecraft crosses the terminator and moves into the nightside. Finally, despite the small volume of data currently available, we show that a clear signature of the influence of crustal magnetic fields on the thermal plasma density fluctuations is visible. Such results are consistent with previously reported remote measurements made at higher altitudes, but crucially, here we sample a new span of altitudes between ∼130 and ∼300 km using in situ techniques. Key Points Data from the Langmuir Probe and Waves instrument reveal density structures in the Mars ionosphere MAVEN samples an altitude range which previously has only been sparsely explored in situ MAVEN/LPW data also reveal the stabilizing influence of intense crustal fields