As a planetary geologist (and a human who needs air to breathe), I can't go to the planetary bodies I study. I have to learn about them from afar, indeed, from millions of kilometers away, using remote sensing. As the name implies, remote sensing is the technique of collecting data on a subject without being in contact with it, usually in the context of airplane or satellite observation.
I worked on NASA's MESSENGER mission. MESSENGER orbited the planet Mercury for four years, collecting all sorts of data on its surface composition, topography, gravity, magnetic field, exosphere, internal structure, and much more. My work was on the analysis and interpretation of its X-Ray Spectrometer (XRS) data, which measured the abundances of important rock-forming elements.
During my postdoc, I used my geology background to compare the XRS chemical maps to other datasets in order to make inferences about Mercury's geological history. For example, here I've overlaid a Mg/Si ratio map over the basemap of Mercury and identified a correlation:
In this map, the color scale from red to blue indicates high to low Mg/Si, a number that gives geologists like myself important insight into the rock on the surface, and by extension, Mercury's geologic history. The black outlines indicate the boundaries of volcanic smooth plains, which have a very distinct composition. The red lines show areas surrounding craters where ejecta was deposited.
Our geochemical maps from the XRS dataset follow the shape of a volcanic lobe well. Irregularities consistent with impact craters suggest that the craters excavated material from beneath the smooth plains there, and it has a different composition. This is information that is impossible to get from Earth!
Remote sensing as a technique fascinates me. On Earth, satellites produce images of our world from a perspective that's totally different from how you and I typical view it on from the surface; for planetary exploration, it brings the planet to me since I can't go to it!