Despite five decades of analysis, many aspects of Mars crater morphology and evolution remain enigmatic, and it seems likely that new types of data will be needed to find the answers. As a final section in this chapter, we offer new approaches to solving these questions. Finding the answers will require a new orbital data set. Our recommendation is for a new data set that is comparable to many that have been collected for other planets in the Solar System and thus well within the capabilities of the National Air and Space Administration (NASA) and other international space agencies.

We take the younger examples, as illustrated in Chapter 4, and show some of the common ways that craters may be modified. Even craters that are classified as morphologically fresh may have experienced modification. This might take the form of chemical weathering of the floor or deposition of eolian or ice deposits within the crater cavity.

This chapter reviews impact craters throughout the Solar System, looking first at craters formed on Earth, where we have the best field knowledge. We then investigate craters formed on airless rocky bodies (the Moon and Mercury), where the cratering process is not affected by atmospheric effects. We follow this with a glimpse of craters on volatile-rich bodies that also lack an atmosphere, specifically Ganymede, 1 Ceres, and Charon. Here the target material is most likely water ice. Finally, we examine craters formed on bodies with thick atmospheres (Venus and Titan) to see what landforms may have been formed by the interaction of the projectile and the ejecta with the atmosphere.

Here we delve into greater detail of the morphology of individual craters. We review what the freshest, and hence the most likely youngest, craters look like.

We introduce the mode of formation of craters on planetary surfaces to set the stage for comparisons of crater morphology throughout the Solar System and on Mars specifically.

We review the principal types of Martian ejecta morphology. We then delve more deeply into the attributes of these ejecta deposits.

In this chapter, we explore more of the ejecta diversity. There is a much wider range of morphologies, particularly when smaller diameter craters or craters formed in the Northern Plains are considered.

We consider the types of information available to the planetary geomorphologist to investigate craters on Mars. This information primarily takes the form of images, as well as topographic and compositional data, collected from Mars orbit by a variety of spacecraft. We then review aspects of the chronology of Mars, from the earliest geologic epoch (the Noachian) until the most recent (the Amazonian), and how the rocks formed during these time periods are distributed across the planet. We discuss that what can be observed on Mars today is not the way in which the planet has appeared throughout its history.

Here we delve more deeply into differences in the ejecta and show some of the rare features and characteristics associated with the freshest examples of craters. When trying to understand the flow processes displayed by the ejecta, these features no doubt provide additional details on the emplacement process as well as illustrate the potential variability across the planet as a function of geographic location.

This chapter gives a brief overview of observational astronomy, using optical instruments and other wavelengths. We present a general formula for the increase in the limiting magnitude resulting from an increased telescope aperture. For light of particular wavelength, the diffraction from a telescope with a specific diameter sets a fundamental limit to the smallest possible angular separation that can be resolved.

The tendency for conservation of angular momentum of a gravitationally collapsing cloud to form a disk gives rise to the disk in our own galaxy, the Milky Way. We explore the main components, including the disk, bulge and halo. Studies of galaxy rotation curves lead us to the existence of "dark matter," the nature of which is unknown but is detectable through its gravitational interactions with normal, baryonic matter. We finish by exploring the super-massive black hole at the Milky Way’s center.

In reality stars are not perfect blackbodies, and so their emitted spectra don’t depend solely on temperature, but instead contain detailed signatures of key physical properties like elemental composition. For atoms in a gas, the ability to absorb, scatter and emit light can likewise depend on the wavelength, sometimes quite sharply. We find that the discrete energies levels associated with atoms of different elements are quite distinct. We introduce the stellar spectral classes (OBAFGKM).