Crater: These bowl-shaped depressions on rocky and icy worlds are formed when an object hits the surface. The largest craters form during asteroid impacts. Smaller craters form both from smaller asteroid impacts and from the impact of boulders that are sent flying during large impacts. When the formation of one crater causes another crater to form it’s called a secondary crater.

Boulders & Rocks: These chucks of the Moon are often formed when a large asteroid excavates a crater and tosses material ranging in size from dust and gravel to many-meter across boulders. Some boulders may be found partially embedded in lava flows, or broken into pieces where they lay on the lunar surface. The rocks and boulders caught in lava flows allow us to measure various properties of the lava, such as its viscosity. When you measure the long axis of the boulder, you are helping us sort them by size. Below a certain size, however, the size measurements aren’t as important, so we just mark “rocks'” centers. 

Flows & Channels: The immense energies of asteroid impacts have the capacity to melt the lunar surface. This molten rock can flow across the cracter walls, floors, and surroundings, leaving behind both channels where it cut through the rock like a river, as well as tongues of lava where it comes to rest atop the surroundings. You may even see overlapping flows where a newer band of lava moves over an old band. 

Cracks: Just as the name implies, cracks are places where the surface of a lunar flow cracked open. This happens as the material cools and tried to contract. The splits in the rock are left behind where material contracted. 

In this project you’ll be mapping Tycho crater (below, Credit: NASA) and the nearby and smaller Little Lowell crater. Both of these craters are rich in melt deposits and littered with smaller craters formed both through secondary impacts and by smaller asteroids that have collided with the Moon’s surface over the years and millenia.