Landing sites are determined using photogeology, which is the science of determining terrain characteristics from remotely-acquired images. Since photographs are the primary source of information about the martian surface, it is helpful to include some terms geologists use when describing terrain they see in photographs of Mars.

The short list here is in alphabetical order.

Aeolian: pertaining to, or caused by, the wind

albedo: a measure of the reflectivity of a surface, used to make a scientific estimate about surface composition

Amazonian: the third period of Martian history, from between 2 and 3.5 billion years ago to the present, characterized by less meteor bombardment and little geological activity

dust storm: the most noticeable weather event on Mars, it is an extended period (several months) of high winds that drive dust particles into a large portion of the atmosphere

ejecta: debris scattered by a meteor impact; ejecta is of particular interest to geologists since it provides the opportunity to sample multiple layers of the crust

flood channel: canyons or streams on Mars that are believed to be the result of liquid water flow over the surface; straight channels indicate that the water flow was rapid, and curved channels suggest a less catastrophic, more continuous process of erosion

fluvial sediment: any dirt, dust, or soil that falls to the bottom of a body of water when a fast moving, sediment-carrying stream encounters a large, slower-moving body of water

geothermal: this refers to the internal heat of a planet, with the implication that the heat indirectly created some kind of surface feature; present-day Mars has no active geothermal processes

Hesperian: the second period of Martian history, between 2 and 3.5 billion years ago, characterized by liquid surface water

lacustrine sediment: any sediment left behind after an ancient lake disappeared

Noachian: the first period of Martian history, between 3.5 and 4.6 billion years ago, characterized by heavy asteroid bombardment and geological activity