THEMIS images reveal the martian surface has more channels than scientists previously thought. The finding hints that erosion by water was more widespread, but may have been episodic.
Mapping of Mars at 100 meter (328 feet) per pixel resolution by the Thermal Emission Imaging System (THEMIS) on Mars Odyssey shows many more channels than known previously.
Some of the channels show a branching (dendritic) pattern that suggests they formed by water flowing over the surface. Several of these channel systems, located in the Echus and Melas Chasma regions, are highly developed and integrated, suggesting the water flowed for geologically long periods of time.
If water flowed over the surface, possible sources include atmospheric precipitation in the form of snow or rainfall.
Geological evidence leads scientists to give the Echus and Melas Chasma channel systems an age of Late Hesperian, which means they formed about 2.9 to 3.5 billion years ago. Scientists have assumed that only the oldest era in martian history, the Noachian, had an atmosphere thick enough to allow surface water.
Because the Noachian ended around 3.6 billion years ago, the channels found by THEMIS suggest either a thick atmosphere continued longer than scientists previously thought, or that wet periods occurred intermittently afterward.
- Mangold, N., C. Quantin, V. Ansan, C. Delacourt, and P. Allemand, Evidence for Precipitation on Mars from Dendritic Valleys in the Valles Marineris Area, Science, 305, 78-81, 2004.