Title:
The Geologic History Of Water On Mars

Abstract:
Features such as valley networks and outflow channels suggest that at one time in the past Mars may have had liquid water on the surface. The interpretation has been that water was present for only a short time, outflow channels formed catastrophically, and the conditions necessary to support liquid water quickly died. Now, however, analyses of new lander and orbiter data are helping investigators to piece together a geologic history of water on Mars that is much more complex. It appears that initially there was a global arid climate capable of supporting rainfall while eroding impact craters as they formed. Gradually these conditions improved where rainfall intensified and a sustained hydrologic cycle became possible, thus forming the valley networks. Initiation of outflow channel formation began when enough water from the atmosphere had infiltrated into the regolith to create the necessary hydraulic head. As Mars lost its primordial atmosphere, favorable conditions
became more localized. Despite the evidence, problems remain in reconciling the geology with the "faint young sun paradox" as well as climatic models that make it difficult to create warmer surface environments on ancient Mars.


Dr. Craddock Bio sketch
Bob Craddock is one of the few people in the world who is a leading expert in both the geologic history of the Moon and Mars, and who also has experience working in the history of spaceflight. As a geologist at the Smithsonian Institution's National Air and Space Museum, he provided the first compelling evidence that rainfall occurred on early Mars, supporting the idea that Mars once had a warm and wet climate that was potentially suitable for life. He also proposed that Martian moons Phobos and Deimos were formed by a giant impact, which is becoming the accepted paradigm. He has conducted extensive Mars analog studies on the basaltic landscapes of Hawaii and fieldwork on the linear dunes in the Australian Outback. He received his first research grant at the age of 27, which makes him one of the youngest principal investigators in NASA history. In 2017, he was recognized by the American Geological Union as one of the most influential planetary scientists in the last 25 years. Dr.
Craddock also works with the Smithsonian Institution's Department of Space History and has helped to document the history of the manned and unmanned spacecraft collection. In 2003, his book on the Apollo 11 mission was awarded 1st prize for Best Educational Resource by the American Association of Museums. The fictional character Anne Clayborne in Kim Stanley Robinson's popular Red Mars science-fiction trilogy is based on Dr. Craddock's research background and scientific thinking.