These kids know more about geology and space travel than most people, knowledge they showed during a visit Friday from a NASA scientist. The fourth- and fifth-graders at Cedar Wood Elementary School in Mill Creek had lots of questions for Joy Crisp, a scientist working on the Mars Exploration Rover Project set for launch in 2003, who discussed her life’s work with rocks. “How far does the RAT grind into the rock?” asked Andrew Liechty, a fifth-grader. His classmates didn’t need to be told that RAT is an acronym for rock abrasion tool, a diamond-studded device on the yet-to-be-named land rovers that will allow scientists to drill and study the insides of rocks on Mars.