1. To better understand the surface features of Mars, do Interactive Exercise 7-2 on the Web. You can print out your results, if requested. 2. What evidence have astronomers accumulated that liquid...

1. To better understand the surface features of Mars, do Interactive Exercise 7-2 on the Web. You can print out your results, if requested.

2. What evidence have astronomers accumulated that liquid water once existed in large quantities on Mars’s surface? What evidence is there that water still exists, under its surface?