1. The surface of Mars is barren like a desert and literally covered with rocks.

2. Rocks that formed in the presence of water could contain traces of past life existing within them.

3. Space probes have been visiting Mars for over four decades.

4. The three purposes of this mission are to map minerals and elements, look for water, and study the planet's radiation environment.

5. Big Joe is the large rock pictured with the Viking lander.

6. Viking landers (1 and 2) were the first spacecraft to land on another planet.

7. The southern hemisphere is where most craters can be found.

8. Any impact that occurred in the northern hemisphere long ago was covered by past lava flows.

9. Hellas Basin is the largest impact crater on the surface of Mars.

10. Polar ice spreads and retreats with the seasons.

11. Olympus Mons is a shield volcano.

12. Olympus Mons has a diameter of 374 miles.

13. The height of Olympus Mons is 16 miles.

14. Olympus Mons is comparable to the state of Arizona in size.

15. Valles Marineris is a large canyon system on the surface of Mars that is 2500 miles long.

16. Valles Marineris, on average, is about 4 miles deep.

17. Valles Marineris was formed by tectonic activity that produced a large crack in the surface of Mars.

18. Phobos means fear.

19. Phobos orbits around Mars three times per day.

20. Deimos has a diameter of 8 miles.