What observational evidence supports the idea that Mercury once shrank by some 20 kilometers in radius?
A) the presence of many impact craters
B) the characteristics of the Caloris Basin
C) Mercury's unusually high density
D) the presence of many long, tall cliffs
Question 2
The primary source of the Sun's energy is:
A) oxidation of carbon in the core.
B) gravitational collapse of the helium coreward.
C) dark energy.
D) the strong force fusing hydrogen into helium.
E) the weak force creating energy from uranium decay.