Answer to Question 1
To ensure that particles from the Sun are not deflected by Earth's magnetic field before the observatories can study them.
Answer to Question 2
Laboratory experiments and theory show that fusion produces neutrinos. Therefore, scientists predict that neutrinos should come from the Sun if fusion is occurring in its core. Theories predict how many and what type of neutrinos should be observed. Thus, the observations that confirm this prediction support the theory.