Why was Voyager 2 an extremely efficient and productive probe? ...

[asan beg]

Why was Voyager 2 an extremely efficient and productive probe?
 
  What will be an ideal response?

Question 2

If the dark nebula are really dark, how do we know they are there?
 
  What will be an ideal response?

[bigsis44]

Answer to Question 1

Using gravitational assists, Voyager 2 was able to visit all four jovian planets, making many discoveries along the way. In effect, one spacecraft performed the equivalent of four missions.

Answer to Question 2

In some cases, they are not thick enough to block all light, so allow some red light through. Even if dense enough, they can still be seen in profile against rich star fields that lie behind them in the plane of the Milky Way.

[asan beg]

Thanks for the timely response, appreciate it

[raili21]

Excellent