So that we do not contaminate it with microorganisms or garbage or other human stuff.

Strength: able to detect planets in a wide range of orbits, as long as orbits aren't face on
Limitations: yield only planet's mass and orbital properties
<em>A</em> - <em>B</em> = (10<em>i</em> - 2<em>j</em> - 4<em>k</em>) - (<em>i</em> + 7<em>j</em> - <em>k</em>)
<em>A</em> - <em>B</em> = 9<em>i</em> - 9<em>j</em> - 3<em>k</em>
|<em>A</em> - <em>B</em>| = √(9² + (-9)² + (-3)²) = √189 = 3√19