To express 5008 km in scientific notation, we want to represent it in the form \( a \times 10^n \), where \( 1 \leq a < 10 \) and \( n \) is an integer.
For 5008 km, we can write it as:
\[ 5.008 \times 10^3 \text{ km} \]
So, the expression of 5008 km in scientific notation is \( 5.008 \times 10^3 \) km.