On a logarithmic scale, Pluto is 2 units from Mercury.
The default base for logarithms is 10, so saying that something is 2 units means that we are raising the base 10 to the power of 2.

Written as a logarithm, this would be:

Whatever number you plug into the function, the answer will be whatever power the base needs to be raised to in order to equal the original number.
For example:

because
