[Old Pedant]

First of all, if you use a <select> as I showed, you avoid the problem of upper/lower case.

Secondly, a switch( ) is by far not the most elegant way to do this. See my scheme.

But if you must use a switch and you must allow human fallible input, then you could do this:

switch ( planet )
{
    case "Mercury": case "mercury": case "MERCURY":
        info = "The planet closest to the sun.";
        break;
    case "Venus": case "venus": case "VENUS":
        ...
}

Do *NOT* forget the break after each same-case-action set!

But better than that would be:

switch ( planet.toLowerCase() )
{
    case case "mercury": 
        info = "The planet closest to the sun.";
        break;
    case "venus": 
        ...
}

And, again, don't forget the breaks.

************

EDIT: See? If I didn't write so much, I wouldn't be last to the party. <grin/>