The Altered Scale

Testing us, Sport? I'd give you about 90%.... points were deducted for using an unusual key signature :)

Yes, it's the seventh 'mode' of the ascending melodic minor - also known as the 'superlocrian' mode or scale.

But a couple of things....

First, it wouldn't be in C. Since it's the seventh mode, that suggests the 'root' scale would be based on Db; since it's a mode of a minor scale, the relative major key would then be Fb, and that demands a key signature of eight flats. You don't see eight flats in music outside of textbooks; publishers abandoned it about 150 years ago.

This scale would normally occur in the key of E, making the relative minor C#, and the seventh degree of the minor scale B#. Raising the sixth and seventh gives your scale:

B#-C#-D#-E-F#-G#-A#-B#

Second, although the scale is normally used over altered dominants, you have to be a little careful... because the third of the scale is flatted, it's minor seventh in character, rather than strictly dominant. It'll work fine over #9 or b9 chords, but you can have some awkward conflicts over dominant chords with natural thirds and unaltered ninths. In situations where the third of the chord is natural, and the ninth isn't altered, you're better off with the whole tone scale:

C-D-E-Gb-Ab-Bb-C

This fits every alteration except the ninth: #4 (Gb), b5 (Gb), and #5 (Ab) without including the b9 interval between your scale and the major third. It also preserves the original tritone (E-Bb) that gives the underlying chord its dominant quality. You keep the dissonance without overdoing it.

To your basic question, the reason we use flats (or sharps) is to maintain the interval relationships when changing to a new key. In this case, the superlocrian has a pattern of H-W-H-W-W-W-W. Moving this pattern to any other key requires sharps or flats to keep the relationships of each scale degree to the tonic intact.

But hey, thanks for playing stump the theory board!