[delta_p_delta_x]

I'd say this is Source Sans. I'm sorry to trivialise Nebula's effort, but this seems much ado about nothing—they warped Source Sans' glyphs to be metrically compatible with Whitney, renamed the result 'Nebula Sans', got a developer and videographer to produce a whole website and mini-documentary on the matter and called it a day.

Excuse me?

[andai]

Reminds me of that Bill Gates quote, "I get the laziest programmer to do the hardest job because he'll find an easy way to do it."