Disney updated their Ultimate Spider-Man website with images of the characters involved.
With that, we get a look at what the new Nova, Sam Alexander, looks like under the helmet, in addition to the following description:
The hyperactive loose cannon of the group. Sam always feels like he has something to prove. Sam's powers derive from the Nova Force, which is channeled through his helmet. These powers include flight, enhanced durability, and the ability to absorb and release pulses of energy. However, Sam does not know the extent of his powers, let alone how they work.
Ultimate Spider-Man airs on DisneyXD April, 1st.