Here's why:
* Adverbs modify verbs, adjectives, or other adverbs. "Excitingly" describes how something is done or how something feels.
* It ends in "-ly," a common ending for adverbs.
For example:
* "He spoke excitingly about his travels." (modifies the verb "spoke")
* "The news was excitingly unexpected." (modifies the adjective "unexpected")