Becoming an ATLAS author usually takes about a year, but occasionally someone makes a significant contribution to a paper prior to fulfilling their authorship qualification and is allowed to sign as an author. That exception is rare, and it is even more rare for that person to be an undergraduate, but this is exactly what happened for Joseph Corrado. In recognition for his contributions to understanding the performance of the Missing Transverse Momomentum triggers, ATLAS colleagues and the Spokesperson granted exceptional authorship. Congratulations Joseph!
See the paper here: https://inspirehep.net/literature/1796953