  We present archival observations of Main-belt asteroid (248370) 2005 QN173
(also designated 433P) that demonstrate this recently discovered active
asteroid (a body with a dynamically asteroidal orbit displaying a tail or coma)
has had at least one additional apparition of activity near perihelion during a
prior orbit. We discovered evidence of this second activity epoch in an image
captured 2016 July 22 with the Dark Energy Camera on the 4 meter Blanco
telescope at the Cerro Tololo Inter-American Observatory in Chile. As of this
writing, (248370) 2005 QN173 is just the 8th active asteroid demonstrated to
undergo recurrent activity near perihelion. Our analyses demonstrate (248370)
2005 QN173 is likely a member of the active asteroid subset known as Main-Belt
Comets, a group of objects that orbit in the Main Asteroid Belt which exhibit
activity that is specifically driven by sublimation. We implement an activity
detection technique, "wedge photometry," that has the potential to detect tails
in images of solar system objects and quantify their agreement with computed
anti-solar and anti-motion vectors normally associated with observed tail
directions. We present a catalog and an image gallery of archival observations.
The object will soon become unobservable as it passes behind the Sun as seen
from Earth, and when it again becomes visible (late-2022) it will be farther
than 3 au from the Sun. Our findings suggest (248370) 2005 QN173 is most active
interior to 2.7 au (0.3 au from perihelion), so we encourage the community to
observe and study this special object before December 2021.
