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Clone from Phase 1doublePoint This 8-orbit mid-cycle proposal requests HST-STIS coronagraphic imaging to confirm a candidate wide-separation protoplanet seen around AB Aur. Near infrared data sets obtained over multiple epochs but only fully analyzed in May 2020 suggest a protoplanet whose colors-spectrum are distinguishable from scattered starlight and whose astrometry hints at orbital motion. Optical imaging roughly contemporaneous with recently scheduled ground-based extreme AO follow-up observations in Fall 2020-Winter 2021 are required. Only optical imaging can conclusively rule out the alternate hypothesisdoublePoint that this signal is a static disk feature. STIS is the only suitable optical high-contrast imaging instrumentdoublePoint its ability to yield unbiased detections of disks and point sources is unmatched by any ground or space-based facility. The analysis will decisively point to one of 3 interpretationsdoublePoint 1) thermal emission from a protoplanet formed by disk instability comma 2) an orbiting disk region heated and puffed up by an unseen planet comma or 3) a non-rotating disk feature whose pathological colors and near-IR variability can be mistaken for an orbiting protoplanet. Our STIS imaging multi-roll reference star differential imaging will easily achieve the required contrast to distinguish these scenarios. If interpretations 1) or 2) are supported comma this candidate would be HST.s first bona fide exoplanet direct imaging discovery comma given the recent controversy over Fomalhaut b. Moreover comma if 1) is correct comma the program rewrites the field.s understanding of planet formation comma decisively demonstrating the existence of multiple mechanisms for forming jovian planetsdoublePoint core accretion AND disk instability.