The Milky Way–Large Magellanic Cloud interaction has reshaped our understanding of how massive satellites drive disequilibrium in their host systems — and Andromeda (M31) tells a strikingly parallel, yet distinct, story. With 6D phase space data now available for nearly a dozen M31 satellites, we can for the first time begin to reconstruct the complex interaction history of the M31 system in detail. In this talk, I will present orbital modeling results for M31 and its most massive satellite, M33. Contrary to the long-held assumption that M33 experienced a recent close encounter with M31, I will show that M33 is most likely on its first infall into M31's halo — a result further corroborated by M33's untruncated HI disk and the orbital histories of cosmological analogs. I will also present preliminary orbital results on M32, a prominent dwarf elliptical galaxy situated near M31's disk. Drawing on insights from the MW-LMC system, I will discuss how M33's passage may be displacing M31's barycenter and influencing the dynamics of its broader satellite population, and what this means for interpreting M31's assembly history.

Speaker: Ekta Patel (Villanova University)

The 2026 Spring Colloquium talks are held on Wednesdays at 3:00 PM. This colloquium is hosted by STScI and will be held as an in-person and virtual event.

You may join in person at STScI’s John N. Bahcall Auditorium or virtually on the STScI Research YouTube channel.

Please direct questions or comments to contact above. The 2026 Spring Colloquium members are: Nimisha Kumari (STScI), Elena Manjavacas (STScI), Jack Neustadt (JHU), Kevin Schlaufman (JHU), Adam Smercina (STScI), Ethan Vishniac (JHU).