In recent years, two entirely new classes of planetesimals have been discovered in the solar system: interstellar interlopers and dark comets. These still-enigmatic objects are challenging our understanding of the behavior and properties of comets and asteroids. In this talk, I will review what has been learned to date from the known interstellar objects and dark comets, highlighting the attributes that are difficult to reconcile with previous models of planetesimal behavior. In particular, I will focus on the discovery and characterization of the third interstellar object 3I/ATLAS. I will discuss its properties in the context of the host population, with a focus on what it tells us about planet formation throughout the galaxy. The Rubin Observatory Legacy Survey of Space and Time (LSST) is poised to further transform our understanding of these classes of objects, and I will discuss the feasibility of future discoveries via ground-based observations as well as possible intercept missions. 

Speaker: Darryl Seligman (Michigan State 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).