Description:

"The Formation and Habitability of Terrestrial Planets around M-dwarfs":

Anna Childs, Postdoctoral Associate

The search for habitable exoplanets around M-dwarf stars is motivated by the star’s long lifetimes, their prevalence in the galaxy, and the high occurrence rates of terrestrial planets found around M-dwarfs.  Yet, the stellar activity and tidal locking in these systems raise concerns about habitability. This study explores another potential issue for habitability in these systems: the absence of necessary asteroid delivery systems to habitable terrestrial planets due to the lack of giant planets exterior to the ice line. By examining observed planetary architectures, it reveals a potential for asteroid belt formation around M-dwarfs, though differing from systems around more massive stars. Next, we focus on placing composition constraints on the TRAPPIST-1 (T1) system from their formation.  We model the formation of the T1 planets starting with Moon-sized bodies near the ice line, incorporating pebble accretion, mergers, migration, and composition evolution. The study reproduces the system's architecture, constraining initial water mass fractions and final compositions, suggesting desiccation for the inner two planets and a primordial hydrosphere for outer planets, with none consistent with a core-free interior.  The predicted inner desiccation of the T1-b and T1-c planets has been recently confirmed by JWST.

"Topological Insulators with Spin Chern Number"

Saptarshi Biswas, PhD Student

Different topological phases are characterized by robust topological invariants, and physically manifest through a bulk-boundary correspondence, as well as exhibit unique electromagnetic response. Often, the topological protection of these phenomena are contingent to certain symmetry protection. One very well-known example in 2D systems is the Quantum Hall effect, which doesn’t require any symmetry restriction, and characterized by a non-trivial Chern number. Generalizing some of the topological features, I will motivate and talk about a different kind topological invariant realized in 2D. Under its umbrella falls quite a generic class of topological systems. The quantum spin Hall effect protected by time reversal symmetry is one example. We will also explore more exotic types of systems which defy the usual topological signatures, yet can be captured by the above method and exhibit a robust topological response.