Planetary Science Directorate


Upcoming SwRI Boulder Colloquia

Colloquia are normally on Tuesdays at 11:00 am in the 4th-floor conference room, except as indicated below in bold text.
Show previous colloquia

For questions or suggestions for speakers, please contact the SwRI colloquium organizers:
Hannah Kaplan, 720-208-7208 or kaplan(at)
Derek Lamb, 720-208-7207 or derek(at)
Katie Primm, 720-240-0124 or kprimm(at)
Raluca Rufu, 303-226-0879 or raluca(at)
Julien Salmon, 720-208-7203 or julien(at)
Kelsi Singer, 303-226-5910 or ksinger(at)

To be added to the SwRI Boulder Colloquia email list, please contact Kelsi Singer, ksinger(at)

Tue Sep 24, 2019
In 5th-floor conference room
11:00 am Mickey Rosenthal University of California, Santa Cruz Perks and Pitfalls of Pebble Accretion — Implications for Planet Formation in the Inner and Outer Disk
Abstract: Much recent work on planet formation has focused on planetary growth through accretion of particles whose aerodynamic properties make them marginally coupled to the local nebula. These moderately sized “pebbles” are small enough to be substantially affected by gas drag, while still being large enough for their trajectories to deviate from the local gas flow. Growth of planets through accretion of these pebbles, often termed “pebble accretion”, has several notable features when contrasted with “traditional” growth that relies on purely gravitational interactions. In particular, in certain regions of parameter space pebble accretion proceeds on timescales that are far more rapid than gravitational growth timescales, meaning that it dominates accretion rates as long as pebbles are available for growth. Furthermore, due to radial drift of pebbles, planetary masses are not limited by locally available material if planets grow through pebble accretion. In this talk, I describe several important features of growth by pebble accretion. Firstly, I demonstrate that growth by pebble accretion qualitatively changes for core masses above a minimum mass scale, above which far more pebble sizes are able to be accreted, and particles can be captured on scales comparable to the planet's hill radius. This change in behavior implies that the early stages of planetary growth must be fueled by processes other than pebble accretion, which can bring planets up to the minimum masses needed for pebble accretion to take hold. I discuss the semi-major axes where gas giant formation can occur if these early stages are dominated by accretion of planetesimals. Finally, I show that consideration of the smallest sizes of particles that can be captured by pebble accretion leads naturally to an upper planetary mass limit known as the “flow isolation mass.” This mass scale naturally results in planetary growth ending at super-Earth masses in the inner disk, where, in the absence of flow isolation, rapid pebble accretion rates imply that planets either stall at sub-Earth masses or run away to become gas giants.
Tue Oct 8, 201911:00 am Dr. Michael Tice Texas A&M University TBD
Mon Nov 4, 201911:00 am Richard Ghail Royal Holloway, University of London The EnVision mission to Venus, Earth's mysterious twin.