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Modeling and Observations of Disks
and Exoplanets Module

Image of the individual Modeling and Observational Studies Module green hexagon icon.The Disks and Exoplanets Module uses thermo-chemical models that build on inputs from the other two modules, along with dynamical simulations to follow the transport and irradiation of organics as disks evolve and form planets. Chemical evolution of prototypical extrasolar nebulae and dynamical simulations that test migratory and in situ planet formation theories will determine disk parameters that are consistent with available observational data from protoplanetary disks and exoplanet surveys.

2016 Summary:

Disk Modeling -

We have developed global protoplanetary disk evolution models that incorporate the formation of planetesimals in a 1+1D viscous evolution framework that combines the effects of photoevaporation, dust evolution, turbulence, and planetesimal formation by the streaming instability. This work shows that, as the gas is removed, regions with an over-density of dust grains are created that lead to the formation of planetesimals on relatively short timescales, i.e., planetesimal formation in the outer disk is a natural outcome of disk evolution. We have also begun incorporating gas-grain chemistry into the disk-modeling network to study transport of ices within disks.

Exoplanets -

Our team is at the leading edge of extrasolar planet discovery, and we are core participants in the long-running Lick-Carnegie Exoplanet Survey. Over the past year we assembled and published a compendium of 60,949 precision radial velocities for 1,624 nearby sun-like stars and red dwarfs. This data, all taken with the Keck-I Telescope over a period of more than 20 years, supports the detection of hundreds of exoplanets, including 60 new candidate worlds. Our planet detection efforts also extend to our own Solar System. Strong dynamical evidence points to the potential existence of “Planet Nine”, a ~10 Earth-mass world on an eccentric ~17,000-year orbit. Our work pinpoints the as-yet unseen object at a distance of 950 AU, with a sky position near RA=3 hours, Dec=0 degrees, and apparent brightness V~23.

 The total mass in solids in different size ranges (color-coded) evolves with time as the diskdisperses, and is shown in the figure above. The streaming instability can efficiently convertdust (<1 cm) into planetesimals (in blue), and in the model here, about 76 Earth masses of dust is converted during the disk lifetime of about 3 million years.




Team members:

Uma Gorti

Gregory P. Laughlin