Li Zeng

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Research Experience


 

June 2015~Now: Simons Postdoctoral Fellow

Simons Collaboration on the Origins of Life

★Mentor: Prof. Stein B. Jacobson

Department of Earth and Planetary Sciences, Harvard University

Project: Uncovering the Chemistry of Earth-like Planets

We propose to use evidence from our solar system to understand exoplanets, and in particular, to predict their surface chemistry and thereby the possibility of life.

An Earth-like planet, born from the same nebula as its host star, is composed primarily of silicate rocks and an iron-nickel metal core, and depleted in volatile content in a systematic manner. The more volatile (easier to vaporize or dissociate into gas form) an element is in an Earth-like planet, the more depleted the element is compared to its host star.

After depletion, an Earth-like planet would go through the process of core formation due to heat from radioactive decay and collisions. Core formation depletes a planet’s rocky mantle of siderophile (iron-loving) elements, in addition to the volatile depletion.

After that, Earth-like planets likely accrete some volatile-rich materials, called “late veneer”. The late veneer could be essential to the origins of life on Earth and Earth-like planets, as it also delivers the volatiles such as nitrogen, sulfur, carbon and water to the planet’s surface, which are crucial for life to occur. These volatiles would be lost in the earlier stages (volatile depletion and core formation), rendering them absent on the planet’s surface, until delivered later when the planet’s surface cooled down enough to retain them.

Finally, the materials delivered to the surface of the planet would be gradually mixed into the planet’s mantle through mantle convection.

By parameterizing and modeling each of these steps properly, we plan to build an integrative model of Earth-like planets from the bottom up. We would like to infer their chemical compositions from their mass-radius relations and their host stars’ elemental abundances, and understand the origins of volatile contents (especially water) on their surfaces, and thereby shed light on the origins of life on them.

 

★Publication:

A Simple Analytical Model for Rocky Planet Interior”. Li Zeng, and Stein B. Jacobsen. ApJ, 837, 164, 2017. (ADS link) (PDF) (PDF)

Variational Principle for Planetary Interiors”. Li Zeng, and Stein B. Jacobsen. ApJ, 829, 18, 2016. (ADS link) (PDF)

Kepler-21b: A rocky planet around a V = 8.25 magnitude star”. Mercedes Lopez-Morales, Raphaelle Haywood, Jeffrey Coughlin, Li Zeng, Lars Buchhave, et al. AJ, 152, 204, 2016. (ADS link) (PDF)

Mass-Radius Relation for Rocky Planets based on PREM”. Li Zeng, Dimitar D. Sasselov, and Stein B. Jacobsen. ApJ, 819, 127, 2016. (ADS link) (PDF)

 

★Publication in preparation:

Elemental Abundance Model of Rocky Planets”. Li Zeng, Stein B. Jacobsen, and Dimitar D. Sasselov.

Platinum as Tracer for Late Veneer Mixing into Early Mantle”. Li Zeng, Stein B. Jacobsen, and Dimitar D. Sasselov.

 

 

 

2009~2015: Harvard University, Ph.D., Astronomy and Astrophysics

Thesis: Interior Structure and Chemistry of Solid Exoplanets

Department of Astronomy, Harvard University

★Advisor: Prof. Dimitar D. Sasselov

Research on the interior structures of exoplanets, thermal evolution of H2O-rich planets, and implementing elemental abundance and mixing calculation for the chemistry of planets.

★Publication:

Characterizing K2 Planet Discoveries: A Super-Earth Transiting the Bright K Dwarf HIP 116454”. Andrew Vanderburg, Benjamin Montet, John Johnson, Lars Buchhave, Li Zeng, et al. ApJ, 800, 59, 2015. (ADS link) (PDF)

Kepler-93b: A Terrestrial World Measured to within 120 km, and a Test Case for a New Spitzer Observing Mode”. Sarah Ballard, William Chaplin, David Charbonneau, Jean-Michel Desert, Francois Fressin, Li Zeng, et al. ApJ, 790, 12, 2014. (ADS link) (PDF)

The Effect of Temperature Evolution on the Interior Structure of H2O-rich Planets”. Li Zeng and Dimitar D. Sasselov. ApJ, 784, 96, 2014. (ADS link) (PDF)

A Detailed Model Grid for Solid Planets from 0.1 through 100 Earth Masses”. Li Zeng and Dimitar D. Sasselov. PASP, 125, 227, 2013. (ADS link) (PDF)

 

 

 

Summer 2008: Summer Internship at Center for Astrophysics

Harvard-Smithsonian Center for Astrophysics

★Mentor: Prof. Dimitar D. Sasselov

Summer research with Prof. Dimitar D. Sasselov and the Walsworth Group on Exoplanet and AstroComb Project.

★The first part of my research was on AstroComb. AstroComb is an instrument using a femto-second laser beam and Fabry-Perot Cavity to produce a super-accurate and stable reference spectrum. With AstroComb, we are expecting an accuracy of cm/s in measuring the Doppler shift of stars. This accuracy will allow us to detect the miniscule effect of an Earth-like planet on a Sun-like star. I wrote a program to simulate the output beam profile of the femto-second laser under various pressures and temperatures.

★The second part of my research was on ocean planet detection feasibility through the Kepler mission and the influence of post-perovskite on the mass-radius relation of Super-Earth. We included post-perovskite in our model and the result shows that radius will be inflated by a few percent compared to the model without post-perovskite given the same mass.

 


 

January 2008: Short Project at Lowell Observatory

Lowell Observatory, Flagstaff, Arizona

★Mentor: Mr. Brian W. Taylor

Research on implementing time delay integration mode (TDI) on (Perkins Re-Imaging System) PRISM on Perkins Telescope.

In January 2008, I went on MIT Astronomy Field Camp (a 9-unit IAP class) to Lowell Observatory. At Lowell, I did a 3-week project with Brian Taylor from Boston University on adding a new working mode, called Time Delay Integration Mode (also called strip scan mode which is different from the usual stare frame mode that most telescopes use), to PRISM (an optical camera system) on Perkins Telescope. Basically we calculated and programmed strip scan mode (viz. TDI mode) on CCD. The detail of this project is explained in the following powerpoint file:

Adding TDI mode to PRISM (Only for education purpose, if using it please cite it properly)

 


 

Summer 2007: Undergraduate Research with Professor Sara Seager

Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology

★Advisor: Prof. Sara Seager

★We Built Computer Models for the interior structure and the atmosphere of extra-solar planets to understand the Mass-Radius relation and atmospheric spectral lines of exoplanets. Our basic assumption for the interior of Earth-like exoplanets is that they all have an iron core, a silicate mantle and a water crust. We also assumed that the temperature dependence of the Equation Of State (EOS) is negligible, which is a very good approximation.

Based on these assumptions, we developed two computer codes in matlab to interpret the bulk composition of solid exoplanets based on their mass and radius measurements. These two codes are available on the website for download. If you have any questions regarding the code, please contact me or Prof. Sara Seager.

Exoplanet Code Download

★Publication:

A Computational Tool to Interpret the Bulk Composition of Solid Exoplanets based on Mass and Radius Measurements”. Li Zeng and Sara Seager. PASP, 120, 983, 2008. (ADS link) (PDF)

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