Earth. Planets. Climate. Life. Get to know four of our students and the breadth of thesis topics from across the EAPS spectrum of research.

MARY KNAPP

In our own solar system, the Earth, Jupiter, Saturn, Uranus, and Neptune produce eerie-sounding radio choruses due to the interaction between the solar wind and the planets’ magnetic fields. It has long been suspected that exoplanets produce similar radio emissions, but no detections have been made to date. My work is focused on observing large ‘super-Jupiter’ exoplanets in very eccentric orbits around their host stars. HD 80606b is a prime example of this class of exoplanets—it is 4 times the mass of Jupiter and has a comet-like eccentricity of 0.93 which brings it within 7 stellar radii of its parent star at closest approach. We use the LOFAR (‘Low Frequency Array’) telescope in the Netherlands to ‘listen’ to HD 80606b and similar planets in the 30-75 MHz range in the hope of detecting their radio songs. If we can detect radio emission from an exoplanet, we can determine how strong the planet’s magnetic field is, how fast it rotates, and perhaps how its interior is structured. Radio observations will complement other methods used to study exoplanets to provide a fuller picture of exoplanetary structure, composition, and evolution. Based on our current understanding of solar system planets, particularly Earth and Mars, we believe that magnetic fields critically affect atmospheric evolution on rocky planets. Taking the first step in this field by detecting radio emission from a Jovian mass planet will pave the way for studies of small, rocky planet magnetic fields and hopefully improve our understanding of exoplanet habitability.

MINGWEI LI

Having personally experienced the periodic haze events in Beijing for several years, I became passionate about helping people to breathe clean air. This is why I was delighted to begin research at EAPS two years ago with the goal of answering an even bigger question: could China address climate change and air pollution at the same time? The context of this question is that greenhouse gases and conventional air pollutants share many common sources, and in the case of China, the dominant source is coal combustion. Therefore efforts to limit coal use in China could be expected to not only help tackle climate change, but also to have air quality co-benefits locally in China and even across the Pacific Ocean in the U.S. In collaboration with the Tsinghua-MIT China Energy and Climate Project, we coupled two state-of-the-art models—an energy-economic model with sub-national detail for China (C-REM) and a global atmospheric chemistry model (GEOS-Chem) to investigate the effects of climate policies in China on air quality. In a carbon intensity scenario which achieves China’s newest commitment to have its CO2 emissions peak in 2030, the annual PM2.5 concentrations are reduced on average by 19 μg/m3 in Eastern China and 0.1 μg/m3 in the U.S. compared to the business-as-usual scenario. We found that although end-of-pipe solutions are still needed to address the near-term air pollution problem in China, a gradual shift away from coal should ensure China will be able to meet both air quality and climate goals in the long term.

LAURA STEVENS

For two summers I’ve been busy traveling to the Greenland Ice Sheet. My fieldwork involves maintaining an array of GPS stations that continuously track the surface position of the ice sheet surrounding a couple of supraglacial lakes—lakes which form on the surface in summer when temperatures rise above freezing. In 2008, my advisors published the first GPS observations of the dramatic exit these lakes make; kilometer-long hydro-fractures rapidly grow and split through the lake bed, draining the entire lake through a kilometer of glacial ice to the bedrock below in a matter of hours [1]. The water from the drainage lubricates the interface between the ice sheet and bedrock, causing the ice sheet to speed up and advect ice faster to the coast. Their exciting finding received significant attention due to the potential implications for Greenland’s future contributions to sea level rise. The next questions to ask were “What is the mechanism that triggers hydro-fractures?” and “Will future warming lead to inland lake drainages causing enhanced ice flow in current slow velocity areas?” We deployed 20 GPS stations near a supraglacial lake and recorded the response to three drainages in 2011–13. We combined our GPS observations with methods from the geophysics/tectonics community to invert the data during the events, allowing us to see the distribution of meltwater at the ice sheet bed before, during and after the drainages. We discovered hydro-fractures were triggered by meltwater that reaches the ice sheet bed in the 6–12 hours before the lake drains [2]. This precursory meltwater caused basal slip and surface uplift in the lake basin, inducing local stress perturbations favoring crack initiation. Our findings allow us to hypothesize that as there are fewer pathways for meltwater to reach the bed in inland regions of the ice sheet, these lakes are less likely to drain in situ via hydro-fractures.

DAVID T. WANG

Last summer, I traveled to the wine country of California to collect fluid samples. Specifically, my fieldwork involved a site called The Cedars in the northern Coast Ranges of California, at which groundwaters seep from exposed units of serpentinite, a rock type formed by weathering of ultramafic mantle rocks. These waters carry copious quantities of hydrogen and methane, and are highly-alkaline (pH values up to 12). Because of the hostile conditions for microbial life, methane from serpentinizing fluids is commonly assumed to be of non-biological origin. I tested this assumption by quantifying 13CH3D, a lowabundance “clumped” form of methane containing two heavy isotopes, in these samples using a prototype highprecision laser spectroscopy instrument [1] similar to that on the Curiosity rover. Working with my advisor Shuhei Ono, fellow graduate student Danielle Gruen, and two dozen colleagues from academia, industry, and government, we have measured 13CH3D in methane samples from major natural reservoirs (gas hydrates, coalbeds, shales) and sources of atmospheric emissions (cattle, wetlands, lakes), as well as methane produced by microbes grown in the lab [2]. We determined that measurement of 13CH3D can be used to distinguish between biological and non-biological methane-generation pathways. Surprisingly, I found that the methane from The Cedars carried an “anticlumped” signal characteristic of biological methane, suggesting that, despite the inhospitable conditions, life survives in this environment. If so, clumped isotope measurements of methane could be a valuable addition to the arsenal of biosignature detection tools, particularly on planets such as Mars where ultramafic rock is abundant.