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Graduate student Jessica Watkins studies landslides on Mars

For third-year UCLA graduate student Jessica Watkins, the “big picture goal” has always been to travel to space as an astronaut.  To achieve her dream meant intense physical training (she was part of Stanford’s 2008 international collegiate rugby championship team) and earning a Ph.D. in a research area relevant to space. Beginning her education as a mechanical engineer, she soon realized it wasn’t for her.  Turning to a course bulletin for inspiration, she found classes about planets and atmospheres in Stanford’s Geological and Environmental Sciences department that would prove to suit her well.

Presently, Watkins works with her advisor, UCLA Professor An Yin, to understand massive landslides in Mars’ Valles Marineris, a network of canyons the size of the continental United States.  Using images and data from NASA’s Mars Reconnaissance Orbiter and satellite images of Earth for comparison, she attempts to determine whether the cause of Martian landslides is tectonic activity, flowing water, glaciers, or something else.  Accordingly, Watkins is trying to determine if any of the minerals in her landslides are hydrated, or wet.  Although she is not studying the astrobiological aspects of the minerals, she said her work is “one small study that could tell us a lot,” including information about the habitability of Mars.

Watkins also examines landslides up close to understand how to best interpret images of Mars’ landslides. During a recent field investigation of a Mars-like landslide in Death Valley National Park, Watkins was surprised that some of her preliminary image interpretations were incorrect. “There are many things about other planets that we might not be able to truly understand just from images,” she said. “Being able to walk around and get your hands on it really makes a difference.”

That’s what drew Watkins to planetary geology.  “UCLA merges geology and planetary science really well,” she said.  “I can use my Earth geology background to study other planets.” This summer, Watkins will collaborate with Mars Science Laboratory (MSL) scientists at the Jet Propulsion Laboratory (JPL) in Pasadena, California in hopes of improving our understanding of Mars’ surface.  In retrospect, Watkins realizes she has always been interested in Mars. “My earliest memory of being interested in Mars was in fifth grade,” she said. “We had to make illustrated books – I wrote mine on Marty the Martian.”

Watch a video profile of Jessica Watkins here.  Learn more about her research here.

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June 26, 2013: Rockets to Radio: Research Projects at the Korean Astronomy and Space Science Institute

The Korean Astronomy and Space Science Institute (KASI) is involved in a wide range of technology and astronomy projects. They operate a very long baseline interferometry network within Korea and jointly with other Asian facilities that among other things, utilizes a multi-band quasi optical input duplexer developed by Han. This allows simultaneous observations of multiple SiO masing transitions between 40 and 130 GHz. They also have a 14m millimeter telescope used for mapping molecular clouds in the 115 Ghz CO line and in other molecular emission. The institute is also involved in rocket projects with Caltech and have recently joined a consortium of Asian countries supporting and observing  at the Caltech Submillimeter Observatory in Hawaii. KASI also has numerous technology development programs.

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The Asteroid Vesta in the Light of Dawn

Posted by Michaela Shopland
An image obtained of the asteroid Vesta from NASA’s Dawn spacecraft from a distance of 3,200 miles. Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

On September 27th, 2007, NASA’s Dawn spacecraft left Earth and began a multi-year journey to two of the largest objects in the solar system’s main asteroid belt.  The first stop on its interplanetary roadtrip was the asteroid Vesta.  Dawn reached the Arizona-sized chunk of primordial rock in 2011, providing scientists with the first close-up view of the asteroid’s ancient surface.

A leftover remnant from the formation of the solar system over four billion years ago, Vesta may be similar in composition to the larger bits of celestial debris that originally came together to form the inner planets.  Scientists studying our planet’s origins hope that Vesta will reveal clues about our past that have long been erased by plate tectonics and weathering on Earth.

“Studying Vesta is like going back to the beginning of the solar system,” said Jennifer Scully, a third-year UCLA graduate student working on the Dawn mission. “It is kind of like a fossil of the sort of bodies that were around that combined to make the Earth,” she said.  Scully, the lead mapper for two large areas on Vesta, makes geological maps of the asteroid’s surface in order to interpret the history of different features and formations.

What she has found so far has been surprising.  “We discovered a lot of things that were unexpected at Vesta,” she said.  Grayscale and color images taken by Dawn’s framing camera show a remarkable range of shades on the surface of Vesta, featuring both very bright and very dark material. “It’s very colorful,” said Scully.  “We think the dark material is residue from meteorites called carbonaceous chondrites that have hit the surface.”

Data from Dawn’s instruments including the camera’s seven color filters, a spectrometer, and a neutron detector help scientists characterize surface deposits and divide Vesta into areas depending on age, composition, and morphology.  But sometimes this close-up view of Vesta raises more questions than answers.

“We found both straight and sinuous gully features and I’m investigating what sort of flow(s) formed them,” said Scully. Whether or not some of the gully features could have been carved by molten rock is under investigation.  “The team has not found any definitive features of volcanism,” Scully said.  “There could have been activity early on, but the evidence has been wiped clean by billions of years of impacts.”

Evidence of many of these impacts is preserved on Vesta’s surface in the form of craters. These craters range in size from being so small that Dawn’s camera can barely resolve them to being so large that they have diameters nearly as big as Vesta. The two largest impact basins on the asteroid, named Veneneia and Rheasilvia, are found in Vesta’s southern hemisphere. Scully is one of many Dawn scientists who are working to connect these impact basins with structures in Vesta’s northern hemisphere. “The current understanding is that each of these large impacts sent shock waves through Vesta, which formed large-scale ridges and depressions on the opposite side,” said Scully.

The Dawn spacecraft does not only examine the surface of an asteroid, it can also give scientists clues about its internal structure.  “From the way the gravity pulls on the spacecraft you can tell about the internal layers and the size of the core,” said Scully.  From examining how Vesta’s gravitational field tugs on Dawn, scientists believe that Vesta has a distinct crust, mantle, and core like Earth.

The same is likely not true for the asteroid Ceres, Vesta’s younger cousin and the next and final stop for the Dawn spacecraft.  After remaining in orbit around Vesta for one year, the Dawn spacecraft took its leave in September of 2012 to begin a three-year journey to Texas-sized Ceres, the largest object in the main asteroid belt located between Mars and Jupiter.  Unlike Vesta, scientists think Ceres may harbor large amounts of water ice under its surface.  Because Ceres is wetter than Vesta, it will present a whole new set of questions.  Scully looks forward to directly comparing the data collected from the two asteroids when the spacecraft arrives at Ceres in 2015.

For Scully, the decision to come to UCLA and work with Professor Christopher Russell was a “no brainer.”  “Getting to work on an actual active mission is pretty awesome.  You get to meet a lot of people and really see how a team works,” she said.  In addition to her work on the geology of Vesta, Scully helped create an online system called Asteroid Mappers where citizen scientists can identify features on Vesta using real data collected by Dawn.

Watch a video profile of Jennifer Scully here.  Learn more about her research here.

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June 20, 2013: Thermophysical Modeling and Measurements of Martian-Like Particulated Materials: Effect of Temperature and Cementing Phases

Thermal infrared imaging of sedimentary terrestrial analogs and neutron remote sensing by the Dynamic Albedo of Neutrons (DAN) instrument on the Mars Science Laboratory (MSL) rover are discussed.  Thermal infrared data have been used on Mars spacecraft for decades, however, the broadband thermal images of various sedimentological features have not been well characterized.  Day-night aerial thermal images were acquired and ground-truth mapping performed for thermophysical characterization of sedimentary features.  Building on this work, surface images could be acquired from a rover mast at specific times of day to be used for autonomous classification of fines and cobbles, as well as unconsolidated and cemented materials.  Pulsed neutron data, like those acquired by DAN, can also be incorporated into rover autonomy.  DAN has the ability to sense anomalous hydrogen-or chlorine-rich features at or near the surface (<60cm depth) during a long duration rover traverse.  Initial results and geochemical classifications from DAN are presented.

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Stratified Flow Past an Obstacle

The laboratory experiments of Browand and Winant (Geophysical Fluid Dynamics, 1972), in which a cylinder is towed horizontally in a uniformly stratified fluid, will be used as a case study in combining laboratory, numerical, and theoretical approaches to idealized flows with geophysical applications.

This talk will focus first on the steady, low topographic Froude number regime characterized by blocking, upstream propagation of long gravity waves and stratified hydraulic control. Laboratory and numerical results will be used to motivate a new theoretical framework that describes the observed accelerated, asymmetric flow over the obstacle crest in terms of reduced gravity single layer hydraulics. The active layer is subcritical upstream, controlled at the crest, and supercritical downstream.

These ideas are then extended to oscillating flows and a new scaling analysis is introduced that clarifies the distinction between linear flows characterized by internal wave radiation and nonlinear flows that exhibit a mix of wave-­‐like and hydraulic-­‐like features. These nonlinear flows oscillate between states in which supercritical jets separate from the lee of the obstacle and are broken apart by a series of shear instabilities. The theoretical and scaling arguments are compared to both laboratory and numerical experiments of oscillating stratified flow past a cylinder.

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On the Development of a Scalable Fully-Implicit Stabilized Unstructured FE Capability for Resistive MHD with Integrated Adjoint Error-Estimate

The resistive magnetohydrodynamics (MHD) model describes the dynamics of charged fluids in the presence of electromagnetic fields. MHD models are used to describe important phenomena in the natural physical world and in technological applications. This model is non-self adjoint, strongly coupled, highly nonlinear and characterized by multiple physical phenomena that span a very large range of length- and time-scales. These interacting, nonlinear multiple time-scale physical mechanisms can balance to produce steady-state behavior, nearly balance to evolve a solution on a dynamical time-scale that is long relative to the component time-scales, or can be dominated by just a few fast modes. These characteristics make the scalable, robust, accurate, and efficient computational solution of these systems extremely challenging. For multiple-time-scale systems, fully-implicit methods can be an attractive choice that can often provide unconditionally-stable time integration techniques. The stability of these methods, however, comes at a very significant price, as these techniques generate large and highly nonlinear sparse systems of equations that must be solved at each time step.

This talk describes recent progress on the development of a scalable fully-implicit stabilized unstructured finite element (FE) capability for 3D resistive MHD with integrated adjoint error- estimation capability. The brief discussion considers the development of the stabilized FE formu- lation and the underlying fully-coupled preconditioned Newton-Krylov (NK) nonlinear iterative solver. To enable robust, scalable and efficient solution of the large-scale sparse linear systems generated by the Newton linearization, fully-coupled multilevel preconditioners are employed. The stabilized FE formulation and robust fully-coupled NK iterative solvers enable the solution of a wide range of flow conditions that include incompressible, low Mach number approximations, Boussinesq, anelastic, and low Mach number compressible flow. In addition the fully-implicit NK formulation allows the development of adjoint-based error-estimation methods. We present some recent representative results employing the adjoint methods to simple Navier-Stokes and resistive MHD verification problems as well as a RANS turbulence model.

We then briefly consider two sets of recent simulation results with relevance to geophysical and astrophysical flows. The first is the break-up of thin Sweet-Parker current sheets into smaller plasmoids that has been the subject of attention as a possible mechanism for fast reconnection in resistive MHD. Various studies, both theoretical and numerical, have shown that the fast formation of small structures is not only possible, but in fact unavoidable for large enough Lundquist numbers. In this study, we have used state-of-the-art computational capabilities to perform simulations of the Fadeev island coalescence problem in the high Lundquist number regime to investigate if thin current sheets dynamically formed in this strongly non-uniformly driven problem are prone to break- up by fast plasmoid instabilities. Our numerical simulations confirm that plasmoid break-up of dynamically formed current sheets occur for S > 106 (with L. Chacon and D. Knoll LANL). Second we present some very recent results for high Rayleigh number thermal convection in cylindrical geometries of various aspect ratios that have relevance to aspects of the SpinLab experiments.

#This work was supported by the DOE office of Science Advanced Scientific Computing Research – Applied Math Research program at Sandia National Laboratory.

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Inverse Cascade in Anisotropic Flows

We examine the inverse cascade of kinetic energy to large scales in rotating stratified turbulence as occurs in the oceans and in the atmosphere, while varying the relative frequency of gravity to inertial waves, N/f . Using direct numerical simulations with grid resolutions up to 1024^3 points, we find that the transfer of energy from three-dimensional to two-dimensional modes is most efficient in the range 1/2 ≤ N/f ≤ 2, in which resonances disappear. In this range, the cascade is faster than in the purely rotating case, and thus the interplay between rotation and stratification helps creating large scale structures. The ensuing inverse cascade follows a −5/3 spectral law with an approximately constant flux.The purely stratified case will also be examined in this context being limit of infinite N/f.

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Baroclinic Critical Layers and Zombie Vortices in Couette-Taylor Flow

We report a new mechanism for creating vortices in a class of flows that are linearly stable and believed, by most researchers, to be also finite-amplitude stable. The vortices should form in stably-stratified Couette flows (both plane and circular), and in protoplanetary disks around forming protostars. Our study was motivated by the fact that protoplanetary disks must have flow instabilities that are capable of transporting angular momentum radially outward so that the protostars can accrete gas and grow into stars. The mechanism that we discovered allows small-amplitude perturbations (i.e., with small volumes and Rossby numbers) to form vortices that are large in volume and amplitude (with a Rossby number of order unity). The mechanism works by exciting neutrally stable baroclinic critical layers, which differ from the usual barotropic critical layers in uni-directional flows (responsible for the much-discussed but rarely-observed Kelvin’s cats-eye vortices). The singularities in the former layers are in their vertical velocities, while the latter are in their stream-wise velocities. The energy of the vortices becomes large, and it is supplied by the kinetic energy of the background shear flow. The vortices we found have an unusual property: a vortex that grows from a single, local perturbation triggers a new generation of vortices to grow at nearby locations. After the second generation of vortices grows large, it triggers a third generation. The triggering of subsequent generations continues ad infinitum so that a front dividing the vortex- dominated flow from the unperturbed flow advances until the entire domain fills with large vortices. The vortices do not advect across the region, the front of the vortex- populated fluid does. The region in protoplanetary disks where we have found this new mechanism is thought to be stable; thus, in the astrophysical literature this region is called the dead zone. Because the vortices we report here arise in the dead zone, grow large, and spawn new generations of vortices that march across the domain, we refer to them as zombie vortices. We consider the mechanism of the zombie vortices’ growth and advance in a proposed lab experiment: circular Couette flow with a vertically stably- stratified Boussinesq fluid (i.e., salt water) with a density that is linear with height. Because this flow is nearly homogenous, the first vortex formed by the initial instability self-replicates in an approximately spatially self-similar manner and fills the domain with a lattice of 3D vortices, which persists, despite the fact that the flow is turbulent.

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A Pressurized Cryogenic Nitrogen Cell to Study Rotating Turbulent Convection

Due to its fluid properties, cryogenic nitrogen can be used to study flows at high Reynolds and Rayleigh numbers in a compact apparatus compared to standard test fluids. We present the design of a new convection experiment with rotation that uses cryogenic nitrogen, and discuss a few scientific problems that can be addressed with it.

The apparatus consists of a 0.5m diameter 1m tall pressure vessel that can hold a pressure up to 35bar, enclosed in a vacuum jacket to improve insulation, and mounted on a rotating table. Several ports on the vessel provide space for different diagnostics and/or optical access to visualize the flow. By using cryogenic nitrogen from its freezing point up to the critical point, we can greatly vary its fluid properties and tune them for different experiment.

Liquid nitrogen below 77K is particularly useful to study highly convective flows where the effect of rotation is important, i.e. at high Rayleigh numbers and low Rossby numbers. In particular with a 20cm diameter liquid nitrogen cell of aspect ratio 1/2 we plan to study the heat transfer scalings in the geostrophic regime at Rayleigh numbers of order 1011 and to test different theories [1, 2, 3].

Nitrogen close to its critical point would yield the highest Rayleigh numbers flows, allowing us to inves- tigate highly turbulent convective cells with large aspect ratios. In such region of the parameter space very limited data is available and several outstanding questions are still open. In particular, we are interested in the large scale structures of the flow and in studying the existence of polygonal convective cells observed in simulations [4]. With a 37cm diameter cell with top and bottom sapphire plates, and aspect ratio 8, we plan to visualize the flow at Rayleigh number as high as 1011 − 1012.

By using both liquid and gaseous nitrogen along the saturated vapor curve, these experiments can be done also in the case of two phase convection.

References

  1. [1]  E. M. King, S. Stellmach, J. Noir, U. Hansen, and J. M. Aurnou, “Boundary layer control of rotating convection systems.,” Nature, vol. 457, pp. 301–4, Jan. 2009.
  2. [2]  E. M. King, S. Stellmach, and J. M. Aurnou, “Heat transfer by rapidly rotating Rayleigh–B ́enard con- vection,” Journal of Fluid Mechanics, vol. 691, pp. 568–582, Jan. 2012.
  3. [3]  K. Julien, E. Knobloch, A. M. Rubio, and G. M. Vasil, “Heat Transport in Low-Rossby-Number Rayleigh- B ́enard Convection,” Physical Review Letters, vol. 109, p. 254503, Dec. 2012.
  4. [4]  J. Bailon-Cuba, M. S. Emran, and J. Schumacher, “Aspect ratio dependence of heat transfer and large- scale flow in turbulent convection,” Journal of Fluid Mechanics, vol. 655, pp. 152–173, May 2010.
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Plasma and Liquid Sodium Laboratory Dynamo Experiments at UW Madison

First measurements of plasma temperature, density, and flow have been made on the Madison Plasma Dynamo Experiment (MPDX) that allow the particle and energy confinement as well as the plasma conductivity (η) and viscosity (ν) to be estimated. The MPDX is designed to create large flowing plasmas with high magnetic Reynolds number Rm = vL/η >> 1000, and an adjustable fluid Reynolds number 10 < Re = vL/ν < 1000, in the regime where the kinetic energy of the flow exceeds the magnetic energy (MA = v/vA >> 1). Simulations provide scenarios for generating large scale “slow” dynamos and small scale “fast” dynamos to be studied. Confinement is provided by alternating rings of 4 kG permanent magnets lining the vessel walls. Stirred is induced using anodes and thermally emissive Lanthanum hexaboride (LaB6) cathodes inserted in the confining magnetic multicusp edge of the plasma in a method first developed by the Plasma Couette Experiment (PCX) at UW Madison. An overview of plasma flows in PCX and MPDX will be presented as well as several experimental setups designed to achieve dynamo in MPDX. Resent results studying the vector turbulent EMF (the β effect) in the Madison Dynamo Experiment (MDE), a liquid sodium experiment at UW Madison will also be presented.