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Prof. Mitchell predicts weather on Titan

Titan in front of Saturn and its rings. Image Credit: NASA/JPL/Caltech/SSI

Saturn’s largest moon, Titan, is an icy world dominated by extensive sand dunes at the equator, methane-filled lakes near the poles, and vast networks of dry riverbeds in between.  Wrapped in a nitrogen atmosphere thicker than Earth’s, Titan is an ideal test bed for studying planetary climate models for UCLA Assistant Professor Jonathan Mitchell.

“Titan is probably the most Earth-like place in the solar system in terms of its very active weather cycle,” said Mitchell. But a weather forecaster on chilly Titan would be more likely to predict a liquid methane downpour than the water-based showers we are accustomed to on Earth.  “Titan is too cold for water to play a role in the weather.  Instead, it rains and hails methane, the natural gas we use as fuel for our stoves,” Mitchell said.

So is Titan a veritable tinder box, an enormous gas leak ready to catch fire at the slightest spark?  Not at all, said Mitchell.  “You might worry about it exploding, but all the oxygen is locked up into water.  If you wanted a lighter that you could carry around on Titan, then you’d carry around a flint with a little vial of oxygen because there is plenty of methane in the air and the limiting ingredient is the oxygen for combustion.”

Titan has surface temperatures nearly 300 degrees Fahrenheit below zero (-180° Celsius).  Water makes up about half the solid body by mass, and where you would expect to find a rocky crust on a terrestrial planet like Earth, Titan’s surface layers are composed mainly of ice.  “Water is essentially Titan’s rock,” said Mitchell.  “These temperatures are so far beyond the realm of human experience that they’re hard to even grasp.”

Despite the frigid conditions, Titan’s climate patterns are technically quite tropical, Mitchell said.  “On Earth, we have a certain temperature difference between the equator and the poles which gives rise to vastly different climates on the surface, like tropical islands versus Antarctica,” he said.  “On Titan, this temperature difference is essentially erased, which makes its climate all tropics.” The subzero weather results from the fact that Titan spins more slowly than Earth, taking sixteen days to complete a full rotation, and also because of its smaller size.  While Titan is larger than Mercury and is the second largest moon in the solar system, it is still less than half the size of Earth.

To be able to understand and predict weather patterns on Titan, Mitchell and his colleagues rely on observations from NASA’s Cassini spacecraft that help them improve their computer simulations.  “We’re looking at the visible and near-infrared images of Titan to survey cloud features and find interesting spatial patterns from the evolution of storms,” Mitchell said.  Because Cassini can only take measurements at Titan during its regular flyby once every few weeks, an accurate computer model is critical to understanding weather patterns on the icy body.

Mitchell’s research may help explain a curious phenomenon called super-rotation, which causes Titan’s atmosphere to circle the planet at speeds higher than expected.  “Super-rotation means that the atmosphere as a whole is spinning faster than the planetary surface,” Mitchell said.  “This is puzzling because we typically think an atmosphere gains its momentum from friction with the surface.”

Since coming to UCLA in 2009, Mitchell has expanded his work to include Earth’s ancient climate, which he hopes will help him to better predict how regional climates will change as the planet warms over the next century.  “We’ve essentially nailed the problem of anthropogenic greenhouse gases warming the planet,” Mitchell said.  “The much harder question is: what will be the resulting impacts?”

Mitchell grew up in rural Iowa where incessant gazing at the stars as a small child led to the occasional tripping injury.  “I’ve always been curious, and that’s what made me a scientist,” Mitchell said.  “I was destined to be looking up.”  As a graduate student at the University of Chicago, Mitchell originally studied cosmology and gravitational lensing.  But after a few years, he switched fields to study the physics of climate on Earth and other planets.  “Cassini was arriving at Saturn about that time so I decided to take a pit stop at Titan, and I haven’t really left since,” he said.

Mitchell, who enjoys singing in small group ensembles in his spare time, has found a home at UCLA.  “Academically, I just can’t imagine a better fit for me.  I have very broad interests and UCLA is a place where you can really expand and learn.”

Watch a video profile of Jonathan Mitchell here.  Learn more about his research here.

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August 2, 2013: Inter-annual Similarites during the Martian Dusty Season and Implications for InSight Landing

We investigated the occurrence of large (regional) dust storms during the martian dusty season—southern spring and summer (Ls 180° to 360°). We used a zonal mean climatology at 50 Pa from TES/MGS and MCS/MRO to identify the regional and global dust storms and then to characterize their extent and evolution. A 200 K contour outlines the season and latitudinal extend of the significant storms in the zonal mean climatology. We find that years without a global dust storm are quite similar. There are three regional storms each of the five years without a global dust storm covered by the two instruments (MY24, MY26, MY29, MY30 and MY31). The exact timing, duration and peak temperatures vary from year  to year, but each of the three storms has distinct characteristics and behavior and overall the years follow a very similar patern. In addition to examining the detailed characteristics of each of the three storms, this has implications for the InSight landing planned for Ls 230°. It may be an exciting and difficult to predict ride through the atmosphere.

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Undergraduate Raquel Nuno searches for water on Mars

When Raquel Nuno isn’t hunting for atmospheric water vapor on Mars, she’s constructing a massive super computer in the basement of UCLA’s Geology building.  Nuno, a recent UCLA graduate with an interest in planetary science, analyzes data collected by NASA’s two Viking spacecraft that orbited Mars from 1976-1980.  She hopes to pinpoint areas where excess water vapor in the Martian atmosphere might trigger the formation of Recurring Slope Lineae, mysterious dark streaks that appear on crater rims and canyon walls during the warmest Martian seasons.   These features, first observed by NASA’s Mars Reconnaissance Orbiter in 2010, may indicate the presence of flowing liquid water beneath Mars’ surface.  “We think Recurring Slope Lineae could mean there is current hydrological activity on Mars,” said Nuno.  “The question we are trying to answer is: where is this water coming from?” To locate potential water sources, Nuno and her advisor, Professor David Paige, have been looking for areas on Mars where the water content in the air is higher than average.  Nuno presented her results during a talk at the American Astronomical Society’s Division of Planetary Science meeting in Reno, NV in October of 2012.

Nuno, who moved to the United States from Portugal at age eleven, is the first person in her family to earn a college degree.  Her unlikely path to planetary science began when she joined the United States Air Force out of high school, working as a medical laboratory technologist.  While in the military, Nuno took classes at six different colleges and universities before enrolling as an undergraduate student at UCLA, her “favorite so far.”  Nuno hopes to pursue a career in academia and she hopes to inspire the next generation of scientists and researchers through teaching.  “Teachers were very important in shaping my interests and career goals,” she said.  “I would like to have that sort of positive impact on other students.”

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ESS Prof. awarded Early Career Award in Planetary Science

 

Professor Jonathan Mitchell with joint appointments in UCLA’s Departments of Earth, Planetary, and Space Sciences (EPSS) and Atmospheric and Oceanic Sciences (AOS) has been awarded a the American Geophysical Union’s (AGU) Ronald Greely Early Career Award in Planetary Science.  As the name indicates, this award is given to individuals ” in recognition of significant early career contributions to planetary science.”  To learn more about Jonathan’s award-winning research, visit his website here.

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July 13, 2013: Twentywonder – A Carnival of the Mind Recap

On July 13th, 2013, the Institute for Planets and Exoplanets participated in the 3rd annual TwentyWonder, an event to benefit the Down’s Syndrome Association of Los Angeles (DSALA). The iPLEX booth, which showcased a sampling of the UCLA Meteorite Gallery Collection and an informational hands-on DIY comet-building activity, was one of dozens of science, art, and performance acts featured at the event held at the L.A. Derby Dolls Doll Factory in Echo Park. Over 1500 people attended the event that the L.A. Times has called “Awesome! An Event PICK!” Overall, it was an excellent evening full of education presented in a “passive and enjoyable” way, said the event’s creator and DSALA-director, Jim Hodgson. For more information about the event, please visit the Twentywonder official website.

http://www.youtube.com/watch?v=Fy6MDC58FI0&feature=youtu.be

A combination of dry ice (solid carbon dioxide), karo syrup, ammonia, and dirt simulate what a real comet could be like. Comets with very elliptical orbits remain very cold for most of their orbit, but when passing close to the Sun are warmed enough that some of the ice is removed by a process called sublimation; this results in the characteristic “tail” feature seen on most comets. The dry ice in the video is sublimating away, simulating what happens when a comet (composed of dirt/dust, ice, and some organic materials) passes close to the Sun.

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The Gemini Planet Imager will directly image planets around young stars

A simulation of dust rings around a star as they may appear through the Gemini Planet Imager. The morphology of the rings shows an offset from the star, indicating the effects of hidden planets.

Most planet-hunting astronomers infer the existence of extrasolar planets by monitoring tiny changes in the parent stars.  With the recently assembled Gemini Planet Imager (GPI), UCLA Assistant Professor Michael Fitzgerald intends to capture images of these extrasolar planets directly.

Scheduled to go online at the Gemini South Observatory in Chile in late 2013, GPI will be able to detect planets in newly formed systems where traditional detection methods would be likely to fail.  Sensitive at infrared wavelengths, GPI targets young planets, which are warmer than their more evolved counterparts in other systems. “When planets form they are initially large and are slowly contracting, releasing their gravitational energy in the form of heat and cooling off as they get older,” Fitzgerald said.  “We need to look at young systems because that’s when their planets are warmest and therefore brightest in the infrared.”

Using a method based on pioneering work by UCLA Professor Ben Zuckerman, the GPI Exoplanet Survey Team has identified and catalogued over 900 nearby young stars that are promising candidates for planet imaging.  They hope to image 600 of these stars and expect to find roughly fifty new planets.  The type of planets most likely to be revealed by GPI are Jupiter-sized gas giants that formed less than one hundred million years ago and are located many Earth-Sun distances away from their parent star.

But the search won’t be easy.  “Stars are a million times brighter than the planets we are looking for, and these are the biggest and brightest planets that we expect to see,” Fitzgerald said.  The GPI experiment utilizes several state-of-the-art innovations to image these elusive planets including a special coronograph that blocks out light from the parent star in order to make the planet more easily visible, and a unique deformable mirror that helps to compensate for atmospheric distortion.

The best picture astronomers can hope for will show an extrasolar gas giant as a single point of light.  “The planet will not be spatially resolved,” Fitzgerald said.  “We’ll see a dot.”  Yet the GPI instrument can glean a surprising amount of information from a tiny speck of light.  Fitzgerald and his colleagues will be able to analyze the composition of these far-off planets using a spectrograph built by UCLA Professor James Larkin, and perhaps even more importantly, they’ll be able to directly image their associated circumstellar disks.

“A lot of these systems are young – the planets have only recently formed and there are a lot of leftover planetesimals which collide and produce debris disks,” Fitzgerald said.  Scattered light from the dusty cloud surrounding the star has a distinct polarization signature that can be separated from the unpolarized starlight by using special filters.  “If we just look at the intensity of the polarized light, the dust jumps out,” Fitzgerald said.  The shape and position of stellar disks around new stars may help scientists like Fitzgerald better understand the formation of our own solar system.  “There is a lot of diversity in the debris disks we see.  Some of them are rings, some are very extended, a few show interesting asymmetry, and some are even offset from the star due to gravitational perturbations from a planet,” Fitzgerald said.  The structure of dusty disks may also provide clues about the orbital dynamics of distant planets.  “The highlight for the Gemini Planet Imager will be looking at the systems where you have both a disk and a planet, because you can immediately put constraints on the orbit of the planet,” Fitzgerald said.  “If you see a nice, symmetric disk, you wouldn’t expect a planet to be plowing through it.”

Fitzgerald, who came to UCLA in 2010, is also collaborating with scientists at NASA’s Jet Propulsion Laboratory in Pasadena, California to develop a way to make precision radial velocity measurements using infrared rather than visible light.  He hopes the technique will help to find planets around young, energetic stars that are too active to yield accurate results in optical wavelengths, and low mass stars which are optically faint.  Fitzgerald has enjoyed forming new interdisciplinary collaborations in his search for extrasolar planets as a member of iPLEX.  “Having iPLEX and integrating all of the departments in terms of exoplanet studies is definitely the way of the future,” he said.

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Fluid dynamics workshop merges theory and experiment

Over two dozen scientists from thirteen different institutions and four countries visited UCLA June 26-28, 2013 for a hands-on workshop entitled “Connecting Theory to Experiments in Geophysical and Astrophysical Fluid Dynamics (GAFD).”  The three-day interdisciplinary workshop, sponsored by the UCLA Institute for Planets and Exoplanets (iPLEX) and Professor Jonathan Aurnou’s SPINLab, brought theorists and experimentalists together to discuss how to integrate their respective techniques and answer key questions in the field of fluid dynamics.

Researchers discussed fluid flow in oceans, atmospheres, and the metallic cores of planets.  These topics have applications ranging from weather and climate on Earth and other planets to magnetism in planets and stars.

UCLA scientists showcased the unique fluid dynamics experiments underway at SPINLAB through interactive lab tutorial sessions.  Workshop attendees examined SPINLab’s rotating magnetic convection device (RoMag) and conducted basic experiments on spinning fluids with tanks mounted on turntables.

Learn more about UCLA fluid dynamics research on the SPINLab website.

Research at the SPINLab was recently featured in the annual iPLEX magazine.  Read the story here.

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ESS Professor awarded NASA’s Exceptional Scientific Achievement medal

Professor Dave Paige of UCLA’s Department of Earth and Space Sciences has been awarded a NASA Exceptional Scientific Achievement Medal.  This award is NASA’s top scientific honor and is given to individuals “for exceptional scientific contributions (specific, concrete scientific achievements) toward achievement of the NASA mission.”   Dave is honored for his “Breakthrough discoveries in the thermal stability of volatiles on the Moon and Mercury”. To learn more about Dave’s work, visit his website here.

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UCLA laboratory puts a spin on fluid dynamics

Simulated “Red Spot” on Jupiter created by rotating forced vortices

The Simulated Planetary Interiors Laboratory, known more fondly as the SPINLab, is a state-of-the-art fluid dynamics research facility among only a handful of such unique labs in the world.  Funded by the National Science Foundation, the group is led by Associate Professor Jonathan Aurnou, who has dedicated over ten years of his life to building functional models of planetary cores and atmospheres.

The daily routine for Jon, his graduate students, post-doctoral scholars and researchers involves spinning large, heat-driven containers of water or liquid metal in order to understand the fundamental physics of rotating bodies.  “We are interested in explaining how strongly turbulent systems, like planetary cores and planetary atmospheres, organize into planetary-scale magnetic fields, jet systems, and vortices,” said Aurnou.

The primary device used in the lab, a rotating magnetic convection device (RoMag), is a fluid-filled cylinder that to Aurnou represents “a parcel of fluid inside a planetary core.” “The idea is to study all the ingredients that are involved in planetary core convection and dynamo generation in their simplified state,” said Jonathan Cheng, a fourth-year graduate student with Aurnou.  Dynamos, large-scale magnetic fields generated from the motions of an electrically conducting fluid, are known to exist within planets, stars and even galaxies.  Yet the detailed physics of these natural dynamos remain largely mysterious.

The Earth has a very organized magnetic field, created by convective motions in its rapidly rotating molten metal core, but other bodies such as Uranus and Neptune, the ice giants, and Jupiter and Neptune, the gas giants, have much “messier” dynamos, Aurnou said.  In his lab, however, Aurnou is more concerned with studying the underlying dynamics of fluid systems than reproducing these dynamos.  “I know there are dynamos. There are dynamos all over the solar system and on just about every star,” Aurnou said.  “I’m interested not so much in building a dynamo in my laboratory, but instead in building experiments that allow me to better understand the fundamental physics that underlie dynamo processes.”
And fundamentals have proved successful so far for the SPINLab.  Using RoMag, the team has been able to show drastic differences in rotating convection systems that are metal versus those that are water.  In water experiments, rapidly rotating systems become turbulent much faster than numerical models had predicted.  The interpretation is that planets with deep-water layers can easily break down into turbulent systems that create disordered dynamos, like those we see on the ice giants.

Marie-Curie fellow Michael Le Bars, has been working in the SPINLab for a year, taking part in a long-standing relationship between the lab and French researchers.  Le Bars investigates mixed systems that are partially convecting and partially layered, like those in our atmosphere, oceans, and stars.  These systems were thought to be well understood, but when Le Bars decided to ship his experiments all the way from France to Los Angeles and try rotating them in the SPINLab, the results were surprising.  “Rotation changes everything,” said Le Bars.  One interesting result was the production of “inverse cascades” that create columns of spinning fluid that cut across stratified layers similar to the Great Red Spot on Jupiter.

The fluid dynamics of most turbulent systems studied in the SPINLab are simply too complex for even the most advanced supercomputers to model or predict, but Aurnou and his team realize the importance of combining the two approaches.  They hope to build bridges between experimental and computational methods in order to determine “how to make models that better describe the examples we see in nature.”

Learn more about SPINLab on their website.  Watch the SPINLab educational film project here.