Tuesday, July 29, 2014
Center for Student Services 360 (Workshop Space) – Center for Student Services

Intro to Course Design Workshop

Earth-Building Bridgmanite

Our planet's most abundant mineral now has a name

Deep below the earth's surface lies a thick, rocky layer called the mantle, which makes up the majority of our planet's volume. For decades, scientists have known that most of the lower mantle is a silicate mineral with a perovskite structure that is stable under the high-pressure and high-temperature conditions found in this region. Although synthetic examples of this composition have been well studied, no naturally occurring samples had ever been found in a rock on the earth's surface. Thanks to the work of two scientists, naturally occurring silicate perovskite has been found in a meteorite, making it eligible for a formal mineral name.

The mineral, dubbed bridgmanite, is named in honor of Percy Bridgman, a physicist who won the 1946 Nobel Prize in Physics for his fundamental contributions to high-pressure physics.

"The most abundant mineral of the earth now has an official name," says Chi Ma, a mineralogist and director of the Geological and Planetary Sciences division's Analytical Facility at Caltech.

"This finding fills a vexing gap in the taxonomy of minerals," adds Oliver Tschauner, an associate research professor at the University of Nevada-Las Vegas who identified the mineral together with Ma.

High-pressure and temperature experiments, as well as seismic data, strongly suggest that (Mg,Fe)SiO3-perovskite—now simply called bridgmanite—is the dominant material in the lower mantle. But since it is impossible to get to the earth's lower mantle, located some 400 miles deep within the planet, and rocks brought to the earth's surface from the lower mantle are exceedingly rare, naturally occurring examples of this material had never been fully described.

That is until Ma and Tschauner began poking around a sample from the Tenham meteorite, a space rock that fell in Australia in 1879.

Because the 4.5 billion-year-old meteorite had survived high-energy collisions with asteroids in space, parts of it were believed to have experienced the high-pressure conditions we see in the earth's mantle. That, scientists thought, made it a good candidate for containing bridgmanite.

Tschauner used synchrotron X-ray diffraction mapping to find indications of the mineral in the meteorite. Ma then examined the mineral and its surroundings with a high-resolution scanning electron microscope and determined the composition of the tiny bridgmanite crystals using an electron microprobe. Next, Tschauner analyzed the crystal structure by synchrotron diffraction. After five years and multiple experiments, the two were finally able to gather enough data to reveal bridgmanite's chemical composition and crystal structure.

"It is a really cool discovery," says Ma. "Our finding of natural bridgmanite not only provides new information on shock conditions and impact processes on small bodies in the solar system, but the tiny bridgmanite found in a meteorite could also help investigations of phase transformation mechanisms in the deep Earth. "

The mineral and the mineral name were approved on June 2 by the International Mineralogical Association's Commission on New Minerals, Nomenclature and Classification. 

The researchers' findings are published in the November 28 issue of Science, in an article titled "Discovery of Bridgmanite, the Most Abundant Mineral in Earth, In a Shocked Meteorite."

Katie Neith
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Tuesday, July 22, 2014
Center for Student Services 360 (Workshop Space) – Center for Student Services

Teaching Quantum Mechanics with Minecraft and Comics

Ditch Day? It’s Today, Frosh!

Today we celebrate Ditch Day, one of Caltech's oldest traditions. During this annual spring rite—the timing of which is kept secret until the last minute—seniors ditch their classes and vanish from campus. Before they go, however, they leave behind complex, carefully planned out puzzles and challenges—known as "stacks"—designed to occupy the underclass students and prevent them from wreaking havoc on the seniors' unoccupied rooms.

Follow the action on Caltech's Facebook and Twitter pages as the undergraduates tackle the puzzles left around campus for them to solve, and get in on the conversation by sharing your favorite Ditch Day memories. Be sure to use #CaltechDitchDay in your tweets and postings.

View photos from the day:


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Thursday, September 25, 2014
Location to be announced

2014 Caltech Teaching Conference

Tuesday, May 13, 2014
Avery Library – Avery House

Semana Latina Keynote Speaker – Dr. Rodolfo Mendoza-Denton

Friday, May 16, 2014
Center for Student Services 360 (Workshop Space) – Center for Student Services

The Role of Writing in Building a Research Career

50 Years Ago: The First Look at a Dry Mars

In 1964, Caltech astronomy professor Guido Münch and Jet Propulsion Laboratory space scientists Lewis Kaplan and Hyron Spinrad pushed the world's second-largest telescope to its limits and dashed—at least for the next few decades—any hopes of finding liquid water on Mars.

Back in the late 1800s, it was widely assumed that Mars was a planet with abundant water, just like Earth. Astronomers were mapping Mars's polar caps, which advanced and retreated as the seasons changed; a dark "wave," apparently of vegetation, which swept from the pole toward the equator every spring; and even ruler-straight lines that might have been canals dug by an alien civilization. Today, we know that the ice caps grow larger because the winters are cold enough to freeze carbon dioxide right out of Mars's thin air; the seasonal darkening is a wind-driven redistribution of the dust that blankets the planet; and the canals were optical illusions enhanced by wishful thinking.

The notion of a moist Mars began to evaporate at the turn of the 20th century. In 1909, Lick Observatory dispatched a team of astronomers to climb Mount Whitney—whose summit, at 14,500 feet, rises above some four-fifths of Earth's atmospheric water vapor. Pointing a small telescope at Mars, the team measured no water vapor in excess of that in the rarefied air around them, although observatory director William Wallace Campbell cautioned the Associated Press that their technique, "the only method known, is not a sensitive one." Campbell diplomatically noted that "the question of life under these conditions is the biologist's problem rather than the astronomer's."

Bigger telescopes make for more sensitive measurements, and by the 1920s the world's largest telescopes were just north of Pasadena at the Mount Wilson Observatory. In 1926, observatory director Walter Adams and Charles St. John wrote in the Astrophysical Journal that "the quantity of water-vapor in the atmosphere of Mars, area for area, was 6 per cent of that over Mount Wilson . . . This indicates extreme desert conditions over the greater portion of the Martian hemisphere toward us at the time." The 60-inch telescope they used was second in size and power only to the adjacent 100-inch Hooker telescope, with which Adams revisited the question in 1937 and 1939 and revised his figures downward. In 1941 he wrote, "If water vapor lines are present . . . they cannot be more than 5 per cent as strong as in the earth's atmosphere and are probably very much less."

The "lines" Adams referred to are spectral ones. The spectrum of light contains all the colors of the rainbow, plus wavelengths beyond, that we can't see. Every gas in the atmosphere—both Earth's and Mars's—absorbs a specific collection of these colors. Passing the light from a telescope through a device called a spectrograph spreads out the rainbow and reveals the missing wavelengths, allowing the gases that absorbed them to be identified.

In those days, spectra were usually recorded as shades of gray on glass plates coated with a light-sensitive emulsion—essentially the same technique photographer Matthew Brady had used to document the Civil War. Once the plates were developed, the missing wavelengths showed up as black lines that were painstakingly analyzed under a microscope. Each line's location indicated its wavelength, while its darkness and thickness were related to the absorber's abundance. And therein lay the problem: the wide, black blots left on the plate by Earth's dense blanket of air made the thin, faint lines from the tenuous atmosphere of Mars hard to see, let alone measure. The best opportunities to find the lines occur at approximately two-year intervals. Earth travels in a tighter orbit around the sun than Mars does, and as we pass Mars on the inside track our close approach maximizes the apparent difference in our velocities. This shifts Mars's spectrum ever so slightly away from Earth's—if you have an instrument powerful enough to discern the separation.

Unfortunately, some passes are closer than others. When Earth overtook Mars in 1963, the latter was at the point in its orbit most distant from the sun. Although the two planets were as close to each other as they were going to get that time around, the velocity effect was minimized—imagine looking out the window of a moving train at a distant farmhouse instead of the nearby telephone poles. But the Hooker's spectrograph had recently been upgraded; Kaplan and Spinrad were expert spectroscopists; and Münch was a wizard at making very sensitive emulsions, so the trio decided to look for the lines anyway. With little prospect for success, the experiment was allotted a set of low-value nights that began more than two months after Earth had passed Mars and started to pull ahead. At its closest approach, Mars had been 62,000,000 miles away; by the time Münch and company got their turn at the telescope, that distance had nearly doubled. Their telescope was no longer the best available, having been overtaken as the world's largest by the 200-inch Hale telescope at Caltech's Palomar Observatory. Even the weather conspired against them; four nights of work yielded exactly one usable exposure.

But as Münch wrote in the January 1964 issue of the Astrophysical Journal, that "strongly hypersensitized" plate gave "a spectrogram of excellent quality which shows faint but unmistakable lines which have been ascribed to H20 in Mars' atmosphere . . . After comparing our plate with other ones found in the Mount Wilson files, we have convinced ourselves that ours is the spectrogram of Mars with the highest resolving power ever taken."

Even so, the lines were barely strong enough to be usable. The preliminary water-vapor calculation, announced in May 1963, had an error factor of 10. It would take another six months to work out the definitive number—a figure equivalent to 0.01 ± 0.006 per cent of the amount of water vapor over Mount Wilson, and 100 times less than the 6 percent Adams and St. John had referred to as "extreme desert conditions" 40 years earlier. Furthermore, a slightly stronger carbon dioxide line enabled a direct estimate of Mars's atmospheric pressure: 25 millibars (2.5 percent of Earth's surface pressure)—one-quarter of the best previous estimates. (Munch and his collaborators noted in passing that although their value for carbon dioxide was not itself surprising, "what would appear indeed surprising is that the . . . value for the atmospheric pressure [is] so low that CO2 itself becomes a major constituent"—entirely unlike Earth, where nitrogen and oxygen make up 99 percent of the air we breathe.) Based on these results, Mars was now officially as arid as the moon, and nearly as airless.

Confirmation would follow in 1965, when JPL's Mariner 4 became the first spacecraft to visit Mars. The behavior of Mariner's radio signal as the spacecraft passed behind Mars revealed that its actual atmospheric pressure was lower still: 5 to 9 millibars, or less than 1 percent of Earth's. And the 20 televised pictures of Mars's cratered, moonlike surface—some shot from as little as 6,000 miles above it—cemented the comparison.

Professor of Physics Robert Leighton (BS '41, MS '44, PhD '47), who had been the principal investigator on Mariner 4's Television Experiment, as it was called, and Associate Professor of Planetary Science Bruce Murray, a member of the TV team, would use Münch's and Mariner's data as cross-checks on a detailed thermal model of Mars that they wrote for Caltech's IBM 7094 mainframe computer—a pioneering feat in its own right. Their results, published in 1966, correctly predicted that most of Mars's carbon dioxide was actually not in the atmosphere, but instead lay locked up in the polar caps in the form of dry ice; the paper also made the unprecedented suggestion that seasonal advance of each polar cap would freeze out so much carbon dioxide that the atmospheric pressure would drop by as much as 20 percent twice every Mars year. These predictions have since been confirmed many times over, and form part of our basic understanding of how Mars works.

And what of water on present-day Mars, which is where this story began? Leighton and Murray wrote that "considerable quantities of water-ice permafrost may be present in the subsurface of the polar regions" just a few tens of centimeters down—permafrost that was finally discovered in 2002 by JPL's Mars Odyssey mission. 

Douglas Smith
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Friday, May 30, 2014

Caltech Teaching Assistant Training for 2014-2015 Year

Caltech Faculty Elected to the American Academy of Arts and Sciences

The American Academy of Arts and Sciences has elected three Caltech faculty members as academy fellows. They are John F. Brady, Chevron Professor of Chemical Engineering and Mechanical Engineering and executive officer for chemical engineering; Kenneth A. Farley, W. M. Keck Foundation Professor of Geochemistry and chair of the Division of Geological and Planetary Sciences; and Fiona A. Harrison, Benjamin M. Rosen Professor of Physics.

"It is a privilege to honor these men and women for their extraordinary individual accomplishments," said Don Randel, chair of the academy's board of directors, of the 204 newly elected fellows and 16 foreign honorary members. "The knowledge and expertise of our members gives the academy a unique capacity—and responsibility—to provide practical policy solutions to the pressing challenges of the day. We look forward to engaging our new members in this work."

Brady works in the area of complex fluids and active matter that includes microstructural elements such as suspensions, colloidal dispersions, and self-propelling particles. Understanding these materials led Brady to develop a novel computational method called Stokesian dynamics. He won the 2012 Fluid Dynamics Prize from the American Physical Society and was elected to the National Academy of Engineering in 1999.

Most of Farley's research has focused on terrestrial geochemistry, but he is now increasingly interested in planetary science and especially exploration of the geochemistry, geology, and geomorphology of Mars. In his laboratory on the Caltech campus, Farley and his group measure noble gases such as helium and neon in rock and mineral samples. One major objective of this work is determining the ages and surface exposure history of Earth's geological features. Farley was recently involved in the first-ever experiments of this type carried out on the surface of Mars, via an instrument on board the Mars Science Laboratory's Curiosity rover. He has received the Day Medal of the Geological Society of America and the Macelwane Award of the American Geophysical Union, and was elected to the National Academy of Sciences in 2013.

Harrison specializes in observational and experimental high-energy astrophysics. She is the principal investigator for NASA's NuSTAR Explorer Mission and uses this satellite, along with other satellites and ground-based telescopes, to understand black holes, neutron stars, and supernova remnants. In her labs at Caltech, Harrison's group develops high-energy X-ray detectors and instrumentation for future space missions. She was elected to the American Physical Society in 2012 and won a NASA Outstanding Public Leadership Medal in 2013.

Also named to the academy this year is Katherine T. Faber, the Walter P. Murphy Professor of Materials Science and Engineering at Northwestern University, who will be joining the Caltech faculty on July 1 as the Simon Ramo Professor of Materials Science. Faber's research focuses on understanding fracture and toughening of brittle materials such as those used for high-temperature coatings for power generation applications. She also works on the fabrication of ceramic materials with controlled porosity. She is cofounder and codirector of the Northwestern University-Art Institute of Chicago Center for Scientific Studies in the Arts (NU-ACCESS), which employs advanced materials science techniques for conservation science. Faber is a Distinguished Life Member of the American Ceramic Society (2013), and became a National Science Foundation American Competitiveness and Innovation Fellow in 2010.

The total number of Caltech faculty named to the academy is now 97.

The academy was founded in 1780 by John Adams, James Bowdoin, John Hancock, and other scholar-patriots "to cultivate every art and science which may tend to advance the interest, honor, dignity, and happiness of a free, independent, and virtuous people." The academy has elected as fellows and foreign honorary members the finest minds and most influential leaders from each generation, including George Washington and Ben Franklin in the 18th century, Daniel Webster and Ralph Waldo Emerson in the 19th, and Albert Einstein and Winston Churchill in the 20th. The current membership includes more than 250 Nobel laureates and 60 Pulitzer Prize winners.

A full list of new members is available on the academy website at https://www.amacad.org/content/members/members.aspx.

The academy will welcome this year's new fellows and foreign honorary members at its annual induction ceremony at the academy's headquarters in Cambridge, Massachusetts, on October 11, 2014.

Cynthia Eller
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