Brown, Farley, and Seinfeld Elected to National Academy of Sciences

Based on their distinguished achievements in original research, three Caltech professors—Mike Brown, Ken Farley, and John Seinfeld—are among the 84 members and 21 foreign associates newly elected to the National Academy of Sciences. The announcement was made this week at the 150th annual meeting of the academy in Washington, D.C.

The three new elections bring the number of living Caltech faculty members who belong to the academy to 73, including four foreign associates. In addition, three current members of the Caltech Board of Trustees are academy members.

In total, there are now 2,179 active members and 437 foreign associates of the National Academy of Sciences.

 

Michael E. Brown, the Richard and Barbara Rosenberg Professor and professor of planetary astronomy

Mike Brown is known for discovering and characterizing bodies at the edge of the solar system. In 2005, he discovered a Kuiper-belt object, later named Eris, which is about the same size as Pluto but 27 percent more massive. That finding led to a scientific debate over how to define a planet, and to the eventual demotion of Pluto to "dwarf planet."

Brown received his undergraduate degree from Princeton University in 1987 and did his graduate work at UC Berkeley, completing his PhD in 1994. He came to Caltech as a visiting associate in 1995 and joined the faculty in 1997. Brown became a full professor in 2005 and was named the Rosenberg Professor in 2008.

Brown has won numerous awards for his work, including the 2001 Harold C. Urey Prize from the American Astronomical Society's Division for Planetary Sciences, a Presidential Early Career Award, a Sloan Research Fellowship, and the 2012 Kavli Prize in Astrophysics.

 

Kenneth A. Farley, chair of the Division of Geological and Planetary Sciences and the W. M. Keck Foundation Professor of Geochemistry

Ken Farley is recognized for his studies of the noble gases and what their concentrations in marine sediments, rocks, minerals, and seawater can tell us about geochemical processes and the timescales over which these processes have operated. He is also currently a participating scientist on NASA's Mars Science Laboratory rover mission.

Farley received a BS from Yale University in 1986 and a PhD from UC San Diego in 1991. He joined the Caltech faculty in 1993 and was appointed professor in 1998. Farley was named the Keck Foundation Professor in 2003, the same year he served as director of the Tectonics Observatory. He became division chair in 2004.

His distinctions include the 1999 James B. Macelwane Medal of the American Geophysical Union, the 2000 National Academy of Science Award for Initiatives in Research, and the 2008 Arthur L. Day Medal from the Geological Society of America, and he was named a 2013 Geochemical Fellow by the Geochemical Society and the European Association of Geochemistry.

 

John H. Seinfeld, the Louis E. Nohl Professor and professor of chemical engineering

John Seinfeld's work has greatly improved our understanding of the origin, chemistry, and evolution of particles, or aerosols, in the atmosphere. He has revealed the role of organic species in aerosols and the process by which vapor molecules become incorporated into particles. Today, his work continues to focus on large questions such as the effects of aerosols on cloud formation and Earth's climate.

Seinfeld received his BS from the University of Rochester in 1964 and his PhD from Princeton University in 1967. He joined the faculty at Caltech that same year, becoming a full professor in 1974 and the Nohl Professor in 1979. He served as executive officer for chemical engineering from 1974 until 1990 and was chair of the Division of Engineering and Applied Science from 1990 until 2000.

Seinfeld is a member of the National Academy of Engineering and a fellow of the American Academy of Arts and Sciences. Among other distinctions, he won the Tyler Prize for Environmental Achievement in 2012, the American Chemical Society's Award for Creative Advances in Environmental Science and Technology in 1993, the Fuchs Award in 1998, the Nevada Medal in 2001, and the Stodola Medal from the Swiss Federal Institute of Technology in 2008. He has also received honorary doctorates from the University of Patras, Carnegie Mellon University, and Clarkson University.

 

The National Academy of Sciences is a private, nonprofit honorific society of distinguished scholars engaged in scientific and engineering research, dedicated to the furthering of science and technology and to their use for the general welfare. Established in 1863, the National Academy of Sciences has served to "investigate, examine, experiment, and report upon any subject of science or art" whenever called upon to do so by any department of the government.

For more information about the academy, or for the full list of newly elected members, visit www.nationalacademies.orgFor an extensive list of Caltech awards and honors, visit www.caltech.edu/content/awards-honors.

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Mars Science Laboratory: The Search for Habitable Environments

Watson Lecture Preview

John Grotzinger, Caltech's Fletcher Jones Professor of Geology, is the project scientist for JPL's newest Mars rover—Curiosity, the Mars Science Laboratory. The rover is exploring the floor of Gale Crater, and Grotzinger will describe its discoveries so far during a free public lecture at 8 p.m. on Wednesday, April 24, in Caltech's Beckman Auditorium.

 

Q: What do you do?

A: I oversee the science team and the way that it interfaces with the engineering team. I started back in 2007 when all the instruments on the rover were still in development. We had to test them all individually and then test how they performed with the rover. There were reviews every step of the way as the instruments were completed and certified for flight. This was a totally different experience for me; getting involved with the mission in the very early stages of development and seeing what goes into the whole process has been the most intense learning experience of my career. I went from having a few graduate students and postdocs to suddenly trying to lead a group of 400 scientists and engineers.

After we launched, the science team spent the next eight months practicing how to use the instruments, and now I'm basically helping work out the path of discovery. We work as a group to figure out what we're going to do with the rover each day. There are probably a dozen meetings in a typical day, of which I attend four to six. For me, the highlight of each day is the science discussion, where we have a two-hour block of time in which different team members present all the science data that we've got, and we just talk about it. It's a lot of fun.

 

Q: Aside from the fact that you're driving around on Mars, which is just inherently cool, what's the best thing about what you do?

A: Nobody ever before has seen what we're seeing. Every day new data arrive. New images of the terrain we're in the course of discovering; new measurements from the analytical instruments. (Mars is behind the sun right now, so we aren't getting any new data, but we should regain contact around the first of May.) The downlink's timing is based on the sol—the Martian day, which is 39 minutes longer than an Earth day—so some days we wake up and the data have arrived hours earlier. Other times, when the data come down later in the day, all the team members who are physically at JPL gather in one or two rooms where the downlink is actually happening. Those hours, days, are really an amazing experience because we really are going where nobody has gone before. And that's pretty special.

 

Q: How did you get into this line of work?

A: In 2003, I got involved with the Mars Exploration Rovers as one of the long-term planning leads. I was at MIT at the time, but I came out to JPL for a year to do that. Two years later, I joined Caltech's geobiology group. What we do on Mars is pretty much what I do on Earth with my students—investigate rocks that are billions of years old and look for evidence of habitable environments. I went to college to be a biologist. I changed majors to chemistry and then finally went into geology.

Geology represents this great nexus of physics and chemistry and biology and math. You get to do it all at the same time, and if you do field geology you get to do it outdoors.

 

 

Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.

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Monday, April 1, 2013
Center for Student Services, 3rd Floor, Brennan Conference Room

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A Window Into Europa's Ocean Lies Right at the Surface

Caltech and JPL researchers find evidence that a jovian ocean is not isolated

PASADENA, Calif.—If you could lick the surface of Jupiter's icy moon Europa, you would actually be sampling a bit of the ocean beneath. So says Mike Brown, an astronomer at the California Institute of Technology (Caltech). Brown—known as the Pluto killer for discovering a Kuiper-belt object that led to the demotion of Pluto from planetary status—and Kevin Hand from the Jet Propulsion Laboratory (JPL) have found the strongest evidence yet that salty water from the vast liquid ocean beneath Europa's frozen exterior actually makes its way to the surface.

The finding, based on some of the first data of its kind since NASA's Galileo mission (1989–2003) to study Jupiter and its moons, suggests that there is a chemical exchange between the ocean and surface, making the ocean a richer chemical environment, and implies that learning more about the ocean could be as simple as analyzing the moon's surface. The work is described in a paper that has been accepted for publication in the Astronomical Journal.

"We now have evidence that Europa's ocean is not isolated—that the ocean and the surface talk to each other and exchange chemicals," says Brown, the Richard and Barbara Rosenberg Professor and professor of planetary astronomy at Caltech. "That means that energy might be going into the ocean, which is important in terms of the possibilities for life there. It also means that if you'd like to know what's in the ocean, you can just go to the surface and scrape some off."

"The surface ice is providing us a window into that potentially habitable ocean below," says Hand, deputy chief scientist for solar system exploration at JPL.

Since the days of the Galileo mission, when the spacecraft showed that Europa was covered with an icy shell, scientists have debated the composition of Europa's surface. The infrared spectrometer aboard Galileo was not capable of providing the detail needed to definitively identify some of the materials present on the surface. Now, using current technology on ground-based telescopes, Brown and Hand have identified a spectroscopic feature on Europa's surface that indicates the presence of a magnesium sulfate salt, a mineral called epsomite, that could only originate from the ocean below.

"Magnesium should not be on the surface of Europa unless it's coming from the ocean," Brown says. "So that means ocean water gets onto the surface, and stuff on the surface presumably gets into the ocean water."

Europa's ocean is thought to be 100 kilometers deep and covers the entire globe. The moon remains locked in relation to Jupiter, with the same hemisphere always leading and the other trailing in its orbit. The leading hemisphere has a yellowish appearance, while the trailing hemisphere seems to be splattered and streaked with a red material.

The spectroscopic data from that red side has been a cause of scientific debate for 15 years. It is thought that one of Jupiter's largest moons, Io, spews volcanic sulfur from its atmosphere, and Jupiter's strong magnetic field sends some of that sulfur hurtling toward the trailing hemisphere of Europa, where it sticks. It is also clear from Galileo's data that there is something other than pure water ice on the trailing hemisphere's surface. The debate has focused on what that other something is—i.e., what has caused the spectroscopic data to deviate from the signature of pure water ice.

"From Galileo's spectra, people knew something was there besides water. They argued for years over what it might be—sodium sulfate, hydrogen sulfate, sodium hydrogen carbonate, all these things that look more or less similar in this range of the spectrum," says Brown. "But the really difficult thing was that the spectrometer on the Galileo spacecraft was just too coarse."

Brown and Hand decided that the latest spectrometers on ground-based telescopes could improve the data pertaining to Europa, even from a distance of about 400 million miles. Using the Keck II telescope on Mauna Kea—which is outfitted with adaptive optics to adjust for the blurring effect of Earth's atmosphere—and its OH-Suppressing Infrared Integral Field Spectrograph (OSIRIS), they first mapped the distribution of pure water ice versus anything else on the moon. The spectra showed that even Europa's leading hemisphere contains significant amounts of nonwater ice. Then, at low latitudes on the trailing hemisphere—the area with the greatest concentration of the nonwater ice material—they found a tiny dip in the spectrum that had never been detected before.

"We now have the best spectrum of this thing in the world," Brown says. "Nobody knew there was this little dip in the spectrum because no one had the resolution to zoom in on it before."

The two researchers racked their brains to come up with materials that might explain the new spectroscopic feature, and then tested everything from sodium chloride to Drano in Hand's lab at JPL, where he tries to simulate the environments found on various icy worlds. "We tried to think outside the box to consider all sorts of other possibilities, but at the end of the day, the magnesium sulfate persisted," Hand says.

Some scientists had long suspected that magnesium sulfate was on the surface of Europa. But, Brown says, "the interesting twist is that it doesn't look like the magnesium sulfate is coming from the ocean." Since the mineral he and Hand found is only on the trailing side, where the moon is being bombarded with sulfur from Io, they believe that there is a magnesium-bearing mineral everywhere on Europa that produces magnesium sulfate in combination with sulfur. The pervasive magnesium-bearing mineral might also be what makes up the nonwater ice detected on the leading hemisphere's surface.

Brown and Hand believe that this mystery magnesium-bearing mineral is magnesium chloride. But magnesium is not the only unexpected element on the surface of Europa. Fifteen years ago, Brown showed that Europa is surrounded by an atmosphere of atomic sodium and potassium, presumably originating from the surface. The researchers reason that the sodium and potassium chlorides are actually the dominant salts on the surface of Europa, but that they are not detectable because they have no clear spectral features.

The scientists combined this information with the fact that Europa's ocean can only be one of two types—either sulfate-rich or chlorine-rich. Having ruled out the sulfate-rich version since magnesium sulfate was found only on the trailing side, Brown and Hand hypothesize that the ocean is chlorine-rich and that the sodium and potassium must be present as chlorides.

Therefore, Brown says, they believe the composition of Europa's sea closely resembles the salty ocean of Earth. "If you could go swim down in the ocean of Europa and taste it, it would just taste like normal old salt," he says.

Hand emphasizes that, from an astrobiology standpoint, Europa is considered a premier target in the search for life beyond Earth; a NASA-funded study team led by JPL and the Johns Hopkins University Applied Physics Laboratory have been working with the scientific community to identify options to explore Europa further.  "If we've learned anything about life on Earth, it's that where there's liquid water, there's generally life," Hand says. "And of course our ocean is a nice salty ocean. Perhaps Europa's salty ocean is also a wonderful place for life."

The Astronomical Journal paper is titled "Salts and radiation products on the surface of Europa." The work was supported, in part, by the NASA Astrobiology Institute through the Astrobiology of Icy Worlds node at JPL.

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Planetary Astronomer Wins Feynman Prize for Excellence in Teaching

PASADENA, Calif.—John A. Johnson, assistant professor of planetary astronomy at the California Institute of Technology (Caltech), has been awarded the Richard P. Feynman Prize for Excellence in Teaching.

Johnson was recognized for his dedication, passion, and innovation in teaching as well as his ability to inspire his students.

The Feynman Prize was established "to honor annually a professor who demonstrates, in the broadest sense, unusual ability, creativity, and innovation in undergraduate and graduate classroom or laboratory teaching." Caltech faculty members, students, postdoctoral scholars, staff, and alumni may nominate a faculty member for the prize. A committee appointed by the provost then selects the winner.

According to the official citation, Johnson "immediately emerged as exceptional—a 'true outlier,' in the words of a committee member."

"Richard Feynman's writing inspired me to pursue physics and astronomy," Johnson says. "It is an amazing honor to have my name in any way associated with his."

Johnson was lauded for his creative teaching methods, in which he eschews traditional lectures and problem sets and instead has students work on problems in small groups. At various times, he has required students to explain what they were learning in a class blog, forbidden discussion of grades, emailed YouTube videos that illustrate the day's material, and brought in guest lecturers to discuss the course material and provide career advice. 

"My goal is to help the students take ownership of their learning by guiding them rather than lecturing them," explains Johnson, who says he learned his teaching philosophy from physicist Ronald Bieniek at the Missouri University of Science and Technology. "I'm very pleased to hear that my students feel I accomplished this goal, and that we all had such an enjoyable time in the process."

In a nomination letter, one student wrote that Johnson "rocked the boat in the astronomy department, challenging our conceptions of how astronomy, and the sciences in general, are taught." Another student wrote, "Classroom experiences that are intellectually engaging, practical, and entertaining are incredibly rare. Through his teaching style, attention to detail, and unique course structure, Professor Johnson provides just such an experience."

Many students cited Johnson's "life-changing" influence beyond academics. One called him "a remarkable teacher who can not only enlighten students in the classroom but also sculpt their spirits for their future careers." A graduate student said, "He reminded me…why I wanted to be a scientist in the first place."

Johnson, whose research focuses on searching for planets around stars other than our sun, earned his BS in physics in 1999 from the University of Missouri-Rolla (now the Missouri University of Science and Technology) and his PhD in astrophysics from the University of California, Berkeley, in 2007. After completing a postdoctoral fellowship at the University of Hawaii Institute for Astronomy, he joined Caltech's faculty in 2009. In 2012, he won the Newton Lacy Pierce Prize from the American Astronomical Society, an Alfred P. Sloan Fellowship, a David and Lucile Packard Fellowship, and a Lyman Spitzer Lectureship from Princeton. Johnson says, however, that of all the awards he has received this past year, he's most proud of the Feynman Prize.

The previous four winners of the Feynman Prize are Paul Asimow, professor of geology and geochemistry; J. Morgan Kousser, professor of history and social science; Dennis Dougherty, the George Grant Hoag Professor of Chemistry; and Jehoshua (Shuki) Bruck, the Gordon and Betty Moore Professor of Computation and Neural Systems and Electrical Engineering. The Feynman Prize has been awarded annually since 1994. Nominations for next year's prize will be solicited in the fall.

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Under the Hood of the Earthquake Machine

Watson Lecture Preview

 

What makes an earthquake go off? Why are earthquakes so difficult to forecast? Professor of Mechanical Engineering and Geophysics Nadia Lapusta gives us a close-up look at the moving parts, as it were, at 8:00 p.m. on Wednesday, February 13, 2013, in Caltech's Beckman Auditorium. Admission is free.

 

Q: What do you do?

A: I study friction as it relates to earthquakes. At a depth of five miles, which is the average depth at which large earthquakes in Southern California occur, the compression on the two sides of the fault is roughly equivalent to a pressure of 1,500 atmospheres. So you can imagine that friction plays an important role. I make computational models that combine our theories about friction with laboratory studies of how materials behave. We try to reproduce what seismologists, geodesists, and geologists see actual earthquakes doing, in order to infer the physical laws that govern them.

Our planet's surface is made up of a bunch of plates that are always moving, and an earthquake happens when the locked boundaries of the plates rapidly catch up with the slow motion of the plates themselves. You get a sudden shearing—a sideways motion that generates the destructive waves that we perceive as shaking.

A number of factors affect this process. If you rub your palms together, you generate heat. An earthquake is a very intensive rubbing of palms, if you will, and so a lot of heat is produced—enough to weaken the rocks and perhaps even melt them.

However, there are pore fluids permeating the rocks—we often get our drinking water from underground aquifers, for example. As these fluids heat up, they expand, which modifies the shearing process. They produce expanding cushions of steam, essentially, which reduce the friction.

The waves generated by the shearing motion put an additional load on the fault ahead of the shear zone, so they actually affect how the shearing progresses. The shear tip sprouts at about three kilometers per second, or 6,700 miles per hour. So an earthquake is a highly dynamic, nonlinear system.

To make things even more interesting, a fault doesn't just sit still for hundreds of years, waiting for the next big earthquake. It's more like a living thing—there are slow slippages between earthquakes that constantly redistribute the forces in the system, and the exact point where an earthquake initiates depends a lot on these slow motions. So we simulate thousands of years of fault history that includes a few occasional, very fast events that last for a few seconds. These calculations are very time-consuming and memory-intense. The Geological and Planetary Sciences Division's supercomputer has several thousand processors, and we routinely use 200 to 400 of them, sometimes for weeks at a time. We would happily use the entire machine, but of course people would yell at us.

 

Q: How did you get into this line of work?

A: I've loved both mathematics and physics since I was a child. I was born in Ukraine, where my mom was a professor of applied mathematics and my dad was a civil engineer. They used to give me math and physics problems from a very early age. I did my undergraduate studies in applied mathematics in Kiev, and I was thinking of going into materials science. I came to the U.S. for graduate school, and my advisor at Harvard was working on materials failure and on earthquakes, which I found very interesting because it combined math and physics with a problem relevant to society.

My PhD was on frictional sliding and some initial models of earthquakes. Caltech is actually the perfect place to continue that, because it has world-class expertise in all relevant disciplines. I have wonderful colleagues, and the really fun part is working with them. I enjoy interacting with the experimentalists and talking to the people who make field observations or do radar measurements from satellites. They have different perspectives, different terminologies, and different views of the problem, so it's fun to try to explain to them what you mean, and to try to understand what they mean. And the most fun, of course, is when you come to an understanding that leads to new science in the end.

 

Q: Speaking of societal relevance, what does your work mean for us here in L.A.?

A: Large earthquakes, fortunately, are relatively rare, so we don't have detailed observations of very many of them. Our models, however, allow us to explore scenarios for potentially very damaging earthquakes that we haven't experienced. For example, faults have locked segments and creeping segments. The San Andreas fault has a creeping segment between Los Angeles and San Francisco, and the assumption has been that this segment will confine a large earthquake to either the southern or the northern part of the fault. Only one large urban area would be affected. However, our models show that a through-going rupture may be possible. If that happens, both Los Angeles and San Francisco are affected, and you have a much bigger problem on your hands.

 

Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.

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John Johnson Wins Astronomy Prize

John A. Johnson, assistant professor of planetary astronomy at Caltech, received the 2012 Newton Lacy Pierce Prize at the 221st meeting of the American Astronomical Society (AAS), in Long Beach, California.

The AAS reserves the Newton Lacy Pierce Prize for North American astronomers, ages 36 and under, for "outstanding achievement, over the past five years, in observational astronomical research based on measurements of radiation from an astronomical object." Johnson received a cash award and an invitation to speak at the AAS conference on January 8.

According to the award citation, Johnson was recognized for "major contributions to understanding fundamental relationships between exosolar planets and their parent stars, including finding a variety of orientations between planetary orbital planes and the spin axes of their stars, developing a rigorous understanding of planet detection rates in transit and direct imaging experiments, and examining possible correlations between planet frequency and the mass and metallicity of their host stars."

"I am very pleased and thankful to the American Astronomical Society for this award," Johnson says. "Thanks to powerful new instruments and an emerging generation of highly motivated explorers, planetary astronomy is an exciting field to be in right now. I am happy to be part of it."

Johnson is one of the founding members of Caltech's new Center for Planetary Astronomy. His recent research findings related to the estimated number of planets in the Milky Way have generated significant interest both within the astronomical community and among the general public.

In addition to the Pierce Prize, Johnson was also a recipient in 2012 of a Lyman Spitzer Lectureship, an Alfred P. Sloan Research Fellowship, and a David and Lucile Packard Fellowship.

 

 

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Heather Knutson Wins Astronomy Award

Heather A. Knutson, an assistant professor of planetary science at Caltech, is the 2012 recipient of the Annie Jump Cannon Award in Astronomy. Knutson received the award at the 221st meeting of the American Astronomical Society (AAS), in Long Beach, California.

The Annie Jump Cannon Award is given to a North American female astronomer within five years of receiving her PhD in the year designated for the award, for outstanding research and the promise of future research. Knutson received a cash prize of $1,500 and an invitation to speak at the recent AAS meeting.

According to the award citation, Knutson is being recognized for her "pioneering work on the characterization of exoplanetary atmospheres. Her groundbreaking observations of wavelength-dependent thermal emission of exoplanets over large fractions of their orbit enable a longitudinal mapping of brightness to reveal details of atmospheric dynamics, energy transport, inversion layers, and chemical composition. This work has expanded the rich field of planetary characterization by providing new windows into the atmospheres of planets beyond the confines of our own solar system. It has inspired numerous other theoretical and observational investigations and will serve as an important technique used with current and future space observatories to gain fundamental insight into the properties of exoplanetary atmospheres."

"It was a pleasure to accept this award from the American Astronomical Society," says Knutson. "It is good to see that studies of exoplanetary atmospheres are gaining some positive attention in the astronomy community."

Knutson is one of the founding faculty members of Caltech's new Center for Planetary Astronomy.

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Friday, January 25, 2013
Annenberg 121

Course Ombudspeople Lunch

Research Update: Atomic Motions Help Determine Temperatures Inside Earth

In December 2011, Caltech mineral-physics expert Jennifer Jackson reported that she and a team of researchers had used diamond-anvil cells to compress tiny samples of iron—the main element of the earth's core. By squeezing the samples to reproduce the extreme pressures felt at the core, the team was able to get a closer estimate of the melting point of iron. At the time, the measurements that the researchers made were unprecedented in detail. Now, they have taken that research one step further by adding infrared laser beams to the mix.

The lasers are a source of heat that, when sent through the compressed iron samples, warm them up to the point of melting.  And because the earth's core consists of a solid inner region surrounded by a liquid outer shell, the melting temperature of iron at high pressure provides an important reference point for the temperature distribution within the earth's core.

"This is the first time that anyone has combined Mössbauer spectroscopy and heating lasers to detect melting in compressed samples," says Jackson, a professor of mineral physics at Caltech and lead author of a recent paper in the journal Earth and Planetary Science Letters that outlined the team's new method. "What we found is that iron, compared to previous studies, melts at higher temperatures than what has been reported in the past."

Earlier research by other teams done at similar compressions—around 80 gigapascals—reported a range of possible melting points that topped out around 2600 Kelvin (K). Jackson's latest study indicates an iron melting point at this pressure of approximately 3025 K, suggesting that the earth's core is likely warmer than previously thought.

Knowing more about the temperature, composition, and behavior of the earth's core is essential to understanding the dynamics of the earth's interior, including the processes responsible for maintaining the earth's magnetic field. While iron makes up roughly 90 percent of the core, the rest is thought to be nickel and light elements—like silicon, sulfur, or oxygen—that are alloyed, or mixed, with the iron.

To develop and perform these experiments, Jackson worked closely with the Inelastic X-ray and Nuclear Resonant Scattering Group at the Advanced Photon Source at Argonne National Laboratory in Illinois. By laser heating the iron sample in a diamond-anvil cell and monitoring the dynamics of the iron atoms via a technique called synchrotron Mössbauer spectroscopy (SMS), the researchers were able to pinpoint a melting temperature for iron at a given pressure. The SMS signal is sensitively related to the dynamical behavior of the atoms, and can therefore detect when a group of atoms is in a molten state.

She and her team have begun experiments on iron alloys at even higher pressures, using their new approach.

"What we're working toward is a very tight constraint on the temperature of the earth's core," says Jackson. "A number of important geophysical quantities, such as the movement and expansion of materials at the base of the mantle, are dictated by the temperature of the earth's core."

"Our approach is a very elegant way to look at melting because it takes advantage of the physical principle of recoilless absorption of X-rays by nuclear resonances—the basis of the Mössbauer effect—for which Rudolf Mössbauer was awarded the Nobel Prize in Physics," says Jackson. "This particular approach to study melting has not been done at high pressures until now."

Jackson's findings not only tell us more about our own planet, but could indicate that other planets with iron-rich cores, like Mercury and Mars, may have warmer internal temperatures as well.

Her paper, "Melting of compressed iron by monitoring atomic dynamics," was published in Earth and Planetary Science Letters on January 8, 2013.

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