Eugene W. Cowan, 90

PASADENA, Calif.—Eugene W. "Bud" Cowan, professor of physics, emeritus, at the California Institute of Technology (Caltech), passed away November 4 in Menlo Park, California. He was 90.

Cowan's research interests included investigations of high-energy interactions of cosmic rays, air-pollution studies, and studies of the earth's magnetism. He was noted for perfecting a cloud chamber capable of operating on a continuous basis. All cloud chambers depend on the condensation of a vapor on the charged ions left by the passage of a speeding particle. Previous cloud chambers had required a sudden, large drop in chamber pressure for condensation to occur, and this had to be followed by a rest period during which no observations could be made. Cowan's innovation eliminated the need for the pressure decrease and thus eliminated the rest period.

Cowan was particularly proud of his work in the early 1950s on the Xi "cascade" particle, the first doubly strange baryon. His cloud-chamber image clearly confirmed the existence of the particle and provided important input that led to the subsequent development of the quark model. His later work focused on the dynamics of the mechanism that generates the earth's magnetic field.

Long recognized for the quality of his teaching, Cowan received the 1986 Associated Students of the California Institute of Technology (ASCIT) Award for Teaching Excellence for his course on classical electromagnetism.

Cowan was born in 1920 in Ree Heights, South Dakota. After receiving his BS at the University of Missouri and his SM at MIT, where he was an instructor in the radar school and at the Radiation Laboratory, he came to Caltech in 1945. Cowan studied under cosmic-ray researcher and Nobel Laureate Carl Anderson. Awarded his PhD in 1948, Cowan became a research fellow in 1948, an assistant professor in 1950, and an associate professor in 1954. In 1961 he was promoted to professor of physics and became an emeritus professor in 1986.

Cowan was awarded four patents, including one for his innovative cloud chamber. He was a fellow of the American Physical Society.

In the Caltech community, Cowan was well known for his regular visits to the Caltech pool. "My father also walked the 2 1/2 miles to and from work for probably more than 50 years, and for much of that time also went daily to the Caltech pool and gym," says his son, Glen, a particle physicist at Royal Holloway, University of London. "His favorite hobby was hiking in the San Gabriel Mountains, and he was often one of the small group of hikers that walked to the physics picnic from the trail head in Sierra Madre. My father truly enjoyed being part of the Caltech community. I believe he was there almost every day from 1945 to 2008. Maybe that's some kind of record." 

In 2008, Cowan and his wife, Thelma, moved from Pasadena to Menlo Park, California, to be near their daughter,  Tina, a geneticist at Stanford University.

Cowan is survived by his wife of 54 years, Thelma Rasmussen Cowan; daughter Tina Cowan Hiltbrand and son Glen Cowan; and grandchildren David and Karin Hiltbrand. 

Kathy Svitil
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Discovering New Worlds

A Conversation with John Johnson

What's the focus of your research?

Broadly speaking, we want to find new planets around other stars, which are commonly referred to as exoplanets. We're building up a huge statistical sample. When you have a large number of planets, you can start looking for patterns, trends, and hints about the planet-formation process. The primary goal of my search for planets is to understand planet formation and therefore to understand the origins of the solar system. My characterization work is focused on individual systems of planets or the planets themselves. We're trying to learn about their physical characteristics, such as their radii, masses, average densities, and atmospheric properties. For systems of planets, we're interested in how planets interact gravitationally with one another. The exact nature of those gravitational interactions gives us hints about how planetary orbits evolve after they form. And that probably has a lot to do with how architectures of planetary systems eventually come to be.

What about this field is exciting?

It gets me out of bed every morning. I literally can't wait to see the latest data. It happened to me just yesterday. I was observing remotely in the basement of Cahill until my collaborators relieved me at about 3 a.m., since I had a full workday the next day and needed to sleep. I went to bed at about 3:30, expecting to sleep until 10:30. But I woke up at 7:30 and started thinking, you know, we just observed this new system we found and it's really wacky. It's a hot Jupiter around a type of star that's not supposed to have any hot Jupiters. If this next observation falls on the predicted curve, and it's likely going to be very real, then I'm going to have to think about how to share this with everybody. I couldn't go back to sleep. I was bone-tired, but I was excited and hyped up, so I got up and started working on the paper.

An artist's rendering of a gas-giant exoplanet orbiting a so-called subgiant star.
Credit: NASA/ESA/G. Bacon (STScl).

I don't know if I would get that level of excitement if I were doing cosmology or if I were studying galaxies—not to say that those fields are not immensely important and have exciting results. I just see new things every day that nobody on Earth has ever seen. It's just really fun being in a field of astronomy that's in its infancy—and being in a place like Caltech where we have Keck access once a month and we can actually watch all this happen.

What got you interested in science in general?

Stephen Hawking. A Brief History of Time—it changed my life. It's kind of clichéd. Half of all physicists are in physics because of that book. That's definitely what got me. Other popular-physics books after that sealed the deal. I was an engineer when I started off as an undergrad, doing aerospace and mechanical engineering. But it wasn't as interesting as discovering things about the universe.

But it all started in college. I can't say that I was one of those kids who begged their dad to buy them a telescope and then used it in their backyards. I had zero interest in astronomy until late in my college career. I was the kid who stayed inside and played with his Legos instead of the kid who went outside and explored under rocks. I was an engineer.

Why should we care about finding exoplanets? They don't plug up oil spills.

Every astronomer goes through that existential crisis. You have to understand that our society as we know it today is shaped largely through a lot of different astrophysical discoveries. The fact that we know Earth orbits the sun came from astronomers 450 years ago. The work that we're doing today is going to impact our culture and our understanding of our place in the universe forever. It's going to happen slowly, but that's what we're in the business of doing. Exoplanets are really good for that because we live on a planet, and we are finding other planets. We're trying to understand the planet we live on—where did it come from? It's the ultimate origin story. We are coming out of the darkness from a couple hundred years ago and we're rubbing our eyes today, realizing that we are on a really small planet around a really average star in an unspectacular part of the galaxy, and we're learning our place in this whole universe. Once we find more planets like our own, it'll further define our place and give us a better universal context for what it means to be human.

Read the full interview in E&S online.

Marcus Woo

Ralph W. Kavanagh, 86

Ralph W. Kavanagh, professor of physics, emeritus, at the California Institute of Technology (Caltech) passed away August 16 in Pasadena, California. He was 86.

Kavanagh was an expert in nuclear physics, primarily focusing on nuclear energy generation within the sun. As a member of Caltech's Kellogg Radiation Laboratory, he performed experiments looking at the fundamental interactions of light nuclei. He helped test some of the first models of evolving stars, which were based on his efforts to measure nuclear reactions thought to occur in the core of the sun.

Kavanagh focused on the steps in the chain that lead to the production of beryllium-7 and ultimately to the emission of neutrinos, the only particles that can escape unscathed from the center of the sun.  These neutrinos carry information about the solar interior and detecting them has become an active branch of astrophysics.  Kavanagh played a prominent role in this subfield through his careful studies of the properties of chlorine-37 and argon-37, the two nuclei involved in the detection of solar neutrinos that reach the earth.

In addition to the usual handful of graduate students he mentored, Kavanagh also taught the Advanced Physics Lab, beginning in the early 1970s and continuing until his retirement in 2000. This two-term course was required of all seniors majoring in physics; the few students committed to a theoretical career were permitted to substitute a thesis instead.  In this lab, Kavanagh followed the pattern established by Caltech physicist Victor Neher, with all exams being a private oral grilling at the conclusion of each experiment. In this fashion, Kavanagh came to know his physics students well and served them as a graduate-school advisor.

Born in 1924 in Seattle, Washington, Kavanagh served in the U.S. Navy from 1942 to 1946 before receiving his BA from Oregon's Reed College in 1950, followed by his MA from the University of Oregon. He received his PhD from Caltech in 1956. He continued at Caltech as a research fellow from 1956 to 1958, eventually becoming full professor in 1970. He became emeritus in 2000.

He was a fellow of the American Physical Society and the American Association for the Advancement of Science.

Outside the classroom, Kavanagh was an ardent classical pianist who was also fond of playing Ping-Pong. He enjoyed sailing and completing crossword puzzles, which he often could do in his head. An avid outdoorsman, he also enjoyed camping and hiking.

His family says he will be remembered for his sharp wit and wry sense of humor, for his high standard of ethics and his compassion for those less fortunate, and for his love of nature.

"Above all, science was not only his career, but his passion and hobby," says his wife, Joyce.

He leaves behind his wife, Joyce Kavanagh; daughters Kathleen Kavanagh, Janet Kavanagh, Stephanie Kavanagh Harlan, and Linda Kavanagh; eight grandchildren, and one great-grandson. His son, William Kavanagh, predeceased him. 

A service will be held at 10 a.m. on October 25, 2010, at the Athenaeum on the Caltech campus.

Jon Weiner
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Two Caltech Scientists Receive 2010 NIH Director's Pioneer Awards

Michael Roukes, Pamela Bjorkman recognized for their "highly innovative approaches" to biomedical research

PASADENA, Calif.—Two scientists from the California Institute of Technology (Caltech) have been recognized by the National Institutes of Health (NIH) for their innovative and high-impact biomedical research programs.

Michael Roukes, professor of physics, applied physics, and bioengineering, and co-director of the Kavli Nanoscience Institute, and

Pamela Bjorkman, Caltech's Max Delbrück Professor of Biology and a Howard Hughes Medical Institute investigator, now join the 81 Pioneers—including Caltech researchers Rob Phillips and Bruce Hay—who have been selected since the program's inception in 2004.

"NIH is pleased to be supporting scientists from across the country who are taking considered risks in a wide range of areas in order to accelerate research," said NIH Director Francis S. Collins in announcing the awards. "We look forward to the result of their work."

According to its website, the program provides each investigator chosen with up to $500,000 in direct costs each year for five years to pursue what the NIH refers to as "high-risk research," and was created to "support individual scientists of exceptional creativity who propose pioneering—and possibly transforming—approaches to major challenges in biomedical and behavioral research."

For Roukes, that means using "nanoscale tools to push biomedical frontiers." Specifically, he plans to leverage advances in nanosystems technology, "an approach that coordinates vast numbers of individual nanodevices into a coherent whole," he explains.

The goal? To create tiny "chips" that can be used to rapidly identify which specific bacteria are plaguing an individual patient—quickly, at the patient's bedside, and without the need for culturing. Similar chips, he says, will be capable of "obtaining physiological 'fingerprints' from exhaled breath" for use in disease diagnostics.

Roukes says the chips will also provide new approaches to cancer research through the analysis of cell mechanics and motility, and will provide less-costly ways to screen libraries of therapeutic drug candidates. Roukes's highly collaborative efforts are aimed at jump-starting what he calls a "nanobiotech incubator" at Caltech.

Roukes received his PhD in physics in 1985 from Cornell University. He has been at Caltech since 1992, and was named founding director of the Kavli Nanoscience Institute in 2004.

Bjorkman's Pioneer project will focus on ways to improve the human immune response to HIV. "HIV/AIDS remains one of the most important current threats to global public health," she says. "Although humans can mount effective immune responses using antibodies against many other viruses, the antibody response to HIV in infected individuals is generally ineffective."

This, she believes, is the result of the "unusually low number and low density of spikes" on the surface membrane of the virus. Antibodies have two identical "arms" with which to attach to a virus or bacterium. In most cases, the density of spikes on a pathogen's surface is high enough that these arms can simultaneously attach to neighboring spikes. Not so with HIV; because its spikes are so few and far between, antibodies tend to bind with only one arm attaching to a single spike. Such binding is weak, says Bjorkman, "much like if you were hanging from a bar with only one arm," and is easily eliminated by viral mutations.

That is why Bjorkman is proposing "a new methodology, designed to screen for and produce novel anti-HIV binding proteins that can bind simultaneously to all three monomers in an HIV spike trimer." A trimer is a protein made of three identical macromolecules; if an antibody can bind to all three proteins at one time, it will "interact very tightly and render the low spike density of HIV and its high mutation rate irrelevant to effective neutralization," Bjorkman explains.

Bjorkman received her PhD in biochemistry and molecular biology in 1984 from Harvard University. She has been at Caltech since 1989, and was named the Delbrück Professor in 2004.

Lori Oliwenstein
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LISA Gravitational-Wave Mission Strongly Endorsed by National Research Council

PASADENA, Calif. — The National Research Council (NRC) has strongly recommended the Laser Interferometer Space Antenna (LISA) as one of NASA's next two major space missions, to start in 2016 in collaboration with the European Space Agency (ESA). LISA will study the universe in a manner different from any other space observatory, by observing gravitational waves. The recommendation was announced August 13 in a press conference at the Keck Center of the National Academies in Washington, D.C. 

In the just-concluded "Astro2010" decadal survey, a panel of experts was convened to look at the coming decade and prioritize all research activities in astronomy and astrophysics, as well as at the interface of these disciplines with physics. The survey recommended LISA highly because of the expectation that observations of gravitational waves in space will answer key scientific questions about the astrophysics of the cosmic dawn and the physics of the universe.

"We are very pleased with the NRC's recognition of LISA's extraordinary research opportunities in astrophysics and fundamental physics," says Tom Prince, professor of physics at the California Institute of Technology (Caltech), senior research scientist at the Jet Propulsion Laboratory (JPL), and the U.S. chair of the LISA International Science Team. Scientists from many European countries participate in LISA either as members of the science team or as members of the LISA International Science Community. "We are looking forward to unveiling a new window on the universe by observing thousands of gravitational wave sources." 

"This recommendation and our excellent reputation in the scientific community encourages us a lot. With LISA we will open up an entirely new way of observing the universe, with immense potential to enlarge our understanding of physics and astronomy in unforeseen ways," says Karsten Danzmann, European chair of the LISA International Science Team.

"In the past it has sometimes been difficult to get mainstream astronomers to recognize the importance of gravitational wave astronomy," says Marcia Rieke, a professor of astronomy at the University of Arizona and vice chair for the Astro2010 subcommittee on programs. "The ranking of LISA is an indication that astronomers are recognizing the opportunities that LISA presents for using gravitational waves to study the universe in a new way." 

"The science case for LISA has become much richer over the last 10 years. On the experimental side, a similar story could be made that what were once novel measurement concepts are now reliable, proven technologies," says LISA science team member Scott Hughes, associate professor of physics at the Massachusetts Institute of Technology. 

"In the 13 years I've been involved with LISA, its technology and science have advanced beyond my wildest first dreams," says Sterl Phinney, professor of theoretical astrophysics at Caltech, current co-chair of the sources and data analysis working group of the LISA science team, and chair of the original LISA Mission Definition Team. "I'm looking forward to its precise measurements telling us if the giant black holes in the centers of galaxies really follow the rules of Einstein's theory of general relativity, and which if any of the ideas about how they get made are correct." 

"This strong endorsement by America's leading astronomers makes it official: LISA has the potential to become one of the most important astronomical observatories of our time," says Bernard F. Schutz, director of the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Potsdam, Germany and co-chair of the sources and data analysis working group of the LISA science team. 

"When LISA was adopted by the ESA in 1995, it was because its observations of gravitational waves would provide powerful insight into the fundamentals of gravity, of Einstein's theory and all its predictions," adds Schutz. "In the last 15 years, astronomers also have learned how LISA can open up hidden chapters in the history of the universe, by listening to the waves made by the very first stars, the earliest black holes, and by some of the oldest stars in existence today. By seeing how the waves from early black holes are stretched out as they move toward us through the expanding universe, LISA can even study the mysterious dark energy."

LISA is designed to be complementary to the ground-based observatories (the Laser Interferometer Gravitational-Wave Observatory, or LIGO, in the United States, and Virgo and GEO-600 in Europe) that currently are actively searching for signs of gravitational waves; both search for ripples in the fabric of space and time formed by the most violent events in the universe, such as the coalescence of black holes, that carry with them information about their origins and about the nature of gravity that cannot be obtained using conventional astronomical tools. The existence of the waves was predicted by Albert Einstein in 1916 in his general theory of relativity.

The LISA instrument will consist of three spacecraft in a triangular configuration with 5-million-kilometer arms (12.5 times the distance from the Earth to the moon), moving in an Earth-like orbit around the sun. Gravitational waves from sources throughout the universe will produce slight oscillations in the arm lengths (changes as small as about 10 picometers, or 10 million millionths of a meter, a length smaller than the diameter of the smallest atom). LISA will capture these motions—and thus measure the gravitational waves—using laser links to monitor the displacements of gold–platinum test masses floating inside the spacecraft. It is slated for launch in the early 2020s. 

LISA will observe gravitational waves in a lower frequency band (0.1 milliHertz to 1 Hertz) than that detectable by LIGO and other ground-based instruments, which are designed to sense sources at frequencies above 10 Hertz.

Because gravitational waves are moving ripples in the curvature of space, and because LISA will sense ripples coming simultaneously from tens of thousands of sources in every direction, the instrument acts more like a microphone listening to sound than like a telescope or a camera taking a picture. This new kind of observing tells us directly about the motion of invisible masses, complementing traditional astronomical observations of light, which reveal only visible atoms.

In the U.S. the LISA project is managed by the NASA Goddard Space Flight Center and includes significant participation by JPL, which is managed by Caltech for NASA. 

LISA's hardware will get its first test in space with the launch of LISA Pathfinder by 2013. This will include a thorough test of a crucial component of LISA's technology: drag-free operation, whereby the spacecraft shield the test masses from external disturbances by precisely monitoring their motions and moving around them to preserve their free fall. LPF recently reached a key phase of development, during which the flight hardware undergoes rigorous pre-flight testing.

Kathy Svitil

NRC Recommends Three Astronomy/Astrophysics Projects with Potential Major Caltech Roles

PASADENA, Calif.—In an announcement August 13 at the National Academies in Washington, D.C., the National Research Council (NRC) recommended three space- and ground-based astronomy and astrophysics projects with potential major roles for researchers at the California Institute of Technology (Caltech): CCAT, a submillimeter telescope to be erected in the Chilean Andes, which will help unravel the cosmic origins of stars, planets, and galaxies; the Laser Interferometer Space Antenna (LISA), designed to detect gravitational waves, ripples in the fabric of space and time formed by the most violent events in the universe; and the development of a Giant Segmented Mirrored Telescope (GSMT)—the Thirty Meter Telescope (TMT) being one of two such telescopes under development—which will yield the clearest and deepest view of the universe.

The recommendations were the result of the Astro2010 a decadal survey, in which a panel of experts was convened by the NRC to look at the coming decade and prioritize research activities in astronomy and astrophysics, as well as activities at the interface of these disciplines with physics.

"It is particularly gratifying to see that Caltech faculty are prepared to play leading roles in three of the major projects identified by the Astro2010 study," says Tom Soifer, professor of physics, director of the Spitzer Science Center, and chair of the Division of Physics, Mathematics and Astronomy at Caltech. "Many of the important discoveries in the coming decades will be based on CCAT, TMT, and LISA, and our deep involvement in these projects will ensure that Caltech remains a vibrant, exciting center for astrophysics."


CCAT was recommended for an immediate start. CCAT is a collaboration between Caltech and the Jet Propulsion Laboratory (JPL), managed by Caltech for NASA; Cornell University; the University of Colorado; and consortia in both Germany and Canada. It will be a 25-meter telescope located on a mountain site in Chile at an elevation of 18,500 feet above sea level. Taking advantage of recent advances in detector technology, CCAT will employ cameras and spectrometers to survey the sky at millimeter and submillimeter wavelengths, providing an unprecedented combination of sensitivity and resolution across a wide field of view. CCAT will reveal young galaxies, stars, and solar systems enshrouded in clouds of dust that make these objects very faint or invisible at other wavelengths.

"We are making rapid progress on all fronts—in detectors, instruments, and new facilities—and this is leading to important scientific discoveries," says Jonas Zmuidzinas, Merle Kingsley Professor of Physics at Caltech, director of the Microdevices Laboratory at JPL, and a CCAT project scientist. "With CCAT, we will gain real insight into the evolution of stars and galaxies."

According to Riccardo Giovanelli, CCAT director and professor of astronomy at Cornell University, "CCAT will allow us to explore the process of formation of galaxies, which saw its heyday about a billion years after the Big Bang, some 13 billion years ago; to peek into the interior of the dusty molecular clouds within which stars and planets form; and to survey the pristine chunks of material left intact for billions of years on the outskirts of our solar system." 

CCAT is a natural complement to the international Atacama Large Millimeter Array (ALMA) project now under construction in Chile, which will provide detailed, high-resolution images of individual objects over narrow fields of view. This complementarity provides a strong impetus to begin construction of CCAT as soon as possible. Indeed, as Nobel Laureate and CCAT Design Review Committee Chair Robert W. Wilson noted, "CCAT is very timely and cannot wait."

This sentiment was echoed in the Decadal Review Committee's report, which stated that "CCAT is called out to progress promptly to the next step in its development because of its strong science case, its importance to ALMA, and its readiness." The Committee recommended federal support for 33 percent of the construction cost for CCAT, as well as support in the operations phase.


The decadal survey recommended LISA as one of NASA's next major space missions, to start in 2016 in collaboration with the European Space Agency (ESA). In the U.S. the LISA project is managed by the NASA Goddard Space Flight Center and includes significant participation by JPL, which is managed by Caltech for NASA.

LISA is designed to be complementary to the ground-based observatories (such as the Laser Interferometer Gravitational Wave Observatory, or LIGO) that currently are actively searching for signs of gravitational waves, which carry with them information about their origins and about the nature of gravity that cannot be obtained using conventional astronomical tools.

The LISA instrument will consist of three spacecraft in a triangular configuration with 5-million-kilometer arms moving in an Earth-like orbit around the sun. Gravitational waves from sources throughout the universe will produce slight oscillations in the arm lengths (changes as small as about 10 picometers, or 10 million millionths of a meter). LISA will capture these motions using laser links to monitor the displacements of gold–platinum test masses floating inside the spacecraft. It is slated for launch in the early 2020s. The instrument will observe gravitational waves in a lower frequency band (0.1 milliHertz to 1 Hertz) than that detectable by LIGO and other ground-based instruments and will sense ripples coming simultaneously from tens of thousands of sources in every direction.

The survey recommended LISA because of the expectation that observations of gravitational waves in space will answer key scientific questions about the astrophysics of the cosmic dawn and the physics of the universe.

"We are very pleased with the NRC's recognition of LISA's revolutionary research opportunities in astrophysics and fundamental physics and we are looking forward to unveiling a new window on the universe by observing thousands of gravitational wave sources," says Tom Prince, professor of physics at Caltech, senior research scientist at the Jet Propulsion Laboratory (JPL), and the U.S. chair of the LISA International Science Team.


The decadal survey rated the development of a Giant Segmented Mirrored Telescope as a high priority. The TMT is one of two such telescopes under development by consortia with major involvement by private and public entities in the U.S., including Caltech.

Building on the success of the twin Keck telescopes, the core technology of TMT will be a 30-meter segmented primary mirror. This will give TMT nine times the collecting area of today's largest optical telescopes and three-times-sharper images. The TMT has begun full-scale polishing of the 1.4-meter mirror blanks that will make up the primary mirror. TMT also has developed many of the essential prototype components for the telescope, including key adaptive optics technologies and the support and control elements for the 492 mirror segments.

The TMT project is an international partnership among Caltech, the University of California, and the Association of Canadian Universities for Research in Astronomy, joined by the National Astronomical Observatory of Japan, the National Astronomical Observatories of the Chinese Academy of Sciences, and the Department of Science and Technology of India.

Kathy Svitil

Caltech Astronomer Finds Planets in Unusually Intimate Dance around Dying Star

PASADENA, Calif.—Hundreds of extrasolar planets have been found over the past decade and a half, most of them solitary worlds orbiting their parent star in seeming isolation. With further observation, however, one in three of these systems have been found to have two or more planets. Planets, it appears, come in bunches. Most of these systems contain planets that orbit too far from one another to feel each other's gravity. In just a handful of cases, planets have been found near enough to one another to interact gravitationally.

Now, however, John A. Johnson, an assistant professor of astronomy at the California Institute of Technology (Caltech), and his colleagues have found two systems with pairs of gas giant planets locked in an orbital embrace.

In one system—a planetary pair orbiting the massive, dying star HD 200964, located roughly 223 light-years from Earth-the intimate dance is closer and tighter than any previously seen. "This new planet pair came in an unexpected package," says Johnson.

Adds Eric Ford of the University of Florida in Gainsville, "A planetary system with such closely spaced giant planets would be destroyed quickly if the planets weren't doing such a well synchronized dance. This makes it a real puzzle how the planets could have found their rhythm."

A paper by Johnson, Ford, and their collaborators describing the planets and their intriguing orbital dynamics has been accepted for publication in the Astronomical Journal (see for a preprint).

All of the four newly discovered exoplanets are gas giants more massive than Jupiter, and like most exoplanets were discovered by measuring the wobble, or Doppler shift, in the light emitted by their parent stars as the planets orbit around them. Surprisingly, however, the members of each pair are located remarkably close to one another.

For example, the distance between the planets orbiting HD 200964 occasionally is just .35 astronomical units (AU)—roughly 33 million miles—comparable to the distance between Earth and Mars. The planets orbiting the second star, 24 Sextanis (located 244 light-years from Earth) are .75 AU, or about 70 million miles. By comparison, Jupiter and Saturn are never less than 330 million miles apart.

Because of their large masses and close proximity, the exoplanet pairs exert a large gravitational force on each other. The gravitational tug between HD 200964's two planets, for example, is 3,000,000 times greater than the gravitational force between Earth and Mars, 700 times larger than that between the Earth and the moon, and 4 times larger than the pull of our sun on the Earth.

Unlike the gas giants in our own solar system, the new planets are located comparatively close to their stars. The planets orbiting 24 Sextanis have orbital periods of 455 days (1.25 years) and 910 days (2.5 years), and the companions to HD 200964 periods of 630 days (1.75 years) and 830 days (2.3 years). Jupiter, by contrast, takes just under 12 Earth years to make one pass around the sun.

Planets often move around after they form, in a process known as migration. Migration is thought to be commonplace—it even occurred to some extent within our own solar system—but it isn't orderly. Planets located farther out in the protoplanetary disk can migrate faster than those closer in, "so planets will cross paths and jostle each other around," Johnson says. "The only way they can 'get along' and become stable is if they enter an orbital resonance."

When planets are locked in an orbital resonance, their orbital periods are related by the ratio of two small integers. In a 2:1 resonance, for example, an outer planet will orbit its parent star once for every two orbits of the inner planet; in a 3:2 resonance, the outer planet will orbit two times for every three passes by the inner planet, and so forth. Such resonances are created by the gravitational influence of planets on one another.

"There are many locations in a protoplanetary disk where planets can form," says Johnson. "It's very unlikely, however, that two planets would just happen to form at locations where they have periods in one of these ratios."

A 2:1 resonance—which is the case for the planets orbiting 24 Sextanis—is the most stable and the most common pattern. "Planets tend to get stuck in the 2:1. It's like a really big pothole," Johnson says. "But if a planet is moving very fast"—racing in from the outer part of the protoplanetary disk, where it formed, toward its parent star—"it can pass over a 2:1. As it moves in closer, the next step is a 5:3, then a 3:2, and then a 4:3."

Johnson and his colleagues have found that the pair of planets orbiting HD 200964 is locked in just such a 4:3 resonance. "The closest analogy in our solar system is Titan and Hyperion, two moons of Saturn which also follow orbits synchronized in a 4:3 pattern," says Ford. "But the planets orbiting HD 200964 interact much more strongly, since each is around 20,000 times more massive than Titan and Hyperion combined."

"This is the tightest system that's ever been discovered," Johnson adds, "and we're at a loss to explain why this happened. This is the latest in a long line of strange discoveries about extrasolar planets, and it shows that exoplanets continuously have this ability to surprise us. Each time we think we can explain them, something else comes along."

Johnson and his colleagues found the two systems using data from the Keck Subgiants Planet Survey—a search for planets around stars from 40 to 100 percent larger than our own sun. Subgiants represent a class of stars that have evolved off the "main sequence," and have run out of hydrogen for nuclear fusion, causing their core to collapse and their outer envelope to swell. Subgiants eventually become red giants—voluminous stars with big, puffy atmospheres that pulsate, making it difficult to detect the subtle spectral shifts caused by orbiting planets.

"Subgiants are rotating very slowly and they're cool," unlike rapidly rotating, hot main sequence stars, "but they haven't expanded enough to be too fluffy and too jittery," Johnson says. "They're 'Goldilocks' stars: not too fast, not too hot, not too fluffy, not too jittery"—and, therefore, ideal for planet hunting.

"Right now, we're monitoring 450 of these massive stars, and we are finding swarms of planets," he says. "Around these stars, we are seeing three to four times more planets out to a distance of about 3 AU—the distance of our asteroid belt—than we see around main sequence stars. Stellar mass has a huge influence on frequency of planet occurrence, because the amount of raw material available to build planets scales with the mass of the star."

Eventually, perhaps 10 or 100 million years from now, subgiant stars like HD 200964 and 24 Sextanis will become red giants. They will throw off their outer atmospheres, swelling to the point where they could engulf the inner planet of their dancing pair, and will throw off mass, changing the gravitational dynamics of their whole system. "The planets will then move out, and their orbits will become unstable," Johnson says. "Most likely one of the planets will get flung out of the system completely"-and the dance will end.

The paper, "A Pair of Interacting Exoplanet Pairs Around the Subgiants 24 Sextanis and HD 200964," was coauthored by Matthew Payne and Eric B. Ford of the University of Florida; Andrew W. Howard and Geoffrey W. Marcy of the University of California, Berkeley; Kelsey Clubb of San Francisco State University; Brendan P. Bowler of the University of Hawai'i at Manoa,; Gregory W. Henry of Tennessee State University; Debra A. Fischer, John Brewer, and Christian Schwab of Yale University; Sabine Reffert of ZAH-Landessternwarte; and Thomas Lowe of the UCO/Lick Observatory.

Kathy Svitil

Astronomers Discover an Unusual Cosmic Lens

PASADENA, Calif.—Astronomers at the California Institute of Technology (Caltech) and Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have discovered the first known case of a distant galaxy being magnified by a quasar acting as a gravitational lens. The discovery, based in part on observations done at the W. M. Keck Observatory on Hawaii's Mauna Kea, is being published July 16 in the journal Astronomy & Astrophysics.

Quasars, which are extraordinary luminous objects in the distant universe, are thought to be powered by supermassive black holes in the cores of galaxies. A single quasar could be a thousand times brighter than an entire galaxy of a hundred billion stars, which makes studies of their host galaxies exceedingly difficult. The significance of the discovery, the researchers say, is that it provides a novel way to understand these host galaxies.

"It is a bit like staring into bright car headlights and trying to discern the color of their rims," says Frédéric Courbin of EPFL, the lead author on the paper. Using gravitational lensing, he says, "we now can measure the masses of these quasar host galaxies and overcome this difficulty."

According to Einstein's general theory of relativity, if a large mass (such as a big galaxy or a cluster of galaxies) is placed along the line of sight to a distant galaxy, the part of the light that comes from the galaxy will split. Because of this, an observer on Earth will see two or more close images of the now-magnified background galaxy.

The first such gravitational lens was discovered in 1979, and produced an image of a distant quasar that was magnified and split by a foreground galaxy. Hundreds of cases of gravitationally lensed quasars are now known. But, until the current work, the reverse process—a background galaxy being lensed by the massive host galaxy of a foreground quasar—had never been detected.

Using gravitational lensing to measure the masses of distant galaxies independent of their brightness was suggested in 1936 by Caltech astrophysicist Fritz Zwicky, and the technique has been used effectively for this purpose in recent years. Until now, it had never been applied to measure the masses of quasar hosts themselves.

To find the cosmic lens, the astronomers searched a large database of quasar spectra obtained by the Sloan Digital Sky Survey (SDSS) to select candidates for "reverse" quasar-galaxy gravitational lensing. Follow-up observations of the best candidate—quasar SDSS J0013+1523, located about 1.6 billion light years away—using the W. M. Keck Observatory's 10-meter telescope, confirmed that the quasar was indeed magnifying a distant galaxy, located about 7.5 billion light years away.

"We were delighted to see that this idea actually works," says Georges Meylan, a professor of physics and leader of the EPFL team. "This discovery demonstrates the continued utility of gravitational lensing as an astrophysical tool."

"Quasars are valuable probes of galaxy formation and evolution," says Professor of Astronomy S. George Djorgovski, leader of the Caltech team. Furthermore, he adds, "discoveries of more such systems will help us understand better the relationship between quasars and the galaxies which contain them, and their coevolution."

Other coauthors of the Astronomy & Astrophysics paper, entitled "First case of strong gravitational lensing by a QSO: SDSS J0013+1523 at z = 0.120," are Malte Tewes and François Rerat of EPFL, Ashish Mahabal of Caltech, and Dominique Sluse of the Astronomical Research Institute in Heidelberg, Germany. The work done at Caltech was supported by the National Science Foundation and the Ajax Foundation.

Images are available at

Kathy Svitil

A Mine for Dark Matter

For two weeks in mid-December 2009, the physics world was abuzz with speculation. The Cryogenic Dark Matter Search (CDMS), which had just finished analyzing its final data set, was rumored to have struck gold—they'd actually detected dark matter, the unknown stuff that makes up nearly a quarter of the universe. The rumors had spread through the blogosphere and into the mainstream media.

In the 1930's, Caltech's Fritz Zwicky first proposed the existence of dark matter to account for mass that appeared to be missing in the Coma galaxy cluster. Although astronomers now have lots of evidence to convince themselves dark matter is out there, no one knows for sure what it's made of. The best guess, however, is the hypothetical weakly interacting massive particle, or WIMP. If WIMPs are all around us, they'd be zooming about at hundreds of kilometers per second. But because they hardly interact with regular matter, you can't see or feel them. There could be billions of them streaming through your body right now. Once in a while, though, a WIMP could crash into an atomic nucleus like a cue ball hitting an eight ball, and that's the idea behind most dark-matter searches, including CDMS.

The CDMS detector consists of 30 hockey-puck-sized crystals of germanium waiting for a WIMP to come along. To block cosmic rays that might confuse the signal, CDMS sits about 230 stories deep in the Soudan Underground Laboratory, a research facility run by the University of Minnesota in the bowels of an old iron mine nestled among the lakes and forests at the northeast tip of Minnesota. The CDMS team numbers nearly 80 people from 16 institutions around the world, including Caltech.

Each CDMS detector is a 230-gram germanium crystal. Six detectors are stacked to form one of the five towers that make up the whole apparatus.
Credit: CDMS Collaboration

Although CDMS is far from alone in trying to detect WIMPs, it's been the standard bearer for the past few years. No experiment has yet detected anything, but each silent result narrows down what WIMPs might look like—any theory that predicts something the experiments don't see has to be refined or ruled out. CDMS has provided the tightest constraints yet, and these latest results, taken over a period of more than a year, have doubled the collaboration's data. If physicists are close to finding WIMP collisions, then CDMS will be the first experiment to do so—which explains why people became so anxious upon hearing the rumors. The hype underscores just how momentous a dark-matter discovery would be. "It's a really exciting topic," says Sunil Golwala, associate professor of physics and a member of the CDMS team. His two graduate students, Zeeshan Ahmed (MS '08) and David Moore, did a lot of the number crunching for the new data. "Suppose you have conclusive evidence that you just discovered the dark matter in the universe," Golwala says. "I mean, that's just amazing."

WIMP fever was running high on December 17, when physicists packed into auditoriums in California and Illinois to hear what, if anything, CDMS had discovered. The Economist had written on that day, "If the rumors are true, a solution to one of the great problems of physics may now be within reach." JoAnne Hewett, a particle physicist at the Stanford Linear Accelerator Center, even liveblogged the event on Cosmic Variance, a popular physics blog. "The excitement in the air is palpable," she wrote. "Not much work is being done—everyone is pretty much talking in the hallways, trying to pass the time until 2:00."

Finally, the results were announced—two events had been found! But before booking flights to Stockholm, the team calculated that there was a 23 percent chance these signals were caused by background—likely collisions with electrons, instead of nuclei, that had snuck past their set of criteria for a true WIMP detection. As Golwala points out, "No one claims discovery with that high of a chance." The team couldn't say they had discovered dark matter, but they couldn't rule it out, either.

So CDMS hasn't revolutionized our understanding of the universe—yet. As for all the hype? "In a couple of months, no one will remember this," Golwala says. Still, their results—published in the March 26 issue of Science—are noteworthy, placing the most stringent constraints yet on what WIMPs could be. "It's an exciting time in the bigger sense, because we've been producing results from this experiment for about five years," he says. "We've been the premier experiment in this field." These data sets are marking the end of the current chapter in dark-matter searches. But new experiments are already under way, and in the next couple of years, a half-dozen more projects will begin—and they'll be many times more sensitive than CDMS. Says postdoc and CDMS team member Jeff Filippini, "It's very possible that in the next five years we might be talking about WIMP astronomy, rather than just trying to detect something."

Read the full story at E&S online.

Marcus Woo

Astronomical Society of the Pacific Honors Caltech Achievements

A constellation of Caltechers has been honored this week by the Astronomical Society of the Pacific, the world's largest general astronomy society. The ASP announced eight 2010 awards for "excellence in astronomy research and education," four of them recognizing people and programs affiliated with the Caltech community.

The honorees are Gerry Neugebauer, Caltech's Millikan Professor of Physics, Emeritus; Robert Quimby, a postdoctoral scholar in astronomy at Caltech; Alex Filippenko, the Goldman Distinguished Professor in the Physical Sciences at UC Berkeley and a Caltech alumnus; and the Spitzer Space Telescope team, based on the Caltech campus and at Pasadena's Jet Propulsion Laboratory. One of NASA's four "Great Observatories," the telescope is operated by Caltech and JPL on behalf of NASA.

The awards will be presented at the ASP awards banquet on August 3 in Boulder, Colorado, as part of the society's annual meeting.

Neugebauer, who joined the Institute faculty shortly after earning his Caltech PhD in 1960, is the recipient of the ASP's Catherine Wolfe Bruce Gold Medal for lifetime achievement in astronomy. The Caltech scientist is widely recognized as one of the pioneers in the field of infrared astronomy, working with colleagues to make the first infrared map of the galactic center, the first infrared survey of the sky, and leading the science team of the Infrared Astronomical Satellite (IRAS), the first space-based telescope to survey the cosmos at infrared wavelengths.  

Quimby, who came to Caltech after earning his PhD at the University of Texas, was honored with the Robert J. Trumpler Award for his outstanding recent PhD thesis, which "led to improved understanding of the detonation process" in certain types of supernovae.He was also cited for his discovery of the "first 'pair instability supernova'—a phenomenon now thought to occur in very massive stars like those that formed at the end of the cosmological 'dark ages,' when the universe's first stars and galaxies condensed out of matter.

Filippenko, who received his PhD from Caltech in 1984, was presented with the Richard H. Emmons Award for excellence in the teaching of college-level introductory astronomy for non-science majors. Internationally known for his research on supernovas, gamma-ray bursts, black holes, quasars, and dark energy, Filippenko has received Berkeley's "best professor" award six times in his career, as well as numerous other national teaching honors, and has produced four astronomy video courses and coauthored an award-winning textbook.

The Spitzer Space Telescope Team received the Maria and Eric Muhlmann Award, which recognizes "recent significant observational results made possible by innovative advances in astronomical instrumentation and techniques." Launched in 2003 as a successor to IRAS, the telescope is carrying out the most detailed and comprehensive survey ever made of the infrared sky.

The team was cited for innovative engineering approaches, including "the extensive use of radiative cooling that extended the cryogenic lifetime of the telescope from the planned nominal mission of two and half years to nearly six before the liquid helium coolant was exhausted."

A newly expanded image of the Helix nebula lends a festive touch to the fourth anniversary of the launch of NASA's Spitzer Space Telescope.
Credit: NASA/JPL-Caltech/ J. Hora (Harvard-Smithsonian CfA)

These technologies kept the telescope cooled to very low temperatures and shielded it from the heat of the sun and other extraneous infrared sources, including Earth and the telescope itself.  

In May 2009, the telescope's liquid coolant ran dry. Spitzer is now in the "warm"phase of its mission, continuing to return scientific data on two infrared channels that are able to operate without coolant.

Established in 1889, the Astronomical Society of the Pacific aims to increase the understanding and appreciation of astronomy by engaging scientists, educators, enthusiasts, and the public to advance science and science literacy through mission-based astronomy and space-science education and public outreach activities. Today, its membership comprises professional and amateur astronomers and educators from more than 70 countries. 

Heidi Aspaturian
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