Astronomers Observe Planets Around Another Star Like Never Before

New instrument reveals exotic nature of four planets orbiting the same nearby star

PASADENA, Calif.—Thanks to a new high-tech gadget, astronomers have observed four planets orbiting a star relatively close to the sun in unprecedented detail, revealing the roughly ten-Jupiter-mass planets to be among the most exotic ones known.

The team, which includes several researchers from the California Institute of Technology (Caltech), describes its findings in a paper accepted for publication by the Astrophysical Journal.

The findings were made possible by a first-of-its-kind telescope imaging system that allowed the astronomers to pick out the planets amidst the bright glare of their parent star and measure their spectra—the rainbows of light that reveal the chemical signatures of planetary atmospheres. The system, dubbed Project 1640, enables astronomers to observe and characterize these kinds of planetary systems quickly and routinely, which has never been done before, the researchers say.

"These warm, red planets are unlike any other known objects in our universe," says Ben R. Oppenheimer, an astronomer at the American Museum of Natural History and the paper's lead author. And the planets are very different from one another as well. "All four planets have different spectra and all four are peculiar."

Astronomers had previously taken images of these four planets, which orbit a star called HR 8799, located 128 light years away. But because a star's light is tens of millions to billions of times brighter than the light from that star's own planets, distinguishing planet light from starlight so as to directly measure the spectra from the planets alone is difficult. "It's like taking a single picture of the Empire State Building from an airplane that reveals the height of the building but also a bump on the sidewalk next to it that is as high as a couple of bacteria," Oppenheimer explains. "Furthermore, we've been able to do this over a range of wavelengths in order to make a spectrum."

In the past, astronomers have been able to take spectra of some planets that pass in front of, or transit, their stars. But with Project 1640, which uses the Hale Telescope at Caltech's Palomar Observatory in Southern California, astronomers can now take the direct spectra of planets orbiting other stars—called exoplanets—that are not transiting. The device blocks the otherwise overwhelming starlight, picks out the faint specks that are planets, and obtains their spectra.  Project 1640 allowed the team to take spectra of all four of the planets around HR 8799 simultaneously, which had never been done for any planetary system before.  

The planets around HR 8799 are at about the same distance from that star as the solar system's gas giants (Jupiter, Saturn, Uranus, and Neptune) are from our sun. But since it's easier to detect transiting planets that are close to their stars, the transiting systems that astronomers have observed have small orbits—often smaller than Mercury's. The new results, therefore, represent the first spectra to be taken of gas giants located so far from their stars—a distance at which the influence of the stars' radiation, flares, and other features are weaker.

"We are now technically capable of obtaining spectra of giant planets in planetary systems like our own, improving on the close-in transiting planet studies done previously," says Lynne Hillenbrand, professor of astronomy at Caltech and a coauthor of the paper. And what the spectra show is that the planets are quite strange. "A remarkable thing about these planets is their unexpected spectroscopic diversity," Hillenbrand says.

One of the most striking abnormalities is an apparent chemical imbalance. Under most circumstances, ammonia and methane should naturally coexist in a planet's atmosphere—where there is one, there is usually the other—unless they are generated in extremely cold or hot environments. Yet the spectra of the HR 8799 planets, all of which have "lukewarm" temperatures of about 1000 Kelvin (1340 degrees Fahrenheit), either have methane or ammonia alone, with little or no sign of their chemical partner. There is also evidence of other chemicals such as acetylene—which has never before been detected on any exoplanet—and carbon dioxide.

The planets also are "redder"—they emit longer wavelengths of light—than celestial objects with similar temperatures. This could be explained by the presence of significant but patchy cloud cover on the planets, the authors say.

HR 8799 itself is very different from our sun, with 1.6 times its mass and five times its brightness. The brightness of this distant star can vary by as much as 8 percent over a period of two days; it produces about 1,000 times more ultraviolet light than the sun. All of these factors could induce complex weather and sooty hazes that would, in turn, cause periodic changes in the spectra.

More data are needed to further explore this solar system's unusual characteristics, the scientists say.

"The spectra of these four worlds clearly show that they are far too toxic and hot to sustain life as we know it," says coauthor Ian Parry, a senior lecturer at the Institute of Astronomy, Cambridge University. "But the really exciting thing is that, one day, the techniques we've developed will give us our first secure evidence of the existence of life on a planet outside our solar system."

The techniques used by Project 1640 require the coordinated operation of four major instruments: the world's most advanced adaptive-optics system, which can make millions of tiny adjustments to the device's two six-inch mirrors every second; a coronagraph that optically dims the star but not other celestial objects in the field of view; an imaging spectrograph that records 30 images in a rainbow of colors simultaneously; and a specialized wavefront sensor that distinguishes between residual starlight that sneaks through the coronagraph and light from planets, allowing scientists to filter out background starlight more effectively.

With these instruments working in concert, the project is able to reveal celestial objects 1 million to 10 million times fainter than the star at the center of one of its images, with only an hour of observations. It is also capable of measuring the orbital motion of objects.

"Our young century has seen seminal advances in exoplanet science, but almost exclusively from indirect observations," says Richard Dekany, a coauthor and associate director for development for Caltech Optical Observatories. "Project 1640 has now added to this revolution the scientific gold standard: directly measured spectra of young giant planets. Our initial findings suggest each of these strange and wonderful giant planets may have a unique story to share."

The researchers are already collecting more data on this system so as to look for changes in the planets over time; they are also surveying other young stars. During its three-year survey at Palomar, which started in June, Project 1640 aims to survey 200 stars within about 150 light years of our solar system.

"In the 19th century, it was thought impossible to know the composition of stars, but the invention of astronomical spectroscopy has revealed detailed information about nearby stars and distant galaxies," says Charles Beichman, executive director of the NASA Exoplanet Science Institute at Caltech. "Now, with Project 1640, we are beginning to turn this tool to the investigation of neighboring exoplanets to learn about the composition, temperature, and other characteristics of their atmospheres."

The title of the the Astrophysical Journal paper is "Reconnaissance of the HR 8799 exosolar system I: Near IR spectroscopy." In addition to Hillenbrand, Dekany, and Beichman, the other Caltech authors are postdocs Christoph Baranec and Sasha Hinkley; former postdoc Justin Crepp (now at the University of Notre Dame); and programmer David Hale, along with a similar number of JPL authors. This work was supported by the National Science Foundation and NASA. Additional funding sources for Project 1640 are listed here.

This story is adapted from a press release by Kendra Snyder of the American Natural History Museum.

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Ryan Patterson Awarded Sloan Research Fellowship

Ryan Patterson, assistant professor of physics at Caltech, is one of 126 young scholars to receive a Sloan Research Fellowship for 2013.

According to the Alfred P. Sloan Foundation, the purpose of the Sloan Research Fellowships is to "stimulate fundamental research by early-career scientists and scholars of outstanding promise." Candidates are nominated by their fellow scientists and chosen by an independent panel of senior scholars. Fellows receive $50,000 to be used to further their research.

"I feel very honored and am thankful to the Alfred P. Sloan Foundation for this fellowship," says Patterson. "The fellowship will be a great help to my research efforts here at Caltech."

Patterson conducts research in particle physics, with a particular focus on elementary subatomic particles known as neutrinos. His research group at Caltech is centrally involved in the Fermilab MINOS and NOvA experiments, which study the characteristics of neutrinos.

Patterson received his BS from Caltech in 2000 and his PhD from Princeton in 2007, then returned to Caltech as an assistant professor 2010. He also recently received an Early Career Research Award from the Department of Energy Office of Science.

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Viewing the Cosmos from the South Pole: An Interview with Jamie Bock

Almost immediately after the Big Bang—roughly after ten trillionths of a trillionth of a trillionth of a second—the universe suddenly grew. Very fast. The entire cosmos, which at the time was smaller than an atom, expanded to the size of a beach ball in less than a millionth of a trillionth of a trillionth of a second—before settling down to a more leisurely rate of growth that continues to this day.

The early universe was filled with energy, and quantum mechanical fluctuations led to tiny variations in its density. Thanks to that rapid early expansion—called inflation—those small quantum fluctuations over time stretched to vast scales, forming cosmic structures like galaxies and galaxy clusters. Inflation stretched space faster than photons can travel, flinging apart different regions of the universe. This means there may be distant parts of the cosmos whose photons are still trying to reach us—and the universe we can see now may be just a tiny fraction of a much larger universe.

But what exactly triggered cosmic inflation? Scientists like Jamie Bock are trying to answer that question and others about what the universe was like during those first moments of existence. Bock is part of Caltech's experimental cosmology group, which devises new kinds of detectors, telescopes, and experiments to study the cosmic microwave background—the Big Bang's afterglow, which fills the entire sky. Bock—who is no stranger to Caltech, as he has been affiliated with the university and JPL since 1994—joined the faculty in the fall. He recently answered some questions about his work.

What are you trying to learn?

We're searching for signatures from the time of inflation. And there's good evidence that a process like inflation happened in the moments after the Big Bang. For example, BOOMERanG, a balloon-borne experiment developed at Caltech, made a measurement in 2000 showing that the geometry of the universe is flat to within experimental precision. Flatness is a fundamental prediction of inflation. This tremendous expansion has taken whatever intrinsic geometry existed before inflation, and by stretching it out, makes the universe now appear flat.

While we know something like inflation happened in the early universe, we don't understand the physics behind it. Conventional wisdom says that inflation is related to exotic physics from some yet-to-be-understood grand unification theory, at energies well beyond what we can probe with particle accelerators on Earth. The exciting thing is that we are now making tests with the microwave background to pin down what exactly  causes inflation.

In particular, inflation makes a background of gravitational waves—ripples in space and time that are still lurking in the universe today. The amplitude of the gravitational-wave background is sensitive to the physical process behind inflation. These gravitational waves make a very small—possibly detectable—polarization signal in the microwave background. If we can detect this polarization signal, or even put a useful upper limit on it, we start to put constraints on what kind of physics caused inflation.

What kind of research does your group do?

I lead an experimental group that builds unique instruments for looking at the early universe. For studying the cosmic microwave background, we have a balloon experiment called Spider—which is a successor to BOOMERanG—that's searching for the polarization signal from inflation. We also have an experiment called the Keck polarimeter array, funded by the Keck Foundation, presently carrying out similar measurements from the South Pole.

Our group has a long affiliation with the Herschel and Planck satellites, which began with the building of focal-plane detectors at JPL, and both have now produced spectacular data that our group is helping to analyze. Planck is coming out with its first cosmology results this year.            

More recently, I've gotten interested in slightly later times in the universe, borrowing techniques from our studies of the microwave background to study the extragalactic background light, a diffuse haze of light produced by early galaxies. Instead of detecting galaxies individually, which would require an enormous telescope, we can study the spatial variations made by many galaxies in this background haze. We can do this with a small telescope, a very efficient way to make observations, and the latest idea we're after is to make images at multiple wavelengths with an imaging spectrometer. Ultimately we hope to learn about the epoch of reionization, a period when the first galaxies started shining.

The Spider, BOOMERanG, and the Keck polarimeter array experiments have all been performed in Antarctica. Do you go often? What kind of work do you and your colleagues do there?

I've been to the pole four times during the summer myself, and some members of the group have wintered over. This year, we're making upgrades to the Keck array, testing the experiment, doing calibrations and measurements. Typically by the end of the season, we're back to observing the sky's microwave background. The station is closed from mid-February to October, and there are no flights in or out during the winter. We leave one person for the winter season to operate the experiment. Next year we plan to launch the SPIDER balloon experiment, which will fly in a circle around the continent during the Antarctic summer season.

What's the South Pole like?

The South Pole is a lot of fun, kind of like a summer camp for scientists. There are social activities every week—volleyball, pub trivia, and bingo night are my favorites. Satellite coverage for email is limited to eight hours a day, so you don't have a lot of distractions. Everything's provided, with great food, a gym, and even a greenhouse. Every morning you put on your winter gear and walk out across the airfield to the laboratory.

Right around now it would typically be about –30°F, a relatively balmy summer temperature. In the winter, it typically goes below –100°F at some point. Even in the summer you have to cover your whole body. The first breath is always a shock coming off the airplane. Some of the shock is due to the fact that the South Pole is at an altitude of 10,000 feet, standing atop two miles of ice. The air's thinner and it's a lot colder than when you get on the plane at the edge of the continent at sea level.

What have you enjoyed about being at Caltech and JPL?

I really value both institutions, and there's a great synergy between them. Caltech has fantastic students and postdocs, and combining their enthusiasm and drive with JPL's world-class professionals and technologies is a truly powerful combination. Working between the two institutions brings a world of new opportunities.

Bock grew up in Ohio before going to Duke University, where he received his BS in physics and math in 1987. He then went to UC Berkeley—where the late Caltech astrophysicist Andrew Lange was his advisor—for his MA and PhD in physics in 1990 and 1994, respectively. Bock then joined JPL as a postdoc, and has since held research positions at JPL and a visiting appointment at Caltech. He's now a professor of physics at Caltech.

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Caltech Senior Wins Churchill Scholarship

Caltech senior Andrew Meng has been selected to receive a Churchill Scholarship, which will fund his graduate studies at the University of Cambridge for the next academic year. Meng, a chemistry and physics major, was one of only 14 students nationwide who were chosen to receive the fellowship this year.

Taking full advantage of Caltech's strong tradition of undergraduate research, Meng has worked since his freshman year in the lab of Nate Lewis, the George L. Argyros Professor and professor of chemistry. Over the course of three Summer Undergraduate Research Fellowships (SURFs) and several terms in the lab, Meng has investigated various applications of silicon microwire solar cells. Lewis's group has shown that arrays of these ultrathin wires hold promise as a cost-effective way to construct solar cells that can convert light into electricity with relatively high efficiencies.

Meng, who grew up in Baton Rouge, Louisiana, first studied some of the fundamental limitations of silicon microwires in fuel-forming reactions. In these applications, it is believed that the microwires can harness energy from the sun to drive chemical reactions such as the production of hydrogen and oxygen from splitting water. Meng's work showed that the geometry of the microwires would not limit the fuel-forming reaction as some had expected.

More recently, Meng has turned his attention to using silicon microwires to generate electricity. He is developing an inexpensive electrical contact to silicon microwire chips, using a method that facilitates scale-up and can be applied to flexible solar cells.

"Andrew is one of the best undergraduates that I have had the pleasure of working with in over a decade," says Lewis. "He excels in academics, in leadership, and in research. I believe he is truly worthy of the distinction of receiving a Churchill Fellowship. " 

As he pursues a Master of Philosophy degree in chemistry at the University of Cambridge over the next year, Meng will work in the group of theoretical chemist Michiel Sprik. He plans to apply computational methods to his studies of fuel-forming reactions using solar-energy materials.

"I'm very grateful for this opportunity to learn a computational perspective, since up until now I've been doing experimental work," Meng says. "I'm very excited, and most importantly, I'd like to thank Caltech and all of my mentors and co-mentors, without whom I would not be in this position today."

According to the Winston Churchill Foundation's website, the Churchill Scholarship program "offers American citizens of exceptional ability and outstanding achievement the opportunity to pursue graduate studies in engineering, mathematics, or the sciences at Cambridge. One of the newer colleges at the University of Cambridge, Churchill College was built as the national and Commonwealth tribute to Sir Winston, who in the years after the Second World War presciently recognized the growing importance of science and technology for prosperity and security. Churchill College focuses on the sciences, engineering, and mathematics." The first Churchill Scholarships were awarded in 1963, and this year's recipients bring the total to 479 Churchill Scholars.

Each year, a select group of universities, including Caltech, is eligible to nominate students for consideration for the scholarship. Meng is the seventh Caltech student to have won the award since the year 2000. A group of Caltech faculty members and researchers work with Lauren Stolper, director of fellowships advising, to identify and nominate candidates. This year, the members of the group were Churchill Scholar alumni John Brady, the Chevron Professor of Chemical Engineering and professor of mechanical engineering; Mitchio Okumura, professor of chemical physics; Alan Cummings, senior research scientist; and Eric Rains, professor of mathematics.

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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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Friday, January 25, 2013

Course Ombudspeople Lunch

A Cloudy Mystery

A puzzling cloud near the galaxy's center may hold clues to how stars are born

PASADENA, Calif.—It's the mystery of the curiously dense cloud. And astronomers at the California Institute of Technology (Caltech) are on the case.

Near the crowded galactic center, where billowing clouds of gas and dust cloak a supermassive black hole three million times as massive as the sun—a black hole whose gravity is strong enough to grip stars that are whipping around it at thousands of kilometers per second—one particular cloud has baffled astronomers. Indeed, the cloud, dubbed G0.253+0.016, defies the rules of star formation.

In infrared images of the galactic center, the cloud—which is 30 light-years long—appears as a bean-shaped silhouette against a bright backdrop of dust and gas glowing in infrared light. The cloud's darkness means it is dense enough to block light.

According to conventional wisdom, clouds of gas that are this dense should clump up to create pockets of even denser material that collapse due to their own gravity and eventually form stars. One such gaseous region famed for its prodigious star formation is the Orion Nebula. And yet, although the galactic-center cloud is 25 times denser than Orion, only a few stars are being born there—and even then, they are small. In fact, the Caltech astronomers say, its star-formation rate is 45 times lower than what astronomers might expect from such a dense cloud.

"It's a very dense cloud and it doesn't form any massive stars—which is very weird," says Jens Kauffmann, a senior postdoctoral scholar at Caltech.

In a series of new observations, Kauffmann, along with Caltech postdoctoral scholar Thushara Pillai and Qizhou Zhang of the Harvard-Smithsonian Center for Astrophysics, have discovered why: not only does it lack the necessary clumps of denser gas, but the cloud itself is swirling so fast that it can't settle down to collapse into stars.

The results, which show that star formation may be more complex than previously thought and that the presence of dense gas does not automatically imply a region where such formation occurs, may help astronomers better understand the process.

The team presented their findings—which have been recently accepted for publication in the Astrophysical Journal Letters—at the 221st meeting of the American Astronomical Society in Long Beach, California.

To determine whether the cloud contained clumps of denser gas, called dense cores, the team used the Submillimeter Array (SMA), a collection of eight radio telescopes on top of Mauna Kea in Hawaii. In one possible scenario, the cloud does contain these dense cores, which are roughly 10 times denser than the rest of the cloud, but strong magnetic fields or turbulence in the cloud disturbs them, thus preventing them from turning into full-fledged stars.

However, by observing the dust mixed into the cloud's gas and measuring N2H+—an ion that can only exist in regions of high density and is therefore a marker of very dense gas—the astronomers found hardly any dense cores. "That was very surprising," Pillai says. "We expected to see a lot more dense gas."

Next, the astronomers wanted to see if the cloud is being held together by its own gravity—or if it is swirling so fast that it is on the verge of flying apart. If it is churning too fast, it can't form stars. Using the Combined Array for Research in Millimeter-wave Astronomy (CARMA)—a collection of 23 radio telescopes in eastern California run by a consortium of institutions, of which Caltech is a member—the astronomers measured the velocities of the gas in the cloud and found that it is up to 10 times faster than is normally seen in similar clouds. This particular cloud, the astronomers found, was barely held together by its own gravity. In fact, it may soon fly apart.

The CARMA data revealed yet another surprise: the cloud is full of silicon monoxide (SiO), which is only present in clouds where streaming gas collides with and smashes apart dust grains, releasing the molecule. Typically, clouds only contain a smattering of the compound. It is usually observed when gas flowing out from young stars plows back into the cloud from which the stars were born. But the extensive amount of SiO in the galactic-center cloud suggests that it may consist of two colliding clouds, whose impact sends shockwaves throughout the galactic-center cloud. "To see such shocks on such large scales is very surprising," Pillai says.

G0.253+0.016 may eventually be able to make stars, but to do so, the researchers say, it will need to settle down so that it can build dense cores, a process that could take several hundred thousand years. But during that time, the cloud will have traveled a great distance around the galactic center, and it may crash into other clouds or be yanked apart by the gravitational pull of the galactic center. In such a disruptive environment, the cloud may never give birth to stars.

The findings also further muddle another mystery of the galactic center: the presence of young star clusters. The Arches Cluster, for example, contains about 150 bright, massive, young stars, which only live for a few million years. Because that is too short an amount of time for the stars to have formed elsewhere and migrated to the galactic center, they must have formed at their current location. Astronomers thought this occurred in dense clouds like G0.253+0.016. If not there, then where do the clusters come from?

The astronomers' next step is to study similarly dense clouds around the galactic center. The team has just completed a new survey with the SMA and is continuing another with CARMA. This year, they will also use the Atacama Large Millimeter Array (ALMA) in Chile's Atacama Desert—the largest and most advanced millimeter telescope in the world—to continue their research program, which the ALMA proposal committee has rated a top priority for 2013.

The title of the Astrophysical Journal Letters paper is, "The galactic center cloud G0.253+0.016: a massive dense cloud with low star formation potential." This research was supported by the National Science Foundation.

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Physics at the Large Hadron Collider

Watson Lecture Preview

Professor of Physics Harvey Newman has been searching for signs of dark matter, extra dimensions, and the elusive Higgs particle at the Large Hadron Collider in Geneva, Switzerland. He'll be reporting from the high-energy frontier of particle physics at 8:00 p.m. on Wednesday, January 9, 2013, in Caltech's Beckman Auditorium. Admission is free.

 

Q: What do you do?

A: I'm a high-energy physicist. Together with my colleague, Professor of Physics Maria Spiropulu, we explore the forces and matter that make up our universe, using the highest energies one can achieve at particle accelerators. These energies are now found in Switzerland, where CERN, the European Organization for Nuclear Research, sends protons traveling at 99.999997 percent of the speed of light crashing head-on into one another inside the Large Hadron Collider, better known as the LHC.

The LHC has two general-purpose detectors: our experiment, the Compact Muon Solenoid, or CMS, and ATLAS. "Compact" means "dense," not "small," and our experiment is relatively compact—it's only as tall as a four-story building, as opposed to ATLAS, which is like a six-story building.

Our lab had a primary role in designing the CMS's electromagnetic calorimeter, which detects high-energy photons and electrons using 76,000 crystals of lead tungstate. These crystals, which Caltech helped develop, together weigh 90 tons, and if they weren't so dense we would need even more of them in order to collect all those particles. And we need to see every particle, as we are looking for pairs of photons—a key signature of the Higgs particle that we've been focusing on for decades. We had first hints by the end of 2011, and by July 2012, CMS and ATLAS had accumulated sufficient evidence to announce the discovery of a Higgs-like particle.

 

Q: What is the Higgs, and why are you looking for it?

A: In 1964, Peter Higgs and others proposed the existence of a field that permeates all of space and would allow the generation of particle masses. The photon, which carries the electromagnetic force, has no mass, but the W and Z particles, which carry the weak force, do. But if you take the unified theory of the electromagnetic and weak interactions and try to put in a mass term for the W and one for the Z, the mathematics don't work. When you rewrite the theory to include the Higgs field, the Z and the W now have mass, the photon stays massless, and you get this other thing called the Higgs particle.

It is really quite amazing that relatively simple mathematical expressions describe how nature works. There's no reason for it, necessarily, but it is a characteristic of the world we live in. Fundamental expressions like F = ma [force equals mass times acceleration] have great predictive power in their own domains, and when you go outside those domains you have to look for something even more fundamental.

So it is for the so-called Standard Model of particle physics. It has been very successful until now, and yet we know that something lies beyond it. It does not have a candidate particle for dark matter, for example. It only describes normal matter, which is just 4 percent of the matter in the universe. And then there's dark energy, which we're not even sure has a "particles and fields" description. That's a frontier where we don't even know yet how to write things down. The Standard Model also does not work in the early universe. If you calculate the mass of the Higgs particle, the calculation blows up when we get to an energy scale that lies between where the universe is today and the moment of the Big Bang.

Caltech has a central role in the search for dark matter and whatever else lies beyond the Standard Model. It's a never-ending journey, and one that has inspired students at Caltech for decades.

 

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

A: I was in the fourth grade in PS 225 in Brooklyn, and one day Mrs. DeSimone put out a cart of books that went way beyond what was in our class. I read them all from end to end, and then I started to read everything in sight. I found Eric Rogers' Physics for the Inquiring Mind, which was a really odd book because there were all these hand drawings. It's clear that he was trying very hard to describe physics to the general public. It was also the biggest book in the library. So I carried it around, and I got fascinated by physics and astronomy, but my undergraduate advisor at MIT was in high-energy physics. I got to do experimental physics at age 17. As a grad student, I took the subway to Harvard to use the Cambridge electron accelerator, where my PhD work showed evidence of what turned out to be the so-called "charmed" quark, which was discovered the following year. That set the course of my career.

 

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From Theory to Reality: An Interview with Jason Alicea

Quantum computers—computers that harness the bizarre laws of quantum mechanics to become vastly more powerful than conventional computers—have been touted as the next leap in technology. Although useful quantum-computing technology is probably years—and possibly decades—away, physicists like Jason Alicea, who joined Caltech's faculty this fall as an associate professor of theoretical physics, are working hard to make it a reality. Alicea's research involves translating purely theoretical ideas into real-life experiments and applications. He recently answered a few questions about himself and his research.

What have you been working on lately in the field of quantum computing?

One thing that my colleagues [who include Caltech's Gil Refael and UC Santa Barbara's Matthew Fisher, both part of the Institute for Quantum Information and Matter at Caltech] and I did recently was to try to understand how to combine very simple components like semiconducting wires, ordinary superconductors, and magnetic fields to build a device that is capable of performing some rudimentary quantum-information processing without the infamous problem of decoherence—in which outside noise spoils the device's quantum properties and ruins any sort of computation it might be doing.

The physics we describe leads to blueprints for devices that may actually appear in a quantum computer down the road, although we're very far from that point.

The basic idea centers around exotic objects known as Majorana fermions that allow one to store and manipulate quantum information in a way that's protected against decoherence. The particular techniques that we originally envisioned turn out to have somewhat limited applications in quantum-information processing. But our ultimate dream would be to still use similar ideas—combining traditional conventional materials that are already available on people's shelves—to design a device that's capable of performing bona fide universal quantum computation without decoherence. We don't know how to do that, but we've made some small steps in that direction fairly recently. That's what I'm most excited about right now.

Were you always interested in science and physics when you were growing up?

Not really. I think this sets me apart from a lot of my colleagues. Often I ask people—like my fellow professors—when they became interested in physics and when they knew they wanted to be physicists. The answer I often get is that it was when they were four or five years old. I had the opposite experience. I didn't really know much about physics until I was fairly far along in college. I entered college as an engineering major with no intention of doing physics. When I was a sophomore and had to take some courses for my engineering curriculum, physics started to draw me in. I had a sort of midcollege crisis trying to decide what I was going to do. It was not an easy switch, but I decided that physics was a better course for me to follow.

Was there something particular about physics that you enjoyed?

Physics was actually extremely difficult for me. In the first physics class I took, I remember doing very poorly in the beginning and I had to work exceptionally hard, doing lots of extra problems that weren't assigned because I just wasn't used to thinking the way one has to in order to do physics. Overcoming that challenge was pretty enjoyable. I also think that I'm naturally more inclined toward fundamental questions of science as opposed to engineering. That wasn't something that was clear to me until I actually had some solid experience in physics.

What do you do when you're not doing physics?

I've been playing piano and keyboard since I was in high school, and when I was in college I played in a band. Recently, I've started to learn the guitar, writing some songs with a friend of mine. We aren't quite aiming to form a bona fide band, but we're looking to go to some open-mike nights. He's a great bass player and I'm the singer slash guitar player, but I'm good at neither. But that doesn't stop me from enjoying myself.

Alicea grew up in Brooklyn before moving to Florida in middle school. After receiving his BS in 2001 from the University of Florida, he came west to California, where he earned a PhD in physics from UC Santa Barbara in 2007. After a stint as a postdoc at Caltech, he spent time as an assistant professor of physics at UC Irvine before returning to Caltech.

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Marcus Woo
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A Close Encounter of the First Kind

Mariner 2 visits Venus in the first successful interplanetary flyby

Fifty years ago today, on December 14, 1962, Mariner 2 became the world's first successful interplanetary mission when it swept some 21,000 miles above Venus's impenetrable veil of clouds. The flyby shattered any remaining illusions that Venus, Earth's near-twin in size and orbit, might be in any way habitable. It was known that Venus's atmosphere was incredibly dense and mostly carbon dioxide. Mariner discovered that it was at least 20 times more dense than Earth's (the latest estimate is 92 times as dense) and confirmed that this thick, insulating blanket trapped the sun's heat, making Venus's surface hot enough to melt lead—even on the night side.

Spaceflight is a high-risk business even today, but back then it was so dicey that JPL built everything in pairs. The Mariners' design was based on JPL's Ranger series of moon probes and used many of the same parts. Four Rangers had been launched by then, none of which had successfully completed their missions. And the moon is right next door, in planetary terms—a mere 239,000 miles, give or take, and a couple of days' journey. Mariner 2's flight path to Venus was a gently curving trajectory 182,000,000 miles long, and it would take 109 days to get there. Attempting a Venus shot was gutsy indeed.

The first Mariner didn't go well. It was blown up by Cape Canaveral's range safety officer within five minutes of launch on July 22, 1962. A succession of errors in the guidance system, including a typo in a critical line of computer code, was sending it plunging toward a watery doom—or worse, toward the Florida coast. Mariner 2 was dispatched to Canaveral post haste, and on August 27, a little more than a month later, it managed to make it into space successfully.

The spacecraft carried six instruments, four of which were designed to study deep space throughout the entire trip. A micrometeorite counter tallied hits from cosmic dust particles, which proved to be far less abundant out in the void than they were near Earth. The plasma detector, designed to study the portion of the sun's outermost atmosphere called the corona, revealed the existence of the solar wind—a continuous stream of plasma "blowing off the boiling surface of the sun into interplanetary space," as Caltech's Engineering & Science magazine reported in October 1962, when Mariner was still millions of miles from Venus. The wind "at times reaches hurricane force with outbursts, such as solar flares, on the sun. Even though this gas is exceedingly tenuous under any terrestrial scale, it is definitely dense enough, and is moving fast enough, to be able to push the interplanetary magnetic field around as it sees fit."

Mariner's magnetometer offered another surprise: Venus, unlike Earth, had no detectable magnetic field. This hinted that Venus probably rotated too slowly to generate one; Mariner's charged-particle detector corroborated this by showing that Venus has no radiation belts equivalent to Earth's Van Allen belts, either.

As Mariner approached Venus, the other two instruments were turned on: a microwave radiometer to measure surface temperatures, and an infrared radiometer to do the same for the atmosphere. Mariner carried no cameras; since Venus was a featureless ball of clouds, there didn't seem to be any point in dragging the extra weight along.

Meanwhile, down on the ground, Caltech postdocs Bruce Murray and Robert Wildey (BS '57, MS '58, PhD '62) and staff scientist Jim Westphal were scanning the face of Venus through the 200-inch Hale Telescope at Palomar Observatory, using a recently declassified infrared detector that had been developed for the heat-seeking Sidewinder missile. The system worked in the 10-micron band—wavelengths about 20 times longer than visible light—and performed up to 50 times better than civilian technology. The detector, a germanium crystal doped with mercury atoms, owed its extreme sensitivity to being cooled to –423° F in a bath of liquid hydrogen. (And yes, the Sidewinders carried a small supply of liquid hydrogen, which would boil off during flight—the thing was designed to blow up anyway.) "It was a mess," Murray, now a professor of planetary science and geology, emeritus, recalled in his Caltech oral history. "It leaked a lot."

Caltech physics professor Gerry Neugebauer (PhD '60) was on Mariner's infrared radiometer team, and about two weeks before the Venus encounter somebody realized that it might be a good idea to try to get some confirmatory data from the ground in case the spacecraft saw something big. The planetary scientists were granted a block of "twilight time" when the sky was too bright for deep-space observations, and in the hours before sunrise on the nights of December 13 through 16, the mighty 200-inch telescope was turned toward Venus. At that focal length, a patch of clouds just a few hundred miles in diameter filled the field of view, but this extreme close-up wasn't recorded as a picture. Instead, a pen line on a paper strip chart wobbled up and down with the intensity of the light received. The telescope methodically worked along horizontal tracks from top to bottom, taking as many as 30 passes to cover the disk.

"On the first night, which was the 13th, we got just these few scans, because we hadn't the slightest idea what we were doing," recalled Westphal (who also became a Caltech professor of planetary science) in an oral history for the Smithsonian Air and Space Museum. Even so, "higher up, the thing was obviously brighter on one side than it was on the other. [On] the other side of the planet, the inverse was true." Wildey wasn't on the mountain that first night, says Westphal, so "Bruce and I . . . stood there and we looked at the damn strip chart [in] the morning twilight; and we said, what do you suppose that is?" They drew a circle representing Venus and laid the strips of paper with the scans on top of it, "and since both of us had a background in geology, we kind of contoured it. . . . Cold at the top, cold at the bottom, and hot at the middle. We both stood there, and we grinned, and we said, we know which way the pole of Venus is!" The tilt of a planet's axis and the rate at which it spins are usually measured by tracking the progress of some landmark across the face of the disk, an impossible feat given Venus's cloud cover. But the atmosphere on a rotating planet will always have a band of warm air running along the equator and cold regions at the poles. "We knew something very fundamental about Venus that nobody [else] knew," Westphal continued.

Not even the Mariner team knew—the spacecraft's radiometers were programmed to scan across the planet's limb, or edge, looking sideways thorough the atmosphere in order to find out how the temperature varied with depth. These scans proved that Venus's stultifying heat was, in fact, radiating from its surface; the atmosphere's upper reaches turned out to be ice-cold.

JPL lost contact with Mariner 2 on January 2, 1963. The spacecraft is still in orbit around the sun, but a replica built at JPL from spare parts is on display in the Smithsonian's Air and Space Museum.

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Douglas Smith
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