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.

Douglas Smith
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Top 12 in 2012

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Top 12 in 2012
Credit: Benjamin Deverman/Caltech

Gene therapy for boosting nerve-cell repair

Caltech scientists have developed a gene therapy that helps the brain replace its nerve-cell-protecting myelin sheaths—and the cells that produce those sheaths—when they are destroyed by diseases like multiple sclerosis and by spinal-cord injuries. Myelin ensures that nerve cells can send signals quickly and efficiently.

Credit: L. Moser and P. M. Bellan, Caltech

Understanding solar flares

By studying jets of plasma in the lab, Caltech researchers discovered a surprising phenomenon that may be important for understanding how solar flares occur and for developing nuclear fusion as an energy source. Solar flares are bursts of energy from the sun that launch chunks of plasma that can damage orbiting satellites and cause the northern and southern lights on Earth.

Coincidence—or physics?

Caltech planetary scientists provided a new explanation for why the "man in the moon" faces Earth. Their research indicates that the "man"—an illusion caused by dark-colored volcanic plains—faces us because of the rate at which the moon's spin rate slowed before becoming locked in its current orientation, even though the odds favored the moon's other, more mountainous side.

Choking when the stakes are high

In studying brain activity and behavior, Caltech biologists and social scientists learned that the more someone is afraid of loss, the worse they will perform on a given task—and that, the more loss-averse they are, the more likely it is that their performance will peak at a level far below their actual capacity.

Credit: NASA/JPL-Caltech

Eyeing the X-ray universe

NASA's NuSTAR telescope, a Caltech-led and -designed mission to explore the high-energy X-ray universe and to uncover the secrets of black holes, of remnants of dead stars, of energetic cosmic explosions, and even of the sun, was launched on June 13. The instrument is the most powerful high-energy X-ray telescope ever developed and will produce images that are 10 times sharper than any that have been taken before at these energies.

Credit: CERN

Uncovering the Higgs Boson

This summer's likely discovery of the long-sought and highly elusive Higgs boson, the fundamental particle that is thought to endow elementary particles with mass, was made possible in part by contributions from a large contingent of Caltech researchers. They have worked on this problem with colleagues around the globe for decades, building experiments, designing detectors to measure particles ever more precisely, and inventing communication systems and data storage and transfer networks to share information among thousands of physicists worldwide.

Credit: Peter Day

Amplifying research

Researchers at Caltech and NASA's Jet Propulsion Laboratory developed a new kind of amplifier that can be used for everything from exploring the cosmos to examining the quantum world. This new device operates at a frequency range more than 10 times wider than that of other similar kinds of devices, can amplify strong signals without distortion, and introduces the lowest amount of unavoidable noise.

Swims like a jellyfish

Caltech bioengineers partnered with researchers at Harvard University to build a freely moving artificial jellyfish from scratch. The researchers fashioned the jellyfish from silicon and muscle cells into what they've dubbed Medusoid; in the lab, the scientists were able to replicate some of the jellyfish's key mechanical functions, such as swimming and creating feeding currents. The work will help improve researchers' understanding of tissues and how they work, and may inform future efforts in tissue engineering and the design of pumps for the human heart.

Credit: NASA/JPL-Caltech

Touchdown confirmed

After more than eight years of planning, about 354 million miles of space travel, and seven minutes of terror, NASA's Mars Science Laboratory successfully landed on the Red Planet on August 5. The roving analytical laboratory, named Curiosity, is now using its 10 scientific instruments and 17 cameras to search Mars for environments that either were once—or are now—habitable.

Credit: Caltech/Michael Hoffmann

Powering toilets for the developing world

Caltech engineers built a solar-powered toilet that can safely dispose of human waste for just five cents per use per day. The toilet design, which won the Bill and Melinda Gates Foundation's Reinventing the Toilet Challenge, uses the sun to power a reactor that breaks down water and human waste into fertilizer and hydrogen. The hydrogen can be stored as energy in hydrogen fuel cells.

Credit: Caltech / Scott Kelberg and Michael Roukes

Weighing molecules

A Caltech-led team of physicists created the first-ever mechanical device that can measure the mass of an individual molecule. The tool could eventually help doctors to diagnose diseases, and will enable scientists to study viruses, examine the molecular machinery of cells, and better measure nanoparticles and air pollution.

Splitting water

This year, two separate Caltech research groups made key advances in the quest to extract hydrogen from water for energy use. In June, a team of chemical engineers devised a nontoxic, noncorrosive way to split water molecules at relatively low temperatures; this method may prove useful in the application of waste heat to hydrogen production. Then, in September, a group of Caltech chemists identified the mechanism by which some water-splitting catalysts work; their findings should light the way toward the development of cheaper and better catalysts.


In 2012, Caltech faculty and students pursued research into just about every aspect of our world and beyond—from understanding human behavior, to exploring other planets, to developing sustainable waste solutions for the developing world.

In other words, 2012 was another year of discovery at Caltech. Here are a dozen research stories, which were among the most widely read and shared articles from Caltech.edu.

Did we skip your favorite? Connect with Caltech on Facebook to share your pick.

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Calculated Science

A new supercomputer helps Caltech researchers tackle more complicated problems

One of the most powerful computer clusters available to a single department in the academic world just got stronger.

The California Institute of Technology's CITerra supercomputer, a high-performance computing cluster of the type popularly known as a Beowulf cluster, was replaced this year with a faster and more efficient system. The new cluster capitalizes on improvements in fiber-optic cables and video chips—the kind found in many gaming devices and mobile phones—to increase processing capacity and calculation speeds. With access to this improved supercomputer, Caltech's researchers are able to use advanced algorithms to analyze and simulate everything from earthquakes to global climate and weather to the atmospheres of other planets.

The new $2 million supercomputer, which is administered by the Division of Geological and Planetary Sciences, performs with five times the computational power of the previous cluster while using roughly half the energy.  It has 150 teraflops of computing capacity, meaning it can perform 150 trillion calculations per second. The upgrade was made possible in part with the private support of many individuals, including members of GPS's chair's council, a volunteer leadership board.

So what does a faster, more energy-efficient supercomputer mean for Caltech's geoscientists and geophysicists?

"There is a whole new class of problems that we can now address," says Professor of Geophysics Mark Simons, who oversees the cluster. "We can not only solve a given problem faster, but because it takes less time to solve those problems, we can choose to work on harder problems."

Simons, for instance, is working to develop models to understand what happens underground after an earthquake—and what is likely to occur in the months and years after—by analyzing ground motion observed on the surface. In 2011, for instance, a Caltech research team led by Simons used data from GPS satellites and broadband seismographic networks to develop a comprehensive mechanical model for how the ground moved after Japan's 9.0 earthquake.

"Mark's team developed the framework allowing them to do millions of computations where seismologists had only been able to do hundreds before," says Michael Gurnis, the John E. and Hazel S. Smits Professor of Geophysics and director of the Seismological Laboratory. "The ability to routinely compute at a level that is so much higher than anyone else had previously done—to have the computational resources immediately available during the hectic days after a devastating earthquake—was an amazing advance for geophysics."

Simons is not alone in using advanced computation to unlock Earth's greatest mysteries. He and Gurnis—who studies the forces driving Earth's tectonic plates—are among a group of 15 GPS faculty members who, with their students, routinely use the cluster. The division is unique among universities in that it provides its faculty with access to such a large computational facility, giving almost any of its researchers the ability to number crunch when they need to—and for extended periods of time.

Research done using computations from the previous cluster led to more than 140 published papers, which crossed the fields of atmospheric science, planetary science, Earth science, seismology, and earthquake engineering.

One of the biggest users of the new cluster is Andrew Thompson, an assistant professor of environmental science and engineering, who uses it to simulate complex ocean currents and ocean eddies. Capturing the dynamics of these small ocean storms requires large simulations that need to run for weeks.

Thanks to the size of Caltech's cluster, Thompson has been able to simulate large regions of the ocean, in particular the ocean currents around Antarctica, at high resolution. These models have led to a better understanding of how changes in off-shore currents, related to changing climate conditions, affect ocean-heat transport toward and under the ice shelves. Ocean-driven warming is believed to be critical in the melting of the West Antarctic Ice Sheet.

"Oceanography without modeling and simulations would be really challenging science," says Thompson, who arrived at Caltech in the fall of last year. "These models indicate where we need improved or more frequent observations and help us to understand how the ice sheets might respond to future ocean circulation variability. It is remarkable to have these resources at Caltech. Access to the Caltech cluster eliminates some of the need to apply for time on federal computing facilities, and has allowed my research group to hit the ground running."

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More Evidence for an Ancient Grand Canyon

Caltech study supports theory that giant gorge dates back to Late Cretaceous period

For over 150 years, geologists have debated how and when one of the most dramatic features on our planet—the Grand Canyon—was formed. New data unearthed by researchers at the California Institute of Technology (Caltech) builds support for the idea that conventional models, which say the enormous ravine is 5 to 6 million years old, are way off.

In fact, the Caltech research points to a Grand Canyon that is many millions of years older than previously thought, says Kenneth A. Farley, Keck Foundation Professor of Geochemistry at Caltech and coauthor of the study. "Rather than being formed within the last few million years, our measurements suggest that a deep canyon existed more than 70 million years ago," he says.

Farley and Rebecca Flowers—a former postdoctoral scholar at Caltech who is now an assistant professor at the University of Colorado, Boulder—outlined their findings in a paper published in the November 29 issue of Science Express.

Building upon previous research by Farley's lab that showed that parts of the eastern canyon are likely to be at least 55 million years old, the team used a new method to test ancient rocks found at the bottom of the canyon's western section. Past experiments used the amount of helium produced by radioactive decay in apatite—a mineral found in the canyon's walls—to date the samples. This time around, Farley and Flowers took a closer look at the apatite grains by analyzing not only the amount but also the spatial distribution of helium atoms that were trapped within the crystals of the mineral as they moved closer to the surface of the earth during the massive erosion that caused the Grand Canyon to form.

Rocks buried in the earth are hot—with temperatures increasing by about 25 degrees Celsius for every kilometer of depth—but as a river canyon erodes the surface downwards towards a buried rock, that rock cools. The thermal history—shown by the helium distribution in the apatite grains—gives important clues about how much time has passed since there was significant erosion in the canyon.   

"If you can document cooling through temperatures only a few degrees warmer than the earth's surface, you can learn about canyon formation," says Farley, who is also chair of the Division of Geological and Planetary Sciences at Caltech.

The analysis of the spatial distribution of helium allowed for detection of variations in the thermal structure at shallow levels of Earth's crust, says Flowers. That gave the team dates that enabled them to fine-tune the timeframe when the Grand Canyon was incised, or cut.

"Our research implies that the Grand Canyon was directly carved to within a few hundred meters of its modern depth by about 70 million years ago," she says.

Now that they have narrowed down the "when" of the Grand Canyon's formation, the geologists plan to continue investigations into how it took shape. The genesis of the canyon has important implications for understanding the evolution of many geological features in the western United States, including their tectonics and topography, according to the team.

"Our major scientific objective is to understand the history of the Colorado Plateau—why does this large and unusual geographic feature exist, and when was it formed," says Farley. "A canyon cannot form without high elevation—you don't cut canyons in rocks below sea level. Also, the details of the canyon's incision seem to suggest large-scale changes in surface topography, possibly including large-scale tilting of the plateau."

"Apatite 4He/3He and (U-Th)/He evidence for an ancient Grand Canyon" appears in the November 29 issue of the journal Science Express. Funding for the research was provided by the National Science Foundation. 

Katie Neith
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A Sky Full of Planets

Think back to the last time you saw the Milky Way—that faint stripe of stars that thickens and brightens as you get farther from city lights. At least 200 billion stars fill the Milky Way, our galaxy. How many planets might orbit those stars? What would those worlds be like? Twenty years ago, it was anybody's guess.  

In the 1990s, astronomers began to discover planets around other stars—so-called exoplanets. Since then, the confirmed count of exoplanets has skyrocketed to more than 850, with thousands of candidates awaiting follow-up. Astronomers now estimate that the stars in our Milky Way have an average of at least one planet each. (The next time you look up into the night sky, think about that.)

The sudden prospect of characterizing so many solar systems in our own galaxy has brought together two once-isolated camps: planetary scientists, who generally focus on the inside of our solar system, and astronomers, who mostly look beyond it. Planetary scientists see an opportunity to learn about our solar system and its origins by putting it into the context of a huge ensemble of other solar systems, and astronomers have a keen interest in what planetary scientists might help them discover about planet formation on a galactic or even larger scale.

To those ends, nine Caltech astronomers and planetary scientists are forming a Center for Planetary Astronomy. Joining together in a single research center will help them maintain fruitful collaborations, collectively attract research funding and fellowships for young scholars, and recruit top students and postdoctoral scholars.

The nascent center's members bring complementary perspectives to the characterization of our newly discovered neighbors. Planetary science professor Geoff Blake, astronomy professor Lynn Hillenbrand, and senior research associate John Carpenter study planet-forming disks of gas and dust around young stars. Mike Brown, the Richard and Barbara Rosenberg Professor and professor of planetary astronomy, and Caltech's infamous Pluto-killer, studies fossil rubble from just such a disk—a fantastic array of thousands of planetesimals and chunks of rock and ice on the fringes of our solar system, known as the Kuiper belt, that yields clues to the primordial solar system. The remaining scientists are focused more on the planets themselves. John Johnson, an assistant professor of planetary astronomy, focuses on the detection and characterization of exoplanets, searches for worlds like Earth, and investigates how stars' masses affect planet formation by studying the relationships between exoplanets and the very different types of stars that they orbit. Heather Knutson, an assistant professor of planetary science, characterizes exoplanets' compositions, temperatures, atmospheres, and even their weather. Yuk Yung, the Smits Family Professor of Planetary Science, studies the atmospheres of planets, and Dave Stevenson, the Marvin L. Goldberger Professor of Planetary Science, studies planetary interiors and how they evolve. Gregg Hallinan, an assistant professor of astronomy, is trying to detect radio signals from exoplanets, which would indicate the presence of magnetic fields that could be a signature of habitability.

The center's members are excited about its potential contribution to the major discoveries that are sure to come in this field. "The unique combination of Caltech's top-ranked astronomical facilities, astronomy program, and planetary science program will allow us to access the deep and broad knowledge about planets and planetary systems that only comes from such a joint endeavor," says Brown.

Says Knutson, "I was trained as an astronomer, but what I do is planetary science. Caltech is one of the few places where we have great conversations between the two groups. And Caltech's resources, in terms of telescopes, give us the opportunity to move quickly and think big." 

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Tuesday, April 9, 2013
Avery Library – Avery House

Spring Teaching Assistant Orientation

How I Landed on Mars

Caltech graduate students on the MSL mission drive science, the rover, and their careers

Caltech geology graduate student Katie Stack says her Caltech experience has provided her with the best of both worlds. Literally.

As one of five Caltech graduate students currently staffing the Mars Science Laboratory mission, Stack is simultaneously exploring the geologic pasts of both Mars and Earth. She and her student colleagues apply their knowledge of Earth's history and environment—gleaned from Caltech classes and field sites across the globe—to the analysis of Curiosity's discoveries as well as the hunt for evidence of past life on the Red Planet.

"Mars exploration is that perfect combination of understanding what is close to home and far afield," says Stack, who studies sedimentology and stratigraphy in the lab of John Grotzinger, the mission's project scientist and Caltech's Fletcher Jones Professor of Geology.

"The mission is providing a different perspective for seeing the world . . . as well as for seeing myself," she adds. "As a graduate student, you often struggle with your place in your academic community, and taking part in the mission is one of the ways that we are just thrown into the mix. We are working on the same level as a bunch of senior scientists, who have a lot of experience, and yet they are asking us questions—seeking our expertise. That's an experience you don't often get to have."

Caltech's graduate student participants on the MSL—who include Stack, Kirsten Siebach, Lauren Edgar, Jeff Marlow, and Hayden Miller, all from the Division of Geological and Planetary Sciences—represent the largest contingent of students from any one institution in a mission that has more than 400 participating scientists. Caltech's strong student presence is aided in large part by the leadership role that faculty are playing in the mission as well as the Institute's close proximity to mission control at the Jet Propulsion Laboratory (JPL), which Caltech manages for NASA.

Caltech's graduate students are among the mission personnel responsible for sequencing the scientific plan and programming the rover each day, as well as for documenting the scientific discussion and decisions at each step of the mission. As the mission's blogger, Marlow also helps share the science team's work with the public.

"The graduate students are the heart of the mission," Grotzinger says. "They are the keepers of the plan and are able to efficiently operate the technology to run the rover every day, especially when senior scientists are unable to do so."

Making the science plans for the rover, says graduate student Kirsten Siebach, is "as close as I get to driving the rover. I can help program it to take pictures, analyze samples, and shoot the ChemCam laser."

"It's always fun when something that I helped command the rover to do, like take a picture, ends up making the news," she adds. "I helped command it to take one such picture of the Hottah outcrop that showed evidence of an ancient streambed."

In addition to staffing operations for the mission, Caltech's students are also key contributors to the scientific analysis of the data and help make decisions about where Curiosity goes.

Before Curiosity landed, for instance, Stack and Lauren Edgar, helped compile a geologic map of the Gale Crater landing ellipse, using orbital images to identify the geologic diversity and relationships among rocks. Their work has continued to serve as a "road map" for the rover's research. Meanwhile, Siebach has been exploring the history of water on Mars, looking at the geomorphology of channel structures and fractures on the planet.

"We really have grown up in the golden age of Mars exploration," Edgar says, noting that while at Caltech, she's had the opportunity to contribute to three Mars rover missions—Spirit, Opportunity, and now Curiosity. "They just keep getting better and better."

In addition to the graduate students, several undergraduate students have taken part in the mission, participating through Caltech's Summer Undergraduate Research Fellowships (SURF) program. This past summer, a student working with Bethany Ehlmann, an assistant professor of planetary science at Caltech and an MSL science team member, helped to characterize and classify hundreds of Earth rock samples for potential comparison with Mars specimens that will be analyzed by the ChemCam instrument. Meanwhile, over the past two summers, Solomon Chang, a Caltech sophomore studying computer science, worked with JPL engineers to model Curiosity's mobility to ensure that it would actually move on Mars as it had been programmed to do.

Those summer projects have ended, but for the Caltech grad students on the MSL team, the work continues. Indeed, says Grotzinger, because many of the mission's scientists will be leaving Pasadena to return to their home institutions during the coming months, the grad students will be called upon to fill additional roles in the rover's daily operation and science.

"One of the great things about working on a mission as a student is that science is a fairly merit-driven process," says Ehlmann, who participated in Mars exploration missions as both an undergraduate and graduate student. "So if you have a good idea and you are there, you can contribute to deciding what measurements to make, can develop hypothesis about what's going on. It's a very inspiring and empowering experience."

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Cassini Turns 15

Some highlights from JPL's mission to Saturn

The Jet Propulsion Lab's Cassini spacecraft roared toward Saturn in a spectacular nighttime launch on October 15, 1997. After two gravity assists from Venus and one each from Earth and Jupiter, the school-bus-sized orbiter arrived at Saturn on June 30, 2004 Pasadena time, putting itself on a wildly looping path designed to give its Earthbound handlers repeated close-up looks at Saturn's rings, all of Saturn's big moons, a good few of the small ones—and, of course, Saturn itself. Saturn and its retinue have not disappointed; new wonders have been revealed with every orbit.

Cassini carried a second spacecraft along for the ride—a probe named Huygens, built by the European Space Agency and designed to land on Titan, Saturn's largest moon. Titan could have been a planet itself, if it hadn't grown up in the wrong neighborhood. Titan is bigger than Mercury (but smaller than Mars) and has an atmosphere that's four times denser at the surface than Earth's is at sea level. The surface, however, had never been seen  before—or at least not clearly. There's so much methane in Titan's atmosphere that the entire moon is wrapped in an impenetrable, orange pall of photochemical smog.

Cassini dropped off its hitchhiker six months after arriving, and on January 14, 2005, Huygens took a two-hour, 28-minute parachute ride through Titan's atmosphere, smelling, tasting, and feeling its winds all the way down. At an altitude of about 40 kilometers, the hydrocarbon haze became transparent, revealing a vista much like the mountain ranges and dry lakes of the Mojave Desert. But because of Titan's average surface temperature of 95 kelvins (nearly –290° F) the gullies on these mountainsides had been carved by methane rain; the mountains themselves proved to be made of water ice frozen as hard as any rock on Earth.

Hyugens made a soft landing on material with the consistency of wet sand and was still broadcasting 72 minutes later when Cassini dropped below Titan's horizon and radio contact was lost. The pictures Huygens beamed back showed that it had come to rest on a sepia-tinted plain strewn with cantaloupe-sized cobblestones of ice that had clearly been rounded by a flowing liquid. It didn't take long to identify this fluid as methane, since Huygens's mass spectrometer detected a puff of the stuff vaporized from the greasy mudflat by the lander's body heat.

Cassini's radar mapper has since confirmed what earlier observations had suggested—that lakes of liquid methane and ethane exist, primarily in Titan's northern hemisphere. One, near the north pole, is the size of Lake Superior. Titan has taken this low-temperature parody of Earth, where methane is water and ice is rock, even further. Cassini's radar has spotted areas where there may be "cryovolcanoes" that ooze slush instead of lava.

Titan, big as it is, is far too small to have retained the warmth that volcanoes—even of ice—demand. However, Cassini found that it flexes like a stress ball in the grip of Saturn's gravity, which induces a 10-meter-tall "solid tide" in Titan's crust. This periodic deformation not only generates heat, but implies the presence of liquid water under the ice. A Titan made of solid rock could only bulge by about a meter, but a liquid would be more susceptible to Saturn's pull. "We have long suspected that Titan, like Jupiter's moons Europa, Ganymede, and Callisto, has a subsurface ocean," says David Stevenson, Caltech's Goldberger Professor of Planetary Science. "These results show that this is very likely the case."

Titan isn't the only satellite of Saturn to join the subsurface saltwater society. The biggest surprise of the Cassini mission has come from Enceladus, a small, undistinguished moon that turns out to be spewing curtains of icy mist from the vicinity of its south pole. These geysers issue from fissures called tiger stripes—dark parallel gashes on Enceladus's otherwise bright surface. These intriguing stripes were discovered in May 2005, and the trajectory of Cassini's next flyby in July was altered to take a closer look. Cassini spotted the geysers on its way in, shortly before whizzing through them at an altitude of about 170 kilometers. A thermal map of the surface below linked the plumes to hot spots with temperatures of some 145 K—on a moon whose average surface temperature does not exceed 70 K. (See "A Nice Place to Visit?" in E&S No. 1, 2006.)

Life is found wherever liquid water exists on Earth. Could this hold for the outer solar system as well? Perhaps, says Professor of Planetary Science Andrew Ingersoll. "The idea of a 'habitable zone' has existed for a hundred years. All the water is frozen out on Mars, and it's all vaporized on Venus. Earth is just right—we have oceans, and we have life. But now, the habitable zone might also include an archipelago of these isolated moons."

Enceladus probably gets its heat by flexing, like Titan, Ingersoll says. "But this would dissipate orbital energy, and eventually Enceladus wouldn't be where it is any more. And neither would the other nearby moons, because they all influence each other." This could mean that the geysering is a relatively recent phenomenon, says Ingersoll. "Or is it cyclic, and we just got lucky enough to see it?"

Getting lucky may be putting it mildly. "You have to get the energy from somewhere," Stevenson observes. The proximate source, he says, could be a moon named Dione, with which Enceladus is in an orbital resonance. Enceladus makes two trips around Saturn for every one that Dione makes, and each time Enceladus catches up, Dione gives it a gravitational tug. Like a child being pushed ever higher on a swing, these gravity assists could nudge Enceladus into an increasingly eccentric orbit, Stevenson says. Eventually enough orbital energy might accumulate to trigger the geysers, which would then erupt for a while as Enceladus's orbit became more circular again. "This cycle might well take a million years or more," Stevenson says. "But Io, Jupiter's volcanic moon, is also overly active. And now you start to get scared, because this means you're looking at a very special time for both of them." If the odds of this coincidence are 1 in 10, it's not so bad; but if they work out to 1 in 100, it's time to find another theory.

Saturn's rings have also held surprises. Cassini arrived just after the northern hemisphere's winter solstice, when the rings were at their maximum tilt relative to the sun. This allowed the spacecraft to measure the sunlight passing through the rings, revealing them to be incredibly thin—a mere 10 to 20 meters thick, on average. During Saturn's equinox in August 2009, Cassini got a never-before-seen view of the rings aimed edge-on to the sun. As the light swept across them, giant shadows were cast by anything sticking up from the surface. Suddenly, towering waves of ice as much as four kilometers tall were thrown into sharp relief. They proved to be disturbances set off by the passage of the nearby moon Daphnis, whose orbit is slightly tilted relative to the ring plane. (Many more discoveries are described in "Cassini's Ringside Seat" in the Spring 2010 issue of E&S.)

And what of Saturn itself? Unlike Jupiter's psychedelic swirls of candy-cane colors bedecked with semipermanent storms such as the Great Red Spot, the bands in Saturn's atmosphere are muted shades of butterscotch. Not that there's nothing going on down there—Cassini has witnessed 10 thunderstorms in its eight-plus years over Saturn, all in the summer skies of the southern hemisphere. But on December 5, 2010, Cassini caught a storm 500 times the size of the others—in the northern hemisphere. The spacecraft heard the storm before it saw it, says Ingersoll. "So everything is very quiet, and then this giant thunderstorm goes off. We were getting copious noise on the radio receiver, and then we see this." What showed up as a tiny white spot in a picture shot that day grew to the diameter of Earth in three weeks, spawning a trail of white clouds that wrapped all the way around the planet. Such storms have been seen once every 30-odd years since 1876. They usually appear late in the northern hemisphere's summer, but this one arrived 10 years early at the beginning of spring.

"Saturn is normally very bland," Ingersoll says, "which makes this giant storm just weird. It's just crying out to be explained." Like thunderstorms on Earth, these storms are driven by convection, as air masses of different temperatures redistribute their heat. But rather than supporting a bunch of small storms all the time, Saturn stores up these heat differences until it unleashes a doozy. In some ways, Ingersoll says, Saturn behaves less like a terrestrial weather system and more like a volcano, in which the pressure builds up for many years before an eruption. Volcanic pressure is contained by layers of rock, but what keeps the lid on Saturn's atmospheric energy?

"To some extent, that same question applies to both Titan's and Saturn's meteorology," Ingersoll says. "There is more methane in Titan's atmosphere waiting to rain out than there is water vapor in the atmosphere on Earth. There's more latent heat stored, too, but only 1 percent as much sunlight to evaporate it. So there are two ways this could work: tremendously violent but infrequent rainstorms, because there isn't much energy to resupply them; or a steady, continuous drizzle. And the choice seems to be the same on both Saturn and Titan. We've seen the storms on Saturn, and we see erosion on Titan. A drizzle won't carve those channels. So that seems to be how weather works. You turn down the energy, and you still get storms. Who knew? That's why we study this stuff."

There's still time to figure it out. Cassini's mission is now planned to run through the northern hemisphere's summer solstice, in May 2017, allowing us to observe one complete change of Saturn's seasons, or a little less than half of a Saturnian year. 

Douglas Smith
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Planetary Weatherman: An Interview with Andrew Ingersoll

Andrew Ingersoll, Earle C. Anthony Professor of Planetary Sciences, has been a leader in the investigation of planetary weather and climate for nearly five decades. His research has included studies of the so-called runaway greenhouse effect that is thought to have boiled away Venus's oceans, the presence of liquid water on Mars, the supersonic winds on Jupiter's moon Io, and the atmospheric dynamics of Jupiter, Saturn, Uranus, and Neptune. He has been a key player on the instrument teams for many NASA/JPL missions, including Pioneer Venus, Pioneer Saturn, Voyager, Mars Global Surveyor, Galileo, and Cassini.

Ingersoll recently spoke more about his research and why he has dedicated his career to exploring atmospheres in outer space. In particular, he spoke, about the Cassini mission—a robotic spacecraft that was launched in 1997 and has been orbiting Saturn, its rings, and its moons since 2004.


What do you study?

In a single word, it is atmospheres. I study the weather and climate of Earth and other planets.



It may be in my genes to like that kind of phenomenon. I like things that I can stick my hands into and feel and imagine. Other branches of physics were too abstract for me. The objects of interest were either too large or too small. I like the human scale.

I also really like the unknowns. At the end of my doctorate in 1966, I could have gone into the fields of meteorology, oceanography, or planetary science. Meteorology seemed too routine because it involved forecasting the weather every day. That's unfair, because there are big challenges, but still, it wasn't as appealing to me as the planets. We knew next to nothing about them in the 1960s and Caltech offered me a nice job as an assistant professor, studying the weather and climate of other planets.


What was the field like when you first started out?

In those days, I felt I was doing what early meteorologists and oceanographers were doing in the 1930s, during the war and right after, which was just kind of getting the basic understanding of what was going on.

In the 1960s, 70s, 80s—and even today—we were and are still building that fundamental understanding of the planets. What are the basic gears? What's making Venus so hot and Mars so cold and Jupiter a striped Christmas tree ball? All of these things are fascinating.


What do we learn from studying the atmospheres of other planets?

By studying the planets—with their wide array of personalities and behaviors—we learn about how atmospheres and how weather and climate work in general and we get a much broader picture and perspective than we could ever get from studying Earth alone. Earth has ice ages—and that's pretty interesting—but we can't look at the ice ages today except by proxies. But we can look at the planets right now.


What have we learned from studying other planets that you are most excited about?

In the broadest sense, we have learned humility—how difficult it is to extend our knowledge of Earth's weather and climate to other planets. The planets continue to surprise us with things we never imagined. For me, the planets themselves are the heroes of the space program. They keep coming through with exciting stuff that was waiting to be discovered.


What have we discovered by studying Saturn through the Cassini mission?

Saturn has everything: rings, magnetosphere, icy moons, a moon—Titan—with a dense atmosphere, and the giant planet itself. In the realm of atmospheres, three things stand out. One is the way Saturn erupts every 20 to 30 years with a giant thunderstorm that wraps around the planet and then dies. Another is the way Titan has developed a methane-based hydrologic cycle complete with lakes, rivers, clouds, and rain. The third is the way Enceladus, a little icy moon, manages to emit plumes of ice particles, water vapor, and other gases despite its low temperatures. The underground plumbing is a big mystery, but it may involve liquid water close to the surface.


What big questions/discoveries are you still interested in pursuing?

Cassini has answered many old questions and raised many new ones, and that's good. It means there is stuff out there waiting to be discovered. I hope to answer a few of the new questions. Also, there is Earth. My career as a planetary scientist has given me a willingness to speculate about processes here on Earth and maybe to see things that other people have missed. Even if it doesn't work out, I am going to take a look at some of the outstanding questions of Earth's weather and climate. For instance, there's a 60-day cycle of tropical rainfall known as the Madden Julian oscillation. That's a long lifetime for a weather pattern, and the models don't reproduce it very well. Also, there are 1000-year cycles recorded in the Greenland ice known as Dansgaard-Oeschger events. That's much shorter than the orbital cycles and may represent sudden turnover of the oceans. Students and I are working on both projects right now.


What's next for you?

I'm involved with Juno, a spacecraft that is going into orbit around Jupiter in 2016. It carries a microwave radiometer that allows us to see down below the clouds at radio wavelengths. We will learn if the weather has roots in the deep atmosphere and whether the roots account for the long-term stability of the cloud features. Juno does many things, but it also gives us our first good look at the poles, where the weather is very unlike that at lower latitudes. Cassini goes on until 2017, and those two spacecraft will keep me busy. And there are always bright students who challenge me to think about new things.


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Caltech Again Named World's Top University in <i>Times Higher Education</i> Global Ranking

PASADENA, Calif.—The California Institute of Technology (Caltech) has been rated the world's number one university in the 2012–2013 Times Higher Education global ranking of the top 200 universities.

Oxford University, Stanford University, Harvard University, and MIT round out the top five.

"We are pleased to be among the best, and we celebrate the achievements of all our peer institutions," says Caltech president Jean-Lou Chameau. "Excellence is achieved over many years and is the result of our focus on extraordinary people. I am proud of our talented faculty, who educate outstanding young people while exploring transformative ideas in an environment that encourages collaboration rather than competition."

Times Higher Education compiled the listing using the same methodology as in last year's survey. Thirteen performance indicators representing research (worth 30 percent of a school's overall ranking score), teaching (30 percent), citations (30 percent), international outlook (which includes the total numbers of international students and faculty and the ratio of scholarly papers with international collaborators, 7.5 percent), and industry income (a measure of innovation, 2.5 percent) make up the data. Included among the measures are a reputation survey of 17,500 academics; institutional, industry, and faculty research income; and an analysis of 50 million scholarly papers to determine the average number of citations per scholarly paper, a measure of research impact.

In addition to placing first overall in this year's survey, Caltech came out on top in the teaching indicator as well as in subject-specific rankings for engineering and technology and for the physical sciences.

"Caltech held on to the world's number one spot with a strong performance across all of our key performance indicators," says Phil Baty, editor of the Times Higher Education World University Rankings. "In a very competitive year, when Caltech's key rivals for the top position reported increased research income, Caltech actually managed to widen the gap with the two universities in second place this year—Stanford University and the University of Oxford. This is an extraordinary performance."

Data for the Times Higher Education's World University Rankings were provided by Thomson Reuters from its Global Institutional Profiles Project, an ongoing, multistage process to collect and validate factual data about academic institutional performance across a variety of aspects and multiple disciplines.

The Times Higher Education site has the full list of the world's top 400 schools and all of the performance indicators.

Kathy Svitil
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Caltech Again Named World's Top University by <i>Times Higher Ed</i>
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