Caltech Researchers Use Stalagmites to Study Past Climate Change

PASADENA, Calif.—There is an old trick for remembering the difference between stalactites and stalagmites in a cave: Stalactites hold tight to the ceiling while stalagmites might one day grow to reach the ceiling. Now, it seems, stalagmites might also fill a hole in our understanding of Earth's climate system and how that system is likely to respond to the rapid increase in atmospheric carbon dioxide since preindustrial times.

Many existing historical climate records are biased to the high latitudes— coming from polar ice cores and North Atlantic deep ocean sediments. Yet a main driver of climate variability today is El Niño, which is a completely tropical phenomenon. All of this begs the question: How do we study such tropical climate influences? The answer: stalagmites.

"Stalagmites are the ice cores of the tropics," says Jess Adkins, professor of geochemistry and global environmental science at the California Institute of Technology (Caltech). He and geochemist Kim Cobb of the Georgia Institute of Technology led a team that collected samples from stalagmites in caves in northern Borneo and measured their levels of oxygen isotopes to reconstruct a history of the tropical West Pacific's climate over four glacial cycles during the late Pleistocene era (from 570,000 to 210,000 years ago).

The results appear in the May 3 issue of Science Express. The lead author of the paper, Nele Meckler, completed most of the work as a postdoctoral scholar at Caltech and is now at the Geological Institute of ETH Zürich.

Throughout Earth's history, global climate has shifted between periods of glacial cooling that led to ice ages, and interglacial periods of relative warmth, such as the present. Past studies from high latitudes have indicated that about 430,000 years ago—at a point known as the Mid-Brunhes Event (MBE)—peak temperatures and levels of atmospheric carbon dioxide in interglacial cycles were suddenly bumped up by about a third. But no one has known whether this was also the case closer to the equator.

 

By studying the records from tropical stalagmites, Adkins and his team found no evidence of such a bump. Instead, precipitation levels remained the same across the glacial cycles, indicating that the tropics did not experience a major shift in peak interglacial conditions following the MBE. "The stalagmite records have glacial cycles in them, but the warm times—the interglacials—don't change in the same way as they do at high latitudes," Adkins says. "We don't know what that tells us yet, but this is the first time the difference has been recorded."

At the same time, some changes did appear in the climate records from both the high latitudes and the tropics. The researchers found that extreme drying in the tropics coincided with abrupt climate changes in the North Atlantic, at the tail end of glacial periods. It is thought that these rapid climate changes, known as Heinrich events, are triggered by large ice sheets suddenly plunging into the ocean.

"In the tropics, we see these events as very sharp periods of drying in the stalagmite record," Adkins says. "We think that these droughts indicate that the tropics experienced a more El Niño–like climate at those times, causing them to dry out." During El Niño events, warm waters from the tropics, near Borneo, shift toward the center of the Pacific Ocean, often delivering heavier rainfall than usual to the western United States while leaving Indonesia and its neighbors extremely dry and prone to forest fires. 

The fact that the tropics responded to Heinrich events, but not to the shift that affected the high latitudes following the MBE, suggests that the climate system has two modes of responding to significant changes. "It makes you wonder if maybe the climate system cares about what sort of hammer you hit it with," Adkins says. "If you nudge the system consistently over long timescales, the tropics seem to be able to continue independently of the high latitudes. But if you suddenly whack the climate system with a big hammer, the impact spreads out and shows up in the tropics."

This work raises questions about the future in light of recent increases in atmospheric carbon dioxide: Is this increase more like a constant push? Or is it a whack with a big hammer? A case could be made for either one of these scenarios, says Adkins, but he adds that it would be easiest to argue that the forcing is more like a sudden whack, since the amount of carbon dioxide in the atmosphere has increased at such an unprecedented rate.

In addition to Adkins, Cobb, and Meckler, other coauthors on the paper, "Interglacial hydroclimate in the tropical West Pacific through the late Pleistocene," are Matthew Clarkson of the University of Edinburgh and Harald Sodemann of ETH Zürich. Cobb is also a former postdoctoral scholar in Adkins's group and has been collaborating on this project since her time at Caltech. The work was supported by the National Science Foundation, the Swiss National Science Foundation, the German Research Foundation, and by an Edinburgh University Principal's Career Development PhD Scholarship.

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From the Ground Up

What's it like to build an entire research program from scratch? It's all about becoming part of a community, according to three brand-new professors: 

"It's very important to generate an environment where people help each other." —André Hoelz 

"I have two challenges getting started here. One is bringing in students and postdocs, and the other is fostering a connection between economics and computer science." —Katrina Ligett

"It is not traditionally a field Caltech has done. . . . So when I was looking at coming to Caltech, the idea of being 'the oceanographer' was an exciting prospect.' —Andrew Thompson

Read "From the Ground Up" in the Spring 2012 issue of Caltech's Engineering & Science magazine. 

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Doug Smith
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Building a Research Program from the Ground Up
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What Triggers a Mass Extinction?

Caltech researchers say habitat loss and tropical cooling were to blame for mass extinction

PASADENA, Calif.—The second-largest mass extinction in Earth's history coincided with a short but intense ice age during which enormous glaciers grew and sea levels dropped. Although it has long been agreed that the so-called Late Ordovician mass extinction—which occurred about 450 million years ago—was related to climate change, exactly how the climate change produced the extinction has not been known. Now, a team led by scientists at the California Institute of Technology (Caltech) has created a framework for weighing the factors that might have led to mass extinction and has used that framework to determine that the majority of extinctions were caused by habitat loss due to falling sea levels and cooling of the tropical oceans.

The work—performed by scientists at Caltech and the University of Wisconsin, Madison—is described in a paper in the early edition of the Proceedings of the National Academy of Sciences.

The researchers combined information from two separate databases to overlay fossil occurrences on the sedimentary rock record of North America around the time of the extinction, an event that wiped out about 75 percent of marine species alive then. At that time, North America was an island continent geologists call Laurentia, located in the tropics.

Comparing the groups of species, or genera, that went extinct during the event with those that survived, the researchers were able to figure out the relative importance of several variables in dictating whether a genus went extinct during a 50-million-year interval around the mass extinction.

"What we did was essentially the same thing you'd do if confronted with a disease epidemic," says Seth Finnegan, postdoctoral scholar at Caltech and lead author of the study. "You ask who is affected and who is unaffected, and that can tell you a lot about what's causing the epidemic." 

As it turns out, the strongest predictive factors of extinction on Laurentia were both the percentage of a genus's habitat that was lost when the sea level dropped and a genus's ability to tolerate broader ranges of temperatures. Groups that lost large portions of their habitat as ice sheets grew and sea levels fell, and those that had always been confined to warm tropical waters, were most likely to go extinct as a result of the rapid climate change.

"This is the first really attractive demonstration of how you can use multivariate approaches to try to understand extinctions, which reflect amazingly complex suites of processes," says Woodward Fischer, an assistant professor of geobiology at Caltech and principal investigator on the study. "As earth scientists, we love to debate different environmental and ecological factors in extinctions, but the truth is that all of these factors interact with one another in complicated ways, and you need a way of teasing these interactions apart. I'm sure this framework will be profitably applied to extinction events in other geologic intervals."

The analysis enabled the researchers to largely rule out a hypothesis, known as the record-bias hypothesis, which says that the extinction might be explained by a significant gap in the fossil record, also related to glaciation. After all, if sea levels fell and continents were no longer flooded, sedimentary rocks with fossils would not accumulate. Therefore, the last record of any species that went extinct during the gap would show up immediately before the gap, creating the appearance of a mass extinction. 

Finnegan reasoned that this record-bias hypothesis would predict that the duration of a gap in the record should correlate with higher numbers of extinctions—if a gap persisted longer, more groups should have gone extinct during that time, so it should appear that more species went extinct all at once than for shorter gaps. But in the case of the Late Ordovician, the researchers found that the duration of the gap did not matter, indicating that a mass extinction very likely did occur. 

"We have found that the Late Ordovician mass extinction most likely represents a real pulse of extinction—that many living things genuinely went extinct then," says Finnegan. "It's not that the record went bad and we just don't recover them after that."

The team used data about North American fossils from the public Paleobiology Database as well as information about the sedimentary rock record from the Macrostrat Database developed by the University of Wisconsin, Madison. Along with Fischer and Finnegan, additional coauthors of the paper, "Climate change and the selective signature of the late Ordovician mass extinction" are Shanan Peters and Noel Heim of the University of Wisconsin, Madison. Finnegan will begin a new appointment at UC Berkeley in the fall. The work was supported by the Agouron Institute and the National Science Foundation.

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Kimm Fesenmaier
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Looking at the Man in the Moon

Caltech researchers explain why the man in the moon faces Earth

PASADENA, Calif.—Many of us see a man in the moon—a human face smiling down at us from the lunar surface. The "face," of course, is just an illusion, shaped by the dark splotches of lunar maria (smooth plains formed from the lava of ancient volcanic eruptions).

Like a loyal friend, the man is always there, constantly gazing at us as the moon revolves around Earth, locked in what's called a synchronous orbit, in which the moon rotates exactly once every time it orbits Earth. But why did the moon settle into an orbit with the man—rather than the moon's crater-covered far side—facing Earth?

Previously, some scientists have thought the fact that we see the man is just the result of a coincidence, a sort of lunar coin toss, says Oded Aharonson, professor of planetary science at the California Institute of Technology (Caltech). But he and his colleagues have now found that is not the case. In the past, the moon spun around its axis faster than it does today, and their new analysis shows that the fact that the man now faces us may be a result of the rate at which the moon slowed down before becoming locked into its current orientation.

Aharonson, along with Peter Goldreich, the Lee DuBridge Professor of Astrophysics and Planetary Physics, Emeritus, and Re'em Sari of the Hebrew University of Jerusalem, describe their findings in a paper published online on February 27 in the journal Icarus.

Although the moon looks spherical, it is actually elongated, almost like a football. Not long after the moon formed just over four billion years ago, while it was still hot and largely molten, Earth's gravity began to stretch its new companion. When the moon cooled, its slightly oblong shape stuck. Today, the man in the moon occupies one of the two elongated ends. 

And the reason he faces us at all times is because the moon rotates around its axis once with each revolution around the Earth, so that the same face is always pointing earthward. A couple billion years ago, give or take, the moon rotated around its axis much more rapidly, so that the inhabitants of Earth would have seen all the different sides of the moon at various times.

Eventually, however, Earth's pull on the moon slowed down its rotation through a dissipative process first explained by Goldreich in the 1960s. Tidal forces tugged on the moon, creating another slight bulge—in addition to the moon's already-elongated shape—that moved to stay on whichever side was closest to Earth at that moment. The bulge continued to point toward Earth as the moon rotated through it, causing the moon's interior to squish and flex as the bulge changed position. The internal friction from this flexing acted as a brake that slowed the moon's spinning until its rotation rate matched its revolution rate, when it settled into a synchronous orbit.

In this way, as a result of Earth's gravity, the moon became locked into an orientation with its long axis pointing toward our planet. The question, then, is why the side that ended up facing Earth is the one with the man—especially since the reverse configuration is actually favored, the researchers say. The side of the moon without the man has higher mountains and an elevated topography, they explain. Based on a naive analysis of the physics, it might be expected for this side to face Earth, because its surface—and its mass—would be closer to Earth.

In the work described in the Icarus paper, the researchers analyzed the physics of the moon and discovered that what determines which side of the moon we see is the rate at which the moon slowed down its spinning—how fast it dissipated its rotational energy. If the moon had lost energy at a significantly different rate—say 100 times faster—than it really did, there would have been a 50/50 chance that the man would face us. In that scenario, Aharonson says, having the man face us would indeed have been merely the result of a coin flip. But, as it turns out, the moon's actual rate of energy dissipation was much slower—and that means the man in the moon had about two-to-one odds of facing us. "The coin was loaded," Aharonson says.

By tweaking the dissipation rate in computer simulations, the researchers were able to simulate moons that resulted with either the man or the mountainous far side facing us every single time. In other words, they were able to load the coin however they wanted.

"The real coincidence is not that the man faces Earth," Aharonson says. Instead, the real coincidence is that the moon's dissipation rate was just the right amount to create such fascinating physics and load the coin.

But there is a caveat, he adds. The researchers' analysis is based on the present-day moon. "In the past, when the moon first locked, it could've had different properties," Aharonson notes. If that's the case, then the explanation for why we see the man might result in different odds. But, if the moon locked into its synchronous orbit relatively recently—within the last billion years or so—then there's a good chance the researchers' analysis is fitting.

The title of the Icarus paper is "Why do we see the man in the moon?" Support was provided by NASA's Lunar Reconnaissance Orbiter project.

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Marcus Woo
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Caltech Geochemist Wins Feynman Prize for Excellence in Teaching

PASADENA, Calif.—Paul D. Asimow, professor of geology and geochemistry at the California Institute of Technology (Caltech), has been awarded the Richard P. Feynman Prize for Excellence in Teaching—Caltech's most prestigious teaching honor.

Asimow was selected for his "exceptional energy, originality, and ability to explain complicated concepts effectively," according to the award citation.

The Feynman Prize was established in 1993 "to honor annually a professor who demonstrates, in the broadest sense, unusual ability, creativity, and innovation in undergraduate and graduate classroom or laboratory teaching." Any member of the Caltech community—including faculty, students, postdoctoral scholars, alumni, or staff—may nominate a faculty member for the award. A committee appointed by the provost selects the winner.

"I'm both utterly surprised and deeply gratified, as the classes I teach are pretty small and specialized," says Asimow, who teaches Introduction to Geology and Geochemistry, and Thermodynamics of Geological Systems, among other courses. "I never expected to be considered alongside the professors who shoulder the hard work of teaching the big classes. I'm inspired by this recognition to keep putting my efforts into improving and updating what and how I teach."

Asimow says he credits his success in academia to a teacher he had as an undergrad at Harvard. "My own career path was determined by one incredible professor, James B. Thompson, Jr., who recently passed away," he notes. "I'd like to acknowledge the legacies of both Feynman and Thompson."

A member of the faculty since 1999, Asimow earned his MS and PhD at Caltech in 1993 and 1997, respectively. His research focuses on characterizing the mineralogy and melting of the earth's mantle, the formation of crust, and the nature of the core-mantle boundary.

Asimow is a member of the American Geophysical Union, the Mineralogical Society of America, the Geochemical Society, and the American Physical Society. He is the winner of the 2003 F. W. Clarke Medal of the Geochemical Society, a 2003 Alfred P. Sloan Foundation Fellow, and the recipient the 2005 James B. Macelwane Medal of the American Geophysical Union. His work was supported by a National Science Foundation CAREER grant from 2003 to 2007.

In nomination letters written by students, Asimow was commended for his enthusiasm, clarity, and depth of knowledge. Several students described him as the professor to whom graduate students in the Division of Geological and Planetary Sciences turn when confused about a paper, when they can't agree on the answer to a scientific question, or when they're starting a new project or finishing a composition. The award citation also highlighted what the committee called a "striking innovation" of Asimow's curriculum for an advanced graduate class in petrology; in that class, he "invites his students to vote on the subject matter of the course on the first day of the term, laying the foundation for the extensive teacher-student interaction that forms a critical part of his teaching style."

"He is as inspiring as he is informative, and a great role model for us aspiring professors," said June Wicks, a graduate student in geochemistry, in her letter nominating Asimow for the prize. "He pours his energy into describing concepts both precisely and thoroughly."

Asimow says that the best thing about teaching at Caltech is its dynamic, engaged, talented, and curious student population.

"It makes all the difference to a teacher when the students are able and willing to interact, question, and even challenge the professor," says Asimow. "With small class sizes and suitable encouragement, I often get a group of students that help me and help each other to explore a subject in a satisfying and complete way. That's very rewarding."

Previous winners of the Feynman Prize in the past four years are J. Morgan Kousser, professor of history and social science; Dennis Dougherty, George Grant Hoag Professor of Chemistry; Jehoshua (Shuki) Bruck, Gordon and Betty Moore Professor of Computation and Neural Systems and Electrical Engineering; and Zhen-Gang Wang, professor of chemical engineering.

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Katie Neith
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Geological Society of America Honors Jason Saleeby

The Geological Society of America has named Jason Saleeby, professor of geology at Caltech, the recipient of their Mineralogy, Geochemistry, Petrology, and Volcanology Division's Distinguished Geologic Career Award for this year. 

The Distinguished Geologic Career Award is given to an individual "who throughout his/her career, has made distinguished contributions in one or more of the following fields of research: mineralogy, geochemistry, petrology, and volcanology, with emphasis on multidisciplinary, field-based contributions." 

Saleeby's research interests include tectonic and geochronological studies in orogenic terranes of western North America, emphasizing the paleogeographic development of the Pacific Basin and its margins.

 

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Allison Benter
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Caltech Oceanographer Tests New Technology at the Bottom of the Earth

The field of study of Andrew Thompson, assistant professor of environmental science and engineering at Caltech, presents not only theoretical challenges but logistical ones as well. That's because he is interested in the circulation and ecology of the Southern Ocean—a cold, remote region near Antarctica—and the role it plays in global climate.  

In particular, he studies a marine area at the eastern tip of the Antarctic Peninsula, part of the Weddell Sea. The hostile environment of the Weddell Sea makes long-term research difficult, so he's part of a team that is seeking to monitor the region with autonomous underwater vehicles called gliders. Last month, Thompson set off on a research cruise to deploy three of these new gliders, as well as some surface drifters that follow the currents and can be tracked with global positioning system (GPS) receivers.

"The currents and fronts in this region are important because they determine the transport and dispersal of krill—an important part of the ocean food chain—and also interact and modify the outflow of dense Antarctic Bottom Water, which eventually sinks to become the densest water in the ocean," says Thompson. "This part of the Weddell Sea is the injection point for krill and these dense water masses into the greater Southern Ocean, " 

The team, which included researchers from the Virginia Institute of Marine Sciences, the British Antarctic Survey, and from the University of East Anglia in the U.K., collected hydrographic data from the ship—such as the temperature, salinity, and density of the water—when they weren't busy with the gliders.

"We captured the signature of dense Antarctic Bottom Water at the shelf break cascading off the continental shelf," says Thompson, who says the group spent a lot of time keeping the gliders out of the way of iceberg C-19, formed in 2002 on the opposite side of Antarctica. "It originally had a surface area of 5500 square km, but is now about 800 square km. We have some great measurements right in the lee of the berg and see evidence of it significantly disrupting the currents in the region."

The team also successfully tested an echo sounder that they attached to the gliders to measure krill biomass. The echo sounder uses sonar to detect krill swarms in the water column.

"A major purpose of the cruise was to demonstrate the capability of ocean gliders to play a key role in future polar ocean observing systems," he says. And so far, the instruments have shown favorable results. The gliders were deployed on January 23; since then, they've been collecting samples and reporting data back to Thompson via satellite when they come to the surface every few hours. At press time, the Caltech glider had just completed its 200th dive. It, along with the other two gliders, will be recovered at the end of the experiment in mid-March.

In addition to research success, the crew, which returned to land in early February, had the chance to experience some marine wildlife in their natural habitat. The boat was visited by a number of friendly humpbacks and, while taking measurements from the sea, researchers found a pod of feeding orcas.

For more pictures and details from the trip, visit Thompson's website. The "journals" section gives personal accounts and images from the voyage.

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Stolper Honored by the Geochemical Society

Edward M. Stolper, Caltech's provost and William E. Leonhard Professor of Geology, has been named the recipient of the Geochemical Society's V. M. Goldschmidt Award for 2012, the highest award of the international geochemical community. The recipient of this award is chosen annually "for achievements in geochemistry or cosmochemistry, consisting of either a single outstanding contribution or a series of publications that have has great influence on the field." Previous Caltech faculty recipients have been Sam Epstein, Clair Patterson, and G.J. Wasserburg.

Stolper's research interests center on studies of the origin and evolution of igneous rocks on the earth and other planets using experiment, theory, and field studies. Recent focuses include studies of Hawaii and other hot spot volcanoes, theory and modeling of the thermodynamics of the melting of planetary interiors, the petrology of Martian meteorites, and the role of volatiles in igneous processes.

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Allison Benter
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Heather Knutson Receives AAS Cannon Award in Astronomy

Caltech assistant professor of planetary science Heather Knutson has been named the recipient of this year's Annie J. Cannon Award in Astronomy by the American Astronomical Society (AAS). The award is given for outstanding research and promise for future research by a North American female astronomer within five years of receiving her PhD.

Knutson's research is focused on characterizing the properties of extrasolar planets, including their temperatures, compositions, and atmospheric circulation patterns using observations of eclipsing systems.

"it's been a great year for the field of exoplanets as a whole, as two of the other AAS prize winners (Caltech's John Johnson and the University of Florida's Eric Ford) also work in this area," said Knutson. "The discovery rate for new extrasolar planets has been growing exponentially in the past few years thanks to new missions such as the Kepler Telescope; with such a rich diversity of systems now available for detailed study, I'm confident that this is a field that will continue to produce exciting new results for years to come. It's my privilege to be right in the middle of it!"

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New Computer Model Explains Lakes and Storms on Titan

PASADENA, Calif.—Saturn's largest moon, Titan, is an intriguing, alien world that's covered in a thick atmosphere with abundant methane. With an average surface temperature of a brisk -300 degrees Fahrenheit (about 90 kelvins) and a diameter just less than half of Earth's, Titan boasts methane clouds and fog, as well as rainstorms and plentiful lakes of liquid methane. It's the only place in the solar system, other than Earth, that has large bodies of liquid on its surface.

The origins of many of these features, however, remain puzzling to scientists. Now, researchers at the California Institute of Technology (Caltech) have developed a computer model of Titan's atmosphere and methane cycle that, for the first time, explains many of these phenomena in a relatively simple and coherent way.

In particular, the new model explains three baffling observations of Titan. One oddity was that Titan's methane lakes tend to cluster around its poles and that there are more lakes in the northern hemisphere than in the south.

Secondly, the areas at low latitudes, near Titan's equator, are known to be dry, lacking lakes and regular precipitation. But when the Huygens probe landed on Titan in 2005, it saw channels carved out by flowing liquid-possibly runoff from rain. And in 2009, Caltech researchers discovered raging storms that may have brought rain to this supposedly dry region.

Finally, scientists uncovered a third mystery when they noticed that clouds observed over the past decade—during summer in Titan's southern hemisphere—cluster around southern middle and high latitudes.

Scientists have proposed various ideas to explain these features, but their models either can't account for all of the observations, or do so by requiring exotic processes, such as cryogenic volcanoes that spew methane vapor to form clouds. The Caltech researchers say their new computer model, on the other hand, can explain all these observations-and does so using relatively straightforward and fundamental principles of atmospheric circulation.

"We have a unified explanation for many of the observed features," says Tapio Schneider, the Frank J. Gilloon Professor of Environmental Science and Engineering. "It doesn't require cryovolcanoes or anything esoteric." Schneider, along with Caltech graduate student Sonja Graves, former Caltech graduate student Emily Schaller (PhD '08), and Mike Brown, the Richard and Barbara Rosenberg Professor and professor of planetary astronomy, have published their findings in the January 5 issue of the journal Nature.

Schneider says the team's simulations were able to reproduce the distribution of clouds that's been observed-which was not the case with previous models. The new model also produces the right distribution of lakes. Methane tends to collect in lakes around the poles because the sunlight there is weaker on average, he explains. Energy from the sun normally evaporates liquid methane on the surface, but since there's generally less sunlight at the poles, it's easier for liquid methane there to accumulate into lakes.

But then why are there more lakes in the northern hemisphere? Schneider points out that Saturn's slightly elongated orbit means that Titan is farther from the sun when it's summer in the northern hemisphere. Kepler's second law says that a planet orbits more slowly the farther it is from the sun, which means that Titan spends more time at the far end of its elliptical orbit, when it's summer in the north. As a result, the northern summer is longer than the southern summer. And since summer is the rainy season in Titan's polar regions, the rainy season is longer in the north. Even though the summer rains in the southern hemisphere are more intense—triggered by stronger sunlight, since Titan is closer to the sun during southern summer—there's more rain over the course of a year in the north, filling more lakes.

In general, however, Titan's weather is bland, and the regions near the equator are particularly dull, the researchers say. Years can go by without a drop of rain, leaving the lower latitudes of Titan parched. It was a surprise, then, when the Huygens probe saw evidence of rain runoff in the terrain. That surprise only increased in 2009 when Schaller, Brown, Schneider, and then-postdoctoral scholar Henry Roe discovered storms in this same, supposedly rainless, area.

No one really understood how those storms arose, and previous models failed to generate anything more than a drizzle. But the new model was able to produce intense downpours during Titan's vernal and autumnal equinoxes—enough liquid to carve out the type of channels that Huygens found. With the model, the researchers can now explain the storms. "It rains very rarely at low latitudes," Schneider says. "But when it rains, it pours."

The new model differs from previous ones in that it's three-dimensional and simulates Titan's atmosphere for 135 Titan years—equivalent to 3,000 years on Earth—so that it reaches a steady state. The model also couples the atmosphere to a methane reservoir on the surface, simulating how methane is transported throughout the moon. 

The model successfully reproduces what scientists have already seen on Titan, but perhaps what's most exciting, Schneider says, is that it also can predict what scientists will see in the next few years. For instance, based on the simulations, the researchers predict that the changing seasons will cause the lake levels in the north to rise over the next 15 years. They also predict that clouds will form around the north pole in the next two years. Making testable predictions is "a rare and beautiful opportunity in the planetary sciences," Schneider says. "In a few years, we'll know how right or wrong they are.

"This is just the beginning," he adds. "We now have a tool to do new science with, and there's a lot we can do and will do."

The research described in the Nature paper, "Polar methane accumulation and rainstorms on Titan from simulations of the methane cycle," was supported by a NASA Earth and Space Science Fellowship and a David and Lucile Packard Fellowship.

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Marcus Woo
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