Summer Interns Return with a World of Experiences

News Writer: 
Shayna Chabner McKinney

Credit: Lance Hayashida/Caltech

Caltech undergraduate students returned to campus this week, many after spending the summer working at companies in biotechnology, technology, and finance, among other fields. These students have had the opportunity to learn firsthand about the career opportunities and paths that may be available to them after graduation. They also had the chance to put Caltech’s rigorous academic and problem-solving training to the test.

In the summer of 2015, nearly a third of returning sophomores, juniors, and seniors were placed in an internship position through Caltech’s Summer Undergraduate Internship Program (SUIP). The program, run through the Institute’s Career Development Center (CDC), helps connect current undergraduate students with a wide range of companies and businesses that can provide practical skills and work experiences that give the students an edge in the future job market.

Many undergraduates find paid summer internships through the CDC, says Lauren Stolper, the director of fellowships, advising, study abroad, and the CDC. The center organizes fall and winter career fairs and offers workshops related to finding internships; provides individual advising on internship options and conducting a job hunt for an internship; organizes interviews for students through its on-campus recruiting program; and provides web-based internship listings and company information through Techerlink, its online job-posting system.

Through the formal establishment of SUIP two years ago—thanks, in part, to the initiative of Craig San Pietro (BS ’68, engineering; MS ’69, mechanical engineering) and with seed money provided by him and three of his alumni friends and former Dabney House roommates, Peter Cross (BS ’68, engineering), Eric Garen (BS ’68, engineering), and Charles Zeller (BS ’68, engineering)—the CDC has been able to dedicate even more time and attention to helping undergraduates secure these important positions, Stolper says.

“Through internships, students have the opportunity to learn more about the practical applications of their knowledge by contributing to ongoing projects under the guidance of professionals,” says Aneesha Akram, a career counselor for internship development/advising, who oversees SUIP.

“Completing summer internships help undergraduates become competitive candidates for full-time positions,” says Akram. “When it comes to recruiting for full-time positions, companies seek out candidates with previous internship experience. We have found that many large companies extend return offers and full-time conversions to students who previously interned with them.”

The infographic at the above right provides a snapshot of Caltech undergraduate internships over this past summer. Students seeking internships for next summer can contact Akram or look at the CDC website for more information.

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New Courses for the 2015–16 School Year

News Writer: 
Lori Dajose

A manuscript from The Old English Orosius dated between the years 892 and 925.
Credit: The British Library

The start of the 2015–2016 school year brings not only new freshmen and faculty, but also new courses.

Several new classes have been added in the Division of the Humanities and Social Sciences. These include a course on Old English Literature, in which students will study literature written in the earliest form of the English language, commonly used in England from roughly 450 to 1100 AD. The new course will be taught by the Weisman Postdoctoral Instructor in Medieval British Literature, Benjamin Saltzman.

“When we speak and write in English, we rarely think about the paths the language took to get to where it is today with all its quirks and varieties: why is it that we say ‘one mouse,’ but ‘two mice’? And if you can figure that out, then why do we say ‘two houses’?” Saltzman says. “Once we take a closer look at this early stage of the language, we gain access to some extraordinary pieces of literature—from riddles to poems about war—and in the process we’ll learn about some of the idiosyncrasies that have persisted in the modern form of the language.”

The Division of Engineering and Applied Science is also introducing three new interdisciplinary mechanical engineering courses, one of which is the Mechanics of Soils. The class will be taught by Professor of Mechanical and Civil Engineering Domniki Asimaki, and will focus on the basic principles of stiffness, deformation, stress, and strength of soils, sands, clays, and silts.

“Soils are very heterogeneous materials. Some are plastic like soft clays, others are brittle like cemented sands, and others are purely frictional like granular media. More frequently we see some mix of these,” Asimaki says. “The top few hundred meters of the earth’s crust, where most of the infrastructure of modern cities is founded on, is roughly made of ‘soils’. Thus, we want to make predictions about the deformation and failure of soils, such as consolidation from groundwater pumping, slope stability failures, foundation capacity of buildings, or liquefaction of sands—so called quick-sands.” The class, she says, aims to provide an understanding of soil behavior from laboratory experiments and field observations, and to develop idealized predictive models that capture aspects of that behavior.

A new course in the medical engineering department, New Frontiers in Medical Technologies, will examine space technologies, instruments, and engineering techniques with respect to their current and potential applications in medicine. The course will allow students to interact with both Caltech researchers in medical engineering and scientists at the Jet Propulsion Laboratory (JPL).

“The history of space exploration and its many spinoffs have taught us that many space technologies are very useful for on-earth medicine,” says Shouleh Nikzad (PhD ’90), a visiting associate in astrophysics and senior research scientist at JPL. She will teach the new course in the spring term.

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Getting the Lead Out

News Writer: 
Douglas Smith

Clair Patterson and distillation apparatus.

In his sleuthing for trace amounts of lead, Caltech geochemist Clair Patterson redistills a reagent in this 1957 photograph. He didn’t trust the purity of commercial chemicals.
Credit: Caltech E&S Magazine, Volume 60, Number 1, 1997

Caltech geochemist Clair Patterson (1922–1995) helped galvanize the environmental movement 50 years ago when he announced that highly toxic lead could be found essentially everywhere on Earth, including in our own bodies—and that very little of it was due to natural causes.

In a paper published in the September 1965 issue of Archives of Environmental Health, Patterson challenged the prevailing belief that industrial and natural sources contributed roughly equal amounts of ingestible lead, and that the aggregate level we absorbed was safe. Instead, he wrote, “A new approach to this matter suggests that the average resident of the United States is being subjected to severe chronic lead insult.” He estimated that our “lead burden” was as much as 100 times that of our preindustrial ancestors—often to just below the threshold of acute toxicity.

Lead poisoning was known to the ancients. Vitruvius, designer of aqueducts for Julius Caesar, wrote in Book VIII of De Architectura that “water is much more wholesome from earthenware pipes than from lead pipes . . . [water] seems to be made injurious by lead.” Lead accumulates in the body, where it can have profound effects on the central nervous system. Children exposed to high lead levels often acquire permanent learning disabilities and behavioral disorders.

When Patterson arrived at Caltech as a research fellow in geochemistry in 1952, he was looking not to save the world but to figure out how old it was. Doing so required him to measure the precise amounts of various isotopes of uranium and lead. (Isotopes are atoms of the same element that contain different numbers of neutrons in their nuclei.) Uranium-238 decays very, very slowly into lead-206, while uranium-235 decays less slowly into lead-207. Both rates are well known, so measuring the ratios of lead atoms to uranium ones shows how much uranium has disappeared and allows the sample’s age to be calculated.

Patterson presumed that the inner solar system’s rocky planets and meteorites had all coalesced at the same time, and that the meteorites had survived essentially unchanged ever since. Using an instrument called a mass spectrometer and working in a clean room he had designed and built himself, Patterson counted the individual lead atoms in a meteorite sample recovered from Canyon Diablo near Meteor Crater, Arizona. In a landmark paper published in 1956, he established Earth’s age as 4.55 billion years.

However, there are four common isotopes of lead, and Patterson had to take them all into account in his calculations. He had announced his findings at a conference in 1955, and he had continued to refine his results as the paper worked its way through the review process. But there he hit a snag—his analytical skills had become so finely honed that he was finding lead everywhere. He needed to know the source of this contamination in order to eliminate it, and he took it on himself to find out.

Patterson’s 1965 Environmental Health paper summarized that work. With M. Tatsumoto of the U.S. Geological Survey, he found that the ocean off of southern California was lead-laden at the surface but that the contamination disappeared rapidly with depth. They concluded that the likely culprit was tetraethyl lead, a widespread gasoline additive that emerged from the tailpipe of automobiles as very fine lead particles. Patterson and research fellow T. J. Chow crisscrossed the Pacific aboard research vessels run by the Scripps Institution of Oceanography at UC San Diego and found the same profile of lead levels versus depth. Then, in the winter of 1962–63, Patterson and Tatsumoto collected snow at an altitude of 7,000 feet on Mount Lassen in northern California. The lead contamination there was 10 to 100 times worse than at sea. Patterson concluded that it had fallen from the skies. Its isotopic fingerprint was a perfect match for air samples from Los Angeles—located 500 miles to the south. It also matched gasoline samples obtained by Chow in San Diego. Furthermore, the isotope fingerprint was different from that of lead found in prehistoric sediments off the California coast.

“The atmosphere of the northern hemisphere contains about 1,000 times more than natural amounts of lead,” Patterson wrote, and he called for the “elimination of some of the most serious sources of lead pollution such as lead alkyls [i.e., tetraethyl lead], insecticides, food can solder, water service pipes, kitchenware glazes, and paints; and a reevaluation by persons in positions of responsibility in the field of public health of their role in the matter.”

Patterson’s paper was his first shot in the war against lead pollution, bureaucratic inertia, and big business that he would wage for the rest of his life. He won: the Clean Air Act of 1970 authorized the development of national air-quality standards, including emission controls on cars. In 1976, the Environmental Protection Agency reported that more than 100,000 tons of lead went into gasoline every month; by 1980 that figure would be less than 50,000 tons, and the concentration of lead in the average American’s blood would drop by nearly 50 percent as well. The Consumer Product Safety Commission would ban lead-based indoor house paints in 1977 (flakes containing brightly colored lead pigments often found their way into children’s mouths). And in 1986, the EPA prohibited tetraethyl lead in gasoline.

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Flowing Electrons Help Ocean Microbes Gulp Methane

News Writer: 
Jessica Stoller-Conrad

Electron microscopy (left), and nanoSIMS analyses (right) of slices of individual microbial consortia allowed for unambiguous identification and analysis of thousands of individual cells. nanoSIMS images such as this one give a quantitative picture of the isotopic composition of each cell, and in turn, a measure of each cell's biosynthetic activity in relationship to each cell's neighbors.
Credit: Shawn McGlynn/Caltech

Good communication is crucial to any relationship, especially when partners are separated by distance. This also holds true for microbes in the deep sea that need to work together to consume large amounts of methane released from vents on the ocean floor. Recent work at Caltech has shown that these microbial partners can still accomplish this task, even when not in direct contact with one another, by using electrons to share energy over long distances.

This is the first time that direct interspecies electron transport—the movement of electrons from a cell, through the external environment, to another cell type—has been documented in microorganisms in nature.

The results were published in the September 16 issue of the journal Nature.

“Our lab is interested in microbial communities in the environment and, specifically, the symbiosis—or mutually beneficial relationship—between microorganisms that allows them to catalyze reactions they wouldn’t be able to do on their own,” says Professor of Geobiology Victoria Orphan, who led the recent study. For the last two decades, Orphan’s lab has focused on the relationship between a species of bacteria and a species of archaea that live in symbiotic aggregates, or consortia, within deep-sea methane seeps. The organisms work together in syntrophy (which means “feeding together”) to consume up to 80 percent of methane emitted from the ocean floor—methane that might otherwise end up contributing to climate change as a greenhouse gas in our atmosphere.

Previously, Orphan and her colleagues contributed to the discovery of this microbial symbiosis, a cooperative partnership between methane-oxidizing archaea called anaerobic methanotrophs (or “methane eaters”) and a sulfate-reducing bacterium (organisms that can “breathe” sulfate instead of oxygen) that allows these organisms to consume methane using sulfate from seawater. However, it was unclear how these cells share energy and interact within the symbiosis to perform this task.

Because these microorganisms grow slowly (reproducing only four times per year) and live in close contact with each other,  it has been difficult for researchers to isolate them from the environment to grow them in the lab. So, the Caltech team used a research submersible, called Alvin, to collect samples containing the methane-oxidizing microbial consortia from deep-ocean methane seep sediments and then brought them back to the laboratory for analysis.

The researchers used different fluorescent DNA stains to mark the two types of microbes and view their spatial orientation in consortia. In some consortia, Orphan and her colleagues found the bacterial and archaeal cells were well mixed, while in other consortia, cells of the same type were clustered into separate areas.

Orphan and her team wondered if the variation in the spatial organization of the bacteria and archaea within these consortia influenced their cellular activity and their ability to cooperatively consume methane. To find out, they applied a stable isotope “tracer” to evaluate the metabolic activity. The amount of the isotope taken up by individual archaeal and bacterial cells within their microbial “neighborhoods” in each consortia was then measured with a high-resolution instrument called nanoscale secondary ion mass spectrometry (nanoSIMS) at Caltech. This allowed the researchers to determine how active the archaeal and bacterial partners were relative to their distance to one another.

To their surprise, the researchers found that the spatial arrangement of the cells in consortia had no influence on their activity. “Since this is a syntrophic relationship, we would have thought the cells at the interface—where the bacteria are directly contacting the archaea—would be more active, but we don’t really see an obvious trend. What is really notable is that there are cells that are many cell lengths away from their nearest partner that are still active,” Orphan says.

To find out how the bacteria and archaea were partnering, co-first authors Grayson Chadwick (BS ’11), a graduate student in geobiology at Caltech and a former undergraduate researcher in Orphan’s lab, and Shawn McGlynn, a former postdoctoral scholar, employed spatial statistics to look for patterns in cellular activity for multiple consortia with different cell arrangements. They found that populations of syntrophic archaea and bacteria in consortia had similar levels of metabolic activity; when one population had high activity, the associated partner microorganisms were also equally active—consistent with a beneficial symbiosis. However, a close look at the spatial organization of the cells revealed that no particular arrangement of the two types of organisms—whether evenly dispersed or in separate groups—was correlated with a cell’s activity.

To determine how these metabolic interactions were taking place even over relatively long distances, postdoctoral scholar and coauthor Chris Kempes, a visitor in computing and mathematical sciences, modeled the predicted relationship between cellular activity and distance between syntrophic partners that are dependent on the molecular diffusion of a substrate. He found that conventional metabolites—molecules previously predicted to be involved in this syntrophic consumption of methane—such as hydrogen—were inconsistent with the spatial activity patterns observed in the data. However, revised models indicated that electrons could likely make the trip from cell to cell across greater distances.

“Chris came up with a generalized model for the methane-oxidizing syntrophy based on direct electron transfer, and these model results were a better match to our empirical data,” Orphan says. “This pointed to the possibility that these archaea were directly transferring electrons derived from methane to the outside of the cell, and those electrons were being passed to the bacteria directly.”

Guided by this information, Chadwick and McGlynn looked for independent evidence to support the possibility of direct interspecies electron transfer. Cultured bacteria, such as those from the genus Geobacter, are model organisms for the direct electron transfer process. These bacteria use large proteins, called multi-heme cytochromes, on their outer surface that act as conductive “wires” for the transport of electrons.

Using genome analysis—along with transmission electron microscopy and a stain that reacts with these multi-heme cytochromes—the researchers showed that these conductive proteins were also present on the outer surface of the archaea they were studying. And that finding, Orphan says, can explain why the spatial arrangement of the syntrophic partners does not seem to affect their relationship or activity.

“It’s really one of the first examples of direct interspecies electron transfer occurring between uncultured microorganisms in the environment. Our hunch is that this is going to be more common than is currently recognized,” she says.

Orphan notes that the information they have learned about this relationship will help to expand how researchers think about interspecies microbial interactions in nature. In addition, the microscale stable isotope approach used in the current study can be used to evaluate interspecies electron transport and other forms of microbial symbiosis occurring in the environment.

These results were published in a paper titled, “Single cell activity reveals direct electron transfer in methanotrophic consortia.” The work was funded by the Department of Energy Division of Biological and Environmental Research and the Gordon and Betty Moore Foundation Marine Microbiology Initiative.

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Europe’s Refugee Crisis: Mass Migration is Biosphere Collapse

Mass migration if biosphere collapse

Mass migration is biosphere collapse

Refugees flowing into Europe and elsewhere globally are the direct result of over-population, ecosystem collapse, climate change, militarism and inequity. Mass migration has the potential to overrun entire societies and human civilization, and even threatens to collapse the biosphere. Migration must be controlled; and refugees and economic migrants assisted to return to productive, sustainable uses of land as close as possible to their place of origin.


First and foremost the mass exodus of refugees and migrants from Africa and the Middle East into Europe is an ecological disaster. Entire regions have overshot the carrying capacity of their land and water; which has been exacerbated by abrupt climate change, and rising human populations with unlimited aspirations for consumption.

An estimated 60 million refugees were forced from their homes by conflict last year. Nearly one billion people live on less than $ 1.50 a day, and many if not most would migrate in search of economic opportunity if given the chance. Today alone 12,000 migrants arrived in Munich, Germany.

It is a physical impossibility for Europe and America to house all of Africa, Middle East, and South America’s true refugees as well as hundreds of millions of poor people that want to migrate to a better life. Trying will lead to global ecological, social, and economic collapse.

For all intents and purposes Earth is fully occupied. There no longer exist large intact ecosystems for refugees to flee to, murder the locals, and cut down natural ecosystems to produce illusory economic progress for a while before moving on repeatedly. We live in a different world that is threatened with global biosphere collapse and we need to adjust our expectations on migration accordingly.

Ecological science knows we have already exceeded numerous planetary boundaries in regard to sustaining a habitable Earth, one of which – as identified by myself in recently published peer reviewed science – is the need to maintain natural and agro-ecological ecosystems across 2/3 of the land, though 1/2 has already been lost. Natural and semi-natural ecosystems that remain are crucial to sustaining local and regional environmental sustainability, as well as the overall well-being of our one living biosphere that makes all life possible.

Earth’s remaining natural capital and thus a livable Earth are profoundly threatened by mass flows of migrants in so many ways. Newly arrived migrants quickly embrace Western style over-consumption, refugee pathways are strewn with rubbish and nature trampled, and protected ecosystems are routinely violated. Ecosystem loss is thus both cause and effect of ecocidal mass migration.

In the flows of refugees to Europe we are witnessing the bioregional scale ecosystem collapse occurring in Africa and the Middle East as it expands its scope to become a global level ecological disturbance. There is no way the biosphere will be sustained with such large, poverty stricken populations on the move.

In many ecological systems it has been noted that when organisms are allowed to migrate at will across their full range, the entire system eventually collapses from overuse. Other more stable species segment their ranges so that while certain regions may see populations that surge and collapse, the population booms do not percolate throughout and destroy the entire ecosystem.

Migration and the overrunning of one culture by another is nothing new, it happened constantly in Europe historically, and the present international system is based upon Europe’s history of ecological colonialism. What are different are the scale, and our failure to correctly diagnose the ecological underpinning of the current mass migration, and that its solutions lie in going back to the land.

If massive hordes of poor people are allowed to traverse the Earth at will, overwhelming remaining natural ecosystems and societies that have shepherded their resources better, then global mass migration will tear down the biosphere.

This is merely stating the obvious, and does not mean we should not help those in need. But haphazard flows of refugees must not be tolerated, as the human family seeks to avert social, economic, and environmental collapse.

There is so much that can be done for those in need. Clearly Syrian refugees can’t be aided in place, but they and all would be refugees and migrants need to be assisted to achieve decent livelihoods from the land in their own bioregion. At some point they can be assisted to return to their homes.

At one time Europe, America, and the West were strong proponents of international law and cooperation. Murderous regimes waging genocide such as Assad in Syria were to be confronted by United Nations forces and eliminated, not allowed to fester and spread destabilizing chaos. Advances in international law were abandoned after 911 and must be rehabilitated and enlarged.

Much of the Middle East is arid, marginal land for agricultural production (in ancient times it was more luxurious, though it has been impacted upon by millennium of poor management). It is virtually certain that climate change has made productive use of this land more difficult, as has soaring population rates. Population growth in the Middle East is unprecedented, growing 44% from 1990-2008. This addition of over 100,000,000 people is more than the land and water resources can support as climate chaos grows.

What we are witnessing with recent mass migration is ecological collapse resulting from over-population, abrupt climate change, and ecosystem loss. And the lure of an unsustainable lifestyle enjoyed by the few. It is well past time it is recognized as such.

The west must do more to bring equity and justice to displaced peoples, particularly as many of the societies and landscapes of developing countries have been ravaged by our insatiable appetite for resources. Simply, if affluent societies won’t share, they will be overrun. At its root, the current refugee crisis is yet more blowback for centuries of military adventurism to prop up our own over-consumption.

More must be done to extend the benefits of an economically secure and free existence to all of Earth’s inhabitants. Massive foreign aid to keep would be refugees as close to their places of origin as possible are necessary, and would cost a fraction of our current expenditures for waging permawar upon the Middle East. Systems of legal migration are essential to minimize disruption and ecological impact, while allowing true refugees fearing imminent persecution some relief.

Entire bioregions are collapsing ecologically, and their human populations must be brought into balance once again with the land. Family planning assistance will be essential. And hundreds of billions must be invested in ecological restoration, permaculture, organic farming, and other sustainable land uses. Sadly, if you destroy your land base, there no longer exists the ability to flee to another.

The focus long-term for the European refugee crisis must be upon international law and foreign aid to solve the refugee and mass migration crises at their source. In the short term, military and policing will be required to stop the flows as close as possible to their origin, and refugee camps setup as efforts commence to help migrants return to their homes as soon as possible.

If huge populations from Africa and South America continue to flee from collapsing bioregions, the small elitist bastions of Europe and United States cannot long stand (much less Australia, Japan and other overdeveloped nations). Some would argue this would be a good thing ecologically and socially. I disagree that society must descend into barbarity to achieve ecological sustainability and a just equitable world, there are other ways.

The land bases of the over-developed nations cannot hold the entire world and the last vestiges of civilization which may kindle a new sustainability paradigm must not be overrun. From the coming anarchy nothing will stand and human existence will plunge into a brutal competition just to survive, as seven billion super predators quite possibly clear every bit of nature, collapsing the biosphere, and ushering in the end of being.

It is vital that global policies for ecological sustainability are put into effect. This includes putting in place controls to ensure orderly migration while helping migrants return to and restore the land in their own place of origins. Where this is not immediately possible, the rich must provide aid to shelter refugees as close as possible to their homes.

Crucially, small families, sustainable lifestyles, peace-making, and greater equity must be stressed globally.

We are well past the point where human populations can ravage local ecosystems and simply migrate to new virgin ecosystems to do the same. Allowing tens or even hundreds of millions of refugees and migrants to march across continents will take down the entire social and environmental system. Some would argue this is the path to rebalancing Earth ecologically. But there are other more humane pathways available to us based upon international cooperation, sharing, equity, and peace making.

The human family had best come together to meet all needs, protect ecosystems and end fossil fuels or we face biosphere collapse and the end of being. This means understanding and responding to the sheer terror and desperation felt by those that are suffering. But for the grace of Gaia, anyone of us could become a migrant at any time.Yet their needs are best met in place as large scale migrations will finish off the natural world. This will require forcibly blocking mass migrations and providing massive aid locally.

Things could be so much better for all on a green, fair Earth. Basic human needs could be met for all while those that are smart and work hard still have more. But we have to change and embrace peace, justice, equity, and ecological sustainability as the meaning of life. Or the biosphere collapses and it is the end.

Internet mediated global self-awareness offers the human family its last best chance to redirect military and corporate welfare expenditures to ecological and social restoration necessary to achieving just and equitable global ecological sustainability. To start, we must recognize current mass migration for what it is, both a cause and symptom of biosphere collapse.


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Where to Land Mars 2020: A Conversation with Ken Farley

News Writer: 
Kimm Fesenmaier

Ken Farley in his laboratory inspecting vacuum lines used to extract and purify noble gases for measurement of rock ages.
Credit: Lance Hayashida/Caltech

In August 2015, more than 150 scientists interested in the exploration of Mars attended a conference at a hotel in Arcadia, California, to evaluate 21 potential landing sites for NASA’s next Mars rover, a mission called Mars 2020. The design of that mission will be based on that of the Mars Science Laboratory (MSL), including the sky-crane landing system that helped put the rover, Curiosity, safely on martian soil.

Over the course of three days, the scientists heard presentations about the proposed sites and voted on the scientific merit of the locations. In the end, they arrived at a prioritized list of sites that offer the best opportunity for the mission to meet its objectives—including the search for signs of ancient life on the Red Planet and collecting and storing (or “caching”) scientifically interesting samples for possible return to Earth.

We recently spoke with Ken Farley, the mission’s project scientist and the W.M. Keck Foundation Professor of Geochemistry at Caltech, to talk about the workshop and how the Mars 2020 landing site selection process is shaping up.


Can you tell us a little bit about how these workshops help the project select a landing site?

We are using the same basic site selection process that has been used for previous Mars rovers. It involves heavy engagement from the scientific community because there are individual experts on specific sites who are not necessarily on the mission’s science team. 

We put out a call for proposals to suggest specific sites, and respondents presented at the workshop. We provided presenters with a one-page template on which to indicate the characteristics of their landing site—basic facts, like what minerals are present. This became a way to distill a presentation into something that you could evaluate objectively and relatively quickly. When people flashed these rubrics up at the end of their presentations, there was some interesting peer review going on in real time.

We went through all 21 sites, talking about what was at each location. In the end, we needed to boil down the input and get a sense of which sites the community was most interested in. So we used a scorecard that tied directly to the mission objectives; there were five criteria, and attendees were able indicate how well they felt each site met each requirement by voting either “low, ” “medium, ” or “high.” Then we tallied up the votes.


You mentioned that the criteria on the scorecard were related to the objectives of the mission. What are those objectives?

We have four mission objectives. One is to prepare the way for human exploration of Mars. The rover will have a weather station and an instrument that converts atmospheric carbon dioxide into oxygen—it’s called the in situ resource utilization (ISRU) payload. This is a way to make oxygen for both human consumption and, even more importantly, for propellant. In terms of the landing site process, this objective was not a driving factor because the ISRU and the weather station don’t really care where they go.


And the other three objectives?

We call the three remaining objectives the “ABC” goals. A is to explore the landing site. That’s a basic part of a geologic study—you look around and see what’s there and try to understand the geologic processes that made it.

The B goal is to explore an “astrobiologically relevant environment,” to look for rocks in habitable environments that have the ability to preserve biosignatures— evidence of past or present life—and then to look for biosignatures in those rocks. The phrase that NASA attaches to our mission is “Seeking the Signs of Life.” We have a bunch of science instruments on the rover that will help us meet those objectives.

Then the C goal is to prepare a returnable cache of samples. The word “returnable” has a technical definition—the cache has to meet a bunch of criteria, and one is that it has to have enough scientific merit to return. Previous studies of what constitutes returnability have suggested we need a number of samples in the mid 30s—we use the number 37.


Why 37?

It may seem strange, but there is a reason for this strange number. Thirty-seven is the maximum number of samples that can be packed into a circular honeycomb inside one possible design of the sample return assembly.

The huge task for us is to be able to drill that many samples. We’ve learned from MSL that everything takes a long time. Driving takes a long time, drilling takes a long time. We have a very specific mandate that we have to be capable of collecting 20 samples in the prime mission. Collecting at least 20 samples will motivate what we do in designing the rover.

It also has motivated a lot of the discussion of landing sites. You’ve got to have targets you wish to drill that are close together, and they can’t be a long drive from where you land. There also has to be diversity because you don’t want 15 copies of the same sample.


After all of those factors were considered, what was the outcome of the voting?

What came out of it was an ordered list of eight sites. One interesting thing about that list was that the sites were divided roughly equally into two kinds—those that were crater lakes with deltas and those that we would broadly call hydrothermal sites. These are locations that the community believes are most likely to have ancient life in them and preserve the evidence of it.

It’s easy to understand the deltas because if you look in the terrestrial environment, a delta is an excellent place to look for organic matter. The things that are living in the water above the delta and upstream are washed into the delta when they die. Then mud packs in on top and preserves that material.


What is interesting about hydrothermal systems?

A hydrothermal system is in some ways very appealing but in some ways risky. These are places where rocks are hot enough to heat water to extremely high temperatures. At hydrothermal vents on Earth’s sea floor, you have these strange creatures that are essentially living off chemical energy from inside the planet. And, in fact, the oldest evidence for life on Earth may have been found in hydrothermal settings. The problem is these settings are precarious; when the water gets a little too hot, everything dies.


What is the heat source for the hydrothermal sites on Mars?

There are two important heat sources—one is impact and the other is volcanic. A whole collection of our top sites are in a region next to a giant impact crater, and when you look at those rocks, they have chemical and mineralogical characteristics that look like hydrothermal alteration.

A leading candidate of the volcanic type is a site in Gusev Crater called the Columbia Hills site, which the Spirit rover studied. The rover came across a silica deposit. At the time, scientists didn’t really know what it was, but it is now thought that the silica is actually a product of volcanic activity called sinter. The presenter for the site showed pictures from Spirit of these little bits of sinter and then showed pictures of something that looks almost exactly the same from a geothermal field in Chile. It was a pretty compelling comparison. Then he went on to show that these environments on Earth are very conducive to life and that the little silica blobs preserve biosignatures well.

So although it would be an interesting decision to invest another mission in the same location, that site was favored because it’s the only place where a mineral that might contain signs of ancient life is known to exist with certainty.


Do these two types of sites differ just in terms of their ancient environments?

No. It turns out that you can see most of the deltas from Mars’s orbit because they are pretty much the last gasp of processing of the martian surface. They date to a period about 3.6 billion years ago when the planet transitioned from a warm, wet period to basically being desiccated. Some of the hydrothermal sites may have rocks that are in the 4-billion-year-old range. That age difference may not sound like much, but in terms of an evolving planet that is dying, it raises interesting questions. If you want to allow the maximum amount of time for life to have evolved, maybe you choose a delta site. On the other hand, you might say, “Mars is dying at that point,” and you want to try to get samples that include a record from an earlier, more equable period.

Since the community is divided roughly evenly between these two types of sites, one of the important questions we will have to wrestle with until the next workshop (in early 2017) is, “Which of those kinds of sites is more promising?” We need to engage a bigger community to address this question.


What happened to the list generated from this workshop?

This workshop was almost exclusively about science. The mission’s leadership and members of the Mars 2020 Landing Site Steering Committee, appointed by NASA, then took the information from the workshop, rolled it up with information that the project had generated on things like whether the sites could be landed on, and came up with a list of eight sites in alphabetic order:

  • Columbia Hills/Gusev
  • Eberswalde
  • Holden
  • Jezero
  • Mawrth Vallis
  • NE Syrtis Major
  • Nili Fossae
  • SW Melas Chasma

What comes next?

Over the course of the coming year, the Mars 2020 engineering team will continue its study of the feasibility of the highly ranked landing sites. At the same time, the science team will dig deeply into what is known about each site, seeking to identify the sites that are best suited to meet the mission’s science goals. I expect that advocates for specific sites will also continue doing their homework to make the strongest possible case for their preferred site. And in 2017, we’ll do the workshop all over again!

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Yung Receives Prize for Planetary Science Research

News Writer: 
Lori Dajose

Yuk Yung, the Smits Family Professor of Planetary Science, has received the 2015 Gerard P. Kuiper Prize from the American Astronomical Society’s Division for Planetary Sciences. The prize, given for outstanding contributions to the field of planetary science, recognizes Yung’s work on atmospheric photochemistry, global climate change, radiative transfer, atmospheric evolution, and planetary habitability.

“His unique integration of observations, laboratory data, and quantitative modeling has yielded pioneering insights into the characterization, origin, and evolution of atmospheres in the solar system,” the award citation notes.

Yung joined the Caltech faculty in 1977. He is a fellow of the American Academy of Arts and Sciences and of the American Association for the Advancement of Science. A longtime collaborator with scientists at the Jet Propulsion Laboratory (JPL), Yung is a coinvestigator on the Ultraviolet Imaging Spectrometer Experiment on the Cassini mission to Saturn and on the Orbital Carbon Observatory-2, a project to map CO2 concentrations on Earth.

Previous recipients of the Kuiper Prize include Professor of Planetary Science Andrew Ingersoll; Peter Goldreich, the Lee A. DuBridge Professor of Astrophysics and Planetary Physics, Emeritus; and Eugene M. Shoemaker, Caltech alumnus (BS’47, MS ’48) and former chair of the Division of Geological and Planetary Sciences.

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