Hear from scientists, engineers and other experts as they offer a fascinating look at JPL missions, science and history.
Riley Duren, chief systems engineer for the Earth Science and Technology Directorate at NASA's Jet Propulsion Laboratory, is reporting from the 2014 United Nations Climate Conference in Lima, Peru.
I mentioned previously that Peru is home to some of the most important forests in the world in terms of their vulnerability to future impacts from climate change and development pressure as well as their potential to mitigate climate change. This underscores the importance of certain elements of the UN Framework Convention on Climate Change. In particular, the Reduction of Emissions from Deforestation and forest Degradation (REDD+) program seeks to address the second-largest human contribution to climate change after fossil fuel use (see Friday's post).
Detailed definitions vary, but deforestation generally refers to conversion of forested lands to some other use -- particularly large-scale agriculture but also mining and expansion of infrastructure and cities. Degradation is distinct and refers to a diminished capacity of forests to store carbon, support ecosystems and other services. Forest degradation is caused by human activity such as commercial logging, fuel wood collection, charcoal production, and livestock grazing as well as natural forces like storms, insect damage and wildfires.
Forests play a critical role in Earth's carbon budget because healthy, growing trees and other forest elements remove and store carbon from the atmosphere -- converting it to "biomass" in trees, shrubs and soil. This makes forests one of the most effective countermeasures for fossil fuel CO2 emissions (see graph, below).
The Earth's evolving carbon budget from the start of the Industrial Revolution through present day. Carbon dioxide (CO2) flux is shown in units of Giga (billion) tons of carbon per year (GtC/year). Fluxes of carbon emitted to the atmosphere are indicated by "+". Fluxes of carbon removed from the atmosphere are indicated by "-". The plot shows the dramatic growth in fossil fuel CO2 emissions since the mid-20th century and slight decline in emissions from deforestation and other land use change. The graph also shows the corresponding growth in the three major carbon sinks: the atmosphere, land (forests) and oceans. The variability or "jumpiness" in the land sink from year to year is likely due to changes in precipitation associated with climate variability like El Nino. The future ability of the land and oceans to remove CO2 from the atmosphere remains an area of great uncertainty. Image source: Global Carbon Project
However, when forests are degraded or destroyed, the storage potential of the forest is reduced or eliminated. Additionally, if the downed trees are burned and/or decay and forest soils are disturbed, they release their stored carbon (sometimes centuries worth) into the atmosphere. So there's an incentive to both keep forests growing to store carbon and to avoid disturbing the carbon already stored in them.
Programs like REDD+ are intended to incentivize governments and landowners to preserve and restore their forests. For example, in carbon-trading programs, governments and business can "offset" their fossil fuel CO2 emissions by purchasing credits from forest owners who can prove they're storing an equivalent amount of emissions by implementing certain protocols, including independent measurement and verification. These efforts are particularly important in the tropics, which are home to most of the world's forest carbon, as well as the countries experiencing the most rapid growth and development pressures, very similar to the period of growth the US underwent in the 1800s.
Over the weekend, I attended the Global Landscape Forum to interact with policy makers, conservation groups and scientists on the subject of forest carbon monitoring. One of the panel sessions featured JPL's Dr. Sassan Saatchi and other experts who described the current capabilities and limitations of remote-sensing tools to assess the status and health of forests, including their carbon stocks and "fluxes" (removals from and emissions to the atmosphere).
The remote-sensing methods discussed included imaging systems like the US Landsat satellites that are being used to track forest-cover change as well as future systems that will improve understanding of forest degradation such as NASA's ICESAT-2 mission, the NASA-India Synthetic Aperture Radar (NI-SAR) and the European Space Agency's BIOMASS mission. The role of flying radar and lidar (laser radar) instruments on aircraft over high priority areas was also discussed.
Of course decisions about forest management involve dimensions other than climate change mitigation -- typically involving a balance between economic growth and the value of existing ecosystem services offered by forests. Biodiversity in particular is gaining prominence in decision-making given the societal and economic value it represents. Biodiversity, which refers to the number of species in a given area, is often highest in forest ecosystems (particularly in the tropics) given they provide a combination of food, shelter and water resources. The information required to evaluate biodiversity is related to, but distinct from, the data used to assess forest carbon. (I'll try to describe the role of remote-sensing in assessing biodiversity in a future post.)
Meanwhile, closing with some personal experience, I'm posting a couple of photos I took while working on my own forest conservation and biodiversity project in Hawaii.
A cloud forest on the flank of Hualalai volcano on the Big Island of Hawaii. The giant, ancient trees and native understory plants thrive in the high-altitude, moist environment provided by the persistent presence of clouds -- providing carbon storage as well as a habitat for threatened plant and bird species. The benefits of the unique Kona weather pattern are offset by the introduction of invasive weeds and destructive feral animals like pigs and sheep.Image credit: Riley Duren
A threatened I'iwi honeycreeper, endemic to the Hawaiian Islands, sips nectar from an Ohia tree blossom. Historically, this species ranged across the Hawaiian Islands but today only survive in a few high-elevation forests given the combined pressure of deforestation and avian malaria at lower elevations from non-native mosquitoes. The I'iwi, like many other Hawaiian bird and plant species, lacks the natural defenses to withstand the combined pressure from development and climate change. Management efforts focus on conserving, restoring and building resiliency in threatened forest habitats. Image credit: Riley Duren
Riley Duren, chief systems engineer for the Earth Science and Technology Directorate at NASA's Jet Propulsion Laboratory, is reporting from the 2014 United Nations Climate Conference in Lima, Peru.
We arrived in Lima, Peru, late last night and made our way to the United Nations climate conference venue this morning -- an impressive complex known locally as the Pentagonito or “Little Pentagon.” As host country and city, Peru and Lima are representative of several key fronts in the international effort to confront climate change. Peru is home to some of the most significant tropical forests on Earth that are the focus of programs to preserve their vital role in storing carbon and critically endangered ecosystems (more about that tomorrow). With a population approaching 10 million people, Lima itself is a rapidly growing megacity -- one of many in the developing world.
The latter topic is the focus of this post and the event I’m participating in later today at the US Center: “Understanding the Carbon Emissions of Cities.” I’ll be joining colleagues from the US National Institute of Standards and Technology, Arizona State University, Laboratoire Des Sciences du Climat et de l'Environnement (France), and Universidade de São Paulo (Brazil) in presenting the motivation for and recent scientific advances in monitoring urban carbon pollution. There won’t be a live stream but the event will be recorded - keep an eye on the US State Department’s YouTube page where it should be posted this weekend.
So what is “carbon pollution” and why should we care about it? Most of us are familiar with the general topic of air pollution; just ask anybody who has asthma or knows a friend or family member with respiratory problems. Cities are notorious sources of air pollutants or smog -- including visible particles (aerosols) and invisible but caustic ozone. One can find many examples of success stories where air quality has improved in response to clean-air standards as well as horror stories in cities lacking such standards. However, this familiar topic of air quality is mostly limited to short-lived pollutants -- compounds that only persist in the atmosphere for hours or days. Those pollutants are important because of human health impacts but they’re not primary drivers of climate change. Carbon dioxide (CO2) and methane (another carbon-based molecule) on the other hand, are long-lived gases that trap heat in the atmosphere for many years. Once CO2 and methane are in the atmosphere, they remain there for a long time -- centuries, in the case of CO2. Most people are unaware of the presence of CO2 and methane because they’re invisible and odorless and don’t have an immediate impact on health, but those gases are THE big drivers of climate change.
There are many sources of CO2 on Earth, including natural emissions that, prior to the industrial revolution, were balanced by removals from natural carbon scrubbers like forests and oceans. However human activity is rapidly changing the balance of CO2 in the atmosphere, leading to an unprecedented growth rate. Most of these human CO2 emissions come from burning fossil fuels like coal and oil. These fossil emissions are responsible for about 85 percent of humanity’s CO2 footprint today and, globally, they’re continuing to accelerate. So any successful effort to avoid dangerous climate change must have fossil CO2 mitigation at its core. Managing methane is also important given its greater heat trapping potential than CO2.
Why focus on carbon from cities? It turns out that urbanization – the increasing migration of people from rural areas to urban centers – has concentrated over half the world’s population, over 70 percent of fossil CO2 emissions and a significant amount of methane emissions into less than 3 percent of the Earth’s land area! So cities and their power plants represent the largest cause of human carbon emissions. In 2010, the 50 largest cities alone were collectively the third largest fossil CO2 emitter after China and the US – and there are thousands of cities. At the same time, in many cases, emissions from cities are undergoing rapid growth because of urbanization.
But there’s also a silver lining here.
Many cities are beginning to serve as “first responders” to climate change. While national governments continue to negotiate over country-level commitments, mayors of some of the largest cities are already taking action to reduce their cities’ carbon footprints, and they’re working together through voluntary agreements. Additionally, the concentrated nature of urban carbon emissions makes measuring those emissions easier than measuring entire countries.
Measuring the carbon emissions of cities is important (you can’t manage what you can’t measure) and challenging given the number of sources and key sectors and uncertainty about how much each contributes to the total carbon footprint. For example, in a typical city, CO2 is emitted from the transportation sector (cars, trucks, airports, seaports), energy sector (power plants), commercial and industrial sectors (businesses, factories) and residential sector (heating and cooking in homes). Likewise, urban methane sources include landfills, wastewater treatment plants, and leaks in natural gas pipelines. Mayors, regional councils, businesses and citizens have a number of options to reduce their carbon emissions. Measuring the effect of those efforts and understanding where and why they’re not having the intended impact can prove critical to successful mitigation. It also has economic implications -- toward identifying the most cost-effective actions and supporting emissions trading (carbon markets) between cities and other sub-national entities.
How can we measure the carbon emissions of cities? That’s the focus of the Megacities Carbon Project and the topic of our event in Lima today. Briefly, this involves combining data from satellites and surface-monitoring stations that track concentrations of CO2, methane and other gases in the atmosphere over and around cities with other, local data sets that contain information about key sectors. Pilot efforts in Los Angeles, Paris, Sao Paulo and other cities are beginning to demonstrate the utility of these methodologies. Satellites like NASA’s Orbiting Carbon Observatory-2 and other future missions, when combined with a global network of urban carbon monitoring stations, could ultimately play an important role in enabling more effective mitigation action by the world’s largest carbon emitters: cities.
Riley Duren, chief systems engineer for the Earth Science and Technology Directorate at NASA's Jet Propulsion Laboratory, is reporting from the 2014 United Nations Climate Conference in Lima, Peru.
Today I'm en route to Lima, Peru, to join the United Nations climate conference. This is the 20th Conference of Parties (COP-20) of the UN Framework Convention on Climate Change (UNFCCC). The meeting is intended to set the stage for an international agreement next year between 195 countries on actions to address climate change. For the next two weeks, diplomats, policy makers, scientists, engineers, economists, and representatives of business and non-profit organizations are convening in Lima to discuss a wide range of options to avoid dangerous climate change and/or attempt to manage the impacts to humanity and the other species that share planet Earth. (More background, here)
As it turned out, I managed to miss my flight yesterday as result of the heavy rains and jammed freeways that ensued from the latest "atmospheric river" event in Los Angeles. But I have to admit, I was far more relieved than annoyed by this break (albeit brief) in California's persistent drought - a sentiment shared by all my neighbors and fellow travelers. Yet another reminder of the critical connections between weather, climate, and society, and what's at stake in efforts aimed at planetary stewardship.
Several JPLers are participating in the meeting given the lab's contribution of applying satellite observations to improve scientific understanding of the Earth and support societal decision-making. Collectively, the efforts of us traveling this week span sea, land and air - each reflecting part of NASA's broader mission to study the Earth as an integrated system.
My colleague Dr. Michelle Gierach is part of the NASA delegation at the US Center and will be talking about the ocean and impacts of climate change on key features like the El Nino Southern Oscillation (ENSO). Dr. Sassan Saatchi, who studies forest carbon, will be a panelist at this weekend's Global Landscapes Forum.
My own work these days is mostly focused on heat trapping or "greenhouse" gases in the atmosphere, like carbon dioxide and methane, and understanding the connections with human activity at the scale of countries, states, cities and individual pollution sources. I spend much of my time working with policy makers and scientists to understand stakeholder needs and design monitoring systems that can support practical decision making. It's a big challenge: These monitoring "system of systems" typically require a suite of Earth observing instruments from the ground, air and space - often fused with data from many other information sources. In addition to the technical challenges, after several years in this field, I continue to marvel at the diversity of perspectives, priorities, institutional cultures and ways of thinking, with implications on what data is required. The social dimensions are every bit as important as the bio-geophysical.
I'll say more in subsequent posts about some specific efforts that are underway and how they connect with events at the Lima conference.
This blog entry from John Grotzinger, the project scientist for NASA's Curiosity Mars rover, was originally prepared for use by the Planetary Society and explains the importance of some of the rover's findings.
It was fun for me to catch up with Emily Lakdawalla of the Planetary Society at the American Geophysical Union meeting, and to discuss our new Curiosity mission results. They focus on the discovery of an ancient habitable environment; we are now transitioning to the focused search for organic carbon. What's great about Emily's blog is that with her strong science background she is able to take complex mission results and translate these into something that can reach a broader and more diverse audience. I'll try to do the same here.
Since we first reported our results on March 12, 2013, from drilling in Yellowknife Bay it has been my experience that lots of people ask questions about how the Curiosity mission, and future missions, will forge ahead to begin with looking for evidence of past life on Mars. There is nothing simple or straightforward about looking for life, so I was pleased to have the chance to address some of the questions and challenges that we find ourselves most frequently discussing with friends and colleagues. The Planetary Society's blog is an ideal place to take the time to delve into this.
I also need to state at the outset that what you'll read below is my opinion, as Curiosity science team member and Earth geobiologist, and not necessarily as its Project Scientist. And I have only worked on Mars science for a decade. However, I can say that many other members of the Curiosity team share this opinion, generated from their own experiences similar to mine, and it was easy for us to adopt these ideas to apply to our future mission. To a large extent, this opinion is shaped by our experience of having spent decades trying to explore the early record of life on Earth. As veterans of the Mars Exploration Rover and Curiosity missions, we have learned that while Mars has significant differences from Earth, it also has some surprising similarities that could be important in the search for evidence of ancient Martian life - a "paleobiosphere," if you will. The bottom line is that even for Earth, a planet that teems with life, the search for ancient life is always difficult and often frustrating. It takes a while to succeed. I'll try to explain why later on.
So here goes....
The Dec. 9, 2013, publication of the Curiosity team's six papers in Science provides the basis for understanding a potentially habitable environment on ancient Mars. The search for habitable environments motivated building the rover, and to that end the Curiosity mission has accomplished its principal objective. This naturally leads to the questions of what's next, and how we go about exploring for organic carbon?
To better understand where we're coming from, it helps to break down these questions and analyze them separately. With future advocacy of missions to Mars so uncertain, and with difficult-to-grasp mission objectives located between "the search for water" (everyone got that) and "the search for life" (everyone wants NASA to get on with it), the "search for habitability" and the "search for carbon" are important intermediate steps. By focusing on them scientists can identify specific materials to study with more sophisticated future missions and instruments, or to select for sample return, or to be the target of life detection experiments.
Note: You can get access to all six of these Science papers here or here. The latter site also has the papers we published back in September. Science has a policy that allows us to post a "referrer link" to our home websites. This redirects the query to AAAS, where the paper can be downloaded without cost.
Let's start with "habitability." We reported the discovery of an ancient lake, and one that formed clay minerals. The presence of clays represents more benign environmental conditions than the acid sulfates found by Spirit and Opportunity. However, clays are not the only thing needed to demonstrate habitability. The bar is high: In brief, a mission needs to demonstrate the presence of water, key elements regarded as the building blocks of life (including carbon), and a source of energy. And you need to find them all together, and at the same instant in geologic time. In turn, each one of these must be characterized further to qualify an environment as having been habitable. Finally, it's never black and white; understanding habitability is part of a broad continuum of environmental assessment, which is why orbiters and earlier rovers and landers are important assets in this process as well.
It is also important to define what group of organisms is being imagined to have inhabited the environments - their requirements will vary. Single-celled microorganisms are a great place to start based on our understanding of the early evolution of life on Earth, which was dominated by microbes for at least the first two billion years of the planet's history. More specifically, the Curiosity team has been focusing on the conditions of habitability relevant to "chemolithotrophs," a group of microbes that feeds on chemical energy available in rocks.
The water of a habitable environment should be relatively fresh, or at least not contain so much salt that the relative abundance of water is so low (what chemists call "water activity") that the osmotic pressure on cells would cause them to collapse. My favorite analog here is honey. Yes, it's an aqueous environment but no, it's not habitable: The sugar content is so high that microbes can't live in it. This is why honey doesn't spoil when not refrigerated. Salt serves the same role as sugar; too much salt inhibits life. Acidity is also important, although microbes have been shown to tolerate an extraordinary range of pH, including the very lowest values encountered in natural environments on Earth. However, more moderate pH favors a greater diversity of microorganisms, and thus more options to explore for emerging life forms. Finally, the water needs to last a long time on the surface; the longer, the better. A flow of water emerging on the surface of Mars from an underground source and boiling off in the presence of Mars' modern low atmospheric pressure is not a good scenario for life. A stable source, such as a very ancient lake, with associated streams, and water flowing through the ground beneath it, is much better. We envision for the lake/stream/groundwater system that Curiosity discovered at Yellowknife Bay that the water could have existed for millions of years potentially. But even shorter periods are viable - the qualitative point here is that the rocks at Yellowknife Bay record more than a one-time event.
Key building blocks of life.
A conventional list of key elements for life will include "CHNOPS" - carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. Previous orbiter and landed missions have provided ample evidence for H, O, and S via observations of sulfate and clay minerals, and P was measured by earlier rovers and landers. Curiosity has done the same. The tricky stuff is N and C and, along with P, they must all be "bioavailable," which means to say they cannot be bound tightly within mineral structures that water and microbial chemical processes could not unlock. Ideally, we are looking for concentrated nitrogen- and phosphorous-bearing sedimentary rocks that would prove these elements were actually dissolved in the past water at some point, and therefore could have been available to enable microorganism metabolism. But in the interim Curiosity has been able to measure N as a volatile compound via pyrolysis (heating up rock powder in the SAM instrument), and P is observed in APXS data. We feel confident that N was available in the ancient environment, however we must infer that P was as well. Two of the Science papers, Grotzinger et al. and Ming et al., discuss this further.
Carbon is the elephant in the room. We'll discuss organic carbon further below, but here it's important to make one very important point: Organic carbon in rocks is not a hard-line requirement for habitability, since chemoautotrophs can make the organics they need to build cellular structures from metabolizing carbon dioxide (CO2). These organisms take up inorganic carbon as CO2 dissolved in water to build cellular structures. Organic carbon could serve as fuel if it was first oxidized to CO2, or could be used directly for biomass, or could be part of waste products. As applied to Mars it is therefore attractive to appeal directly to CO2, presumed to have been abundant in its early atmosphere. Curiosity does indeed see substantial carbon generated from the ancient lake deposits we drilled. The CO2 that was measured is consistent with some small amount of mineral carbon present in those lake mudstones. These minerals would represent CO2 in the ancient aqueous environment. Furthermore, it is possible that Martian organic sources have been mixed with inorganic sources of carbon in the mudstone; however, any organic contributions from the mudstone would be mixed with Earth-derived sources during analysis (see Ming et al. paper).
All organisms also require fuel to live and reproduce. Here it is essential to know which kind of microorganism we're talking about, since there are myriad ways for them to harvest energy from the environment. Chemolithotrophs derive energy from chemical reactions, for example by oxidizing reduced chemical species like hydrogen sulfide or ferrous iron. That's why Curiosity's discovery of pyrite, pyrrhotite, and magnetite are so important (see Vaniman et al. and Ming et al. papers). They are all more chemically reduced than their counterparts discovered during earlier missions to Mars (for example, sulfate and hematite). Chemolithotrophic microbes, if they had been present on Mars at the time of this ancient environment, would have been able to tap the energy in these reduced chemicals (such as hydrogen sulfide, or reduced iron) to fuel their metabolism. If you are interested in more detail regarding these kinds of microbial processes I can strongly recommend Nealson and Conrad (2000) for a very readable summary of the subject.
The next section describes where I think we're headed in the future. We'll continue to explore for aqueous, habitable environments at Mt. Sharp, and along the way to Mt. Sharp. And if we discover any, they will serve as the starting point for seeing if any organic carbon is preserved and, if so, how it became preserved.
Now there's a ten-dollar word. Taphonomy is the term paleontologists use to describe how organisms become fossilized. It deals with the processes of preservation. Investigations of organic compounds fit neatly in that category. We do not have to presume that organic compounds are of biologic origin. In fact, in studies of the Earth's early record of life, we must also presume that any organic materials we find may be of inorganic origin - they may have nothing to do with biology. Scientific research will aim to demonstrate as conclusively as possible that the materials of interest were biogenic in origin. For Earth rocks that are billions of years old, it's rare to find a truly compelling claim of ancient biogenic carbon. Here's why.
On a planet that teems with life, one would presume these discoveries would be ordinary. But they aren't, and that's why fossils of almost any type, including organic compounds (so-called "chemofossils"), are so cool - it's because they are rare. That's also why taphonomy emerged as an important field of study. We need to understand how biologic materials become recorded in Earth's rock record. It's important in understanding modes of organism decomposition, to interpret ancient environmental conditions, and in reconstructing ancient ecosystems. But there also is one other reason that is particularly relevant for early Earth, and even more so for Mars: If you want to find something significant, you have to know where to look.
To explore for organics on Mars, three things have to go right. First, you need to have an enrichment of organics in the primary environment where organic molecules accumulate, which is large enough so that your instrument could detect them. Second, the organics have to survive the degrading effects associated with the conversion of sediment to rock. Third, they must survive further degradation caused by exposure of rock to cosmic radiation at Mars' surface. Even if organics were once present in Martian sediment, conversion to rock and exposure to cosmic radiation may degrade the organics to the point where they can't be detected.
Organics degrade in two main ways. The first is that during the conversion of sediment to rock, organics may be chemically altered. This generally happens when layers of sediment are deposited one on top of the other, burying earlier-deposited layers. As this happens, the buried sediment is exposed to fluids that drive lithification - the process that converts sediment to rock. Sediments get turned into rocks when water circulates through their pores, precipitating minerals along the linings of the pores. After a while the sediment will no longer feel squishy and it becomes rigid - lithified.
During the process of lithification, a large amount of water may circulate through the rock. It can amount to hundreds, if not thousands, of times the volume of the pore space within the rock. With so much water passing through, often carrying other chemicals with it, any organics that come into contact with the water may be broken down. Chemically, this occurs because organics are reduced substances and many chemicals dissolved in water are oxidizing. Those two chemical states don't sit well together, and this tends to drive chemical reactions. Simply put, organics could be broken down to the point where the originally organic carbon is converted into inorganic carbon dioxide, a gas that can easily escape the lithifying sediment. Water on Mars may be a good thing for habitability but it can, paradoxically, negatively affect the preservation of organics.
Now, if any organics manage to escape this first step in degradation, then they are still subject to further degradation when the rock is exhumed and exposed to the surface of Mars. There it will be bombarded by cosmic radiation. I won't go into the details here, but that is also bad news for organics because the radiation tends to break apart organic molecules through a process called ionization. The upper few meters of a rock unit is the most susceptible; below that the radiation effect rapidly dies away. Given enough time the organics could be significantly degraded.
The Hassler et al. paper just published in Science reports that the surface radiation dose measured by Curiosity could, in 650 million years, reduce the concentration of small organic molecules, such as amino acids, by a factor of 1000, all other factors being equal. That's a big effect - and that's why we were so excited as a team when we figured out how to measure the cosmogenic exposure age of rocks we drilled (see Emily's blog and the Farley et al. paper). This gives us a dependable way to preferentially explore for those rocks that have been exposed for the shortest period of time. Furthermore, it is unlikely that organics would be completely eliminated due to radiation effects and the proof of this is that a certain class of meteorites - the carbonaceous chondrites - have been exposed to radiation in space for billions of years and yet still retain complex organics. This provides hope that at least some types of organics should be preserved on Mars.
Being able to account for the radiation history of rocks that Curiosity might drill is a very big step forward for us in the search for organic molecules. It is a big step forward in learning how to explore for past life on Mars (if it ever existed there). Now we have the right tools to guide the search for rocks that might make the best targets for drilling. Coupled with our other instruments that measure the chemistry and mineralogy of the rocks, to help select those that might have seen the least alteration of organics during burial, we have a pretty good sense of what we need to do next. That's because we have been through this before on Earth.
Over the years Emily has written many blogs dedicated to the discovery of interesting minerals on Mars. There are many reasons for this, but I'll suggest one more that may grow in importance in years to come.
Believe it or not, the story starts with none other than Charles Darwin. In pondering the seemingly instantaneous appearance of fossils representing complex and highly differentiated organisms in Cambrian-age rocks (about 500 million years ago), Darwin recognized this as a major challenge to his view of evolution. He explained the sudden appearance of fossils in the record by postulating that Cambrian organisms with no known antecedents could be explained by "record failure" - for some unknown reason, older rocks simply didn't record the emergence and evolution of life's beginning. Conditions weren't suitable to preserve organisms as fossils.
Most of that story goes on in the direction of evolutionary biology, and we'll skip that, rather focusing instead on learning more about taphonomy. What is important for Mars was the discovery of minerals that could preserve evidence of early microorganisms on Earth. (For a good read on Precambrian paleobiology, try Andy Knoll's "Life on a Young Planet: The First Three Billion Years of Evolution on Earth.")
We now know that pre-Cambrian time represents about 4 billion years of Earth's history, compared to the 540 million years represented by Cambrian and younger rocks that Darwin had studied. (See Emily's blog on the Geologic time scale.) We also know now that the oldest fossil microbes on Earth are about 3.5 billion years old, and that in between there is a compelling, but very sparse record of the fossil organisms that Darwin had anticipated. However, what's even more remarkable is that it took 100 years to prove this. And this was with hundreds, maybe thousands, of geologists scouring the far corners of the Earth looking for evidence.
The big breakthrough came in 1954 with the discovery of the "Gunflint microbiota" along the shores of Lake Superior in southern Canada. A University of Wisconsin economic geologist, Stanley Tyler, discovered microscopic threads of what we now understand to be fossil bacteria in a kind of rock called "chert". Chert is a microcrystalline material formed of the mineral quartz, or silicon dioxide, which precipitates very early in waters that contain microbial colonies. It forms so early that it turns the sediment almost instantly into rock, and any microbes become entombed in a mineral so stable it resists all subsequent exposure to water, and the oxidizing chemicals dissolved in water, for billions of years.
As it turned out, this was the Rosetta stone that helped decipher the code to the field of pre-Cambrian paleontology. It took almost 10 years for the discovery to be fully appreciated (the initial report in Science was viewed with much skepticism), but once it was confirmed, in the mid-1960s, the field exploded. Once geologists and paleontologists knew what to search for, they were off to the races. Since that initial discovery, other magic minerals have been found that preserve ancient microbes, sometimes with spectacular fidelity. But chert is still the mineral of choice, and I never pass by it in the field without collecting some.
We don't know yet what magic minerals exist on Mars that could have trapped and preserved organics. Clays and sulfates hold promise, and that's why we're so interested in them. Silica, perhaps similar to terrestrial chert, has been observed from orbit at a few places on Mars, and in Spirit rover data from Gusev crater. The great thing about Gale crater as a landing site is that we have so many choices in this trial-and-error game of locating a mineral that can preserve organic carbon.
The figure below provides some sense of the impact of this discovery. It is modified from a similar figure published in a very nice summary by Bill Schopf, a Professor of Paleontology at UCLA. Bill also was a very early participant in this race for discovery and has made a number of very significant contributions to the field.
In studying Mars, the importance of this lesson in the search for life preserved in the ancient rock record of Earth cannot be overstated. Curiosity's discovery of a very Earth-like ancient habitable environment underscores this point. With only one or two rovers every decade, we need to have a search paradigm: something to guide our exploration, something to explain our inevitable failures. If life ever evolved on Mars, we need to have a strategy to find it. That strategy begins with the search for organics, and regardless of their origin - abiotic or biotic, indigenous to Mars or not - they are important tracers for something more significant. Curiosity cannot see microfossils, but it can detect organic compounds. And just as with microfossils on Earth, we first have to learn where organics on Mars might be preserved. So that's what we're going to try and do.
In today's universe, it seems unimaginable that a planetary spacecraft would leave the comfort of its terrestrial perch without some kind of imaging system on board. But in the early 1960s, as NASA's Jet Propulsion Laboratory was reveling in the success of its first planetary mission to Venus and setting its sights on Mars -- a destination whose challenges would unfurl themselves much more readily than they had with Venus -- for some scientists, the question of camera or none was still just that, a question.
Bud Schurmeier, project manager for NASA's Ranger missions, a few years ago recalled, "There were a lot of scientists who said, 'Pictures, that's not science. That's just public information.' Over the years, that attitude has changed so markedly, and so much information has been obtained just from the photographs."
The recent passing of former JPL Director and career-long planetary imaging advocate Bruce C. Murray, 81, is a reminder of how different our understanding of the planets -- and our appreciation of them -- would be without space-based cameras.
This truth was evident as early as 1965, when NASA's Mariner 4, carrying an imaging system designed by a young Murray and his colleagues, arrived at Mars. It marked the world's first encounter with the Red Planet, a remarkable achievement in itself. But for an anxious press, public and mission team, the Holy Grail lay in catching that first glimpse of Mars up-close.
It was a waiting game that was too much for some. For everyone, in fact:
What resulted became known as "The first image of Mars." And in many ways it symbolizes -- more than any of the actual 22 photographs captured by Mariner 4 -- how significant this opportunity to truly "see" Mars had been.
Now, nearly 50 years after Mariner 4's arrival at Mars, imaging systems are an integral piece of our quest to understand the planets and the universe beyond, playing key roles in scientific investigations, spacecraft navigation and public support for missions. It's because of that first image that we can now look at that red dot in the night sky and picture what has become our new reality of Mars:
Dear Fellow Martians,
While the Curiosity rover is busy exploring the Martian surface, I am going to school as a sophomore at Shawnee Mission East High School in Prairie Village, Kan. I am very involved in my school's environmental club, and this year we started a composting program in our cafeteria.
I've also taken on a role in my local Sierra Club chapter's energy efficiency campaign. I think caring for our planet goes hand-in-hand with science and exploration. It is something that is very important to me.
In February, I rode a bus to Washington, D.C., with 40 other people to attend the Forward On Climate Change rally. The bus ride was a little over 24 hours, but it didn't feel that long at all. I had so much fun meeting and talking with people who had similar passions and motivations to those that I have. The rally and its immense energy opened my eyes to the things I could accomplish in my own community.
In May, I visited my grandparents in Beijing, China. Saying goodbye is always hard, because I absolutely love seeing them, talking to them, and being with them.
This week, I started my internship at JPL, one of my favorite places in the entire world. I am sure this will be the first of many letters that I will write to you. I can't wait to tell you more about my experiences in Pasadena as my summer continues.
With love, Clara
Aug. 5, 2012: Curiosity lands in Gale Crater. I watch from Earth, crying and shouting on the edge of my seat.
Sept. 27, 2012: Curiosity finds evidence of an ancient streambed. I play my third tennis match of the season, and share the rover's exciting discovery with my parents when I get home from school.
March 12, 2013: A rock sample analysis shows ancient Mars could have supported microbial life. I write about it in my chemistry assignment.
June 10, 2013: This is the first day of my internship at JPL, a day I have been dreaming about since I was a little girl. I don't know how I got to be so lucky.
For the past 18 months, NASA's Cassini spacecraft has been orbiting Saturn in practically the same plane as the one that slices through the planet's equator. Beginning with the Titan flyby on May 22, navigators started to tilt Cassini's orbit in order to obtain a different view of the Saturnian system. The measure of the spacecraft orbit's tilt relative to Saturn's equator is referred to as its inclination. The recent Titan flyby raised Cassini's inclination to nearly 16 degrees. Seven more Titan flybys will ultimately raise Cassini's inclination to nearly 62 degrees by April 2013. On Earth, an orbit with a 62-degree inclination would pass as far north as Alaska and, at its southernmost point, skirt the latitude containing the tip of the Antarctic Peninsula.
You may wonder why this change has been planned and how this feat is achieved. The "why" is to allow scientists to observe Saturn and the rings from different geometries in order to obtain a more comprehensive three-dimensional understanding of the Saturnian system. For instance, because Saturn's rings lie within Saturn's equatorial plane, they appear as a thin line when viewed by Cassini in a near-zero-degree orbit inclination. From higher inclinations, however, Cassini can view the broad expanse of the rings, making out details within individual ringlets and helping to unlock the secrets of ring origin and formation. Some of those images have already started to come in.
At higher inclinations, Cassini can also obtain excellent views of Saturn's poles, and measure Saturn's atmosphere at higher latitudes via occultation observations, where radio signals, sunlight or starlight received after passing through the atmosphere help to determine its composition and density.
The "how" is by using the gravity of Titan -- Saturn's largest moon by far -- to change the spacecraft's trajectory. Like the rings and Cassini's previous orbit, Titan revolves around Saturn within a plane very close to Saturn's equatorial plane. As Cassini flies past Titan, Titan's gravity bends the spacecraft's path by pulling it towards the moon's center -- similar to a ball bearing rolling on a smooth horizontal surface past a magnet. Near Titan, the motion is confined to a plane containing the spacecraft's path and Titan's center of mass. If this "local" plane coincides with Cassini's orbital plane about Saturn, the trajectory's inclination will remain unchanged. However, if this plane differs from Cassini's orbital plane about Saturn, then the bending from Titan's gravity will have a component out of Cassini's orbital plane with Saturn, and this will change the tilt of the spacecraft's orbit. Repeated Titan flybys will raise Cassini's orbit inclination to nearly 62 degrees by April of next year and then lower it back to the Saturn equatorial plane in March 2015.
Gravity assists are key to Cassini's ever-changing orbital geometries. Onboard propellant alone would quickly become depleted attempting to accomplish these same changes. A gravity assist can be characterized by the amount of "delta-v," or change in the velocity vector, it imparts to a spacecraft. Delta-v may of course also be imparted to the spacecraft via rocket engines and, either way, alters the spacecraft's orbit. The eight Titan gravity assists responsible for raising Cassini's inclination to 62 degrees will provide a delta-v of 15,000 mph (6.6 kilometers per second). For comparison, Cassini's rocket engines had only enough propellant after initially achieving orbit around Saturn to deliver about 2,700 mph (1.2 kilometers per second) of delta-v. That's 15,000 mph of capability spread over 11 months via gravity assists versus a modest 2,700 mph of capability spread over more than 13 years via rocket engines! Because delta-v is a vector, it may change both the speed and direction of Cassini at a point along its orbit, so the speed of Cassini is not changing by 15,000 mph, but mostly all of the directional changes sum to 15,000 mph. To give these values some context, Cassini's speed typically varies between as low as 2,500 mph (1.1 kilometers per second) and as high as 79,000 mph (35 kilometers per second) relative to Saturn between apokrone and perikrone, the farthest and closest points from Saturn along its orbit. Gravity assists from the initial prime mission Titan flyby in 2004 to the final Solstice Mission Titan flyby in 2017 will provide nearly 200,000 mph (90 kilometers per second) of delta-v, leveraging the onboard propellant by a ratio of 75 to 1. The bulk of the Saturn tour trajectory is shaped by gravity assists, while the role of onboard propellant is to fine-tune the trajectory.
At the end of year 2015, Cassini will again begin climbing out of Saturn's equatorial plane in preparation for its grand finale. After reaching an inclination of nearly 64 degrees, a Titan gravity assist in April 2017 will change Cassini's perikrone so that Cassini will pass through the narrow 2,000-mile (3,000-kilometer) gap between Saturn's atmosphere and innermost ring. Twenty-two spectacular orbits later, one final distant Titan gravity assist will alter Cassini's course for a fiery entry into Saturn's atmosphere to end the mission.
A lunar eclipse occurs when the Earth is positioned between the sun and the moon. Although the Moon passes through the Earth's shadow, the lunar disk remains partially illuminated by sunlight that is refracted and scattered by the Earth's atmosphere.
Refraction is the bending of light that occurs when the rays pass through media of different densities (our atmosphere is more dense near the surface and less dense higher up). Scattering of sunlight by molecules of air also deflects the light into different directions, and this occurs with much greater efficiency at shorter (bluer) wavelengths, which is why the daylight sky appears blue. As we view the sun near sunrise or sunset the light traverses a longer path through the atmosphere than at midday, and when the air is relatively clear, the absence of shorter wavelengths causes the solar disk to appear orange.
Tiny airborne particles, also known as aerosols, also scatter sunlight. The relative efficiency of the scattering at different wavelengths depends on the size and composition of the particles. Pollution and dust in the lower atmosphere tends to subdue the color of the rising or setting sun, whereas fine smoke particles or tiny aerosols lofted to high altitudes during a major volcanic eruption can deepen the color to an intense shade of red.
If you were standing on the Moon's surface during a lunar eclipse, you would see the Sun setting and rising behind the Earth, and you'd observe the refracted and scattered solar rays as they pass through the atmosphere surrounding our planet. Viewed from the Earth, these rays "fill in" the Earth's shadow cast upon the lunar surface, imparting the Moon's disk with a faint orange or reddish glow. Just as we sometimes observe sunrises and sunsets with different shades of orange, pink or red due to the presence of different types of aerosols, the color of the eclipsed lunar disk is also affected by the types of particles that are present in the Earth's atmosphere at the time the eclipse occurs.
In addition to the awesome views they offer, lunar eclipses have always provided scientific clues about the moon's shape, location and even surface composition. Although there will continue to be opportunities for observers to examine and reflect on fundamental concepts about the moon, such as its origin and interior structure, more modern tools are aiding these observations.
When it comes to understanding what a moon or a planet is made of remotely -- short of touching it or placing seismometers on its surface or probes below the surface -- classical physics comes to the rescue. By measuring the magnetic and gravitational forces that are generated on the inside and manifested on the outside of a planet or moon, we can learn volumes about the structure of its interior.
A spacecraft in the proximity of the moon can detect these forces. In the case of gravity, the mass of the moon will pull on the spacecraft due to gravitational attraction. If the spacecraft is transmitting a stable radio signal at the time, its frequency will shift by an amount exactly proportional to the forces pulling on the spacecraft.
This is how we weigh the moon and go further by measuring the detailed distribution of the densities of mountains and valleys as well as features below the moon's surface. This collection of information is called the gravity field.
In the past, this has lead to the discovery mascons on the moon, or hidden, sub-surface concentrations of mass not obvious in images or topography. If not accounted for, mascons can complicate the navigation of future landed missions. A mission, human or robotic, attempting to land on the moon would need to have a detailed knowledge of the gravity field in order to navigate the landing process safely. If a spacecraft sensed gravitational pull higher than planned, it could jeopardize the mission.
The Gravity Recovery and Interior Laboratory (GRAIL) mission, scheduled to launch in September, is comprised of twin spacecraft flying in formation with radio links between them to measure the moon's gravity field globally. This is because a single spacecraft with a link to Earth would be obstructed when the spacecraft goes behind the moon, leaving us with no measurement for nearly half of the moon, since the moon's far side never faces the Earth. The GRAIL technique may also reveal if the Moon has a core with a fluid layer.
So as you go out to watch the lunar eclipse on the night of Dec. 20, think about how much we've learned about the moon so far and what more we can learn through missions like GRAIL. Even at a close distance from Earth, the moon remains a mystery waiting be uncovered.
Worldwide today, it is estimated that nearly 1.1 billion people live without access to adequate water supplies and about 2.6 billion people lack adequate water sanitation. Improved understanding of water processes at global and regional scales is essential for sustainability.
Researchers at JPL recently launched the Western Water Resource Solutions website to highlight activities that apply NASA expertise and data to water resource issues in the western United States.
One focus area for this new site is the hydrologic cycle and using global satellite observations of the Earth to improve our understanding of water processes on a regional and local level. The western United States is expected to bear the brunt of impacts to water resource availability because of changing precipitation patterns, increasing temperatures, and a growing population. California is already starting to feel the impacts and is taking action to develop new adaptive management practices to ensure a safe and reliable water supply, while maintaining healthy ecosystems throughout the state.
NASA researchers at Ames Research Center, the Jet Propulsion Laboratory, and Marshall Space Flight Center are currently working with water managers to apply NASA expertise and data to water resource issues in California. The project partners with universities, agencies and other stakeholders, to utilize information from a number of sources, including existing ground observations and models.
This project is only one of several NASA initiatives aimed at providing actionable scientific information on water quality and the water balance worldwide. These other projects include development of better estimates of snow pack, groundwater monitoring, soil moisture and evapotranspiration, water quality, and monitoring fragile levee systems.
In addition to raising awareness about current water resource challenges, the new website highlights NASA's capability to use satellite and airborne data to help solve some of these challenges.
Learn more about the Western Water Resource Solution Group at: http://water.jpl.nasa.gov/
Written as part of Blog Action Day 2010