Cosmic Distribution of Chemical Complexity
Louis Allamandola, Lead Co-Investigator
Co-Investigators: Scott Sandford, Andrew Mattioda, Murthy Gudipati
Ames Postdocs: Joseph Roser, Nathan Bramall, Michel Nuevo, Christiaan Boersma
Collaborators: Max Bernstein, Els Peeters, Jan Cami, Jamie Elsila Cook, Jason Dworkin
TEAM MEMBERS PRESENT RESEARCH AT NAI EXECUTIVE COUNCIL MEETING
Team members were invited to present their research at the NASA Astrobiology Institute (NAI) Executive Council meeting held on January 17-18, 2013, at Ames Research Center.
Principal Investigator, Dave Des Marais, talked about the overall theme of the Ames Team research, "Early Habitable Environments and the Evolution of Complexity," and explained the four approaches to understanding the origins of life.
Lou Allamandola continued with his presentation, "Tracking Cosmic Carbon's Evolution from the Solar System Across the Universe." He explained how researchers are taking Astrochemistry and Astrobiology out of the lab and into space by integrating laboratory work with different spacecraft missions and concepts associated with organics in space and extraterrestrial samples.
ORGANICS PROBABLY FORMED EASILY IN EARLY SOLAR SYSTEM
Complex organic compounds, including many important to life on Earth, were readily produced under conditions that likely prevailed in the primordial solar system. Scientists at the University of Chicago and NASA's Ames Research Center came to this conclusion after linking computer simulations to laboratory experiments.(Animation By Fred Ciesla)
Fred Ciesla, assistant professor in geophysical sciences at the University of Chicago, simulated the dynamics of the solar nebula, the cloud of gas and dust from which the sun and the planets formed. Although every dust particle within the nebula behaved differently, they all experienced the conditions needed for organics to form over a simulated million-year period.
"Whenever you make a new planetary system, these kinds of things should go on," said Scott Sandford, a space science researcher at NASA Ames. "This potential to make organics and then dump them on the surfaces of any planet you make is probably a universal process."
Although organic compounds are commonly found in meteorites and cometary samples, their origins presented a mystery. Ciesla and Sandford describe how the compounds possibly evolved in the March 29 edition of Science Express. However, how important a role these compounds may have played in giving rise to the origin of life remains poorly understood.
Sandford has devoted many years of laboratory research to the chemical processes that occur when high-energy ultraviolet radiation bombards simple ices like those seen in space. "We've found that a surprisingly rich mixture of organics is made," Sandford said. These include molecules of biological interest, including amino acids, nucleobases, and amphiphiles, the building blocks of proteins, RNA and DNA, and cellular membranes, respectively. Irradiated ices should have produced these same sorts of molecules during the formation of the solar system, he said. But a question remained. Could icy grains traveling through the outer edges of the solar nebula, in temperatures as low as minus 405 degrees Fahrenheit (less than 30 Kelvin), become exposed to UV radiation from surrounding stars?
Ciesla's computer simulations reproduced the turbulent environment expected in the solar nebula. This "washing machine" action mixed the particles throughout the nebula, and sometimes lofted them to high altitudes within the cloud, where they could become irradiated. "Taking what we think we know about the dynamics of the outer solar nebula, it's really hard for these ice particles not to spend at least part of their time where they're going to be exposed to UV radiation," Ciesla said. The grains also moved in and out of warmer regions in the nebula. This completes the recipe for making organic compounds: ice, irradiation and warming. "It was surprising how all these things just naturally fell out of the model," Ciesla said. "It really did seem like this was a natural consequence of particle dynamics in the initial stage of planet formation."
For more information about the NASA Ames Astrochemistry Laboratory, visit: http://www.astrochemistry.org
A 21st CENTURY TOOL TO STUDY THE EVOLUTION OF COSMIC CARBON: The Ames PAH IR Spectroscopic Database
Infrared emission from Polycyclic Aromatic Hydrocarbons (PAHs) shows they are omnipresent across the Universe and that they play key roles in astrochemistry, the formation of stars and planets, and possibly life itself. Since astronomical PAHs make up the most abundant reservoir of accessible cosmic carbon, they are very important to Astrobiology. The Ames PAH IR Spectroscopic Database, developed here over the past two decades, has been key to establishing the presence of PAHs in space and is now being developed into a new probe of astronomical environments spanning the Universe. This database is a large, coherent set of laboratory measured and DFT (Density Functional Theory) computed infrared spectra of PAHs from C10H8 to C130H28.
The database and tools we have developed are on the web at www.astrochem.org/pahdb.
Among the many tools available are ways to search through the PAH database, select, compare and download spectra, convert absorption to emission spectra, make direct comparisons with astronomical spectra, etc. A separate suite of IDL tools, the AmesPAHdbIDLSuite, is offered that allows even more powerful analysis of astronomical PAH emission spectra. Together these advanced tools provide straightforward use of the database. After summarizing the current status of the database and tools, today's talk previewed an analyses of the over 1000 IR spectra NASA's Spitzer Space Telescope measured to create a spectral map of The Iris Nebula (NGC 7023). This preview showed how the Ames Database can be used to systematically interpret vast amounts of spatial information and the detailed insight gained into PAH photo-driven chemical evolution and PAH population changes in different environments.
ASTROCHEMISTRY LABORATORY HOSTS A YURI'S NIGHT BOOTH ON "SCOUTING FOR LIFE"
The Astrochemistry Laboratory hosted an informative, hands-on booth for Yuri's Education Day at NASA Ames Research Center on April 8, 2011. Ames Team members Christiaan Boersma, Nathan Bramall, Andrew Mattioda, Michel Nuevo, Joe Roser and Scott Sandford demonstrated how scientists use spectroscopy or light in the search for life in the Universe.
Students were allowed hands-on access to several instrument concepts under development in the laboratory for Astrobiology missions. These concepts focus on Ultra-Violet (UV) induced fluorescence in astrobiologically interesting molecules, allowing them to be easily identified on either a planet's surface or in subsurface soils. After a short demonstration on fluorescence and spectroscopy, students used a remote controlled rover, equipped with a UV source and wireless camera, to move across a Mars landscape identifying signs of alien life. The visitor's were also given a peak below the surface of Mars via a UV fluorescence penetrometer system. Penetrometers are direct push instruments that allow scientific exploration of subsurface soils. Both instrument concepts proved to be extremely popular with the students, with most people waiting in line to see the rover move across the Martian landscape or to gain a glimpse of the possible life below the Martian surface.
ELLIS PARK ELEMENTARY SCHOOL STUDENTS EXPERIMENT WITH SOFIA'S INFRARED CAMERA
On April 15, 2011, Andrew Mattioda demonstrated the uses of infrared light to over one hundred 4th and 5th graders at the Ellis Park Elementary School in Sunnyvale, California. Using the SOFIA (Stratospheric Observatory for Infrared Astronomy) project's infrared camera the students were able to watch the heat flow in hot and cold glasses of water, look through a NASA plastic bag and modify their appearance in the infrared using ice cubes. Special thanks goes to Darlene V. Mendoza who helped coordinate the use of the SOFIA equipment for this demonstration.
NASA NANOSATELLITE O/OREOS CELEBRATES 100 DAYS IN SPACE STUDYING LIFE
What is about the size of a loaf of bread, weighs 12 pounds and has been in space for over 100 days? It's the nanosatellite O/OREOS (Organism/ORganics Exposure to Orbital Stresses), NASA's first Astrobiology Small Payloads (ASP) mission that launched into orbit on November 19, 2010. The mission seeks answers to fundamental astrobiology questions about the origin, evolution and distribution of life in the universe.
O/OREOS is NASA's first "CubeSat" with two distinct, completely independent science experiments on a single satellite. It's also the first nanosatellite to conduct autonomous biological and chemical measurements in the region of space known as the exosphere.
According to Antonio Ricco, instrument scientist for O/OREOS and a researcher at NASA Ames Research Center, Moffett Field, CA, "This is enabling us to study organics, microorganisms and astrobiology in the space environment in real time."
O/OREOS transmits its radio signals to ground control stations and spacecraft operators in the Mission Control Center at Santa Clara University, Santa Clara, CA. Nearly daily, two-way communications with the spacecraft provides valuable information about its health, status and science data, and gives scientists the ability to fine tune the science payloads' operating parameters. The NASA Astrobiology Institute (NAI) assists in the communication with O/OREOS by providing an NAI fellowship to Santa Clara University student, Anthony Young. While this fellowship aids the O/OREOS mission, it also provides Young with an educational, hands-on experience in both satellite communications and astrobiology.
On December 3, 2010, two weeks after O/OREOS deployed, the first of three biological experiments began operating automatically within the Space Environment Survivability of Living Organisms (SESLO) payload; and was successfully completed just 24 hours later. On February 18, 2011, the second part of the SESLO biological experiment began and also was successfully finished in one day. The experiment is designed to characterize the growth, activity, health and ability of microorganisms commonly found in soil and salt ponds in a dried and dormant state - Bacillus subtilis and Halorubrum chaoviatoris - to adapt to the stresses of outer space by rehydrating, or "feeding," and growing them using liquid nutrients. Scientists will compare the microbes' population density and the medium's color change at three different times during the mission to determine how and if their behavior changes with longer exposure to radiation and weightless conditions in space.
Hours after reaching orbit, O/OREOS activated its other science experiment payload, called the Space Environment Viability of Organics (SEVO), which monitors the stability and changes in four classes of biologically important organic molecules as they are exposed to space conditions, most notably sunlight completely unfiltered by Earth's atmosphere. For the SEVO experiment, scientists selected organic molecules distributed throughout our galaxy, as well as organic "biomarkers" of life as we know it on Earth. O/OREOS houses the organic samples in "micro-environments" relevant to space and planetary conditions. The experiment exposes the organic compounds to solar ultraviolet (UV) light, visible light, trapped-particle and cosmic radiation. Scientists will determine the stability of the molecules by studying changes in UV, visible, and near-infrared light absorption. Two of the SEVO scientists, Nathan Bramall and Andrew Mattioda are members of the NAI Ames Team.
"Using the sun as its light source, O/OREOS has made nearly 500 periodic spectral measurements of the organic materials, and 200 of those have been transmitted to us so far," said Pascale Ehrenfreund, O/OREOS project scientist at George Washington University, Washington, D.C. "We are excited to see the payload's miniature spectrometer and sample positioning systems working so well and are grateful to our operations team at Santa Clara University."
The Small Spacecraft Division at Ames manages the O/OREOS payload and mission operations with the professional support of staff and students from Santa Clara University.
NASA AMES SCIENTISTS RELEASE UNIQUE COLLECTION OF INFRARED SPECTRA
Duplicating the harsh conditions of cold interstellar space in their laboratories and on their computers, NASA Astrobiology Institute Ames team scientists have created a unique database of polycyclic aromatic hydrocarbon (PAH) spectra, which is primarily used to interpret mysterious infrared (IR) emission detected by ground, air and space-based observatories.
The value of the NASA Ames PAH IR Spectral Database extends far beyond the immediate needs of NASA and the field of astronomy. The PAH spectral database has a large and diverse set of applications. PAHs are a major product of combustion -- they remain in the environment and are carcinogenic. Consequently, they are important to scientists, educators, policymakers and consultants working in the fields of medicine, health, chemistry, fuel composition, engine design, environmental assessment, environmental monitoring and protection. The PAH database is a new tool for people working in all these fields.
The database contains over 800 spectra of PAHs in their neutral and electrically charged states, and tools to download PAH spectra ranging in temperature from -470 to 2000 degrees F. PAHs are flat, chicken-wire shaped, nano-sized molecules that are now known to be abundant throughout the universe, but often in exotic forms not readily available on Earth. They are thought to be produced in outflows from carbon-rich stars by processes similar to combustion in oxygen-poor flames that produce PAH-rich soots on Earth.
Mysterious infrared radiation from space was discovered from astronomical observations made in the 1970s and 1980s. While the infrared signature hinted that PAHs might be responsible, laboratory spectra of only a handful of small, individual PAHs were available to test this idea. These were only for neutral PAHs, not for PAHs as they were expected in interstellar space: electrically charged, free, very cold, individual molecules in the gas. The only spectra available were of tiny crystals containing many PAH molecules stuck together and suspended in oils and salt pellets: these PAHs were not isolated, not cold, and not charged. By the mid-1990s, observations from space showed this infrared emission was surprisingly common and widespread across the universe, implying that the unknown carrier was abundant and important. The need to measure PAH spectra under astronomical conditions was critical to make progress.
To provide these spectra, a team of scientists led by Louis Allamandola at NASA Ames Research Center developed a program in the late 1980s to measure PAH spectra under simulated astronomical conditions. According to Allamandola, there are now about 800 spectra in the database: 600 spectra have been theoretically computed and 200 spectra have been measured in the laboratory. The theoretical spectra span the range from 2 to 2000 microns, the experimental spectra cover 2 to 25 microns.
Christiaan Boersma is one of the three astronomers on the team who routinely uses the PAH IR Spectra Database to interpret astronomical observations. Boersma worked on the design and development of the current spectra website and its user tools. "The spectra in the database have given insights into the composition of the PAHs in space that were impossible to obtain any other way," Boersma said. "In the near future these spectra will be especially valuable for interpreting observations made with NASA's new airborne observatory, the Stratospheric Observatory for Infrared Astronomy and the European Space Agency's Herschel Telescope. These telescopes are pioneering the far-infrared radiation region, opening a new window on the sky. Because the database shows that PAHs have many far-infrared transitions, PAHs will add to the pioneering discoveries made by these observatories."
The easy-to-use website allows users to sort through long tables of numbers and to interact graphically with the data. The database can be interrogated using many criteria, such as PAH charge, composition and spectral signatures. Several tools allow users to do initial data analysis online. For example, spectra can be combined to create a 'composite' spectrum that can be directly compared to an unknown. In addition, all data can be downloaded. "Future plans are to expand the database with new sets of data and add useful tools along the way,'' Boersma said. Formerly at the University of Groningen in the Netherlands, Boersma is now a NASA postdoctoral fellow at Ames.
Charles Bauschlicher, Jr., also at NASA Ames, is one of the first computational chemists to calculate the infrared spectra of PAHs and their ions. Using quantum chemical calculations he and Alessandra Ricca of the SETI Institute, computed all of the spectra in the computational portion of the database. "When we started this project our hope was to help interpret the experimental spectra, but over time our computational capabilities grew to a point that we were able to study molecules much larger than can be studied in the laboratory," Bauschlicher said. "In addition, we were soon using theory to study species that are very difficult to create and measure in a laboratory, but could be common in space."
Ricca added, "I am very excited about the future of this research, because we have only scratched the surface of what theory can contribute to our understanding of PAHs. For example, we are now studying clusters of large PAHs and extremely large individual PAHs containing more than 100 carbon atoms."
Andrew Mattioda, also at NASA Ames, and Douglas Hudgins now at NASA Headquarters, are both experimental physical chemists who have measured all of the spectra in the experimental portion of the database under astrophysically relevant conditions. "We accomplished this feat by first isolating the molecules in an inert matrix at very low temperatures, nearly -450 degrees F, much like the molecules are isolated in space. We then measured the spectra of both the neutral and ionized PAHs," Mattioda said.
Mattioda's and Hudson's work includes PAHs containing a nitrogen atom in the molecule's framework, molecules affectionately known as PANHs. "PANHs are very important in biochemistry as well as in the search for life elsewhere in the universe," Mattioda said. "Our laboratory research has revealed previously unknown spectroscopic and electronic properties of PAHs and PANHs. We are rewriting the organic chemistry textbooks where polycyclic compounds are concerned. Given the biological processes that rely on PAH-type molecules, understanding the distribution of PAHs in the universe could provide insight into the distribution of life in the universe."
Els Peeters, formerly a postdoctoral fellow at NASA Ames, and now a professor of astronomy at the University of Western Ontario, pioneered the application of the spectral database to astronomical spectra, and guided the direction of its expansion from the astronomer's perspective. Analyzing observational data obtained with the Infrared Space Observatory and the Spitzer Space Telescope, Peeters identified several classes of astronomical PAH spectra that are related to different types of astronomical objects. "Just as with handwriting and language analysis, by comparing the spectral signature from each of these different astronomical objects with the different PAH signatures in the database, we were able to pinpoint the types of PAHs in these objects." Peeters said. "When you realize that this works not only in our galaxy, but across the universe, it's pretty amazing."
According to Peeters, scientists are now able to use each 'letter' in the spectral signature to study specifics about the PAHs in space -- their electrical charge, size and shape, etc. In addition, the NASA scientists who created the PAH IR Spectral Database have found small but real mismatches within the database, indicating that something was missing. Bringing together all the information on cosmic emission has revealed the types and amounts of different PAHs present in space and how they evolve from their birth site in red giant stars, to the interstellar medium between the stars, and ultimately into star-forming regions and proto-planetary disks.
"Thanks to this synthesis of lab data with astronomical observations, just as a weatherwoman uses satellite pictures to forecast the weather, these emission bands are being developed into a diagnostic tool to probe the local environmental conditions in our galaxy, out to nearby galaxies and all across the distant universe," said Peeters.
Jan Cami, a former postdoctoral fellow at NASA Ames and now a professor of physics and astronomy at the University of Western Ontario, laid the conceptual foundation for the database and the website. Cami developed algorithms to match astronomical observations with spectra from the database. "Having the capability to almost perfectly reproduce astronomical observations with Earth-based laboratory experiments and theoretical calculations is very cool and rewarding," Cami said. "That alone makes the NASA Ames PAH database unique -- it is the only database in the world with enough PAH information to be relevant to astrophysical environments. Not only that, the database reveals what kind of PAHs like to hang out together and in what corner of the universe they do so."
Creation of the PAH IR Spectral Database has led to some unexpected scientific results: 1) a significant fraction of PAHs in space are negatively charged, which was thought unlikely until now; 2) emission at certain wavelengths originates from smaller molecules, while larger molecules dominate other wavelength ranges.
Douglas Hudgins joined the team in the 1990s and pioneered the experimental techniques that are now routinely used in many laboratories to measure PAH spectra under extraterrestrial conditions. Now a program scientist at NASA Headquarters, Hudgins is thrilled to see the Ames database coming to fruition. "The reason that NASA's Astrophysics Division supports laboratory research is because the resultant data are essential for analyzing and interpreting the observations of NASA's space observatories. Doing the experiments and calculations are only part of the job. It is just as important to get those data into the hands of scientists in a convenient and useful format and this new database will do exactly that," Hudgins said.
According to Allamandola, the NASA scientists who created the PAH Spectral Database began their work motivated to test the PAH hypothesis and provide the spectra needed to exploit the PAH model and develop it into a new "probe" of the wide variety and vast number of astronomical objects that show the PAH emission spectrum. "This field has exploded far beyond my wildest dreams and, in my opinion, this spectral database is what broke the spell that astrochemistry was limited to simple species and marginal for astrophysics," Allamandola said.
"Thanks to the incredible sensitivity of the Spitzer Space Telescope, the PAH signature is seen across the universe, removing any doubt of the importance of these species. There is even evidence for PAH emission from very distant galaxies at red shifts of three, indicating these complex organic molecules were produced only a few billion years after the Big Bang. This means that enough carbon was available to drive a rich organic chemistry far earlier in the history of the universe than people thought only a few years ago," stated Allamandola. "When you consider that the discovery of simple, garden-variety molecules like ammonia, formaldehyde and carbon monoxide in space made headlines in the 1960s and 1970s, this is incredible. Until then, space was thought to be chemically barren. If this isn't enough, Messier 82 (the prototype nearby starburst galaxy about 12 million light years away) and Spitzer have shown there are even PAHs in the space between galaxies. Beyond a doubt, PAHs are an important part of modern astrophysics."
Pioneering observations made by the European Infrared Space Observatory and the unprecedented sensitivity of NASA's Spitzer Space Telescope have seen the PAH infrared signature from many astronomical objects within our galaxy and from most other galaxies across the universe. This database and accompanying user tools will see immediate use by astronomers throughout the world as they probe PAH emission to the edge of the universe with increasingly sensitive telescopes.
For additional information:
The PAH Spectral Database and tools are available at www.astrochem.org/pahdb
The Astrophysical Journal Supplement Series published, "The NASA Ames Polycyclic Aromatic Hydrocarbon Infrared Spectroscopic Database: The Computed Spectra," which describes the website and details about the computational spectra in the database.
This research is supported by the Space Science and Astrobiology Division at NASA Ames Research Center and the Science Mission Directorate at NASA Headquarters, Washington, D.C.
NASA AND THE NAVAJO NATION "STORY OF THE STARS" EDUCATOR WORKSHOP
On January 28-29, 2010, the NASA and the Navajo Nation project team hosted a large-scale workshop for educators across the Navajo Nation. Over 100 teachers participated, despite the worst snowstorm in Arizona in 25 years, some traveling hours through severe conditions. On the first day, the teachers heard background lectures from both cultural expert Leroy Nelson, and astrobiologist Scott Sandford from the NAI Ames team. On the second day, the team trained teachers on classroom use of the six activities in the S' Baa Hane' (Stars in the Sky) booklet, intercultural materials developed by the project in 2006.
The guiding philosophy for the project is that by bringing together the cultural and scientific perspectives, a "dual-learning" environment is created in which learners are invited to discover and define the points of conceptual overlap for themselves. The project's efforts are focused entirely on the benefit to Navajo teachers and students, empowering them to teach both culture and science more effectively.
For the past five years, the project has progressed and evolved into a successful collaboration involving members of the education communities of both NASA and the Navajo Nation, led by the NASA Astrobiology Institute and the Navajo Nation Department of Dine Education. It began as a NASA Explorer Institute project in 2005, in which a "focus group" of educators from the Navajo Nation detailed the desirable characteristics of a partnership with NASA. It continued with funding from the NASA Office of Education through 2006, during which time the S' Baa Hane' classroom materials were developed, bringing NASA astrobiology science and Navajo cultural knowledge together in K-12 hands-on activities. Two grants from NASA's Science Mission Directorate took the project further, one providing short-term support for the educator workshop, and another providing long-term support to develop a "companion" volume to S' Baa Hane' focused on the Moon.
For more information contact Daniella Scalice: email@example.com.
LOU ALLAMANDOLA GIVES CHEMICAL EVOLUTION LECTURE AT SACRAMENTO CITY COLLEGE
Lou Allamandola was the guest speaker for the Sacramento Valley Astronomical Society's general meeting on January 15, 2010, at Sacramento City College. The topic of Allamandola's discussion was "From Infrared Astrophysics to Astrobiology," and it focused on the chemical evolution of cosmic materials and their relevance to astrobiology.
Allamandola spoke about the great strides that have been made in our understanding of interstellar material -- the gas and dust that exist between the star systems within a galaxy -- due to advances in infrared astronomy and laboratory astrophysics. Ionized polycyclic aromatic hydrocarbons -- better known as PAHs -- extraordinarily large molecules by earlier astrochemical standards, are widespread and abundant throughout much of the cosmos.
In cold molecular clouds, the birthplace of planets and stars, interstellar atoms and molecules freeze onto extremely cold dust and ice particles forming mixed molecular ices dominated by simple elements such as water, methanol, ammonia, and carbon monoxide. Within these clouds, and especially in the vicinity of star and planet-forming regions, these ices and PAHs are processed by ultraviolet light and cosmic rays forming hundreds of far more complex elements, some of biogenic interest. Eventually, these are delivered to primordial planets by comets and meteorites. Because these materials are the building blocks of comets and related to carbonaceous micrometeorites, they are likely to be important sources of complex organic materials delivered to habitable planets (including the primordial Earth) and their composition may be related to the origin of life.
In 1984, Allamandola established the Astrochemistry Laboratory at NASA Ames where he still works today, pioneering laboratory studies of interstellar and planetary ices. He is responsible for opening up the field of interstellar PAHs with Xander Tielens and John Barker, and is heavily involved in the laboratory studies of PAHs under relevant interstellar conditions. Formally trained as a specialist in low temperature spectroscopy at the University of California at Berkeley, followed by postdoctoral research on energy transfer at cryogenic temperatures at Oregon State University, he worked for seven years in the Astrophysics Laboratory at Leiden University in the Netherlands where he developed the techniques required to prepare and study laboratory analogs of interstellar/pre-cometary ice grains using spectroscopic methods. Allamandola has also participated in astronomical measurements of infrared spectra using the Kuiper Airborne Observatory, the NASA Infrared Telescope Facility, and the United Kingdom Infrared Telescope.
REPRODUCING A BUILDING BLOCK OF LIFE IN THE LABORATORY
By Ruth Marlaire, NASA Ames Research Center
NASA Ames astrobiologists studying the origin of life have reproduced uracil, a key component of our hereditary material, in the laboratory. They discovered that an ice sample containing pyrimidine exposed to ultraviolet radiation under space-like conditions produces this essential ingredient of life.
Pyrimidine is a ring-shaped molecule made up of carbon and nitrogen and is the basic structure for uracil, part of a genetic code found in ribonucleic acid (RNA). RNA is central to protein synthesis, but has many other roles.
"We have demonstrated for the first time that we can make uracil, a component of RNA, non-biologically in a laboratory under conditions found in space," said Michel Nuevo, research scientist on the NAI Ames Team. "We are showing that these laboratory processes, which simulate occurrences in outer space, can make a fundamental building block used by living organisms on Earth."
Nuevo is the lead author of a research paper titled "Formation of Uracil from the Ultraviolet Photo-Irradiation of Pyrimidine in Pure Water Ices," Astrobiology, Vol. 9, No. 7, published October 1, 2009.
Ames astrobiologists have been simulating the environments found in interstellar space and the outer solar system for years. During this time, they have studied a class of carbon-rich compounds, called polycyclic aromatic hydrocarbons (PAHs), which have been identified in meteorites, and are the most common carbon-rich compound observed in the universe. PAHs typically are six-carbon ringed structures that resemble fused hexagons, or a piece of chicken wire.
Pyrimidine also is found in meteorites, although scientists still do not know its origin. It may be similar to the carbon-rich PAHs, in that it may be produced in the final outbursts of dying, giant red stars, or formed in dense clouds of interstellar gas and dust.
"Molecules like pyrimidine have nitrogen atoms in their ring structures, which makes them somewhat whimpy. As a less stable molecule, it is more susceptible to destruction by radiation, compared to its counterparts that don't have nitrogen," said Scott Sandford, a space science researcher on the NAI Ames Team. "We wanted to test whether pyrimidine can survive in space, and whether it can undergo reactions that turn it into more complicated organic species, such as the nucleobase uracil."
In theory, the astrobiologists thought that if molecules of pyrimidine could survive long enough to migrate into interstellar dust clouds, they might be able to shield themselves from radiation destruction. Once in the clouds, most molecules freeze onto dust grains (much like moisture in your breath condenses on a cold window during winter). These clouds are dense enough to screen out much of the surrounding outside radiation of space, thereby providing some protection to the molecules inside the clouds.
Scientists tested their hypotheses in the Ames Astrochemistry Laboratory. During their experiment, they exposed the ice sample containing pyrimidine to ultraviolet radiation under space-like conditions, including a very high vacuum, extremely low temperatures (approximately - 340 degrees Fahrenheit), and harsh radiation. They found that when pyrimidine is frozen in water ice, it is much less vulnerable to destruction by radiation. Instead of being destroyed, many of the molecules took on new forms, such as the RNA component uracil, which is found in the genetic make-up of all living organisms on Earth.
"We are trying to address the mechanisms in space that are forming these molecules. Considering what we produced in the laboratory, the chemistry of ice exposed to ultraviolet radiation may be an important linking step between what goes on in space and what fell to Earth early in its development," said Stefanie Milam, NAI Ames Team researcher and a co-author of the research paper.
"Nobody really understands how life got started on Earth. Our experiments demonstrate that once the Earth formed, many of the building blocks of life were likely present from the beginning. Since we are simulating universal astrophysical conditions, the same is likely wherever planets are formed," explained Sandford.
Additional team members who helped perform the research and co-author the paper are Jason Dworkin and Jamie Elsila, two astrobiologists at NASA's Goddard Space Flight Center, Greenbelt, Maryland.
For more information about the NAI Ames Team’s Astrochemistry Laboratory, visit: http://www.astrochemistry.org/
AMES TEAM RESEARCH
NEWS AND HIGHLIGHTS:
Cosmic Distribution of Chemical Complexity
Disks and the Origins of Planetary Systems
Mineralogical Traces of Early Habitable Environments
Origins of Functional Proteins and the Early Evolution of Metabolism