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Executive Summary

The Goddard Team addresses this central question: Did delivery of exogenous organics and water enable the emergence and evolution of life? In short: Why is Earth wet and alive? Along with the origin of Earth’s water, we seek to better understand which organic compounds are generated in the interstellar and proto-planetary environments and later delivered to planets. We address this goal through observational, theoretical, and laboratory work.

Our investigations embody an integrated program of (a) pan-spectral astronomical observations of comets, circumstellar disks, and exoplanet environments, (b) models of dynamical transport in the early Solar System, (c) laboratory studies of extraterrestrial samples, and (d) realistic laboratory and numerical simulations of inaccessible cosmic environments. Synergistic integration of these areas is essential for testing whether delivery of the building blocks of life – exogenous water and prebiotic organics – enabled the emergence and development of the biosphere. In this summary, we highlight aspects of our accomplishments in this reporting period – year one of our five-year award.

In recent decades it has become increasingly evident that certain types of asteroids – and the even more primitive comets – are rich in diverse classes of organic species. Moreover, comets/asteroids and their fragments are the only natural materials available to study actual prebiotic chemistry in detail, since plate tectonics on Earth has largely erased (or significantly altered) the prebiotic chemical record in the oldest terrestrial rocks. Decoding the messages hidden within these icy and rocky bodies is critical.

The solar system formed from a dense interstellar cloud core. Such cores are very cold (10-50 K), and their dust grains are coated with ices comprised of water and organic compounds. Many of these organics have potential relevance to the origin or early evolution of life, if delivered to planets. The survival of these organics through the violent birth-phase of a star is less certain. Properties of the young star (its mass, spectral energy distribution, whether it formed in isolation or as a multiple star, etc.) play a key role in controlling the evolution of organic material in the proto-planetary disk. The location within the disk is important since the nature and effectiveness of such processing depends strongly on distance from the young star, on distance above the nebular mid-plane, and on time.

The ultimate delivery of these organics to young planets and their moons also evolves with time, as the impacting bodies grow in size and as the nebula clears. Since 2005, fundamental advances have changed our concept for transport and mixing of material within the protoplanetary disk of our Solar System, via gravitational scattering in the first billion years of Solar System evolution.

Our major research objective is to broadly establish sources of prebiotic organic compounds and to understand their history in terms of universal processes that are expected to take place on any newly formed planet. Toward this end, our “Research Plan” is organized as follows:

We address three major aspects of the hypothesized exogenous delivery:

• What material was delivered? We sample material in/from primitive bodies identified as plausible “carriers”, and establish its compositional diversity – including isotopic, chiral, and nuclear spin signatures.
• How was prebiotic matter synthesized and processed in the solar nebula, prior to being incorporated into such carriers? We relate the measured properties to taxonomic classes of primitive bodies (comets, meteorites), and to nebular models for chemical evolution.
• Can we find evidence for such processes through the study of extra-solar planetary systems? We compare isotopic and chemical signatures in currently forming planetary systems with signatures of primitive materials in our own system.
• What dynamical mechanisms delivered these primitive bodies to early Earth? Could this evidence inform our understanding of the delivery of exogenous prebiotic matter to Earth? [Note: this topic was suspended in year one, owing to inadequate funding. It will be resumed in future years if Team funding is restored to the levels originally proposed.]

We also address key aspects of testing the habitability of other worlds, and thus testing the uniqueness of Earth:

• Can we find evidence for habitability elsewhere in the present day Solar System and habitable environments in extra-solar planets? We address these questions with cutting edge spectroscopy of planets & icy worlds in the solar system and in exoplanetary systems.

Team members also address instrument protocols for future in situ investigations that can extend our knowledge of the complexity of organic compounds on mission targets relevant to astrobiology. Under CAN-3, we developed protocols for amino acid detection through derivitization; they are now awaiting use on the Curiosity rover on Mars. Under CAN-3 and CAN-5, we advanced the methodology for laser desorption of high-mass organic compounds, and the instrumental heir to that work is being prepared for flight on ExoMars 2018. Under CAN-7 funding, we are developing protocols for analyzing informational polymers; when applied to comets and asteroids, they will test directly our predictions and observations of organics synthesized and processed in the proto-solar nebula. When applied to Mars and the plumes of icy moons, they can quantify the presence and abundance of complex organics and informational polymers related to the origin of life.

Progress during 2015:
This twelfth year of our Astrobiology Program saw major emphasis on research collaborations across disciplines. GCA Team members conducted a vigorous and highly productive research program in all four topical areas despite restricted funding. We conducted many investigations in the laboratory and in the field (mainly astronomical), as summarized below and in the individual Reports of progress.

Team members participated in numerous meetings and workshops, presenting scientific results in many invited and contributed talks. GCA members appeared as lead-, principal-, or co-author on many distinct scientific publications during this reporting period. Individual citations appear in the Bibliography at the end of this Report.

Highlights of GCA Research in 2015:

From the Interstellar Medium to Planets
As part of their studies related to the carbon inventory of the outer Solar System and the interstellar medium, GCA members from the Cosmic Ice laboratory provided new insights on the important question of the physical structure of interstellar and protoplanetary ices (see project report by Hudson et al.). They discovered that all previous low-temperature publications on solid CH₄ sampled the compound’s crystalline phases and not the amorphous one that was usually claimed and which is more astronomically relevant. They then extended this work to CO₂ and showed that what had been assumed by astrochemists for about 30 years to be IR spectra of amorphous CO₂ was actually of the crystalline solid. They succeeded in producing the amorphous material and published spectral results, the first such work available for CO₂. Reassessments of results from many earlier laboratory and observational papers are needed in light of this new work.

Formative Processes in Proto-Planetary and Debris disks
Team members at Goddard continued studies of gas-phase organic chemistry in the interstellar medium and during the earliest stages of formation of Solar-type stars (see project report by Charnley et al.), including observational studies of nitrogen fractionation (Wirstrom et al. 2015) and organic molecule production and destruction in the protostellar environment (Taquet et al. 2015).

Team members at CalTech (G. Blake et al.) conducted a joint laboratory and observational program aiming to investigate the chemistry of water and simple organics in the protoplanetary disk analogs of the early solar nebula, in comets, and in the atmospheres of extrasolar planets. The laboratory work has required the creation of novel high-bandwidth instruments (from the microwave to the THz regimes) that can probe both gaseous and solid state (liquid and solid) materials. Particular emphasis has been placed on the study of small chiral, that is handed, organic species, with a view toward establishing whether the homochirality exhibited by life on Earth is stochastically or deterministically derived. Laboratory studies are combined with astronomical observations from the radio (VLA, GBT, ALMA) to the far infrared (SOFIA, Herschel archival data) and infrared (Keck/VLT, Spitzer archival data). A recent highlight is the first detection of a chiral species toward the Galactic Center (see report by Blake et al.).

Team members of the Cosmic Dust Laboratory worked to understand the rates and products of surface-mediated reactions (gas-grain) that could occur in nebular environments, which span a large range in parameter space (time, temperature, pressure, catalyst composition and secondary reactions). Hydrogen, carbon monoxide and nitrogen gases were abundant in the primitive solar nebula, as were silicate dusts and metallic grains. These gases can react on such grain surfaces to produce an abundance of carbon-bearing products that include volatile hydrocarbons, amines, alcohols, aldehydes, and acids as well as more complex, less volatile species such as carbon nanotubes. Refractory carbonaceous deposits efficiently catalyze additional surface reactions. In 2015, the team confirmed that surface mediated reactions in simulated protostellar environments are much more complex than previously believed. The ratio of solid carbon deposited onto grain surfaces versus the volatiles released back into the gas phase depends strongly on temperature and time, on the properties of the initial catalyst (composition and surface area), and on the previous history of the catalyst – e.g., on the run number (used as a proxy to track the relative amount of previously deposited carbon). Even more interesting, the surface area increased with time, for all catalysts studied, as carbon deposits formed on or even within grain surfaces. In addition, the order of the overall reaction appears to be a function of temperature. In 2015, they found that bare iron wires catalyze formation of long fibers of carbonaceous material resembling nanotubes (see report by Nuth et al.).

GCA astronomer Marc Kuchner invited the public to help him discover new planetary systems through a new interactive website. At DiskDetective.org, launched last year, volunteers view data from NASA’s Wide-field Infrared Survey Explorer (WISE) mission and three other surveys. WISE measured more than 745 million objects, representing the most comprehensive survey of the sky at mid-infrared wavelengths ever taken. Among these objects are thousands of planetary systems waiting to be discovered, and recognizable by the dusty disks that surround them. The project has now identified more than 3000 objects of interest and is preparing its first paper for publication, with a list of 39 new disk candidates. Kuchner led several new initiatives to follow up the best targets from the Disk Detective project with observing programs on seven telescopes (see report by Kuchner et al.).

Kuchner’s disk modeling efforts resulted in some interesting new results as well. It is widely known that debris rings often shine brighter on the side nearest the star they orbit, a phenomenon called “pericenter glow”. Kuchner’s team discovered that at long wavelengths, this effect is reversed. So for example, recent ALMA images of the debris ring around Fomalhaut should be re-interpreted as showing “apocenter glow”.

Messengers from the Early Solar System – Comets
A major part of GCA research features observational programs designed to quantify the chemical composition of comets and to assess their potential for delivering pre-biotic organic materials and water to the young Earth and other planets. We published numerous papers on cometary science based on data acquired at infrared and millimeter wavelengths, emphasizing their composition based on primary volatiles. See GCA project reports by Charnley et al., DiSanti et al., and Villanueva et al. for this reporting period.

For most comets, measurements of primary volatiles (ices contained in the cometary nucleus) exist for only a single date or for very few dates, questioning whether such ‘momentary’ measurements represent the bulk content of the nucleus. The early discovery of the dynamically new, sun-grazing comet D/2012 S1 (ISON) was extremely rare in that it permitted planned measurements of the abundances of sublimed ices over a large range of heliocentric distances (R_h). Using high-resolution infrared spectroscopy at Keck-2 and the NASA-IRTF, the GCA Team measured production rates for H₂O and eight trace gases (CO, C₂H₆, CH₄, CH₃OH, NH₃, H₂CO, HCN, C₂H₂) on ten pre-perihelion dates that spanned a wide range in heliocentric distance (from 1.21 to 0.34 AU). This project addressed the evolution in molecular production and composition as the comet approached the Sun, undergoing successive disruptions until it disintegrated completely. A sensitive search for HDO was also obtained for comparison with other comets, and with water in Earth’s oceans (Gibb et al. (2016). Details appear in the report by DiSanti et al.

We continued a program of interferometric and single-dish mm/sub-mm cometary observations at various observatories in the US and abroad (see report by Charnley et al.). A study of volatile production in comet C/2009 P1 (Garradd) was published (Gicquel et al. 2015) and the first detections of ethanol and glycolaldehyde in a comet were reported (Biver et al. 2015). We used the Atacama Large Millimeter and sub-millimeter Array (ALMA) to determine the utility of the methanol molecule for measuring physical conditions in the coma of comet C/2012 K1 (PanSTARRS) (Cordiner et al. 2015).

Messengers from the Early Solar System – Meteorites
Team members in the Astrobiology Analytical Laboratory (AAL) published seven refereed papers in 2015 (see report by Dworkin et al.). This year, they completed analysis of the amino acid distribution across the last of the carbonaceous chondrite groups, the CK meteorites and the related R chondrites. Burton et al. (2015) showed that the proportion of amino acids present as n-ω-amino acids in the R and CK chondrites are very similar to the amino acid distributions of CO and CV chondrites and ureilites measured previously, but differ appreciably from aqueously altered CI, CM and CR chondrites. Aponte et al. (2015) demonstrated that relative abundances of amines and amino acids from the Orgueil and Murchison meteorites reflect different chemical and processing histories. Based on preliminary data by our 2015 GCA summer fellow, we are developing methods to use aromatic hydrocarbons as a probe into the organic chemistry of these same meteorites with our new NPP fellow (See report by Mumma et al. on URAA program).

Members of the Cosmic Ice Lab and the AAL completed a new project concerning heterocycle chemistry in meteorites. The first molecular targets were nicotinic acid and its isomers (Smith et al. 2015). They found that cosmic radiation acting on ices containing CO₂ and pyridine, two known meteoritic molecules, would produce quinolinic and nicotinic acids – molecules that participate in the nicotinamide adenine dinucleotide (NAD) biosynthetic pathway (see GCA reports by Hudson et al., and Dworkin et al.).

Early Mars –
Members of the AAL continued to support interpretation of organic analyses of Martian soils sampled by Curiosity rover (Surface Analysis at Mars instrument), via laboratory analog investigations. Additional details are given in the Mars report (Glavin et al.) and in Freissinet et al. (2015).

The issue of survival of biomolecules on Mars over long time intervals against exposure to cosmic radiation also received attention. Members of the Cosmic Ice Lab completed a first set of radiation experiments to measure the destruction rate of glycine in CO₂ ice. Gerakines et al. (2015) showed that glycine at a subsurface depth of 5-10 meters embedded in CO₂-ice on Mars would not survive more than 100 million years, but could survive for 2-4 Gyr if stored in H₂O-ice.

GCA members published the first global maps of HDO and H₂O ever achieved for Mars (Villanueva et al. 2015), and received major media attention. Our infrared measurements of atmospheric D/H on Mars revealed strong geographical variability and a D/H ratio in water much higher (7-fold) than that in Earth’s ocean water (VSMOW), indicative of a significant loss of water from Mars (see Report by Villanueva, Mumma et al.). They showed that Mars lost an ocean equal in volume to the Earth’s Arctic and that once covered about 20% of the planet’s surface. The strong geographic and seasonal changes of D/H on Mars today may point to the presence of multiple water reservoirs of varying sizes, which lose water to and (may) gain it from the atmosphere over time. They also reported the most sensitive search to date for sulphuretted species on Mars, by employing radio observatories (Khayat et al. 2015). This work lead to improved limits on active volcanism on Mars. Related work on active chemistry (singlet-O₂) on Mars and studies with future space assets (JWST and ExoMars/Trace Gas Orbiter) rounded out seven papers published in 2015.

Observing Exoplanet and Disk Systems –
In this reporting period, Team members published their analysis of thermal emission from WASP-33b, one of the hottest exoplanets known (Haynes et al. 2015). This massive hot planet provides the best opportunity to determine whether stratospheric temperature inversions exist in Jupiter-mass planets – a key factor in interpreting their spectra and determining their composition. The final results strongly suggest the presence of water emission at 1.4 µm due to a thermal inversion as well as emission from TiO at shorter wavelengths, making WASP-33b the first planet with a spectrally confirmed inversion. They also simulated the thermal emission spectra of WASP-33b as observed with three different JWST instruments (see report by Mandell et al.)

Team member Roberge leads a project to create high-fidelity spatial and spectral models of extrasolar planetary systems (“Finding the Needles in the Haystacks”), for use in developing future exoplanet direct imaging missions. GCA 2015 summer research associate Tiffany Jansen developed a “Haystacks” model of a planetary system with a Jupiter-mass planet at 1 AU from a Sun-twin star; an Earth-like moon orbits the Jovian (see reports by Roberge et al., and Mumma et al. on the URAA program). Team members also considered the detection of Exo-Earths and they established parameters needed for their detection (Stark et al. 2015; see report by Roberge et al.).

With Roberge, 2014 URAA Associate Brittany Miles (UCLA) analyzed two sets of spectra of the disk star 49 Ceti, obtained with HST taken 5 days apart. The first visit showed ionized carbon that was outgoing from the central star at velocities of up to -372 km/s. In the second visit, the gas was infalling towards the central star at velocities of up to 258 km/s. No other absorption lines from circumstellar gas varied between the two visits. They found that the infalling gas was within 0.2 AU of the central star at the time of transit and also appears to have a super-solar carbon-to-oxygen ratio (C/O > 1.5). This work strengthens the connection between star-grazing exo-comets and the variable gas in the 49 Ceti disk. Most interestingly, the super-solar C-to-O ratio in the gas coming directly from star-grazing exo-comets may point to a different chemical history for planet formation around this 2.7 solar-mass star (see report by Roberge et al.). This work was prepared for publication in 2015.

Advanced Instrument development –
Robotic planetary missions enable critical in situ investigations into the character, diversity and distribution of organic compounds in their native environments. Accordingly, GCA members develop novel techniques and protocols for organic molecule analysis on future flight applications (see reports by Brinckerhoff and Dworkin). As examples: Burton, Dworkin, & Mumma were instrumental in developing a partnership with Oxford Nanopore that has manifested in the Biomolecule Sequencer that will fly on the ISS this spring – a stepping stone to developing this technology for planetary astrobiology (see Dworkin report). Detection of individual oligomeric molecules through nanopore technology is also being prioritized and ramped up for performance definition (see Brinckerhoff report). An undergraduate student will work on this technology as a 2016 URAA fellow, in support of NAI objectives.

Among other efforts, Brinckerhoff et al. continue to advance laser time-of-flight mass spectrometer (TOF-MS) protocols for organics analysis on a range of potential mission scenarios, including comet, asteroid, and Titan landers. With 2015 NAI support, they demonstrated that a second pulsed laser can be used to induce fragmentation of ions in a molecular beam, much in the same way that RF excitation and collisions cause fragmentation in an ion trap, enabling MS/MS in even a highly-miniaturized TOF-MS.

Building the Community:
Undergraduate Research Associates in Astrobiology (URAA)
2015 saw the twelfth session of our summer program for talented science students (Undergraduate Research Associates in Astrobiology), a ten-week residential research program hosted by Goddard Space Flight Center and the University of Maryland, College Park (http://astrobiology.gsfc.nasa.gov/education.html). At summer’s end, each Associate reported his/her research in a power point presentation projected nation-wide to member Teams in NASA’s Astrobiology Institute, as part of the NAI Forum for Astrobiology Research (FAR) Series. The research summaries, students, and mentors are described in our Report on this program (Undergraduate Research Associates in Astrobiology).

Communication and Public Outreach:
This area saw reduced activity in 2015, owing to the re-formulation of Education responsibilities and governance within the Federal Government, and the concomitant absence of funding for these activities. However, Goddard offered a Center-wide Open House for the public in fall 2015 (the first in many years), and many GCA members staffed table displays and lab activities that communicated our research in frontier scientific areas. During this event, multiple GCA Team members also served as voluntary scientist-docents at our Astrobiology Walk, the highly-acclaimed world-class outdoor exhibit installed at the Goddard Visitor Center. In addition, GCA Team members delivered a large number of public lectures on Astrobiology-related topics to public audiences.

Since 2008, GCA collaborator Boncho Bonev (Catholic University of America) has developed custom designed curricula for four university courses, which directly integrate the research interests of the Goddard Center for Astrobiology (GCA) into undergraduate and graduate education. Understanding the motivation for, accomplishments of, and emerging challenges met by ongoing NAI research has been an element in Bonev’s courses on integrated science and general astronomy. Expanding this effort in 2015, Bonev developed and implemented a new 100-level course in introductory physics at Towson University, MD. This course was offered to non-science majors in fulfillment of General Education requirements (3 credits). Of a 24-student full roster, twelve were from underrepresented groups. Focused on the fundamentals of physics, the class included modules on solar system formation and astrobiology, implementing the approach of GCA in testing the hypothesized contribution of small bodies (comets, asteroids, meteorites) to the delivery of exogenous water and prebiotic organic matter to early Earth.