Planetary Inventory of Organics and Water, and the Origin of Life

Introduction

A research theme that runs through a number of the current NAI partner teams is that of examining the source of chemical complexity in space (the ISM, protoplanetary disks, meteorites), the chemical evolution of these materials into organics of astrobiological interest (amino acids, nucleobases, sugars, etc.) and the delivery of such organics (and water) to planets where they may play a role in the origin and early evolution of life.

Many of the activities, past and current, of the NASA Ames and NASA Goddard NAI Teams are particularly focused on using laboratory and observational techniques to establish the inventory of astrobiologically relevant materials that may be formed in space by abiotic processes. One aspect of this work has been the simulation of astrophysical environments and study the chemistry that can occur in them. Cold environments that contain mixed molecular ices that are exposed to ionizing radiation are of particular interest. These include environments like interstellar dense molecular clouds, protostellar disks, and the surfaces of out Solar System objects like comets, planetary moons, and Kuiper Belt Objects.

Past work, much of it done by members of the NASA Ames and NASA Goddard Teams, has shown that the irradiation of ices in these environments is expected to abiotically produce a host of astrobiologically interesting compounds that includes amino acids, sugars and related compounds, nucleobases, quinones, and amphiphiles (e.g. Dworkin et al. 2001; Bernstein et al. 2002a,b; Nuevo et al. 2014). Such materials, if delivered to the surfaces of newly formed planets, may play key roles in the origin and early evolution of life on them.

The current work being done under this synergy theme addresses the origin of amphiphiles. These are a class of chemical compounds that have the interesting ability to self-assemble into vesicular structures. These types of compounds may have been found in some primitive meteorites (Deamer & Pashley 1989) and are know to be produced when realistic astrophysical ice analogs are exposed to ionizing radiation (Dworkin et al. 2001)

The complex organic materials created when simple, astrophysically relevant ice mixtures are exposed to ionizing radiation contain compounds that spontaneously self-organize when place in liquid water.  The image on the left was taken in visible light and shows an example of the structures that result.  The image on the right is of the same field of view but illuminated with UV light and demonstrates that these structures contain compounds that are fluorescent (Dworkin et al. 2001). The complex organic materials created when simple, astrophysically relevant ice mixtures are exposed to ionizing radiation contain compounds that spontaneously self-organize when place in liquid water. The image on the left was taken in visible light and shows an example of the structures that result. The image on the right is of the same field of view but illuminated with UV light and demonstrates that these structures contain compounds that are fluorescent (Dworkin et al. 2001).

Since amphiphiles can spontaneously self-organize into vesicles, their delivery to the Earth may have played an important role in the early stages of the origin of life (Deamer et al. 2002).

Despite the suggestion that amphiphiles exist in meteorites and can be created abiotically by exposing mixed-molecular ices to ionizing radiation, we currently know very little about the nature and diversity of their structures. We also know very little about the characteristics of the vesicular structures they make, i.e., how their stability is affected by pH, salinity, the presence of other molecules, and so on.

Activities
2015-16

For the NAI CAN7 cycle, the NASA Ames, NASA Goddard, and MIT NAI teams are working together to better understand this potentially important class of compounds. As part of the project, the NASA Ames team are using their cryovacuum systems to irradiate astrophysically relevant ices and produce organic residues that contain amphiphiles. The three teams will then use to a variety of analytical techniques to try to determine the chemical nature of the population of amphiphiles and the physical properties of the vesicles they make. The same techniques will be used to study the amphiphiles found in meteorites. This will allow us to compare the laboratory and meteoritic amphiphiles to determine the extent of their similarities/differences. This will also allow us to compare both of these populations to the materials that make up modern cell membranes.

The NASA Ames and MIT teams have gathered some additional resources to assist with this effort. Dr. Michel Nuevo of NASA Ames has been awarded an NAI DDF grant to assist with the work done on this project at NASA Ames.

AT MIT, Dr. Roger Summons, PI of the Complex Life Team, has been awarded a grant by the Simons Foundation Collaboration on the Origins of Life (SCOL) to fund Dr. Heather Throckmorton to work on this project at MIT.

References:

Bernstein, M. P., Dworkin, J. P., Sandford, S. A., Cooper, G. W., & Allamandola, L. J. (2002a). Racemic Amino Acids from the Ultraviolet Photolysis of Interstellar Ice Analogues. Nature 416, 401-403.

Bernstein, M. P., Elsila, J. E., Dworkin, J. P., Sandford, S. A., Allamandola, L. J., & Zare, R. N. (2002b). Side group Addition to the PAH Coronene by UV Photolysis in Cosmic Ice analogs. Astrophys. J. 576, 1115-1120.

Deamer, D. W. & Pashley, R. M. (1989). Amphiphilic components of the Murchison carbonaceous chondrite: surface properties and membrane formation. Orig. Life Evol. Biosph. 19, 21–38.

Deamer, D., Dworkin, J. P., Sandford, S. A., Bernstein, M. P., & Allamandola, L. J. (2002). The First Cell Membranes. Astrobiology 2, #4, 371-381.

Dworkin, J. P., Deamer, D. W., Sandford, S. A., & Allamandola, L. J. (2001). Self-Assembling Amphiphilic Molecules: Synthesis in Simulated Interstellar/Precometary Ices. Proc. Nat. Acad. Sci. USA 98, 815-819.

2015 Director's Discretionary Fund Projects

Determining the Composition of Amphiphiles in the Organic Residues Produced from the UV Irradiation of Astrophysical Ices
Lead Investigator: Michel Nuevo (NASA Ames Team, Bay Area Environmental Research Institute)
Co-investigators: Scott Sandford (NASA Ames Team), Roger Summons (MIT Team)

Self-assembling vesicles spontaneously form when the organic fraction of carbonaceous chondrite meteorites are dissolved. Laboratory simulations have demonstrated that all the organics found in meteorites can be formed from the ultraviolet irradiation of ice mixtures. This proposal aims to carry out the first systematic analysis of laboratory ice irradiation organic residues to determine the nature and composition of the vesicle-forming amphiphilic compounds present. The results will be discussed in the context of the origin of life. This foundational proposal brings together two NAI teams at Ames and MIT, with likely extension to the Goddard team, and fosters a unique synergy within the Planetary Inventory of Organics and Water and the Origin of Life theme.