The goal of the research carried out in the New York Center for Astrobiology is to understand the cosmic history of the materials and processes that lead to the development of life. Tracing the evolutionary pathway from atoms to life involves study of the formation of new molecules within interstellar clouds, the evolution of these clouds as they condense to form new solar systems, and the mechanisms by which they are delivered and combined on planets like Earth and Mars to form suitable environments for life. Our research will also attempt to identify biomarkers that may be used to identify life elsewhere, e.g., on Mars.
To accomplish this goal requires a highly multidisciplinary approach to our research. Our activities include several distinct but related research projects:
Interstellar Origins of Preplanetary Matter
Organic molecules that originated in interstellar space are known to exist in our solar system: they are detected in meteorites remnants from the time when the planets were formed that fall to the Earth today. This part of our investigation seeks not only to understand how these molecules came to exist, but also to explore how universal they are: do the same processes lead to a rich supply of organic molecules in other emerging solar systems in other parts of our Galaxy?
To answer these questions, we are using telescopes on Earth and in space that are designed to obtain data in the infrared region of the electromagnetic spectrum. The observations enable us to determine not only what molecules are present but also to explore their evolution. We find, for example, subtle difference in the spectral features observed in a cold interstellar cloud compared with a warm “protoplanetary” disk surrounding a newly formed star. The data can be used to constrain theoretical models of the physics and chemistry of the clouds and disks, allowing us to identify key chemical pathways and thus to characterize their organic inventories. Analogs of the young Sun will be studied in a variety of star-forming environments, enabling us to compare possible scenarios for the birth of our own solar system and to examine the range of initial conditions that might give rise to habitable planets elsewhere. Our research will also lead to important comparisons between interstellar processes and the remnants of planet formation (the comets, asteroids and meteorites) in our solar system. Interplanetary materials that fall to Earth are known to contain key biomolecules such as amino acids and sugars, and our research will shed light on how they are formed and what significance they may have for the origin of terrestrial life.
Processing of Precometary Ices in the Early Solar System
Conditions and processes in interstellar space endow new planetary systems with many of the simple molecules needed to build life. The solar nebula and other protoplanetary disks form by gravitational collapse of a dense core within an interstellar cloud. A key question to be addressed in this section of the research is the extent to which prebiotic molecules of interstellar origin were modified during the formation of the solar system. Until recently, it was widely believed that interstellar molecules emerged intact from this process. However there are now good reasons to doubt this conventional wisdom. The spectra of ice features toward regions of low-mass star formation imply that the ices have been thermally processed, i.e., they have been subject to transient heating, the most likely cause of which is heating by shock waves.
Researchers in our Center will use supercomputer simulations and mathematical analysis to produce theoretical models of shock waves in the early solar system. These models take as their starting point the probable composition of the dust and ices in the precursor interstellar cloud, as determined by observations discussed in the previous section, and predict how they are modified by shocks of various types and intensities. The models will lead to predictions that can be tested by observation of young stars, using major NASA facilities such Spitzer, SOFIA and the James Webb Space Telescope.
Pathways for Exogenous Organic Matter to the Early Earth and Mars
Comets are rich in ices and organic molecules and were almost certainly important sources of biogenic elements to early Earth and Mars. However, because of their relatively high encounter speeds (averaging some 50 km/s), comets may be relatively inefficient sources of organic compounds to these planets. In contrast asteroids, although less rich in organics, may have been more important because their much lower encounter speeds (average 15 to 20~km/s) allow significant quantities of unaltered material to reach the surfaces of the terrestrial planets. A major question we propose to investigate is the relative contributions of the thermally-altered asteroidal organics versus relatively pristine cometary organics to early Earth and Mars.
The planned research will study the conditions within asteroidal bodies that formed, altered and destroyed organic compounds. We will identify the sources and quantify the rates of organic-bearing asteroidal material delivered to the early Earth and Mars. Our research requires acquisition of telescopic spectra of selected asteroids. In our previous work, we have developed a data-analysis procedure that allows the capabilities of the spectrometer on NASA's Infrared Telescope Facility to be exploited to the fullest, resulting in spectra of extraordinary quality that permit detailed investigations of asteroid mineralogy and thermal histories. Characterizations of the target asteroids will be derived from analysis of the spectra. We will study compositional variations across the asteroid belt, especially in regions which most effectively provided material to the early Earth and Mars, and estimate the abundance of meteoroids and interplanetary dust particles that delivered organic molecules to the these planets.
Impact History in the Earth-Moon System
The influx of interplanetary debris onto the early Earth may have been beneficial to life as a source of essential raw materials, but it also represents a serious hazard. Large crater-forming bolides must have been ubiquitous in the early solar system, as craters are seen on all ancient solid surfaces from Mercury to the moons of the outer planets. The Earth is anomalous in showing few impact craters for reasons that are well understood: geologic activity and erosion removes them on timescales much shorter than the age of the solar system. In contrast, lacking an atmosphere and significant tectonic activity, the Moon retains an ancient record of past impacts. As the Earth’s nearest neighbor, the Moon is therefore being studied as a proxy for the Earth. Researchers in the Center are working to reconstruct the bombardment history of the Moon to investigate the flux of impacting bodies as a function of time, to establish the epoch when the flux of sterilizing impacts declined and the Earth became habitable in the face of this threat. For example, it will be possible to distinguish between “late heavy bombardment” and “monotonic decline” hypotheses for the rate of impacts over time.
The lunar samples gathered by the Apollo astronauts have been on Earth for several decades now, but they still represent a vital resource for research. With modern geochemical and geochronological techniques that were not available more than a decade ago, the chemical memory of past impacts can be extracted and read. Glass spherules formed by the heat of impact will be identified and investigated. By examining the age distribution of samples from different lunar landing sites it will be possible to reconstruct the impact history of the Moon, and hence, of the Earth.
Vistas of Early Mars: In Preparation for Sample Return
Mars is a major target for Astrobiology, arguably the most probable body in our solar system beyond the Earth to host life. Past and current NASA and ESA missions have demonstrated beyond reasonable doubt that water was once present on the Martian surface. Indeed, it is probable that Mars was relatively “warm and wet” around the time that life was developing on Earth some 3.5 billion years ago.
In the next decade, NASA plans a Mars Sample Return mission. The samples will be gathered from carefully selected landing sites that appear most promising as environments for present or past life. The ability to analyze in the laboratory real samples of Martian soil from known locations on the planet will be an unprecedented development in Mars exploration (what ever the result!). To better prepare for the selection and detailed analysis of such samples, members of the Center will investigate terrestrial analogs of minerals known to exist on the Martian surface from data obtained by previous missions. We have designed laboratory experiments to assist in the identification and characterization of past habitable environments on Mars, and to support deductions about the existence of Martian life. We will evaluate the potential of likely Martian minerals not only to record the timing of aqueous events but also to test for the existence of life through preservation of isotopic biosignatures.
The Environment of the Early Earth
Understanding the chemical state of the earliest atmosphere and ocean is critical to any theory of the origin of life on Earth. It is widely accepted that primitive life was established 3.5 billion years ago, and may have existed much earlier, but investigations of the earliest epoch of the Earth’s history are greatly hindered by the general lack of a preserved geological record: the oldest rocks are substantially altered or destroyed over time by weathering and recycling of the crust. However, some chemical and geologic markers of early Earth still remain to provide a glimpse into the distant past. We have developed techniques that will enable an experimental assessment and characterization of the potential for zircons and other minerals surviving from the Hadean eon to retain chemical memories of prevailing conditions at the time of their formation. The goal is to provide a window into the chemical environment of Earth's near-surface and the early hydrosphere and atmosphere, and hence to better assess the suitability of early Earth as a host for complex organic molecules and life itself.
Prebiotic Routes to RNA on the Early Earth and Mars
The “RNA World” hypothesis is the current paradigm for the origins of terrestrial life. This hypothesis proposes that the first life on Earth was based on RNA instead of DNA, and that RNA subsequently catalyzed life based on DNA. Our research is aimed at testing a key component of the paradigm, i.e., the efficiency with which RNA molecules form and grow under realistic conditions.
Catalysis on montmorillonite clays has long been regarded as a feasible mechanism for abiotic production and polymerization of key biomolecules such as RNA on early Earth. Research by James Ferris and others has shown that RNA chains some 50 units long can be formed in the laboratory from activated RNA monomers using montmorillonite as a catalyst. Future research will investigate the reactions of these RNAs to generate the more complicated RNAs that may have been essential in the first life. In addition, we will test other clay minerals, similar to montmorillonite, which may catalyze the formation of RNA from starting materials other than activated RNA monomers. We will also investigate how widespread catalytic clays are likely to have been on the early Earth and on Mars.
|Home | People | Research | Programs | Outreach | Resources | Seminars | WAMC Interviews | Contact|
New York Center for Astrobiology
|Rensselaer Polytechnic Institute | About RPI | Virtual Campus Tour | Academics | Research | Student Life | Admissions | News & Events
Copyright ©2008 Rensselaer Polytechnic Institute