How does life begin and evolve? Is there life elsewhere in the Universe? What is the future of life on Earth and beyond? Today, NASA’s Astrobiology Institute (NAI) is not only asking these age-old questions, it is actively seeking answers. In June 2003, it selected as its first cross-disciplinary team a group of UH researchers under the direction of IfA astronomer Karen Meech. This new NAI Lead Team will investigate the astrophysical, cosmochemical, geological, and biological processes that link the history and distribution of life in the Universe to that of water.
Founded in 1997, NAI is a multidisciplinary virtual research institute headquartered at NASA Ames Research Center in California. It has 16 lead teams distributed across the United States and a large number of international partners.
The Water and Life Connection
We humans, and all life on Earth, are aqueous beings. Our cells are made mostly of a water solution packaged in membranes. The aqueous chemistry in these cells is responsible for growth, reproduction, and life. Water’s chemical properties and the way it responds to changes in temperature make it an ideal medium for biological activity, so much so that it is considered essential for recognizable life. Unlike many compounds, water expands upon freezing, and its ice floats, a property that is crucial for the persistence of aquatic habitats under freezing surface conditions. In addition to its direct role in biology, water is also a predominant determinant in the geology, geochemistry, and climate of our planet. It influenced structure and early evolution of the solar system itself, aspects of which dictate the habitability of Earth. Water and life are connected on many scales, from the interstellar medium to microbial habitats, and through many processes, astrophysical, geological, geochemical, and biological.
Cross-disciplinary Team in Hawaii
The University of Hawaii is located in a unique island setting, and because of this, has developed several centers of research excellence: the Institute for Astronomy and the School of Ocean and Earth Science and Technology (SOEST), which includes the Hawaii Institute of Geophysics and Planetology, the Department of Geology and Geophysics, and the Department of Oceanography. Our NAI team takes advantage of the UH’s Pacific location, the excellence of these specialized research units, and UH’s unique research facilities to build a new interdisciplinary research and education framework around this water theme.
Water in the Cosmos
Water is the medium in which the chemistry of all life on Earth takes place. Water is the habitat in which life first emerged and in which much of it still thrives. Water has modified Earth’s geology and climate to a degree that has allowed life to persist to the present epoch.
Cosmically, water is not uniformly abundant, and its incorporation into Earth-size planets is not necessarily constant. Water forms in the interstellar medium and in the denser molecular clouds that give rise to star-forming regions. Differences in the relative abundance of elements and their isotopes, and in the chemical reactions that take place among the gases the abundance of water in those regions. Our team will use the powerful new submillimeter and infrared facilities on Mauna Kea to quantify the presence of water ice in the interstellar clouds, and to characterize and understand the environments where water exists in space. Because of the high abundance of water ice in the interstellar medium, water has played a vital role in physical and chemical processes that have led to the formation of astrobiologically important molecules. UH NAI team members will perform cutting-edge laboratory chemistry experiments to address for the very first time the important questions of how the basic life ingredients form out of nonliving matter in extraterrestrial environments, such as molecular clouds, and the crucial role that water plays in their formation.
Comet ices preserve a chemical record of this precursor interstellar material, and detailed remote measurements of the hydrogen isotopes in these icy bodies has shown that comets contributed some, but not all, of the water to Earth’s oceans. Comets are also rich in the organic materials that are essential for life on Earth, and team members will investigate the inventory of both organics and ices in them.
We will also use laboratory equipment to study the minerals in meteorites that formed as a result of interaction with liquid water early in the solar system. These minerals preserve a record of aqueous activity in their parent bodies that provides information about the abundance and distribution of water in the primordial solar nebula. The cosmochemical record in meteorites shows that a large range of water abundance existed in the early solar system, perhaps because of the removal of water from the warm interior of the primordial nebula. Planets forming from planetary building blocks from different parts of the early solar system would have received different inventories of water. Comet and meteorite impacts played a role in helping bring this water not only to Earth, but to our neighboring planets Venus and Mars as well.
The Case of Water on Mars
Mars is the planet most resembling Earth. It contains unambiguous evidence for the activity of past and present water, and is probably the most likely to host or have hosted extant or extinct life. Studies of the history and action of water on Mars are of great importance in this regard. Our studies will model the hydrothermal and low-temperature alteration of crustal minerals and rocks by water, and team members will combine this with data from Earth observations and recent Mars missions to assess its water inventory and habitability. The detection by the Mars Global Surveyor of copious ground ice and recently carved gullylike landforms raises the possibility that liquid water is close to the surface of present-day Mars.
Water has been involved in life since its first appearance on the early Earth. The leading theories of the origin of life postulate that prebiotic chemistry occurred in low-temperature aqueous solutions that were supplied with prebiotic molecules by atmospheric chemistry, or in the hydrothermal brines produced by high-temperature water-rock interactions. The first three billion years of the drama of life on this planet were played out entirely in aquatic environments. Water is also involved in geochemical reactions that maintain surface conditions permissive of life. The presence of water significantly alters the properties of minerals in Earth’s crust and mantle, something crucial to the operation of plate tectonics. These geologic processes in turn drive many of the biogeochemical cycles important to Earth’s habitability.
Our team will investigate the water-rock chemistry in the deep oceans and its relation to habitats for life. The reaction between silicate rocks and water, particularly at high temperatures (for example, at submarine hot springs near mid-ocean ridges), produces aqueous fluids and altered mineral surfaces whose chemical imbalances are potential energy sources for life. Besides water, life also requires a source of carbon and nutrients, and an environment that is conducive to the propagation of genetic information. Many aquatic environments on Earth are challenging or “extreme” from the point of view of better understand what may limit the origin and persistence of life in aquatic habitats elsewhere in the Universe. These extreme environments include lava-water interfaces in the Hawaii Volcanoes National Park as the magma from Kilauea flows into the ocean, as well as steam geysers, high-altitude lakes (such as Lake Waiau on Mauna Kea), and field work in volcanically active Iceland. We will focus here on a comparative study of microbial biodiversity and metabolic activity in these extreme aquatic habitats.
What controls the abundance and distribution of water?
We will develop an integrated model of planetary water and its early history on Earth-like planets, which can be used to explore the time-evolution of water on the early Earth, as well as Earth-size planets whose space environment or composition differs from Earth’s. Extraterrestrial aquatic environments may be far more extreme than most encountered on Earth. Water inventories and cycles on Earth-size planets around other stars may be quite different from our own. Planetary water abundance may be a very sensitive function of the chemistry in the planet-forming nebula, the water abundance in that nebula, the presence of giant planets, and factors such as ultraviolet radiation from the central star.
The search for life and water will expand outside the solar system (such as the NASA Terrestrial Planet Finder) capable of detecting and characterizing Earth-size exoplanets and their environments. Advanced adaptive optics on Mauna Kea and facilities such as the Keck interferometer (the combined use of both Keck telescopes)will play a role
in the characterization of the water-bearing exoplanets. The 30-meter Giant Segmented Mirror Telescope now in the planning stages will allow for the detailed study of protoplanetary disks around stars and the planetary systems forming in them. It will also enable scientists to see giant gas planets orbiting other stars and to do a detailed physical investigation of their nature, properties, and chemical composition. By developing and testing models and exploring the outcomes of alternative scenarios, we seek to determine what controls the abundance and distribution of water and hypothetical aqueous habitats in other planetary systems.
Article reprinted with permission from Na Kilo Hoku Newsletter No.10, Winter 2004, from the Institute for Astronomy, University of Hawaii.