Steven J. Dick

The landscape of life

Earth is a planet that exhibits an immense biomass and an incredible biodiversity. Yet, the question arises as to whether the diversity as observed on Earth reflects the limits of life or whether life elsewhere in the universe could manifest an even greater diversity. To examine the question further, I review some of the limits of life as observed on Earth and then ask what specific adaptation mechanisms could reasonably occur on other planets and moons to extend the limits of life to environmental conditions usually not found on our planet. As we currently do not have any convincing evidence for the existence of extraterrestrial life, these extensions must remain in the field of scientific speculation. Yet, given the enormous creativity and flexibility exhibited by the organisms we know from our planet, it would be odd if life could not adapt to some of the conditions exhibited on other planets. Thus, my conjecture is that life in the universe would exhibit a much larger variety of forms and functions than life on Earth. The landscape of life provides important basic information when preparing for the discovery of extraterrestrial life. We are familiar with life on Earth, but life might be so strange on another world that we might not recognize it; especially since there is not even a commonly accepted definition of what life actually is. Thus, it is important to be not too constrained and Earth-centric if we do not want to take the risk to miss it even if an organism is in plain sight. This applies to all life, from microbial to more complex, and also to signals from technologically advanced civilizations. Thus, open-mindedness for this quest is an imperative. The range of life on Earth The conditions under which life can persist are incredibly broad; however, the range under which life can originate is likely to be much smaller. Since the origin of life is an unsolved puzzle, I will focus on the persistence of life, particularly under which environmental stresses life exists on Earth. The life most familiar to us, consisting of organisms that live at conditions similar to those we are accustomed to, is generally referred to as mesophilic life. However, during the evolution of life, organisms, particularly microorganisms, conquered nearly all available environmental niches on and within our planetary crust.

Current approaches to finding life beyond Earth, and what happens if we do

Three broad approaches exist in the search for extraterrestrial biology: (1) discover life in the Solar System by direct exploration; (2) find chemical signatures for biology in the atmospheres of exoplanets; or (3) detect signals (radio or optical) transmitted by intelligent beings elsewhere. In this chapter I describe each of these approaches, and then elaborate the multiple ways that we might learn of technologically competent civilizations. I also discuss why societys immediate reaction to the discovery of extraterrestrial intelligence would be less dramatic than often assumed. In all three cases the search for life beyond Earth is the ultimate remote sensing project. With few exceptions (such as sample return missions) this is exploration at a distance. While some reconnaissance is done by spacecraft, the majority of the effort consists of sifting through information brought to us in a storm of photons, either optical or radio. Introduction The idea of extraterrestrial biology is hardly new, with written speculation on the subject dating back two millennia and more (Dick, 1982). The first scientific searches are more recent, beginning with Johannes Kepler who, observing the Moon in detail through an early telescope, thought he recognized features carved by rivers. These, he reasoned, were sure signs of biology. Kepler also believed that craters were the surface manifestations of underground cities constructed to protect the citizenry from the relentless sunshine of the two-week lunar day (Dick 1982, 75–77; Basalla 2006, 21). These pioneering observations were plagued by naive, anthropocentric assumptions and a lack of information on the true environments on these worlds. Such bugaboos continued to affect attempts to find cosmic company for centuries, extending to the enthusiastic study of Mars by astronomer Percival Lowell. In a series of books, lectures, and articles extending from 1894 until his death in 1916, Lowell proclaimed the existence of a vast, hydraulic civilization on the Red Planet (Crowe 1986; Dick 1996). Just as Kepler had done, he appealed to morphological evidence – straight-line features that he interpreted as canals – to back up these assertions. Lowells claims were spurious, although one could argue that the falsity of his discoveries was due more to poor observation than poor interpretation (the trap that had snared Kepler). If the linear features described by Lowell actually existed, they would have been compelling evidence for intelligent beings.

The philosophy of astrobiology: The Copernican and Darwinian philosophical presuppositions

Contrary to common wisdom, science is not exclusively defined by its methods and theories, nor is it constituted only by substantiated empirical hypotheses. Rather, philosophical presuppositions are also a crucial part of the scientific endeavor. Astrobiology, like any scientific field that seeks to learn and understand nature, rests on such philosophical presuppositions. We do not experience nature as a clean slate, as the tabula rasa upheld by the seventeenth–eighteenth-century Empiricists. Philosophical presuppositions guiding science are general, universal claims about nature that transcend limited experience. For example, the notion that natural laws necessarily hold not only on our planet or in our galaxy but in the universe at large cannot be proved or disproved empirically. Nevertheless, it is on the basis of the universal applicability of natural laws that astrobiological research is conducted. Likewise, any other branch of the natural sciences could not function and advance without this principle. Furthermore, philosophical presuppositions express general guiding evaluations of reality that by definition are not open to observation or experience. The claim that nature was created and designed by an intelligent designer or the denial of this claim cannot be empirically settled. Yet, it is the notion that natural processes depend on natural causes and not on supernatural purposes which guides science. Although the status of philosophical assumptions in science clearly differs from that of theoretical-empirical claims, these two elements are deeply connected. The interaction between the theoretical-empirical and the philosophical becomes apparent when science is examined historically. I argue that this interaction, shaped to a large extent by social and cultural factors, has resulted in the last few centuries in the establishment of the evolutionary naturalistic worldview. The major defining feature of this worldview is the rejection of supernatural teleology as necessary for the scientific study and understanding of nature. Philosophical presuppositions of astrobiology The natural sciences of today function within the framework of the naturalistic worldview. It is the robustness of this framework which provides validity also to branches of science that are still at the stage of establishing their fundamental data, notably the study of the origin of life on Earth and astrobiology. It has been claimed that the problem of the origin of life, yet unsolved, is the “soft underbelly of evolutionary biology” (Scott 1996).

Introduction: Astrobiology and society

The search for life in the universe, once the stuff of science fiction, is now a robust research program with a well-defined roadmap and mind-bending critical issues (Des Marais et al., 2008; Dick, 2012; Dick and Strick, 2004; Sullivan and Baross, 2007). The science of astrobiology – and there is no longer any doubt it is a science, simplistic slogans about “a science without a subject” notwithstanding – is funded by NASA and other institutions to the tune of tens of millions of dollars of ground-based research, not to mention the hundreds of millions spent on space-related missions. Biogeochemists study extremophile life on Earth, biologists study the origins of life, a bevy of spacecraft have orbited or landed on Mars, others have found potentially life-bearing oceans on Jovian and Saturnian moons as well as organic molecules on Titan, and the Kepler spacecraft has discovered thousands of planets beyond the solar system – all just a prelude to future studies. Recent US Congressional hearings on astrobiology indicate it is a hot topic in the policy arena (United States Congress, 2013 and 2014). And international interest is also strong, particularly within the European Space Agency. Although no life has yet been found beyond the Earth, the search for such life has arguably been a driver of the space program since its inception, has inspired multidisciplinary research on Earth, and is the subject of great popular interest that shows no signs of abating. As this volume illustrates, it is also a perennial theme in science fiction literature, igniting dreams of other worlds. Given both scientific and popular interest in astrobiology it is important for scholars, practitioners, and policymakers to examine the societal implications of discovery in the event of success. Substantial studies have been undertaken on the societal impact of other scientific endeavors such as the Human Genome Project, biotechnology, nanotechnology, and spaceflight. Even closer to astrobiology’s core interests are planetary protection protocols, which are certainly studies of potential impact since one of their goals is to prevent a catastrophic “Andromeda Strain” scenario, in the terminology of Michael Crichton’s 1969 novel. We should be under no illusion that millions of dollars are going to be spent to study the implications of finding extraterrestrial life – not, that is, until it is discovered, in which case the floodgates may open as they did with the Human Genome Project, now in the form of a practical problem rather than a theoretical one.