What is Astrobiology? “Astrobiology is the study of life in the universe. It investigates the origin, evolution, distribution, & future of life on Earth, & the search for life beyond Earth. Astrobiology addresses three fundamental questions: 1) How does life begin & evolve? 2) Is there life beyond Earth & how can we detect it? 3) What is the future of life on Earth & in the universe?” (http://astrobiology.arc.nasa.gov/) http://astrobiology.gly.bris.ac.uk/img/Astrobio-origins.jpg

Is Life Rare? Hard to image, given the potentially large number of ELPs. But we have no evidence of life outside of our own Earth. Is life common? - Life may be a natural process and part of the universe. - Universe may be full of life. - Earth is not “special”. Is life rare? - Origin of life a rare event, perhaps a singular event despite the abundance of ELPs. - Earth is “special”.

Figure 20–18 The Far Side. Fig. 20-18, p.428

Defining Life…on Earth What are the commonly cited traits? Life does stuff that distinguishes it from other stuff (for instance, computer viruses) Replicates/reproduces Uses energy to maintain “chemical disequilibria” Evolves/adapts Life does stuff longer than if it weren’t alive (“life evades the decay into equilibrium” - Erwin Schöedinger, 1944)

Defining Life…on Earth Life is a chemical system in disequilibrium with environment unique trait of replicating itself undergoes Darwinian evolution

Basic Requirements of Life Carbon Electrons Energy Water Other nutrients

Earth’s timescale Fig. 26-9, p.599 FIGURE 26-9 Complex life has developed on Earth only recently. If the entire history of Earth were represented in a time line (left), we would have to magnify the end of the line to see details such as life leaving the oceans and dinosaurs appearing. The age of humans would still be only a thin line at the top of our diagram. If the history of Earth were a year-long videotape, humans would not appear until the last hours of December 31. Fig. 26-9, p.599

Harold Urey and Stanley Miller (1953), University of Chicago

What is an Extreme Environment? Environment that threatens access to basic requirements the integrity of biomolecules

Extremophiles Genetic Diversity Metabolic Diversity Organisms living in extreme habitats on Earth Who, what, & where are they? Genetic Diversity Metabolic Diversity

Genetic Diversity For one thing, microbes constitute the vast majority of Earth’s genetic diversity. This “tree of life” is like a map of genetic relatedness. The distance (length of the lines) between one group and another indicates how genetically related they are. Plants, animals, and fungi (three of the original five kingdoms) all plot in one tiny area of the tree (as represented by Zea (corn), Homo (humans), and Coprinus (fungi)). The great majority of what is out there, in the sense of genetic diversity, is microbial life. Tree Credit: Norm Pace, U. Colorado

Macroscopic life exhibits two main strategies Metabolic Diversity Macroscopic life exhibits two main strategies Photosynthesis based on excreting oxygen Cellular respiration based on consuming oxygen (or other oxygen-containing compounds)

Microbial life exhibits these strategies and many more! Photosynthesis & cellular respiration actually performed by “kidnapped” microbes increased ability to find resources under a variety of circumstances  many more niches in which to live Hydrothermal vent bacteria (Divediscovery.whoi.edu)

Extremophiles on Earth Many examples of tolerance to extreme environments temperature pressure salinity pH desiccation radiation

Life in Extreme Environments Examples of extreme habitats & extremophile inhabitants Potential environmental stressors Some physiological adaptations

Some Categories of Organisms Adapted to Extreme Habitats - Low pH (< 5) - High pH (> 9) - No O2 Within rock High salinity High hydrostatic pressure Very cold temp. Very hot temp. Very limited H2O Acidophiles Alkaliphile Anaerobe Endolith Halophile Barophile Psychrophile Thermophile Xerophile

Deep Sea Hydrothermal Vents www.noaa.gov

Life Elsewhere Studies of life in extreme environments on Earth have led us to focus on some prime places to look for life Mars Europa (moon of Jupiter) Titan (moon of Saturn)

Offers environmental conditions where some form Habitable Worlds Photo of Jupiter with moons Europa (near Red Spot) and Callisto (left) - 2001 Cassini Spacecraft image. Offers environmental conditions where some form of life could originate or survive. (NOT whether the planet has life or not). Growing evidence for: - Habitability of Early Mars - Habitability of Oceans of Europa (moon of Jupiter) Artists’ rendition of what Early Mars may have looked like

FIGURE 26-10 (a) Meteorite ALH84001 is one of a dozen meteorites known to have originated on Mars. It was claimed that the meteorite contained chemical and physical traces of ancient life on Mars, including what appear to be fossils of microscopic organisms (b). The evidence has not been confirmed, and the validity of the claim is highly questionable. Fig. 26-10, p.601

FIGURE 23-16 The gravitational influence of Europa on the passing Galileo spacecraft shows that the little moon has differentiated into a dense core and rocky mantle. Magnetic interactions with Jupiter show that it has a liquid-water ocean below its icy crust. Heat produced by tidal heating could flow outward as convection in such an ocean and drive geological activity in the icy crust. Fig. 23-16, p.518

FIGURE 15-2 An artist’s conception of our Milky Way Galaxy, seen face-on and edge-on. Note the position of the sun and the distribution of globular clusters in the halo. Only the inner halo is shown here. Fig. 15-2, p. 307

FIGURE 26-11 The life zone around a star (green) is the region where a planet would have a moderate temperature. M stars are not good candidates because they are cool and their life zone is small. F stars have a large life zone but evolve too quickly to allow the rise of complex life. K and G stars like our sun seem the best candidates in a search for intelligent life. Fig. 26-11, p.602

Chapter Opener: The characteristics of almost 100 planets discovered around nearby Sun-like stars.

Milky Way galaxy has 100 billion (100,000,000,000) stars. Hubble Space Telescope image of Sedna- takes 10,500 years to circle the Sun! Life in the Universe Our Solar System has planets, dwarf planets, moons, asteroids, comets, and interplanetary dust. Milky Way galaxy has 100 billion (100,000,000,000) stars. Universe has 100 billion (or more) galaxies. Many stars have planets. Some like Jupiter and Saturn. Some may be like Earth. Potential for a large number of Earth-like planets (ELPs). Interplanetary Dust Particle -10 µm across made by dying and exploded stars

Table 26-1, p.607

FIGURE 26-14 Radio noise from various sources makes it difficult to detect distant signals at wavelengths longer than 30 cm or shorter than 1 cm. In this range, radio emission from H atoms and from OH marks a small wavelength range dubbed the water hole, which may be a likely place for communication. Fig. 26-14, p.606

Arecibo Radio Observatory (Puerto Rico) 305-meter diam. Phoenix Project 1995-present survey of 1000 nearby stars at freq. of 1000-3000 MHz Project SERENDIP 1979-present “piggy-back” survey using various radio telescopes. Arecibo observations (1992-present) scan each sky pointing every 1.7 seconds over 168 million channels centered on 1420 MHz. This enormous data load is farmed out to SETI@home

(Hat Creek, California) Allen Telescope Array (Hat Creek, California) 350 6-meter dishes (2008) This privately-funded (mostly by Microsoft co-founder Paul Allen) telescope will be primarily used by the SETI Institute for SETI surveys. It will be able to scan a wide field of view (2.5 degrees) over a wide frequency range (0.5-11.2 GHz) at each pointing. Over 50 dishes are already in place and taking data for several projects.