Astronomy 141 - Life in the Universe - Autumn Quarter 2009

What are the observed properties of stars? This lecture is a quick review of the basic observational properties of stars, introducing luminosity, spectral classification, the luminosity-radius-temperature relation, and the Hertzsprung-Russell (H-R) diagram. This sets up the empirical basis of subsequent lectures on the lives and deaths of stars. Recorded live on 2009 Nov 9 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

Why is the Earth habitable today but Venus and Mars not? This lecture explores the question of planetary habitability from the perspective of the stability of liquid water on the surface of planetary bodies. We will see how the amount of sunlight and the greenhouse effect in the atmosphere combine to create a classic Goldilocks problem: whether or not a planetary surface has stable liquid water is a question of not being too hot or too cold. This defines the Habitable Zone for the present-day Sun. However, the size of a planet also plays a role, and we will expand the concept of habitability to include the type of atmosphere a planetary body can or cannot retain. Finally, because the Sun changes brightness slowly over its lifetime, the location of the habitable zone is time-dependent. We will define the Continuous Habitable Zone, and discuss implications, and limitations, of the idea of habitable zones, looking forward expanding our search for life to worlds around other stars. Recorded live on 2009 Nov 5 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

Among the 61 known moons of Saturn, two stand out: Enceladus and Titan. Giant Titan is the only moon in our Solar System with a substantial atmosphere, composed of nitrogen and methane, dense enough to maintain a weather cycle with methane analogous to the water cycle on Earth, even including great lakes of liquid methane and ethane at the poles. Enceladus has fountains of water vapor and ice particles that coat its surface in fresh ices, and indicates the presence of liquid water beneath its icy surface. Is this just pockets of tidal-heated water, or hints of a deep global liquid water ocean. I will describe new results on these two children of Saturn, and the possibilities they have for finding life, or life-like conditions, elsewhere in our Solar System. Recorded live on 2009 Nov 4 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

The four large Galilean Moons of Jupiter seem unlikely places to look for life; at first glance they should be cold, dead, icy worlds. Instead we find tremendous geological diversity, and two big surprises: volcanically-active Io, and icy Europa. Io is the most volcanically active world in the Solar System, heated by tides from Jupiter. Europa is even more surprising: its icy surface is young, with few impact craters and extensive signs of recent repaving by liquid water. Even more surprising is the distinct possibility that underneath Europa's ice is a deep liquid water ocean, heated by tides from Jupiter. We will review the evidence for Europa's liquid sub-ice ocean and look at its potential as an abode of life. If there is life to be found anywhere in the Solar System beyond Earth, beneath the ice of Europa may be the best place to look. Recorded live on 2009 Nov 3 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

Is there life on Mars? We begin with a brief historical survey of the idea of inhabitable Mars, from Herschel to Lowell, and look at how the idea of Mars and Martians is deeply embedded in the popular culture. We then turn to spacecraft explorations of Mars, and how they have changed our view of the Red planet. We will discuss the on-going search of Martian life, past and present, particularly the Viking 1 and 2 experiments, the Allan Hills Meteorite controversy, Mars Methane, and recent important results from the Phoenix lander. We'll end by briefly noting future directions in Mars exploration. Recorded live on 2009 Nov 2 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

For many, the most likely place in the Solar System to search for life beyond the Earth is Mars. This lecture describes the properties of Mars, a desert world with a thin, dry, cold carbon dioxide atmosphere. I will review evidence that has begun to point unequivocally to the conclusion that Mars had flowing and standing liquid water on its surface in the past, perhaps during the first billion years or so. If Mars had a warm, wet past, did life also get a start there? Recorded live on 2009 Oct 30 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

Having completed our tour of the Solar System, we now turn to a discussion of the requirements for life, and where those requirements might be satisfied elsewhere in the Solar System. Some - energy, complex chemistry, and liquid water - seem obvious, but they are not the only possibilities or considerations. At the end, we will have a short list of possible places to look, some expected, others surprising. Recorded live on 2009 Oct 29 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

We turn our attention to the Giant Planets of the outer Solar System: the gas giants Jupiter and Saturn, and the ice giants Uranus and Neptune. We will review their structure and properties, and then examine their systems of moons, with special attention to the giant moons. While the Jovian planets themselves seem unlikely places to hunt for life in our Solar System, a few of their largest moons may be more promising than appears at first sight. We'll explore this further in subsequent lectures in this unit. Recorded live on 2009 Oct 28 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

We follow our tour of our Solar System with an in-depth comparison of the Terrestrial Planets. In particular, we want to contrast and compare their geological and atmospheric histories. This will inform our inquiry into whether or not we expect to find life on these worlds. Recorded live on 2009 Oct 27 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

This first lecture of Unit 4 - Life in the Solar System - is a quick tour of our Solar System reviewing the planets, dwarf planets, moons, and small bodies that make up our celestial home. This lecture will introduce many of the places we will be considering in detail over the next two weeks, and which we'll find around other stars. Recorded live on 2009 Oct 26 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

We end our exploration of life on the Earth with a look at death in the fossil record. This lecture looks at the role asteroidal impacts have played in the history of the Earth, and their possible role in mass extinction events in the fossil record. We will discuss near-earth asteroids, historical impacts, and the K-T event in which a massive asteroid impact caused a mass extinction of species that included all non-avian dinosaurs among its victims, opening up the biosphere to the dominance of mammals. We'll look at other mass extinctions during the past 500Myr, and talk about whether extinction-class impacts are in our future. Recorded live on 2009 Oct 22 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

In this lecture we step back and look at the history of life on Earth from the first signs of life at start of the Archaean Eon 3.5 billion years ago to just up to the present day. We will review the appearance of photosynthesis and the rise of oxygen in the atmosphere in the Proterozoic, the appearance of the first eukaryotes and sexual reproduction, and the Cambrian explosion of plant and animal species at the start of the Phanerozoic Eon, and briefly review the changes in life to the present day from the Cambrian Explosion to the colonization of land by plants and then animals. Most of the lecture will be where most of the time was spent, in the early, microbiological Earth. Recorded live on 2009 Oct 21 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

How did life arise from non-life? Frankly, we don't know, but current experimental work is aimed at trying to understand how it might work in biochemical terms. This lecture sets out the problem of "abiogenesis", and describes our current thinking about the likely origins of life on Earth. We will review the classic Miller-Urey experiment, and look at its insights and limitations, discuss meteoritic sources of amino acids, and the basic requirements needed for protolife. I will then describe in outline two scenarios that are active areas of origins research: the RNA World model and the Metabolism First model. Finally, I will very briefly mention Exogenesis and Panspermia, which don't really address the problem of abiogenesis so much as move it elsewhere. Recorded live on 2009 Oct 20 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

What are the first recognizable forms of life that we find in the geological record? How far back can we go in geological time and still find life? This lecture reviews three lines of evidence that have emerged in recent years to suggest that life may have emerged very early on the young Earth, perhaps within a few hundred million years of the end of the epoch of heavy bombardment. I will describe fossil stromatolites, microfossils, and carbon isotope data that are used to explore these questions. Recorded live on 2009 Oct 19 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.

Extremophiles are organisms that are adapted to survive in extreme environments. This lecture describes the challenges that extremes of heat, cold, acidity, salinity, and radiation pose to organisms, and show examples of how evolution has nonetheless allowed some organisms to adapt to not just survive but thrive in such extreme conditions. Finally, we will explore the possible limits of life on Earth, and find that while you can make things pretty extreme and still have organisms adapt, you reach the limit if there is no water. Rather than being oddballs, these organisms give us important insights into the origins of life on Earth, and widens the possibilities for life on other worlds. Recorded live on 2009 Oct 16 in Room 1005 Smith Laboratory on the Columbus campus of The Ohio State University.