Lecture 02: Astronomical Numbers

A new podcast, Astronomy 141, Life in the Universe, is available for those interested in continuing an exploration of topics in modern astronomy.

Are we alone in the Universe? This lecture explores the question of how we might go about finding life on planets around other stars. Rather than talking about speculative ideas, like the Drake Equation or SETI, I am instead taking the approach of posing it as a problem of what to look for among the exoplanets we have been discovering in huge numbers in the last decade. I describe the basic requirements for life, and how life on Earth is surprisingly tough (extremophiles). I then give a definition of the Habitable Zone around a star, and present the Goldilocks Problem of how a planet must be neither too hot, too cold (for liquid water) or too big or too small to be hospitable to life. From there I then review the problem of how to go about finding Earth-like planets (Pale Blue Dots) around other stars, and if we do find them, what spectroscopic signatures of life, called biomarkers, we can look for to see if they have some form of life like we understand it on them. Recorded on 2007 Nov 30 in 1000 McPherson Lab on the Columbus campus of The Ohio State University. This is the final lecture for Autumn Quarter 2007.

Are there planets around other stars? Are there Earth-like planets around other stars? Do any of those harbor life? Intelligent life? We'd like to know the answers to all of these questions, and in recent years we've made great progress towards at least answering the first. To date, more than 260 planets have been found around more than 200 other stars, most in the interstellar neighborhood of the Sun, but a few at great distance. This lecture reviews the search for ExoPlanets, discussing the successful Radial Velocity, Transit, and Microlensing techniques. What we have found so far are very suprising systems, especially Jupiter-size or bigger planets orbiting very close (few hundredths of an AU) from their parent stars. Recorded 2007 Nov 29 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

Comets are chance visitors from the icy reaches of the outer Solar System. In this lecture I describe the properties of comets, their historical importance, and introduce the "dirty snowball" model of a comet nucleus. At the end of class I created a model of a comet nucleus from common household and office materials, unfortunately I could not arrange for a videographer in time. Recorded 2007 Nov 28 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

Beyond the orbit of Neptune lies the realm of the icy worlds, ranging in size from Neptune's giant moon Triton and the dwarf planets Pluto and Eris, all the way down to the nuclei of comets a few kilometers across. This lecture discussed the icy bodies of the Trans-Neptunian regions of the Solar System, discussing the basic properties of Triton (the best studied such object), Pluto, Eris, and the Kuiper Belt, introducing the dynamical families of Trans-Neptunian Objects that record in their orbits the slow migration of Neptune outwards during the early history of the Solar System. The Kuiper Belt is the icy analog of the main Asteroid Belt of the inner Solar System: both are shaped by their gravitational interaction with giant gas planets (Jupiter for the asteroids, Neptune for the KBOs), and are composed of leftover raw materials from the formation of their respective regions of the Solar System. Recorded 2007 Nov 27 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.