Lecture 44: Comets

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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.

Asteroids are the leftover rocky materials from the formation of the Solar System that reside primarily in a broad belt between the orbits of Mars and Jupiter. This lecture reviews the physical and orbital properties of Asteroids, and discusses the role of Jupiter and orbital resonances in dynamically sculpting the Main Belt of Asteroids. Once again, we see how the history of the dynamical evolution of our Solar System is written in the orbits of its members. Recorded 2007 Nov 26 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

All Jovian planets have rings. We are most familiar with the bright, spectacular rings of Saturn, but the other Jovian planets have rings systems around them. This lecture describes the different ring systems and their properties, and discusses their origin, formation, and the gravitational interactions - resonances, perturbations, and shepherd moons - that govern their evolution. Recorded 2007 Nov 21 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

Saturn is attended by a system of 60 known moons and bright, beautiful rings. Today we will explore the moons of Saturn. Among the highlights are Saturn's lone giant moon, Titan, the 2nd largest moon in the Solar System and the only one with a heavy atmosphere. The atmosphere of Titan is mostly nitrogen with a little methane, but the temperature and pressure are such that methane plays the same role on Titan that water plays on the Earth: it can be either a solid, gas, or liquid. The Cassini and Huygens probes have recently shown that there is evidence of liquid methane flows and mudflats, and even liquid methane lakes as big as the Great Lakes or Caspian seas on Earth. The other moon of interest is Enceladus. The shiniest object in the Solar System, Enceladus has spectacular fountains - cryovolcanos - that spew water vapor from reservoirs created in its tidally-heated interior. This ice repaves much of the surface of Enceladus, giving it a young, shiny surface, and builds the E ring of Saturn. Recorded 2007 Nov 20 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

Jupiter has its own personal solar system in miniature of 63 known moons. Most are tiny, irregular bodies that are a combination of captured asteroids and comets, but it is the 4 largest, the giant Galilean Moons: Io, Europa, Ganymede, and Callisto, that is of greatest interest to us in this lecture. Each is a fascinating world of its own, with a unique history and properties: volcanically active Io, icy Europa which may hide an ocean of liquid water beneath the surface, the grooved terrain of Ganymede, and frozen dirty Callisto with the most ancient surface of the four. Recorded 2007 Nov 19 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.

The Ice Giants Uranus and Neptune are the outermost major planets of our Solar System. Internally they small rocky cores surrounded by deep, slushy ice mantles and shallow hydrogen atmospheres, quite unlike the massive cores and deep metallic hydrogen mantles of Jupiter and Saturn. This lecture describes their basic properties: the origin of their vivid blue/green colors, their composition, structure, and weather. At the end we'll contrast and compare their properties to those of the Gas Giants. Recorded 2007 Nov 15 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.