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

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 200 planets have been found around 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 Doppler Wobble, 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. The existance of a significant population of so-called "Hot Jupiters" may be telling us that planetary migration can be much more extreme that we saw in our own Solar System, or that these planetary system formed in a very different way than ours. It seems appropriate to end this class with more questions than answers, but that's where the science becomes most exciting. Recorded 2006 Dec 1 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

What is a planet? Is Pluto a planet? This lecture traces the debate on the nature of what it means to be a planet by taking an historical approach, looking at how the question has arisen with the discovery of the asteroids and later Pluto and the Kuiper Belt. Many of the issued raised at the 2006 IAU General Assembly meeting were raised two centuries before after the discovery of Ceres and Pallas. We will end with the new definition of a planet, and why Pluto is better understood as a Dwarf Planet, among the two largest objects of the class of small icy bodies of the outer solar system, than as the smallest of the planets. Recorded 2006 Nov 30 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Comets are occasional visitors from the icy reaches of the outer Solar System. This lecture discusses the orbits, structure, and properties of comets, and introduces the "dirty snowball" model of a comet nucleus. The end of class was a demo where I created a model of a comet nucleus from common household and office materials. Imagine a twisted combination of Alton Brown and Emeril Lagasse with a PhD in Astrophysics and you get the idea. We were not able to arrange for a videographer to come, but we did get some stills before the batteries died on the digital camera. The pictures are on the lecture webpage. The lecture is slightly abbreviated because we did the student evaluation of instruction surveys before class started. Recorded 2006 Nov 29 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Beyond the orbit of Neptune is the realm of the icy worlds, ranging in size from Triton, the giant moon of Neptune, and the dwarf planets Pluto and Eris, all the way down to the nuclei of comets. 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 2006 Nov 28 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Asteroids are the leftover rocky materials from the formation of the Solar System that reside mainly in a broad belt between the orbits of Mars and Jupiter. Meteoroids are fragments of asteroids or bits of debris from passing comets that occasionally pass through our atmosphere as meteors, and even more rarely survive the fiery passage to reach the ground as a meteorite. This lecture reviews the physical and dynamical (orbital) properties of Asteroids and Meteoroids, and discusses the role of Jupiter and orbital resonances in dynamically sculpting the Main Belt. Recorded 2006 Nov 27 in 100 Stillman Hall 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 physics - resonances and shepherd moons - that govern their evolution. Recorded 2006 Nov 22 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Saturn is attended by a system of 56 known moons and bright, beautiful rings. The Moon system is the focus of our attention today. Saturn has one giant moon, Titan, which is the 2nd largest moon in the Solar System, and the only one with a heavy atmosphere. On Titan, the atmosphere is mostly nitrogen and methane, but the temperature and pressure are such that methane plays the same role that water plays on the Earth: it can be either a solid, gas, or liquid. I will review tantalizing evidence from the Cassini and Huygens probes that there is, in fact, liquid methane and maybe even liquid methane lakes on Titan. Most of the other moons are ancient, icy, and heavily cratered - geologically dead worlds - but one, Enceladus, is a big surprise. 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 2006 Nov 21 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Jupiter is surrounded by a solar system in miniature of 63 known moons. Most (59) are tiny, irregular bodies that are a combination of captured asteroids and comets. The 4 largest are the giant Galilean Moons: Io, Europa, Ganymede, and Callisto. 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 2006 Nov 20 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Uranus and Neptune are the smallest and outermost of the 4 Jovian planets. While superficially similar to Jupiter and Saturn, there are substantial differences. Uranus and Neptune have smaller rocky cores surrounded by deep, slushy ice mantles and relatively thinner hydrogen atmospheres, quite different from the massive cores and deep metallic hydrogen mantles of Jupiter and Saturn. We will also ask why they appear blue, look at their internal energy and weather, and then review the properties of the Jovian planets as a group. Recorded 2006 Nov 16 in 100 Stillman Hall on the Columbus campus of The Ohio State University.

Jupiter and Saturn are the largest planets in the Solar System, and the prototype of the Jovian Gas Giant planets. This lecture focusses on the planets themselves, looking at their composition, atmospheres, and internal structures. We will leave discussion of their fascinating systems of rings and moons for next week. Recorded 2006 Nov 15 in 100 Stillman Hall on the Columbus campus of The Ohio State University.