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

Astronomy 141 Podcast Teaser

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.

Lecture 46: ExoPlanets - Planets around Other Stars

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.

Lecture 45: Is Pluto a Planet?

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.

Lecture 44: Comets

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.

Lecture 43: Icy Worlds of the Outer Solar System

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.

Lecture 42: Asteroids and Meteoroids

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.

Lecture 41: Planetary Rings

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.

Lecture 40: The Saturn System

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.

Lecture 39: The Moons of Jupiter

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.

Lecture 38: Uranus and Neptune

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.

Lecture 37: Jupiter and Saturn

Having completed our tour of the terrestrial planets, we want to step
back and compare their properties.  In particular, we want to look at
the processes that drive the evolution of their surfaces, their
interiors, and their atmospheres.  Recorded 2006 Nov 14 in 100 Stillman
Hall on the Columbus campus of The Ohio State University.

Lecture 36: Worlds in Comparison - The Terrestrial Planets

Mars, fourth planet from the Sun, is a cold desert planet with a thin,
dry carbon-dioxide atmosphere.  The geology of Mars, however, shows
signs of an active past, with hot-spot volcanism, and tantalizing signs
of ancient water flows.  While a cold, dead desert planet today, Mars'
past may have been warmer and wetter, with liquid water during the first
third of its history.  This lecture will review the properties of Mars,
and discuss the evidences of its active past.  Recorded 2006 Nov 13 in
100 Stillman Hall on the Columbus campus of The Ohio State University.

Lecture 35: The Deserts of Mars

Venus, the second planet from the Sun, is perpetually veiled behind
opaque clouds of sulfuric acid droplets atop a hot, heavy, mostly carbon
dioxide atmosphere.  In size and apparent composition, however, it is a
near twin-sister of the Earth.  Why is it do different?  This lecture
reviews the basic properties of Venus, and examines the similarties and
differences with the Earth.  Recorded 2006 Nov 9 in 100 Stillman Hall on
the Columbus campus of The Ohio State University.

Lecture 34: Venus Unveiled

Mercury is the innermost of the planets, a hot, dead world that has been
heavily battered by impacts.  This lecture reviews the basic properties
of Mercury, particularly its surface and interior.  Recorded 2006 Nov 8
in 100 Stillman Hall on the Columbus campus of The Ohio State
University.

Lecture 33: Battered Mercury

How did the Solar System form?  This lecture examines the clues in the
present-day dynamics (orbital and rotation motions) of the planets and
planetary composition to the formation of the solar system.  We will
then describe the accretion model, where grains condense out of the
primordial solar nebula, grains aggregate by collisions into
planetesimals, then gravity begins to work and planetesimals grow into
protoplanets.  What kind of planet grows depends on where the
protoplanets are in the primordial solar nebula: close to the Sun only
rocky planets form, beyond the Frost Line ices and volatiles can
condense out, allowing the growth of the gas giants.  The whole process
took about 100 million years, and we as we explore the solar system we
will look for traces of this process on the various worlds we visit.
Recorded 2006 Nov 7 in 100 Stillman Hall on the Columbus campus of The
Ohio State University.

Lecture 32: The Origin of the Solar System

We start our exploration of the Solar System with a quick overview of
its constituent parts.  I will take as my starting point that Pluto,
Eris, and Ceres are Dwarf Planets according to the 2006 IAU decision.
This decision, which is not without controversy, will be one of the
questions we will revisit during these lectures.  Recorded 2006 Nov 6 in
100 Stillman Hall on the Columbus campus of The Ohio State University.

Lecture 31: The Family of the Sun

What is the structure of the Moon, and what physical processes have
shaped its surface?  In this lecture we turn to our nearest celestial
neighbor, the Moon, to see a world quite different than the dynamic
Earth.  We will discuss the surface features of the Moon (the Maria
and cratered highlands), see how crater density tells us the relative
ages of terrain, and look at the composition of Moon rocks returned
by astronauts and robotic probes.  We also discuss the interior
of the Moon, and review what we know about lunar history and formation.
Recorded 2006 Nov  2 in 100 Stillman Hall on the Columbus campus
of The Ohio State University.

Lecture 30: The Moon

What is the composition and structure of the Earth's atmosphere?  Why is
it as warm as it is, and how did it form?  These are the questions for
today's lecture.  The Earth's atmosphere is a complex, dynamic, and
evolving system.  We will discuss the composition and structure of the
atomsphere, the nature of the different thermal layers, the Greenhouse
Effect, and the Primordial Atmosphere and atmospheric evolution.  This
will give us a basis for comparison when we begin to examine other
planetary atmospheres in future lectures.  Recorded 2006 Nov 1 in 100
Stillman Hall on the Columbus campus of The Ohio State University.

Lecture 29: The Earth's Atmosphere

What is the structure of the Earth?  What better place to begin our
exploration of the Solar System then with the best-studied planet, the
Earth.  This lecture discusses the interior structure of the Earth,
introducing the idea of differentiation, how geologists map the interior
of the Earth using seismic waves, and the origin of the Earth's magnetic
field.  We then discuss the crust of the Earth, which is divided into 16
tectonic plates, and explore how plate motions driven by convection in
the upper mantle have shaped the visible surface of our planet over its
dynamic history.  Recorded 2006 Oct 31 in 100 Stillman Hall on the
Columbus campus of The Ohio State University.

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