Episodes
Course finale and summary. We look back over where we've been the last
eleven weeks, and bring together all of the main themes of this course
on Life in the Universe. Recorded live on 2009 Dec 4 in Room 1005 Smith
Laboratory on the Columbus campus of The Ohio State University.
Published 12/04/09
How will life, the Universe, and everything end? This lecture looks at
the evolution of our expanding Universe to project the prospects for
life into the distant cosmological future. Recent observations show
that we live in an infinite, accelerating universe. I will trace the
evolution of the universe from the current age of stars into the future.
The final state of the Universe will be cold, dark, and disordered, and
ultimately inhospitable to life as we understand it or perhaps...
Published 12/03/09
What is the future of life on Earth and in our Solar System? The Sun is
the source of energy for life on the Earth, but it will not shine
forever. This lecture looks at the impact of the various stages of the
evolution of the Sun on the habitability of the Solar System, with
particular emphasis on the continued habitability of the Earth. I will
refer to state-of-the-art computer models of the Sun to get is
properties at various stages in its past and future life. NOTE: Due to
a recorder...
Published 12/02/09
What does extraterrestrial life look like? This lecture explores
current thinking about what extraterrestrial life might be like not by
guessing their appearances, but instead applying lessons learned from
our growing understanding of how evolution and biochemistry work on
Earth. I will discuss Universal versus Parochial characteristics,
Convergent Evolution, Radical Diversity, and other ideas from
evolutionary biology that might inform how life might emerge on other
worlds. We will then...
Published 12/01/09
So, Where is Everybody? Interstellar colonization, in principle, is an
exponential growth process that would fill the galaxy in a few million
years even with a very modest star flight capability. This is a small
fraction of the lifetime of the Milky Way Galaxy, so the Galaxy should
be teaming with life. But, we so far have no compelling evidence of
extraterrestrial visitations, alien artifacts, or any other evidences
that the Galaxy is populated. Physicist and Nobel Laureate...
Published 11/30/09
If we ever detect life elsewhere, how will we go visit? This lecture
considers the challenges of interstellar travel and colonization. The
problem is one of basic physics (the enormous energy requirements of
star flight) coupled with the vast, irreducible distances between the
stars. I will describe various starship concepts that use reasonable
extrapolations of current technologies (nuclear propulsion and solar
sails), ignoring for our discussions science-fiction exotica...
Published 11/25/09
Is anybody out there? This lecture reviews the ideas behind SETI, the
Search for Extra-Terrestrial Intelligence, an effort to find other
intelligent communicating civilizations by tuning in on their radio or
other electromagnetic communications. I will discuss the basic
approaches being taken by various SETI efforts, and what we expect to
find. In addition to listening, we have also been broadcasting,
intentionally or otherwise, messages into space, and we have sent
physical artifacts with...
Published 11/24/09
How many intelligent, communicating civilizations live in our Galaxy?
We have no idea. One way to approach the question and come up with
quasi-quantitative estimates is the Drake Equation, first introduced by
radio astronomy Frank Drake in the 1960s. I will use the Drake equation
as an illustration of the issues related to the question of
extraterrestrial intelligence, and to set the stage for future lectures
on the likelihood of finding other intelligences in our Universe.
Recorded live on...
Published 11/23/09
Are there other Earths out there? Do they have life on them? This
lecture looks at the search for ExoEarths - Earth-sized planets in the
habitable zones of their parent stars, and what we might learn from
measuring them. The ultimate goal of all planet searches is to find
other Earth's, what the late Carl Sagan so poetically called
the "pale blue dot" as seen from the depths of space. This lecture
discusses what we might learn about such planets from studies of our own
Earth,...
Published 11/19/09
What are the properties of the 400+ exoplanets we have discovered so
far? This lecture reviews the properties of exoplanets, and finds a
couple of surprises: Jupiter-mass planets orbiting close to their parent
stars, and Jupiter-mass planets in very elliptical orbits. Both seem to
require some mechanism for migration: strong gravitational interactions
with either the protoplanetary disk or other giant planets to cause the
planets to move inward from their birth places beyond the "Ice...
Published 11/18/09
Are there planets around other stars? This lecture reviews the methods
used to hunt for exoplanets and the results thus far. I will describe
direct imaging methods, indirect methods relying on the gravitational
influence of the planet on its parent star, planetary transits in which
a planet blocks part of its parent star's light, and gravitational
microlensing. There has been an explosion in our knowledge of planets
around other stars, from little or nothing in the early 1990s to more
than...
Published 11/17/09
What stars are near the Sun? Now that we have some idea of what we are
looking for - rocky planets in the habitable zones of low-mass
main-sequence stars - what are the prospects near the Sun? This lecture
examines the hunting ground for planets, the nearby stars that make up
the Solar Neighborhood. I will describe our nearest neighbor, the
Proxima Centauri/Alpha Centauri triple system, and then look at the
properties of our nearest stellar neighbors. What we will find is that
G-type...
Published 11/16/09
Which stars are the most hospitable for life? This lecture examines the
factors affecting the habitability of stars, with a goal of
understanding where we should search for life-bearing planets. We will
do this by generalizing the idea of a Habitable Zone developed for the
Sun back in Lecture 30. In this context, we find that the best places
to search for life would be rocky planets in the habitable zones of
low-mass main-sequence stars. There are a number of caveats we will
discuss -...
Published 11/13/09
What happens to a star when it runs out of hydrogen in its core? This
lecture describes the post main-sequence evolution of stars. What
happens depends on the star's mass. Low mass stars swell up into Red
Giants, and eventually shed their envelopes and end their lives as white
dwarf stars. High mass stars become Red Supergiants, and if large
enough, end their lives in a spectacular supernova explosion that leaves
behind a neutron star or black hole. The explosion itself creates
massive...
Published 11/12/09
Why do stars shine? How long do they shine? This lecture describes the
physics of stars on the main sequence, describes the mass-luminosity
relation of main sequence stars, introduces nuclear fusion power and the
nuclear fusion lifetimes of stars. From this we gain an important
insight into one of the criteria we might apply to the search for life
around other stars: we want planets around low-mass main sequence stars
that can shine more or less steadily for more that 500 Myr to 1...
Published 11/10/09
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.
Published 11/09/09
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...
Published 11/05/09
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...
Published 11/04/09
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...
Published 11/03/09
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...
Published 11/02/09
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...
Published 10/30/09
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...
Published 10/29/09
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...
Published 10/28/09
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.
Published 10/27/09