Astronomy 141 - Life in the Universe - Autumn Quarter 2009 episodes:

• November 17, 2009Lecture 36: Exoplanets - Planets Around Other Stars

  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 400 planets around some 340-odd stars as of today. Recorded live

  on 2009 Nov 17 in Room 1005 Smith Laboratory on the Columbus campus of

  The Ohio State University.

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• November 16, 2009Lecture 35: The Solar Neighborhood

  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 stars like the Sun are uncommon, only about 7% of all nearby

  main-sequence stars. Red dwarfs, on the other hand, are very common,

  about 75%. To find Sun-like main sequence stars, we will have to extend

  our search to larger distances into our Milky Way galaxy proper.

  Recorded live on 2009 Nov 16 in Room 1005 Smith Laboratory on the

  Columbus campus of The Ohio State University.

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• November 13, 2009Lecture 34: Habitable Zones around Stars

  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 - tidal locking, stellar flares, and UV radiation - and

  limitations to the approach, but it seems to be a good place to start

  our search. Recorded live on 2009 Nov 13 in Room 1005 Smith Laboratory

  on the Columbus campus of The Ohio State University.

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• November 12, 2009Lecture 33: The Deaths of Stars

  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 quantities of heavy elements, which then seed interstellar space

  with metals to be incorporated into subsequent generations of stars.

  Recorded live on 2009 Nov 12 in Room 1005 Smith Laboratory on the

  Columbus campus of The Ohio State University.

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• November 10, 2009Lecture 32: The Lives of Stars

  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 billion

  years - maybe longer if our goal is to find intelligent life. Recorded

  live on 2009 Nov 10 in Room 1005 Smith Laboratory on the Columbus campus

  of The Ohio State University.

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• November 09, 2009Lecture 31: The Properties of Stars

  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.

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• November 05, 2009Lecture 30: Goldilocks and the Three Planets

  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 the

  present-day Sun. However, the size of a planet also plays a role, and

  we will expand the concept of habitability to include the type of

  atmosphere a planetary body can or cannot retain. Finally, because the

  Sun changes brightness slowly over its lifetime, the location of the

  habitable zone is time-dependent. We will define the Continuous

  Habitable Zone, and discuss implications, and limitations, of the idea

  of habitable zones, looking forward expanding our search for life to

  worlds around other stars. Recorded live on 2009 Nov 5 in Room 1005

  Smith Laboratory on the Columbus campus of The Ohio State University.

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• November 04, 2009Lecture 29: The Children of Saturn

  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 icy surface. Is this just pockets of tidal-heated water, or

  hints of a deep global liquid water ocean. I will describe new results

  on these two children of Saturn, and the possibilities they have for

  finding life, or life-like conditions, elsewhere in our Solar System.

  Recorded live on 2009 Nov 4 in Room 1005 Smith Laboratory on the

  Columbus campus of The Ohio State University.

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• November 03, 2009Lecture 28: The Galilean Moons of Jupiter

  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 surprising is the distinct possibility that underneath Europa's ice

  is a deep liquid water ocean, heated by tides from Jupiter. We will

  review the evidence for Europa's liquid sub-ice ocean and look at its

  potential as an abode of life. If there is life to be found anywhere in

  the Solar System beyond Earth, beneath the ice of Europa may be the best

  place to look. Recorded live on 2009 Nov 3 in Room 1005 Smith

  Laboratory on the Columbus campus of The Ohio State University.

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• November 02, 2009Lecture 27: Is There Life on Mars?

  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 recent important

  results from the Phoenix lander. We'll end by briefly noting future

  directions in Mars exploration.

  Recorded live on 2009 Nov 2 in Room 1005 Smith

  Laboratory on the Columbus campus of The Ohio State University.

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