Lecture 34 Exobiology Life Elsewhere in the Universe

1
Lecture 34 Exobiology- Life Elsewhere in the
Universe

• What does our knowledge of the solar system tell
  us about the existence of life elsewhere in the
  universe?

2
Exobiology A scientific discipline without
subject matter. At present no examples known of
life outside the Earth

• Present status of exobiology is intelligent
  speculation on the processes that led to life on
  Earth, and the degree to which they are
  reproduced elsewhere.

3
Astronomical contributions to exobiological
speculation what astronomical factors were
necessary for the origin and development of life?
4
A major astronomical constraint life took a long
time to develop
5
On Earth, it took 4 billion years from formation
to the appearance of complex, multicellular life
(Cambrian Explosion). This requires the star
to remain relatively constant for a very long
time.
6
Fortunately, stars like the Sun are very numerous

• A rough estimate 20 billion stars in the Milky
  Way galaxy

7
Contrary opinions about common life in the
universe

• Rare Earth Hypothesis, after book Rare Earth
  by Brownlee and Ward Asserts that a large
  number of improbable events were necessary for
  the development of life on the Earth. These are
  unlikely to be duplicated elsewhere, so higher
  life is extremely rare in the universe.

8
An example of a (possible) cosmic oddity
necessary for life on Earth
9
Recent research suggests that the Earths large
moon may have stabilized Earths obliquity
(tilt), and prevented a chaotic wandering of the
Earths axis. If Earths moon is rare, its
stabilizing influence is also rare.
10
Second argument against (intelligent life)
elsewhere Fermi Paradox
18 Scorpii may be several hundred million years
older than the Sun

• If higher life, and intelligent life, is common
  in the galaxy, why dont we see evidence of their
  technology?

11
We should begin to get answers in the next 10
20 years

• The Terrestrial Planet Finder Mission (TPF)
  mission find terrestrial planets and determine
  if they have life

12
The TPF approach look for bioindicators in
the spectra of terrestrial planets

• Earth has spectral lines of different gases than
  Mars and Venus