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?

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.

Astronomical contributions to exobiological speculation: what

astronomical factors were necessary for the origin and development of life?

A major astronomical constraint: life took a long time to develop

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.

Fortunately, stars like the Sun are very numerous

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

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.

An example of a (possible) cosmic oddity necessary for life on Earth

Recent research suggests that the Earth’s large moon may have

stabilized Earth’s obliquity (tilt), and prevented a chaotic

wandering of the Earth’s axis. If Earth’s moon is rare, its

stabilizing influence is also rare.

Second argument against (intelligent life) elsewhere: Fermi

Paradox

If higher life, and intelligent life, is common in the galaxy, why don’t we

see evidence of their technology?

18 Scorpii – may be several hundred million years older than the Sun

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

The TPF approach: look for “bioindicators” in the spectra of

terrestrial planets

Earth has spectral lines of different gases than Mars

and Venus