Recap the Black Holes
Describe the conditions for a stellar black hole to
Describe the tidal effects and time dilation near a
Describe the X-ray observations of a black hole
Describe Hawking’s proposal on white holes
Is there any experimental support for this idea ?
Discuss the galactic black holes
Origin of Life on Earth
Characteristics of Life
Life in our Solar System
Astrobiology: interdisciplinary research
field on exobiology, the study of planets in
the solar system and beyond, space flights,
origins of life.
Exobiology: the study of organisms that
originate outside Earth. It also encompasses
Origin of Life on Earth (I)
Chemical Evolution - the process that manufactured
molecules and compounds of increasing complexity.
Supernovas produced heavy atoms, which were
combined to form molecules and compounds, which
were subsequently condensed into asteroids, planets
and new stars.
Recent astrophysical experiments demonstrated the
fact that asteroids can contain complex aromatic
molecules, which could lead to life under certain
physical conditions (the Miller-Urey experiment)
Origin of Life on Earth (II)
ammonia, water and
hydrogen (the Miller
- Urey experiment).
formed in the air and
accumulated in the
Origin of Life on Earth (III)
2nd phase: simple organic molecules under heat bond
to create macromolecules peptides proteins, fat
molecules, complex sugars)
3rd phase: macromolecules are organized into cells
which resemble living things (coacervates).
4th phase: nucleic acids control the reproductive and
internal activities of coacervates.
5th phase: natural selection of the cells which can use
energy most efficiently and reproduce more rapidly.
6th phase: self-sufficient autotrophic bacteria
Characteristics of Life
Composed of cells; 1-cell amoeba
But viruses do not contain cells and have
all the other characteristics of life)
Require energy for metabolism and
locomotion – ATP molecules
Sexual or asexual reproduction
Inherit traits from parents (heredity)
Respond to stimuli in their environment (light, heat etc)
Maintain a state of internal balance (homeostasis)
Adapt to their environment and evolve
While chemosynthetic theory explains the development of
life, biological evolution explains the origin of millions
of life forms.
Evolution is the progressive change of genes in a population.
The mechanism that weeds out the positive changes from
negative changes is natural selection, a concept
developed by Charles Darwin. This mechanism will ensure
the survival of the fittest.
Evolution is slow, gradual change without a clear direction
(not towards something better, or from simple to complex).
Contrary to popular belief, humans are not on top of the
evolutionary ladder; we are just another branch on the bush
of life. Extra-terrestrial life can be very different.
Extremophiles are organisms which can live in
in caves miles underground,
in sulphuric acid,
in the hot water heated by submarine volcanoes
in the cold of the Antarctic.
Humans are limited by the need for oxygen,
the boiling and the freezing points of water and the low
tolerance for extreme acidity or alkalinity. But life has evolved
to fill every possible niche on Earth and this might give an idea
The Habitable Zone
As the mass of the star increases the habitable zone moves further from the star.
Life in the Solar System
A habitable zone is the region around a star
where liquid water could exist at the surface.
Today only Earth has liquid water at the surface.
The size of the planet and the existence of
tectonic activities are also important. Too small
planets do not hold onto an atmosphere, while
too large planets will pull it to the surface.
Life could exist outside the habitable zone but we
expect that it is very different from the life on
Life on Mars (I)
Mars had some tectonic activity long time ago (we can
still see the volcanoes). The CO2 released by its
volcanoes heated the atmosphere and allowed for
water to exist on the surface.
Images from Mars show riverbeds as evidence that it
had water in the past.
Because of a very low density of the atmosphere
Mars cannot retain heat and today it has an average
temperature of –60 degrees and no liquid water at the
The Pathfinder mission to Mars initiated the
examination of soil around riverbeds.
Life on Mars (II)
Meteorites were found as coming
from Mars with signs of life
In 1996 NASA announced that a small
meteorite (ALH84001) discovered in Antarctica
contains globules of carbonates, formed by the
decompo-sition of bacteria on Mars. Other
scientists formulated other theories about the
creation of these carbonates (they used the fact
that the size of these bacteria was too small) and
the debate is still open.
Panspermia is a theory which
supports the idea that life is spread
Life on Venus
Like Mars, Venus has an atmosphere of CO2, but
unlike Mars its atmosphere is extremely dense.
Being closer to the Sun, Venus has higher
temperatures, which not only evaporates water but
also causes volcanoes activity. This leads to CO2 and
the greenhouse effect which further increases the
surface temperature (average 482 degrees !).
On Earth we have biogeochemical cycles (carbon and
nytrogen) which stop the greenhouse effect from
happening (but industrialization threatens this
Life on Europa and Titan
There is strong indirect evidence that Europa
(one of the moons around Jupiter) has an ocean
under a thick crust of ice. We know that deep
sea volcanic vents can generate tube worms. But
Europa ocean has little sources of energy.
Titan (one of Saturn’s moons) has liquid
methane and ethane, solid ice, and smog
particles raining from space. Life there would be
very different from life on Earth.