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CHAPTER 21
The
Chemistry of
the Solar
System
21.3 The Possibility
of Life Elsewhere
Life on Earth
What does life look like?
A tadpole
Soil bacteria
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Humans and plants
21.3 The Possibility of Life Elsewhere
Searching for life beyond Earth
Key questions before searching for extraterrestrial life:
- What are the physical and chemical conditions under which life can exist?
- Do those conditions exist outside of Earth? If so, where?
- How would we recognize alien life if we found it?
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21.3 The Possibility of Life Elsewhere
Chemosynthetic life
In the deep ocean, at very high pressure
and in absolute darkness, hydrothermal
vents release acidic, superheated water
that contains heavy metals.
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21.3 The Possibility of Life Elsewhere
Chemosynthetic life
In the deep ocean, at very high pressure
and in absolute darkness, hydrothermal
vents release acidic, superheated water
that contains heavy metals.
Still chemosynthetic life exists at
hydrothermal vents!
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21.3 The Possibility of Life Elsewhere
Life deep underground
Only recently, scientists discovered living colonies of bacteria 2.8 km underground
with no organic materials around. Deep bacteria like Bacillus infernus are considered
thermophiles (heat lovers) because they thrive at 75oC (167oF).
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21.3 The Possibility of Life Elsewhere
Evidence for life on Mars
Four experiments:
1) A mass spectrometer looked for
organic compounds.
2) A gas exchange experiment
looked for O2, CO2, H2, CH4 and
N2.
3) A labeled release experiment
involved a 14C-labeled nutrient
solution.
4) A pyrolytic release experiment
used light and 14CO2.
The results from Viking were inconclusive because samples were small,
and the instruments were not as sophisticated as they are today.
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21.3 The Possibility of Life Elsewhere
Evidence for life on Mars
In 2008, the Phoenix mission landed on Mars and found:
1) water in the form of ice
2) salts and perchlorate (ClO4). Perchlorate is not a signature of life, but some
microorganisms on Earth are fueled by processes that involve perchlorate.
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21.3 The Possibility of Life Elsewhere
Life on Europa?
Europa is Jupiter’s sixth moon
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21.3 The Possibility of Life Elsewhere
Life on Europa?
In 1997 the Galileo
spacecraft showed that
the surface of Europa
is criss-crossed with
strange lines, and there
are almost no craters.
Why do many
scientists believe that
Europa is a likely
candidate for
extraterrestrial life?
Europa’s surface from 200 km altitude
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21.3 The Possibility of Life Elsewhere
Life on Europa?
Ice crust
Water ocean
Scientists believe that the
surface is made of water ice,
which hides water oceans
that are 200 km deep!
The deepest oceans on Earth
are less than 10 km deep.
It is believed that the water
remains liquid because of
Rock mantle
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Iron-rich core
Jupiter’s gravity causing
strong tides and frictional
heating.
21.3 The Possibility of Life Elsewhere
Life on Titan?
In 2005, the Cassini-Huyens spacecraft showed that Titan is like a planet,
with oceans, rivers, mountains, and even weather!
Titan is Saturn’s sixth moon.
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21.3 The Possibility of Life Elsewhere
Life on Titan?
In 2005, the Cassini-Huyens spacecraft showed that Titan is like a planet,
with oceans, rivers, mountains, and even weather!
Titan offers abundant organic liquids and a dense nitrogen atmosphere.
Scientists believe that, except for the cold (–180oC), these conditions are
similar to the early Earth. If Titan has underground caves that are
warmer, the chances of finding life will be much greater.
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21.3 The Possibility of Life Elsewhere
Life on Earth can exist under extreme conditions:
high temperature, high pressure, without light, among toxic chemicals, without
organic materials
The most likely places to find extraterrestrial life are on:
1) Mars
Water (ice) was found, along with salts and perchlorate
2) Europa
Vast oceans are believed to exist below the crust of ice
3) Titan
This moon has a diverse landscape and even weather.
Organic materials were found in abundance and, except for the
extreme cold, the conditions are similar to what the early Earth
might have been.
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21.3 The Possibility of Life Elsewhere