North Hawaii News Articles from CFHT
Life in the Universe I: Earth
One of the newest and most exciting branches of astronomy is
astrobiology, the study of all living things in our Universe, wherever
they might be (here on Earth, on Mars, or around another star) and whatever
form they might take (a single cell, a huge elephant or a Star Trek like
extravagant creature). One branch of astrobiology is exobiology, the study
of life outside of Earth.
I will surprise no one by stating that there is Life on Earth: single
cell beings, multicellular ones, plants, animals, intelligent life-forms
(that's you)... We take that for granted, and sometimes assume that
because Life is thriving here on Earth, it probably is elsewhere in our
Universe. Same for intelligent life.
But, what is Life, exactly? How can we define it? What general
conditions (temperature, pressure, etc.) are suitable for life? Where in
our Solar System could life exist? How can we prove that something is
alive, or inert?
What is life? Scientists have not yet found a suitable definition that
would precisely include what we know is alive, and exclude what we know
is not. A gecko may be a "living system with a definite boundary,
continually exchanging material with its surrounding, but without
altering its general properties, at least over some period of time", but
so is fire, and fire is not alive!
We may adopt a "Darwinian evolution" definition, which includes
self-reproduction, genetic variation and natural selection over the
course of time, but then, how long do we have to wait for a sign of
evolution in a sample we think might be alive? Hours? Months? Years?
For every definition that seems reasonable, whether based on metabolism,
physiology, biochemistry, genetics or thermodynamics, there are
counter-examples of living systems that do not fit that particular
definition. Moreover, some chemical reactions sometimes mimic life and
might fool us into thinking we have detected a new life-form. What is
alive and what is not, can be a tricky question.
We think that life (as we know it) requires in general a source of energy
(usually sunlight), a source of carbon (food) and liquid water (remember
that our bodies are mostly constituted of water). We also think of
reasonable temperature and pressure conditions, and presence of oxygen
(just think of the summit of Mauna Kea, where there is only 60% of the
oxygen available at sea level, and no animal or plant live - Do you
think anything could survive, then, with no oxygen at all?).
But in recent years, scientists have discovered life-forms on Earth
where no one could have expected them because one or more of those
requirements for Life is missing.
For example, some insects or small reptilians live deep in the dark, in
caves that never see the Sun. Those creatures do not have eyes, since
they are not useful at all! But they eat plants they find in those caves,
reproduce, and die.
Tube worms, spider crabs and even fish survive near sources of very hot
water and minerals spewing from the Earth's center, almost crushed by
enormous pressure at 3-5 km (2-3 miles) below the ocean's surface. These
animals eat microorganisms that use the minerals coming out of those
"smokers", as they are called.
Some bacteria happily swim in geothermal sources where the temperature
is above the boiling point of water; the upper limit so far is 115
degrees C (239 degrees F)!
It is also possible to find bacteria and multicellular life-forms in rock
cores brought from miles down when looking for oil and natural gas, or
in tiny cracks of some granite rocks.
Antarctica is known to be a much colder place than Hawaii, with average
winter temperatures of -60 degrees C (-76 degrees F) that can go as high
as 14.6 C (58.3 F) or as low as -89.2 C (-128.6 F); nevertheless,
bacteria, yeast, fungi and algae are present in the snow near the
surface of the frozen continent, as well as deep in the ice. These
microorganisms survive the extremely cold temperature by hibernating
during the winter. Some of those organisms have even been revived after
being frozen for over 200,000 years!
Simple life forms can even survive on the Moon! In 1969, after almost 3
years on the Moon, bacteria that had hitchhiked from Earth on the
U.S. Surveyor moon lander was retrieved by Apollo astronauts and found
to have survived by hibernating. The hundred or so organisms survived
launch, the vacuum of space and Moon, years of harsh radiation from the
Sun, deep-freeze at an average temperature of only 20 degrees above
absolute zero (-253 C, or -425 F), and no nutrient, water or energy
Many other examples can be found, such as bacteria that live inside
nuclear reactors or even in sulfuric acid pools!
If some life-forms can manage to live in those extreme environments,
could then similar beings exist on hot and airless Mercury,
pressure-crushing Venus, dry and cold Mars, gaseous Jupiter, the frigid
Moon? Where in our Solar System are our best chances of finding Life?
For the moment, scientists concentrate their search for life on Mars,
Europa (one of Jupiter's moon) and Titan (Saturn's main satellite), and
we will visit those potential life harbors in a coming article...
Canada-France-Hawaii Telescope Corporation
Jan. 4, 2001