North Hawaii News Articles from CFHT
Life in the Universe II: our Solar System
In a previous article, we saw that the study of Life in the Universe is
a new and exciting branch of astronomy. Besides the common examples of
life we see every day (plants, animals...), there are life-forms which
thrive in very unusual environments, usually considered toxic and
deadly, such as boiling water, acid pools, dark and deep ocean floors,
frozen soils, and even radioactive chambers!
If some life-forms can manage to live in those extremes environments
here on Earth, could similar creatures exist elsewhere in our Solar
System, where we know there is no air, sometimes no water, not even
There are 3 promising spots that could harbor Life in our Solar System
(besides the Earth): Mars, Europa (one of Jupiter's moon) and Titan
(Saturn's main satellite). Let's take a look a them.
Since Percival Lowell's book "Mars as the Abode of Life" was published
in 1908, in which the famous astronomer and observer of the Red Planet
presented his theory that Mars' canals were built by intelligent beings,
many have looked there for signs of life.
In the 1970's, the Viking Landers conducted 3 types of experiments to
detect life on the surface of the planet. Although no firm conclusions
could be made about the presence or absence of life, these experiments
started the search for life in our Solar System.
When a Martian meteorite discovered in Antarctica was found in 1996 to
contain organic compounds, carbonate globules supposedly associated with
bacterial life, and worm-like structures that resembled what might be
the fossil remains of Martian microorganisms, scientists thought they
had their first proof of life outside of Earth.
Unfortunately, not all scientists agree with the conclusions, because
other processes (such as chemical ones) not related to life can produce
what was found in that meteorite. Despite later similar finds in other
Martian meteorites, not every scientist is convinced that there once was
life on Mars.
One argument is that Mars is a dry, desolate planet. Without water, how
could life appear and grow? We have known for a while that the northern
polar cap of Mars is made of frozen water (the other one is made of
frozen carbon dioxide), and that faint water vapor clouds sometimes
float above the surface of the Red Planet. But what about liquid
Although there are no signs of liquid water on Mars now, there are many
indications that Mars probably once had lakes, rivers, maybe even
oceans. Those visual evidences come from images taken by spacecrafts,
such as the Mars Global Surveyor. Some of those pictures show gullies,
channels, deltas, and ground water seepage, in hundreds of
locations. But some scientists argue that, for example, the canyons were
carved by massive floods of carbon dioxide and solid debris instead of
liquid water. There is also a lack of ancient lake shorelines signs in
places where they are expected. So, once again, not everyone is
convinced water once flowed on Mars, but scientists continue to
Further away is Europa, a satellite of Jupiter, close in size to our
Moon. When Voyager 2 snapped pictures of Europa in 1979, it showed a
smooth surface with a network of dark lines which crisscross its
surface. It was then suspected that Europa's surface was made up of ice
mixed with rocky material; models of Europa's interior showed that
beneath a thin crust of water ice, Europa could have deep oceans. Later,
in 1996, the space probe Galileo found indications of a salty liquid
ocean at least 7 km (4.5 miles) deep, under the icy crust.
The presence of liquid water is very exciting, but how could liquid
water exist in such a cold place, far away from the Sun? One possibility
is tidal heating, where the gravitational attraction from Jupiter and
some if its other moons squeezes the satellite, making the surface
expand slightly in some places and contract in others, causing friction
and generating heat.
Another possibility is raised by a phenomenon recently discovered here
on Earth, in Antarctica. Lake Vostok is a huge body of liquid water four
kilometers under the ice of Antarctica. This lake is 400 meters (1310
feet) deep. How can liquid water exist so deep and in such a cold
environment? Scientists are not sure yet, but pressure of the ice
above, or heat from Earth's core, may keep the temperature high enough
to melt the ice. Could the same process maintain the liquid water under
Europa's icy surface? Would that water be suitable for life?
Almost twice as far, around the ringed giant planet Saturn, is Titan.
This big satellite (bigger than Mercury and Pluto!) has an atmosphere
rich in hydrocarbon and nitrogen. The hydrocarbon elements are the
building blocks for amino acids necessary for the formation of life, so
some scientists think that this is our best bet for the presence of
We just saw 3 examples of places in our Solar System which might harbor
life. Assuming that there is life on one of those celestial bodies,
would we be able to detect it? One way to know is to use the tools we
have on a target where we are sure there is life. In 1990, the space
probe Galileo, now at Jupiter, passed near the Earth and used the
spacecraft's instruments to try to detect life... here on Earth!
The observations showed an enormous quantity of molecular oxygen, much
more than what was found on the other planets of our Solar
System. Although there are many processes by which oxygen can be
produced (UV sunlight splitting water molecules, for example), life is
the easiest one to explain the vast amounts found. Galileo also detected
chlorophyll, indicating the presence of plants, covering most of the
land area of the Earth. Methane was also detected, even though in an
oxygen atmosphere, none should exist! Therefore, it comes from
somewhere, and life is one possible source.
The search for Life is a hard one, even in our own Solar System. Very
few places have reasonable conditions favorable to life. And even if
life existed on Mars, Europa or Titan, our technology is not quite
developed enough to easily prove the existence of life. But that's no
reason to stop searching.
Life exists on Earth, and could exist on a few other places in our Solar
System. How about around other stars? That will be the subject of a
Canada-France-Hawaii Telescope Corporation
Jan. 11, 2001