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 sunlight?

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 water?

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 accumulate evidences.


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 life.

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 future article...

Nadine Manset
Resident Astronomer
Canada-France-Hawaii Telescope Corporation
Jan. 11, 2001