Among the countless planets and moons that exist in the
vastness of space, the Earth is the only example that we have SO FAR, of a
place where Nature has come to life, where Nature has learned to see, to hear,
and to fly, and lately where Nature is coming to know Itself. Despite all that we have learned about
biology on Earth, our knowledge is still very limited. But the discovery of just one instance of
life beyond our planet would instantly double the number of examples of living
systems available for study. Biologists
would then study life, not as a special case but as a property of the Cosmos,
just as physicists study gravity or astronomers study the nuclear reactions
that occur in the same way in all stars of the universe. And if that one instance of extraterrestrial
life were in our own Solar System –on
the planet MARS, for instance– then the chances would be good that many of
our Sun’s neighboring stars would also have a planet, or perhaps a moon, that
is home to its own version of life.
During the
last few decades we have begun to send out probes that have enabled us to
examine at close range other planets and the planet that has most caught our
attention is MARS.
We humans have always found MARS to be intriguing. Because of it appears reddish in the sky,
the people of the early eastern Mediterranean and Mesopotamian civilizations
believed that the planet had something to do with blood. And so, the ancient Canaanites (Israelites
and Phoenicians) called it Maadim, a name derrived directly
from the Hebrew word for blood (dam),
and they reveared the planet as an incarnation of the war-god, whom the nearby
Greeks called Ares. Further west, in
places such as early Rome, people had quite a different view of Mars, for they
saw it not as a war-god but as a god of spring, growth, and fertility. Eventually, as the Phoenicians and then the
Greeks spread out, the eastern idea began to dominate. And yet, ironically, it is now thought that
Mars may be fertile afterall, one of the few places in our Solar System where
living things could be growing and thriving.
But how did we get to this point? As our ancestors came to understand that the
Earth and Mars were both planets orbiting a common star, Sol, they began to wonder
whether the two planets might have quite a bit in common. Perhaps, Mars even harbored some kind of
life, some imagined. However, it was
not until the late 19th century that this idea became popular and it
was not until the 1960s that humanity could do anything other than imagine.
With the
advant of space flight in the 1960s, the pace of our quest for Martian life was
accelerated. In 1965, Mariner
4 became the first probe of human design to fly successfully to Mars,
passing the planet at an
altitude of 9,846 kilometers (6,118 miles).
To many, the discoveries were disappointing, particularly outside
of the science community, where
popular culture of the time still included elements remaining from the days
when astronomer Percival Lowell had
announced to the world that he believed Mars to be inhabited –by intelligent
beings. [hyperlink to Percival Lowell]
Now by the
time of Mariner 4 it did make sense
that Mars, like Earth, should have had some kind of life. Afterall, scientists knew that Mars had in
fact received the correct ingredients
to have produced primitive cells under the right conditions. The astronomer, Carl Sagan, and others had calculated that more than enough organic
material –that is material made of large molecules containing carbon–
constantly entered the Martian atmosphere from space. Sagan called this material the stuff of life and that’s
literally what it is.
Of course,
none of the investigators involved in the Mariner
4 mission had seriously expected to find any signs of the intelligent,
technologically advanced beings that Lowell had imagined. In the more than 3.5 billion years that life
has existed on Earth, technological civilization capable of such a planetary
engineering project has been on Earth for only a few decades. Therefore, it is highly unlikely that two
civilizations of intelligent, technologically-active beings would arise
independently on neighboring planets at the same time in the history of the
Solar System. The Mariner 4 scientists did not expect to find any alien cities –nor
did they expect canals. Still, the investigators had hoped that
the onboard television camera would reveal a planet that was more or less
similar to Earth, perhaps even exhibiting signs of vegetation or some other
familiar kind of life.
When Mariner 4 arrived, it took
22 photographs; the first close up pictures of the Martian surface. But the photographs showed no
vegetation. The scientists found only a dry
surface covered with craters –much like the surface of the Moon– and with an
atmosphere much thinner than previously thought.
One of the 22 Mariner
4 images taken in 1965.
This one was taken from 13,000 km
from the planet’s surface. Courtesy of NASA Goddard Space Flight Center.
http://nssdc.gsfc.nasa.gov/imgcat/html/object_page/m04_09d.html
The mission
demonstrated that the brainwork that had gone into Lowell’s canals had been the
product not of intelligent Martians but of intelligent –and very imaginative–
humans. Nevertheless, there was
evidence suggesting that, quite unlike the Moon, waterways of some sort had
possibly existed at some time in the Martian past –not canals but perhaps
rivers or streams.
Mariner 6 and
Mariner
7 arrived at Mars four days apart in the middle of 1969. Like Mariner
4 four years earlier, these were flyby missions, meaning that the
probes did not enter into orbit around Mars and that, consequently, time was
limited. But the pair of spacecraft
approached within approximately 3,550 kilometers (2,200 miles) of the planet
and together transmitted nearly 200 photographs to Earth. These pictures included the Martian north
and south poles as well as Phobos – one of the planet’s two
moons, named for the son of Ares. The
ships also carried instruments that scientists used to study the Martian
atmosphere. Mariner 6 and Mariner 7
set the stage for the Mariner 9 mission of 1971.
Unlike the last three probes that had quickly flown by
the planet with limited time for observations, Mariner 9 entered into orbit where, after waiting out a dust storm,
the craft spent a year sending thousands of photographs back to Earth, covering
almost 100% of the Martian surface. The
duststorm had unfortunately doomed two Soviet (Russian) spacecraft, Mars 2 and Mars 3, to failure as they tried to actually land on the
planet. The Mariner 9 pictures revealed rough terrain with varied coloration,
mountains and volcanoes whose shapes suggested erosion by wind. Furthermore, Mariner 9 was able to take a closer look at the possible waterways
of the past that had been suggested six years earlier by Mariner 4.
Here is a composite of photographs
from Mariner 9, showing channels that look as though carved by flowing
water. Courtesy of NASA, cited by Windows to the Universe
http://www.windows.ucar.edu/tour/link=/mars/images/mariner9_channel_jpg_image.html
Like wind, flowing water also erodes surfaces over time
and, based on the erosion patterns revealed by the Mariner 9 photographs, it now looked more likely that at some point
in the past Mars had been more like the Earth.
Might the impressions left by ancient rivers have created an illusion of canals for Lowell? Perhaps.
But conclusive
evidence of past water on the Martian surface would not come until thirty-three
years later, with NASA’s 2004 Mars
Exploration Rover Mission, wherein two probes landed on the Martian
surface: One, called Spirit,
landed within the Gusev Crater. The
other, called Opportunity, landed at a place called Meridiani Planum. Each of these landed probes delivered to the
surface a robotic roving vehicle equipped with cameras and other
instruments. On account of the Mars
Exploration Rover Mission, we now have solid evidence that parts of the Martian
surface, Meridiani Planum in
particular, were once underwater. [hyperlink to MER water discoveries]
Here is an artist’s rendering of a river flowing into
lake on Mars at some point in the past. Illustration from NASA Jet Propulsion Laboratory, cited
by Rednova http://www.rednova.com/news/stories/1/2003/11/14/story001.html
To what extent water covered the Martian surface is unknown. Perhaps the surface water consisted of a
system of rivers and streams flowing into small lakes, such as the one pctured
above. Or, perhaps there was enough
water so that the planet had seas or even an ocean.
If Mars had large amounts of liquid water in the
past, its surface would have looked something like this. Illustration from NASA Jet Propulsion Laboratory, cited
by Rednova http://www.rednova.com/news/stories/1/2003/11/14/story001.html
These questions await future missions. Furthermore, in order to determine how long
ago the Martian surface was wet, future probes will have not only to land on
Mars but will have to collect samples and bring them to Earth to be examinined
in laboratories. There is little doubt
that Meridiani Planum is now a major
candidate for such a Mars sample return mission, although it will be some years
before such a mission will take place.
Meanwhile, a major question has now been answered; Mars was indeed a
wetter planet at some point in the past, and probably warmer too.
With water, an
ideal temperature, and an abundance of organic molecules – that is, Sagan’s
stuff of life – Mars of the past could have in fact provided an ideal
environment for the emergence of lifeforms.
We know that single-celled life was abundant on Earth by approximately
3.5 billion years ago. Like the
skeletons of animals and the leaves of plants, microorganisms under the right
conditions are able to leave impression that can be preserved in the rock
record for ages. We call these
impressions fossils. Here is a picture of how they look:
Did tiny life forms
similarly thrive on ancient Mars? And,
if so, might their decendants survive somewhere on the dried-out Mars of
today? Back in 1971, most of the
scientists of the Mariner 9 team were
not very hopeful about this possibility.
Among the mission scientists, however, there was at least one
optimist. This was Gilbert Levin. In addition
to cameras, Mariner 9 carried other
instruments, including one designed to study the gasses of the Martian
atmosphere. Because life can manifest
itself by leaving clues in the atmosphere of a planet, Levin has often referred
to Mariner 9’s sensitivity to the
various atmospheric gases as a “hidden life-detection experiment”. [hyperlink
to Mariner 9 Hidden Life Detection Experiment]
Viking 1
and Viking
2, launched during the 1970s also played a major role in our
exploration of Mars. These two probes
were humanity’s first space missions devoted specifically to the search for
extraterrestrial lifeforms. They were
also the first terrestrial objects to successfully land and function on the
surface of another planet, although five years earlier the ill-fated Soviet Mars 3 had managed to reach the Martian
surface and survive for a few seconds before her instruments failed. The Viking probes carried several
instruments and their findings left scientists faced with a great mystery. [hyperlink to Viking]
Fortunately, thanks to the Mars
Exploration Rober Mission, we may be about to solve the Viking mystery. [hyperlink
to Mossbauer]
The definitive answer to the question of whether or not Mars harbors microorganisms awaits the delivery of sophisticated astrobiology instruments
Around the same time that NASA landed Spirit and Opportunity on the Martian surface, the European Space Agency (ESA) almost succeeded delivering to Mars the very instrument package that is needed. In fact, it is thought that the ESA probe, called Beagle 2, did indeed land on the planet’s surface, although, sadly, communication was lost. Named in honor of Charles Darwin’s sea ship, the Beagle 1, Beagle 2 carried an instrument designed to look for organic molecules and to do so even more capably than the Viking probes.
Here is an artist’s rendering of how the Beagle 2
probe would have looked on the surface of Mars. Courtesy of the European Space Agency (ESA)
http://www.esa.int/SPECIALS/Mars_Express/SEMPM75V9ED_0.html
If the stuff of life is on the Martian surface, Beagle 2 would have found it. Also, Beagle 2 had an instrument capable of detecting minute quantities of CH4 gas, if present in the Martian atmosphere. And if there is CH4 in the atmosphere, scientists believe it could only come from microorganisms. Such organisms are common on Earth and are known as methanogens. [hyperlink to Mars Microbiology] Whether or not there are any such organisms on Mars, we may find out within a few years, perhaps from a Beagle 3, or perhaps from a future NASA or Russian Mars probe.
If we find that microorganisms exist currently on Mars, or that fossils exist indicating that life was at least present on the planet in the past, we may wish to send teams of astronaut-scientists, although currently no such program has yet been initiated or authorized. What seems certain however, is that when humans do travel to Mars, they must do so as a species, as citizens of the Earth, not as representatives of one country or another.
Currently, only the United States, Russia, and China have launched humans into space and, if humanity survives the next few decades, it is likely that these as well as other nations would together contribute to the first human missions to Mars. However, planetary-scale missions require planetary-scale budgets. Therefore, international cooperation will not only set an example for similar cooperation on Earth-bound projects but will be necessary so that no single nation takes on the enormous economic cost of human Mars missions. So, if you want to be one of the first human explorers to Mars, start learning foreign langauges, especially Russian, Chinese, Japanese, French, and German. Since it is much easier to learn a new langauge when you are young, do not take this advice lightly. Remember the lesson of Percival Lowell and the canali. Ask your parents to find out about special schools that emphasize languages, as well as math and science.