ATLAS OF THE UNIVERSE
The Search for Life on Mars
T
he most successful Mars probes to date have been the
two Vikings, each of which consisted of an orbiter and
a lander. Viking 1 was launched on 20 August 1975, and
in the following June was put into a closed orbit round
Mars. It continued the mapping programme of Mariner 9,
and some of the images were very detailed; one showed
a rock on which light and shadow effects gave an uncanny
look of a human face – a fact which was not overlooked
by scientific eccentrics. On 20 July 1976, the lander was
separated from the orbiter, and was brought gently down
partly by parachute braking (useful even in the thin
Martian atmosphere) and partly by rocket braking. The
landing site was Chryse, (the Golden Plain) at latitude
22 degrees North, longitude 47.5 degrees West. The first
images showed a red, rock-strewn landscape under a pink
sky; temperatures were very low, reaching a maximum
of 31 degrees C near noon and a minimum of 86
degrees C just after dawn.
The main task of Viking 1 was to search for life.
Material was scooped up, drawn into the spacecraft and
analysed chemically for traces of organic substances. The
results were sent back to Earth and were at first decidedly
puzzling, but it has to be admitted that no positive signs of
life were found. The results from Viking 2, which landed
in the more northerly plain of Utopia on 3 September
1976, were similar. Windspeeds were measured, and the
first analyses of the surface material carried out; the main
constituent is silica (over 40 per cent).
If there is any life on Mars today it must be very lowly
indeed. Whether the situation was different in the past is
not certain because of the evidence of old riverbeds; at
some periods Mars may have been less unfriendly than
it is now, and it is at least possible that life appeared,
dying out when conditions deteriorated. We will know forFirst colour picture
from Viking 1. The lander of
Viking 1 came down in
the ‘golden plain’ of Chryse,
at latitude 22.4°N, longitude
47.5°W. The picture shows
a red, rock-strewn landscape;
the atmospheric pressure at
the time was approximately
7 millibars. The first analysis
of the surface material was
made from Viking: 1–44 per
cent silica, 5.5 per cent
alumina, 18 per cent iron,
0.9 per cent titanium and
0.3 per cent potassium.The search for life.
Viking 1 drew in material
from the red ‘desert’,
analysed it, and sent back
the results. It had been
expected that signs of
organic activity would be
detected, but this proved
not to be the case. It is
too early to say definitely
that Mars is totally lifeless,
but this does seem to be
indicated by the available
evidence. Both the Viking
landers have long since
ceased to operate, so
that for a final decision
we must await the results
from a new spacecraft.
There are already plans
to send a probe to Mars,
collect material, and return
it to Earth for analysis.C Atl of Univ Phil'03stp 2/4/03 3:06 pm Page 86