pass over a specific area at a particular time of day. If
the orbit is Mars synchronous (i.¢., a period of 245 37")
the viewing interval will be one day. Intervals of
two or more days ean be readily achieved with orbits of
somewhat longer periods, permitting more than one area
to be revisited frequently under similar lighting eondi-
tions.

Landers

The techniques described so far—ground-based ob-
servations, flvbys, and orbiters—will necessarily use
remote sensing methods. They will make valuable
contributions to our understanding of the atmoxphere
and surface, and may also produce results that are sug-
gestive of an indigenous biota (e.g., the presence of
atmospheric constituents in nonequilibrium amounts
and inexplainable by abiological processes). However,
it is generally agreed that in order to detect unequivo-
cally the presence or absence of life, we must land on the
surface and make direct measurements. This stage we
are now entering with the Viking Project.

The Viking Project consists of two combination
orbiter-lander missions in 1973. The orbiter’s role has
not been completely determined, but it will work with
the lander asa team. It can accomplish this in at least
three different ways: (1) by surveying possible lander
sites before the lander is detached from the orbiter, (2)
by observing the atmosphere and surface in the neighbor-
hood of the lander in order to relate the Jander’s mea-
surements to its environment, and (3) by serving as a
high capacity data relay link between the lander and
earth. Once its primary mission is over, the orbiter
may be used to extrapolate the detailed findings of the
team to other areas of the planet and to do site survey
work for future landers. The orbiter payload will not
be determined until at least December 1969. However,
it is expected that high priority measurements will be
visible imagery and ir observations to determine water
vapor and surface temperature.

The most exciting part of this mission is certainly the
lander. After separation from the orbiter, the lander
capsule will enter the atmosphere, slow down by aero-
dynamic braking, deploy a parachute, and finally jet-
tison the parachute and turn on retro-rockets for a soft
landing. During descent, measurements of atmo-
spheric structure, including composition by a mass
spectrometer, are envisioned.

After a soft landing, a variety of investigations will be
carried out. Final selection of the payload will not be
made until December 1969. Typical of what could
constitute the actual payload are:

Facsimile camera: both high and low resolution
pictures.

Surface sampler—pyrolyzer-gas chromatograph
Mass spectrometer: organic analysis of the soil,
analysis of the atmosphere.

Direct biology measurement: measure various
life-related functions such as metabolism, growth,
etc.

jov - re

Meteorological sensors! measure winds, pressure,

temperature.

Other high priority instruments for this first hinder
are a three-axis seisymometer and a uv photometer.

The lander's life isa minimum of three days with a goal
of ninety days. Power will come from batteries, with
either solar cells or a radioisotope thermoelectric gen-
erator (RIG) serving as the source for periods longer
than the three-day minimum.

Other Missions

NASA plans to place a small spin-stabilized space-
eraft, called a planetary explorer, in orbit around ALars
in 1973. The objective of this mission will almost cer-
tainly be investigations of the solar wind interaction
with the planet and of the ionosphere. Thus, it will be
of minor interest for exobiologieal studies.

Additional exploration of the surface by lander,
including rovers, is clearly desirable. Tfowever, it is
premature to present a schedule and capabilities for such
missions.

Some Exabiological Speculations

In putting this issue together, ] requested Joshua
Lederberg to offer some comments on the theoretical
aspects of exobiology. His contribution is brief, but
significant, since it gives the flavor of the subject.
Rather than include it as a separate paper, I have added
it to this Introduction.

Va

fal is

mars Through a Crysta

J. Lederberg

The editor of this feature had asked me to comment
on the theoretical expectations for the character of life
on Mars, if any, and how this might be revealed by the
missions of 1969 and 1971 which emphasize optical
methods of analysis.

Such a comment was much easier to write a few years
ago? when the chance of experimental verification was
less imminent. It must also be added that cur growing
knowledge of the Martian environment since 1905
(Mariner IV) has made it difficult to paint any facile
picture of Martian life. The most difficult obstacle is
the apparent lack of water, according to several lines of
evidence. On the other hand, sinee the average sub-
surface temperature of Mars is about —G6O°C, the
Martian crust might contain any amount of water (as
icc) in the range of milligrams to kilotons per square
meter.2 The extent of the solid phase is, of course, im-
material to the equilibrium with the observable atmo-

July 1969 / Vol. 8, No.7 / APPLIED OPTICS 1269
 

sphere and consistent with any observation so far. It
is, however, quite crucial to any plausible models of bio-
logical systems on the planet. An important challenge
to forthcoming reconnaissance missions is the evaluation
of subsurface ice (permafrost). It is, however, not easy
to predict just how such a feature will be revealed, if at
all, to remote observation. At subkilometer resolutions,
it is barely possible that volcanic formations and asso-
ciated clouds might be delineated photographically and
confirmed by ir mapping. More comprehensive land
form observations or analysis of diurnal and seasonal
changes might also be contributory.

In the face of these discouragements, most biologists
(including myself) have been quite conservative in our
stated expectations about Martian life (always with the
qualification, “if any”). Published speculations center
on “primitive vegetation.” In fact, this view is no bet-
ter justified than any other. The contemporary life
system is surely coupled to solar energy, but it might
have originated “in the beginning” from cosmic rather
than atmospheric processes.‘ The aridity and thin at-
mosphere of Mars do not, then, necessarily bear on the
liketihood of the origination of life or on its initial com-
plexity. If solar uv flux is high at the surface, or-
ganisms will need shielding, but this is easily available
with a few microns’ thickness of iron oxides. However,
the conveyance of solar energy from the surface with
moisture a meter below will require an elaborate struc-
ture (like the root system of a leafy plant) or as an alter-
native, a food chain of mobile microorganisms.

Once this is granted, however, there are no theoretical
limits to the evolution of herbivores and their predators,
roughly analogous to animal life on earth. Nor is there
any rigorous argument against, intelligent life which,
indeed, might have sequestered all the available mois-
ture in more congenial, subsurface habitats.

To assert these possibilities is not to express any deep-
seated conviction for or against them. It speaks rather
to the need to keep an open mind and an open eye for the
unexpected that will be the main harvest from the mis-
sions now initiated.

 

Recent analyses of the Mars atmosphere are trying to
offer some more conercte possibilities for the metabolic
system (which has a limited bearing on the over-all
complexity of any organisms). Carbon may be present
on Mars in many different forms, but only CO and CQ,
are now revealed by direct measurement. With both
compounds present, however, it is hard to imagine that
their metabolic interconversion is excluded from Mar-
tian life. (That CO is a general cell poison on earth is
immaterial; note that terrestrial bacteria are known
that also oxidize CO.)

In fact, the exergonic reaction: 2CO + HO >
CHO + 22 cal might allow for the synthesis of carbo-
hydrate without photosynthesis within the organism,
being driven ultimately by the inorganic photolysis of
CO:. ro

It is not obvious how the actual occurrence of such
reactions could be verified short of a lander mission.

At this stage, such proposals are. hardly more than
idle speculations. However, they illustrate the way in
which more detailed, rigorous information about the
Martian environment ean guide our efforts to frame the
most reasonable designs for detecting that elusive
Martian life, if any.®

References

1. J. Lederberg, Science 132, 393 (1960).

2. J. Lederberg, Nature 207, 9 (1965).

3. J. Lederberg and D. B. Cowie, Science 127, 1473 (1958).

4. C. Sagan and J. Lederberg, Proce. Natl. Acad. Sci. 48, 1473
(1962),

. L. Kaplan, Jet Propulsion Laboratory ;

tion.

6. For general accounts see: NASA SP-3030, Handbook of the
Physical Properties of the Planet Mars (Government Printing
Office, Washington, D.C., 1967); NASA SP-179, The Book of
Mars, by Samuel Glasstone (Government Printing Office,
Washington, D.C., 1968); Biology and the Exploration of Mars
C. 8S. Pittendrigh, W. Vishniac, and J. P. T. Pearman, Eds.
‘(National Acadamy of Science—National Research Council,
Washington, D.C., 1966).

qr

private communica-

 

 

oe é »
Vede O.

exploration of Mars, the first part of which appears in this July
NASA's Office of Space

eo... ee gE

Donald G. Rea is the editor of the feature on exobiology and the

issue. The second part will be published next vear. Dr. Rew is depity director of Planetary Prosrams of

Science and

1270 APPLIED OPTICS / Vol. 8, No.7 / July 1969

}

Applications,

Dc
Coy t

Int
Cc
rocl.
cluc
gre:
of ¢
cert.
inte
core
itive
man
this
rock
forn
surf.
year
and
intin
inter
mos}
regai
mate
eart]:
astre
geop’
and t
orof
ciplit
andd
and ¢
proce

Thi
fornia

Ree