A major goal of a manned Mars mission is to explore the planet and to investigate scientific questions for which the intensive study of Mars is essential. The systematic exploration of planets was outlined by the National Academy of Science. The nearest analogy to the manned Mars mission is the Apollo program and manned missions to the Moon, but the analogy is limited. The case is argued here that Mars may have to be explored far more systematically than was the pre-Apollo Moon to provide the detailed information necessary if plans are made to use any of the resources available on Mars. Viking missions provided a wealth of information, yet there are great gaps in the fundamental knowledge of essential facts such as the properties of the Martian surface materials and their interaction with the atmosphere. Building on a strong data base of precursor missions, human exploration will allow great leaps in understanding the Martian environment and geologic history and its evolutionary role in the solar system

Blanchard, Douglas P.

English

NASA Technical Reports Server

N87-17768
PI_TARY SCIENCE QUESTIONS
FOR
1_ EXPLOi_TION OF ltta.RS
Douglas P. Blanchard
NASA Johnson Space Center
Houston, TX
ABSTRACT
A major goal of a manned Mars mission is to explore the planet and
to investigate scientific questions for which the intensive study of Mars
is essential. The systematic exploration of planets has been outlined by
the National Academy of Science. The nearest analogy to the manned Mars
mission is the Apollo program and manned missions to the Moon, but the
analogy is limited. The case is argued here that Mars may have to be
explored far more systematically than was the pre-Apollo Moon to provide
the detailed information necessary if we plan to use any of the resources
available on Mars. Viking missions provided a wealth of information, yet
there are great gaps in our fundamental knowledge of essential facts such
as the properties of Martian surface materials and their interaction with
the atmosphere. Building on a strong data base of precursor missions,
human exploration will allow great leaps in our understanding of the
Martian environment and geologic history and its evolutionary role in the
solar system.
INTRODUCTION
The exploration of the planets is among the most exciting and chal-
lenging endeavors of science and the human curiosity. The ability to
send spacecraft to other bodies of the solar system is a recent develop-
ment in human history. Surely the astronomers of many centuries ago
would be envious of our opportunities.
A major stated goal of a manned Mars mission is to explore the
planet and to investigate scientific questions for which the intensive
study of Mars is essential. The orderly exploration of the solar system
proceeds within a logical framework which has been carefully debated and
is well documented. (1'2'3'4) But, that logical plan for the orderly
exploration of the Moon and the planets and their moons can be disrupted
by external events and budgetary contingencies. Still, for whatever the
reason we are allowed to follow our fancy to Mars, the fundamental
566
https://ntrs.nasa.gov/search.jsp?R=19870008335 2020-03-20T12:29:14+00:00Z
scientific problems and questions should be kept in the forefront of our
planning. This mission is an integral part of the overall strategy for
the study of Mars, building on the knowledge from preceding missions and
forming the foundation for subsequent missions.
This paper will look at the logical plan for planetary exploration
and compare that to a sketch of the exploration of the moon which culmi-
nated in the landing of twelve men on the Moon's surface. It wlll look
at what we have learned from previous missions to Mars and discuss some
of the specific scientific priorities for the exploration and study of
Mars.
THE PLANETARY EXPLORATION MODEL
The primary scientific goals in exploring the solar system
are to determine the composition, structure, and environment of
the planets and their satellites in order to define the pres-
ent morphology and dynamics of the solar system and wlth the
purpose of making major steps In understanding the processes by
which planets formed from the solar nebula and how they evolved
wlth time and how the appearance of llfe In the solar system is
related to the chemical history of the system. The investi-
gation of the interplanetary and interstellar medium is
considered an intrinsic part of such an endeavor.
Space Science Board 1975 (1)
Models for the exploration of the planets have been presented by the
SSB (Space Science Board of the National Academy of Sclences) (1'3) and
Complex Committee on Planetary and Lunar Exploratlon (2) of the Space
Science Board. The models identify three stages In the unmanned explora-
tion of any planetary body: (I) Reconnaissance stage of flyby and hard
lander missions; (2) Exploration stage of orbiter and entry probe
missions; and (3) Intensive study stage of soft landers and sample
returns. Nlsslons involvlng humans represent a special case of intensive
study as well as an advanced stage In themselves.
The solar system exploration strategy as stated by the SSB (1)
follows the principle that the overall exploration of the solar system
should advance more or less evenly for all of the planets, sending
"reconnaissance" missions to all of the planets before we move Into the
"exploration" and "intensive study" of any of them. The principle is
admittedly tempered by the technlcal dlfflculty of even the most
rudimentary mission to distant outer planets. Consequently, the plan
calls for advancing the exploration of selected inner planets whlle
567
continuing the reconnaissance of the outer planets. A manned mission to
Mars is a significant anomoly to this orderly exploration plan. The
decision to undertake this mission will be made on many considerations in
addition to purely scientific issues.
MANNED PLANETARY EXPLORATION BASED ON THE LUNAR ESPERIENCE
Human events and budgets affect the orderly course of planetary
exploration. The Apollo program of lunar exploration is an example in
which political events strongly influenced both the objectives and the
pace. It is likely that the commitment to send humans to explore Mars
will have much in common with the commitment to send humans to explore
th(_ Moon. It may be fruitful to examine the hmar exploration experience
for" lessons that can be applied to the manned mission to Mars.
The race to the Moon was conducted by the U.S. and U.S.S.R. along
roughly equivalent developmental paths (Tables 1 and 2). Both programs
progressed through the reconnaissance phase using flybys and hard
landers, and through the exploration phase with orbiters and soft
landers. Finally, the U.S.S.R. returned samples with three automated
landers, and the U.S. returned samples and explored the Moon with six
landing teams.
The exploration stage of lunar science was truncated by the politi-
cal urgency to land men on the Moon before 1970. As a result, we still
do not have high quality global maps nor do we have global mineralogical
and chemical data. In some respects we have more complete global
coverage of Mars than we do of the Moon because of the extended coverage
of Mariner 9 and the two Vlki,ig orbiters. 0nly now, with attention
returning to the Moon and with a lunar base a possibility, is a more
systematic exploration of the whole Moon getting started with the pro-
posed Lunar Geochemical Observer (LGO).
There are important lessons to be learned from the Apollo exper-
ience. Scientifically and developmentally, the Apollo missions were an
anamoly. As long as the Apollo missions were totally self-sufficient and
the objectives of the missions were primarily engineering objectives,
there was little need for more detailed exploration, h lunar base will
not. be a totally self-sufficient system. It wlll need to use some of the
resources available on the Moon. As a result, there is a need to resume
the detailed global exploration of the Moon with LGO and to follow with
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570
intensive study of selected areas, with possibly
returns.
The exploration phase for Mars may have to be far
and thorough than was the pre-Apollo exploration of
automated sample
more systematic
the Noon. The
thoroughness of the prelandtng exploration will depend on the extent to
which the proposed manned MaPs mission will use systems that depend on
being recharged using locally available resources on the Martian surface.
The Mars manned exploration scenario is made somewhat simpler If It can
regenerate at least some of its simpler systems at Mars. To enable any
such simplification, we will need a detailed knowledge of the Martian
surface and certain knowledge of the regions of Mars that wll] have
proven resource potential. The pace of Martian exploration may he some-
what slower than was possible for the Moon because of the infrequent
opportunities and the technical difficulty. Nevertheless, as evidenced
by Mariner and Viking orbiters, well planned capable precursor missions
such as those planned for the observer class missions of the planetary
exploration program can add Immensely to our knowledge base.
OUR PRESENT KNOWLEDGE OF MARS
The reconnaissance stage of the exploration of Nars was accomplished
by the Narlner flyby missions of the 1960's and Mariner 9 Nars orbiter in
1971. After several unsuccessful Russian attempts to visit the planet,
the U.S. continued systematic exploration with the Viking landers and
orbiters In the late 1970's. Wlth the data from these exploratory mls-
sions, our understanding has progressed to the level to support the
beginning of the detailed exploration of the planet.
Wlth Viking, a more intensive investigation of Nars began. It was
discovered that there are only very low levels of hydrocarbons and no
direct evidence of llfe (4) (Table 3). The tenuous atmosphere is depleted
in nitrogen and generally enriched In the heavy isotopic species of the
atmospheric gases. We have only the simplest idea of the composition of
the materials on the Nartian surface (5) (Table 4). The polar caps appear
to have permanent water ice and seasonal carbon dioxide Ice. Water,
while present in the atmosphere, is present only In small amounts. A
major scientific question is the evolution and fate of the Nartlan atmos-
phere and the history of the volatlles (5) (Table 5).
5'/1
TABLE 3
VIKING MARS SCIENCE HIGHLIGHTS
No definite evidence for biological activity In soil, despite unu-
sual chemical reactions produced in life detection experiments.
Surface rocks resemble basalt; surface chemistry resembles altered
basalt.
Polar cap in North made largely of water ice, with lesser amounts
of solid carbon dioxide.
Isotope ratios of carbon and oxygen in the atmosphere resemble those
In the Earth's atmosphere.
Loss of nitrogen to space has produced isotopic ratios on Mars that
are different than those on Earth; the heavy isotope of nitrogen
(15N) has been preferentially retained.
Abundant erosional channels on surface suggest that Mars could
have had a denser atmosphere in the past and may have had
liquid water on its surface.
Noble gas abundances (At and Ne) suggest that Mars has a lower
volatile content than either Venus or Earth.
Red color on the surface is due to oxidized iron.
Soil is fine grained and cohesive, like firm sand or soil on
Earth.
Water compounds and sulfur compounds are present in soil.
Small-scale land forms formed by aeollan (wind) processes.
Typical surface temperatures range from about -84 ° C at night
to -29 ° C in the afternoon.
Surface pressure of the atmosphere (only 0.8 percent of the
Earth's) varies seasonally in accordance with the sublimation
of the polar caps.
Martian moons (Phobos and Delmos) are grooved, indicating that
inclplent fracturing has occurred; they are heavily cratered
and may be captured asteroids.
572
TABLE 4
COMPOSITION OF MARTIAN SURFACE MATERIALS (5)
CHRYSE CHRYSE CHRYSE UTOPIA
FINES DURICRUST DURICRUST FINES
ESTIMATED
ABSOLUTE
ERRORS
St02
A1203
Fe203
Ngo
Ca0
K20
T102
so3
Cl
SUN
44.7
5.7
18.2
8.3
5.6
<0.3
0.9
7.7
0.7
91.8
44.5
n/a
18.0
n/a
5.3
<0.3
0.9
9.5
0.8
n/a
43.9
5.5
18.7
8.6
5.6
<0.3
0.9
9.5
0.9
93.6
42.8
n/a
20.3
n/a
5.0
<0.3
1.0
6.5
0.6
n/a
5.3
1.7
2.9
4.1
1.1
0.3
1.2
0.3
TABLE 5
COMPOSITION OF ATMOSPHERE AT MARTIAN SURFACE (5)
Carbon dloxtde 95.32_
Nltrogen 2.7_
Argon 1.6_
Oxygen 0.13_
Carbon monoxide 0.07_
Water vapor 0.03_
Neon 2.5 ppm
Krypton 0.3 ppm
Xenon 0.08 ppm
Ozone 0.03 ppm
ISOTOPE RATIOS
RATIO EARTH MARS
C12/C13 89 90
016-^18/u 499 50014 15
N NA 36 277 165
_:_ r 292 3000
/Xe 132 0.97 2.5
573
MARS SCIENCE GOALS AND PRIORITIES
COMPLEX (2) divides the strategies for the exploration of the inner
planets into two groups, one for bodies without atmospheres and one for
bodies with atmospheres. Their recommendation was to make the triad of
planets with atmospheres the focus of the exploration attention in the
period of 1977-1987.
The three planets Earth, Venus, and Mars were seen by COMPLEX to
represent a "natural experiment in planetary evolution." The first
experiment produced Earth with its abundant volatiles and free water in
the oceans and atmosphere. Water on the Earth plays a central role in
the morphology of the planet and in the origin and sustenance of llfe.
The second experiment produced Venus. Venus has been nearly completely
degassed but has very little water in its atmosphere. Presumably, many
of the light volatiles, including water, have been lost to the intense
heating that characterizes the Venus surface. Mars is the product of the
third experiment. Mars has lost much of its atmosphere but has not been
thoroughly degassed as a planet. Substantial amounts of liquid water
have clearly played a role in the formation of the surface morphology of
the Martian surface, yet no liquid water is known to exist on the surface
today (and probably none has been on the surface since very early in the
planet's evolution). Is Venus a more thoroughly evolved Earth? Has Mars
been cut short in its evolution and does it still retain the potential to
develop into an Earth-like planet that in some future era may also be
hospitable to life?
The science objectives for the study of Mars in the post-Viklng era
are primarily geological and geophysical. With the first order knowledge
that present llfe on Mars is unlikely, the objectives for further study
are defined by the need for primary information about the planet Mars and
its atmosphere which is essential to understand its place in the evolu-
tion of the solar system. This same information is important in the
debate over the probability of past life on Mars. After the Earth, Mars
is the next-most-llkely planet for the support of llfe. Although the
essential elements for life are present, no proof of present life has
been forthcoming.
Careful studies of the surface materials and the evidence therein
for interactions between the atmosphere and the Martian surface may prove
574
extremely valuable for understanding the evolution of the Martian atmos-
phere. Precise dating of the surface rocks and soils will allow the
major geologic processes to be put into chronological sequence. Strati-
graphy of carefully recovered cores and samples from layered deposits
will give Insight into the more recent effects of geological processes
and the nature of the processes themselves.
A list of science objectives has been assembled by the Solar System
Exploration Committee (SSEC) (4) for the exploration of Mars. The list
(Table 6) defines the basic science tasks on Mars. Many of the tasks
require global perspective and are appropriate for precursor orbiters and
soft landers. Other tasks are clearly appropriate for and could benefit
greatly from the human presence on the surface of Mars. The missions to
Mars defined for the NASA Core Program of Planetary Missions address the
objectives for global exploration of Mars. Mars Geochemical Climatologi-
cal Orbiter (MGCO) will gather data on the global chemistry and the
global atmospheric circulation. The Mars Aeronomy mission will explore
the intricacies of the upper atmosphere and Its interaction with the
solar wind. The Mars Network Mission will collect fundamental geophysi-
cal Information on the planet as well as surveying the composition of
surface material and taking meteorological data using multiple penetra-
tors and their surface stations.
Clearly, the intensive study of the local materials is the area of
science most greatly aided by the presence of human explorers. The
global scale objectives are best done with orbiting Instruments and
observers, but they too are greatly aided by having "ground truth" esta-
blished for them by human explorers.
CONCLUSIONS
Comparison of the Apollo and manned Mars missions leads to the
conclusion that their analogy is a limited one. We will need to do a far
more thorough exploration of Mars at a global level and Intensive study
at a local level before we launch a manned mission than was done for the
Apollo missions. The chief discriminator is the need to depend on any of
the Martian resources as an essential element of the manned Mars mission
plan. While there is a good start in uncovering the mysteries of Mars,
there are many fundamental pieces of Information that are lacking, espe-
cially concerning the exact nature of the surface materials and their
575
TABLE 6
PRIMARY SCIENCE OBJECTIVES FOR THE EXPLORATION OF MARS (4)
-- Characterize the internal structure, dynamics, and
physical state of the planet.
-- Characterize the chemical composition and mineralogy of
surface and near surface materials on a regional and
global scale.
-- Determine the interaction of the atmosphere and the rego-
lith.
-- Determine the chemical composition, distribution, and
transport of compounds that relate to the formation and
chemical evolution of the atmosphere.
-- Determine the quantity of polar Ice and estimate the
quantity of permafrost.
-- Characterize the dynamics of the atmosphere at a global
scale.
-- Characterize the planetary magnetic field and its inter-
action with the upper atmosphere and the solar wind.
-- Characterize the processes that have produced the /and-
forms of the planet.
-- Determine the extent of organic chemical and biological
evolution of Mars and explain how the history of the
planet constrains these evolutionary processes.
-- Search for evidence of the signature of the early atmos-
phere In the ancient sediments.
576
interaction with the atmosphere. Manned exploration of Mars will be most
helpful for the detailed understanding of these phenomena at various
local areas of Mars.
REFERENCES
1. Space Science Board, "Report on Space Science 1975,"
National Academy of Sciences, Washington, D.C. 1976.
2. Committee on Planetary and Lunar Exploration, Space Science
Board, "Strategy for the Exploration of the Inner Planets:
1977-1987," National Academy of Sciences, Washington, D.C.
1978.
3. Committee on Planetary Biology and Chemical Evolution, Space
Science Board, "Post-Viking Biological Investigation of
Mars," National Academy of Sciences, Washington, D.C. 1977.
4. Solar System Exploration Committee, NASA Advisory Council,
"Planetary Exploration Through Year 2000 - A Core Program,"
U.S. Government Printing Office, Washington D.C. 1983.
5. Carr, Michael H. (Editor), "The Geology of the Terrestrial
Planet," NASA SP-469, U.S. Government Printing Office,
Washington, D.C. 1984.
577


Planetary science questions for the manned exploration of Mars

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