Destination Mars

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Module 12 Mars - the Red Planet
Activity 1 Destination Mars
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Learning Outcomes
In this Activity, we will investigate (a) Mars
vital statistics, and (b) Missions to Mars
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(a) Mars Vital Statistics

• Now well look at the bulk properties of our
  other planetary neighbour, Mars, and compare them
  to those of Earth and Venus.

Again, structurally all three have much in common
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Earth
Venus
Mars
crust
crust
core
core
mantle
mantle
M 0.81 M?
M M?
M 0.11 M?
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• As Mars has two natural satellites, Phobos and
  Diemos (see later), the mass of Mars can be
  calculated by observing their orbits and using
  Keplers Third Law.

As well as being much smaller than Earth (only
53 ofEarths diameter), Mars turns out to have
a much lower density than does Earth - so its
interior must be significantlydifferent. In
particular, its core must be smaller and probably
less dense too.
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Earth
Venus
Mars
Av. Distancefrom Sun
1 AU
1.52 AU
0.72 AU
Mars is half as far again from the Sun as is
Earth, whichmeans that it receives less than
half as much sunlight (intensity per square
metre).We will see that the distances between
the planets quickly increase as we move out from
the Sun.
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Earth
Venus
Mars
Av. Distancefrom Sun
1 AU
1.52 AU
0.72 AU
Length of Year
1 y ?
0.62 y ?
1.88 y ?
A year on Mars takes almost twice as long as a
year on Earth.
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Earth
Venus
Mars
Av. Distancefrom Sun
1 AU
1.52 AU
0.72 AU
Length of Year
1 y ?
0.62 y ?
1.88 y ?
Length of solar day
117 d? retrograde
1 d?
1.03 d?
Surprisingly, a day on Mars is almost the same
lengthas one on Earth.This would be very
convenient for any future settlerson Mars.
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Earth
Venus
Mars
Av. Distancefrom Sun
1 AU
1.52 AU
0.72 AU
Length of Year
1 y ?
0.62 y ?
1.88 y ?
Length of solar day
117 d? retrograde
1 d?
1.03 d?
Inclinationof axis
3o
23.5o
24o
Another convenient coincidence? Almost identical
axis tiltsgive the Earth and Mars similar
seasonal patterns - exceptthat seasons on Mars
last almost twice as long.
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Earth
Venus
Mars
Av. Distancefrom Sun
1 AU
1.52 AU
0.72 AU
Length of Year
1 y ?
0.62 y ?
1.88 y ?
Length of solar day
117 d? retrograde
1 d?
1.03 d?
Inclinationof axis
3o
23.5o
24o
Accelerationdue to gravity
g?
0.38g?
0.90g?
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• Objects weigh only about 40 of their terrestrial
  weight when on Mars.
• Settlers on Mars would need to make adjustments
  to cope with the reduced gravity.

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• The main reasons why we are not likely to plan
  settlements on Venus involved the atmosphere and
  surface temperature.
• Lets look at the bulk properties of the
  atmosphere and surface temperature on Mars

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Earth
Venus
Mars
av. albedo
0.39
0.16
0.76(cloud tops)
The rusty orange-red, cloudless surface of Mars
is much less reflective than cloud-covered Venus
or even Earth.
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Earth
Venus
Mars
av. albedo
0.39
0.16
0.76(cloud tops)
atmosphere
96 CO2 3.5 N2 0.2 H2O acids
78 N2 21 O2 0.03 CO2 2 H2O
95 CO2 2.3 N2 trace O2 H2O
Like Venus (and the primeval Earth), Mars has an
atmosphere composed mostly of carbon dioxide.
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Earth
Venus
Mars
av. albedo
0.39
0.16
0.76(cloud tops)
atmosphere
96 CO2 3.5 N2 0.2 H2O acids
78 N2 21 O2 0.03 CO2 2 H2O
95 CO2 2.3 N2 trace O2 H2O
av. surface pressure
90 patm
1 patm
0.02 patm
Unlike Venus, the atmosphere that Mars has
managed to retain is very thin indeed, as you
would expect given the low acceleration due to
gravity.
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• Atmospheric pressures on Earth only become as low
  as 0.02 patm at an altitude of 40 km.

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Earth
Venus
Mars
av. albedo
0.39
0.16
0.76(cloud tops)
atmosphere
96 CO2 3.5 N2 0.2 H2O acids
78 N2 21 O2 0.03 CO2 2 H2O
95 CO2 2.3 N2 trace O2 H2O
av. surface pressure
90 patm
1 patm
0.02 patm
surface temperature
472oC
- 50oC ? 50oC
- 140oC ? 20oC
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• Average temperatures on Mars are cooler than on
  Earth, as you would expect for a planet 50
  further from the Sun.

With almost no appreciable atmosphere to insulate
it, temperature changes on Mars can be quite
severe - up to 100oK between night and day at
the equator in summer.
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(b) Missions to Mars

• Although Mars is not our closest planetary
  neighbour, it is the most accessible one. Its
  history appears to be similar enough to that of
  Earth to make the study of Mars important for our
  understanding of our own planet too.

In the long term, Mars is the most likely site if
humans ever attempt to colonize and terraform
a planet other than our own.
There have been several space missions to Mars,
and more are planned. Here well give a very
brief summary of each
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• Mariner 9

The Mariner Mars 71 mission originally consisted
of two spacecraft on complementary missions, but
Mariner 8 failed to launch properly. Mariner 9
then combined the mission objectives of both.
The spacecraft was turned off in October 1972.
The Mariner 9 mission resulted in a global
mapping of the surface of Mars, including the
first detailed views of the volcanoes, Valles
Marineris, the polar caps, global dust storms
and the satellites Phobos and Deimos.
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• Viking Mission to Mars

NASA's Viking Mission was composed of Viking 1
Viking 2, each consisting of an orbiter and a
lander. The primary mission objectives were to
obtain high resolution images of the Martian
surface, characterize the structure and
composition of the atmosphere and surface, and
search for evidence of life.
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• Viking 1 was launched in August 1975 and arrived
  at Mars in June 1976. One month later the Viking
  1 Lander separated from the Orbiter and touched
  down at Chryse Planitia Viking 2 was launched in
  September 1975 and entered Mars orbit in August
  1976. The Viking 2 Lander touched down at Utopia
  Planitia a month later.

The Viking 1 orbiter
The Orbiters imaged the entire surface of Mars at
a resolution of 150 to 300 meters, and selected
areas at 8 meters. NASA powered down the Viking
2 Orbiter in 1978 and the Viking 1 Orbiter in
1980.
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• The Viking Landers sent back images of the
  surface, took surface samples and analyzed them
  to determine their composition and look for signs
  of life, studied the composition of the
  atmosphere and Martian meteorology, and deployed
  seismometers.

The Viking 1 lander
The Viking 2 Lander stopped sending signals to
Earth in April 1980, and the Viking 1 Lander
stopped in November 1982, after transmitting
over 1400 images of the two sites.
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• The Phobos Project

The USSR launched two missionsto Phobos, one of
the naturalsatellites of Mars, in July 1988.
The mission plan intended the twospacecraft,
Phobos 1 and Phobos 2, to be placed intoMars
orbit so that they would be in an almost fixed
position50 m above the surface of Phobos - and
aim laser andion beams at Phobos in order to
determine its chemicalmakeup.
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Phobos 1 failed in September due to a sofware
error.Phobos 2 operated normally, gathering
data on the Sun, interplanetary medium, Mars,
and Phobos.
Shortly before the final phase of the
mission,during which the spacecraft was to
approach within 50 m of Phobos' surface and
release two landers, one a mobile 'hopper', the
other a stationary platform, contact with Phobos
2 was lost due to a malfunction of the on-board
computer.
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The Mars Observer
Launched in September 1992, Mars Observer, the
first of the planned Observer series of
planetary missions, was designed to study the
geoscience and climate of Mars.
To quote NASA, Contact with Mars Observer was
lost in August 1993, three days before scheduled
orbit insertion, for unknown reasons and has not
been re-established. It is not known whether the
spacecraft was able to follow its automatic
programming and go into Mars orbit or if it flew
by Mars and is now in a heliocentric orbit.
Although none of the primary objectives of the
mission were achieved, cruise mode data were
collected up to loss of contact.
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• Mars Pathfinder

The Mars Pathfinder, the second of NASA's
low-cost planetary Discovery missions, landed
successfully on Mars in July 1997. The mission
consistedof a stationary lander and a surface
rover, with the primary objective of
demonstrating the feasibility of low-cost
landings on and exploration of the Martian
surface.
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• Pathfinder directly entering the planet's
  atmosphere and landed by bouncing on inflated
  airbags. The lander operated nearly three times
  its design lifetime of 30 days, while the rover
  operated 12 times its design lifetime of seven
  days.

As we will see in a later Activity, the
Pathfinder provided strongevidence that its
landing site underwent massive flooding bywater
two billion years ago. It also provided
unexpected evidence which is still being
analysed that the rocks at its landing site,
while basaltic in nature, were rather different
to what was expected on the basisof similar
geology on Earth and from the study of
meteoritesbelieved to have originated on Mars.
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Mars Global Surveyor
The Mars Global Surveyor (MGS) mission is the
replacement for the Mars Observer mission. To
quote NASA, The science objectives involve high
resolution imaging of the surface, studies of the
topography and gravity, the role of water and
dust on the surface and in the atmosphere of
Mars, the weather and climate of Mars, the
composition of the surface and atmosphere, and
the existence and evolution of the Martian
magnetic field.
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The spacecraft began its Mars orbit insertion in
September 1997. The primary mapping mission
will begin about March, 1999. The spacecraft
will be in a "sun-synchronous" orbit so that
each image will be taken with the sun at the same
mid-afternoon azimuth, for a planned period of
one Martian year.
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The Mars Global Surveyor will also be used to
relay data to Earth from further U.S. and
international missions. Mars Global Surveyor is
the first spacecraft in a decade-long exploration
of Mars by NASA, with launches planned every 26
months, to take advantage of the times when Earth
and Marsare closest to each other in their
orbits around the Sun. These planned missions
involve sending orbiters, landers, rovers, and
probes to Mars.
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Mars Climate Orbiter and Polar Lander
The Mars Surveyor '98 program is made up of two
spacecraft launched separately, the Mars Climate
Orbiter and the Mars Polar Lander. The two
missions will study Martian weather and climate,
and water and carbon dioxide levels.
The Mars Climate Orbiter was launched
successfully in December 1998.
Mars Climate Orbiter
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The Mars Polar Lander is planned to land less
than 1000 km from the Martian south pole, near
the edge of the carbon dioxide ice cap in Mars'
late southern spring. The terrain appears to be
composed of alternating layers of clean and
dust-laden ice, and may represent a long-term
record of the climate, as well as likely source
of volatile compounds such as water and carbon
dioxide.
Mars Polar Lander
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Nozomi
Nozomi (Japanese for Hope) is a Mars orbiting
mission designed to study the martian upper
atmosphere and its interaction with the solar
wind and to develop technologies for use in
future planetary missions. The mission will also
relay images of Mars' surface.
Nozomi was launched successfully in July 1998.
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Follow this link to see a list of Internet sites
containing more information about these Mars
missions!
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• In the next Activity we will go on to look at
  what thesespace missions have told us about the
  atmosphere and surface of Mars.

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Image Credits
NASA Venus globe http//nssdc.gsfc.nasa.gov/imag
e/planetary/venus/venusglobe.jpg Earth
globe http//pds.jpl.nasa.gov/planets/welcome/eart
h.htm Mars globe http//pds.jpl.nasa.gov/planets/w
elcome/thumb/marglobe.gif Mars - Valles
Marinerishttp//nssdc.gsfc.nasa.gov/image/planeta
ry/mars/marsglobe1.jpg Mars Polar Lander
http//nssdc.gsfc.nasa.gov/thumbnail/spacecraft/MA
RS98L.gif Nozomi http//nssdc.gsfc.nasa.gov/thumb
nail/spacecraft/98-041A.gif
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NASA Viking 1 orbiter http//nssdc.gsfc.nasa.go
v/thumbnail/spacecraft/75-075A.gif Viking 1
lander http//nssdc.gsfc.nasa.gov/thumbnail/space
craft/75-075C.gif Phobos Missionhttp//nssdc.gsfc
.nasa.gov/thumbnail/spacecraft/phobos_mars.gif Mar
s Pathfinder http//nssdc.gsfc.nasa.gov/planetary
/thumbnail/marspath_sol65.gif Mars Global
Surveyor http//nssdc.gsfc.nasa.gov/planetary/bann
er/mgs_orbit_pic.gif Mars Observer http//nssdc.gs
fc.nasa.gov/thumbnail/spacecraft/92-063A.gif Mars
Climate Orbiter http//nssdc.gsfc.nasa.gov/thumbna
il/spacecraft/98-073A.gif
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• Now return to the Module 12 home page, and read
  more about space missions to Mars in the Textbook
  Readings.

Hit the Esc key (escape) to return to the Module
12 Home Page
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More information can be obtained about these Mars
missions on the Internet at the following
sites The Viking Mission, http//nssdc.gsfc.na
sa.gov/planetary/viking.html The Phobos
Project, http//nssdc.gsfc.nasa.gov/planetary/phob
os.html Mars Observer, http//nssdc.gsfc.nasa.go
v/cgi-bin/database/www-nmc?92-063A Mars
Pathfinder, http//nssdc.gsfc.nasa.gov/planetary/m
esur.html Mars Global Surveyor, http//mpfwww.jpl.
nasa.gov/mgs/index.html Nozomi, http//nssdc.gsfc.
nasa.gov/cgi-bin/database/www-nmc?98-041A Mars
Climate Orbiter http//nssdc.gsfc.nasa.gov/cgi-bin
/database/www-nmc?98-073A Mars Polar
Lander http//nssdc.gsfc.nasa.gov/cgi-bin/database
/www-nmc?MARS98L
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Details on more planned Mars missions can be
found onthe Internet at NASAs Mars home
page,http//nssdc.gsfc.nasa.gov/planetary/planets
/marspage.html together with a very useful
timeline of all attempted and future Mars
missions, athttp//nssdc.gsfc.nasa.gov/planetary/
chronology_mars.html
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• Back to the Activity!

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