Mission to Mars: Project Based Learning Benchmark...
Transcript of Mission to Mars: Project Based Learning Benchmark...
Mission to Mars: Project Based Learning Benchmark Lessons
Dr. Anthony Petrosino, Department of Curriculum and Instruction, College of Education, University of Texas at Austin
Benchmarks content author: Elisabeth Ambrose, Department of Astronomy, University of Texas at Austin
Project funded by the Center for Instructional Technologies, University of Texas at Austin
http://www.edb.utexas.edu/missiontomars/bench/bench.html
2
Table of Contents
Mars as a Solar System Body 4
Place in the Solar System 4
Physical Properties and Composition 5
The Moons of Mars 7
Mars geography 8
Mountains 10
Volcanoes 10
Valleys 11
Craters 12
Surface Rocks 14
Crust Composition 16
Atmosphere composition 17
Ice caps 17
Conditions on Mars 18
Gravity 18
Atmosphere 18
Weather, winds, storms 19
Temperatures, seasons, climate 20
Length of year 22
Length of day 22
Water on Mars 22
3
Polar Ice Caps 22
Water channels 23
Surface Water 25
Previous, Current, and Future Missions to Mars 25
Mariner 4 25
Mariner 6-7 26
Mariner 9 26
Viking 1-2 27
Mars Pathfinder/Sojurner Rover 27
Mars Global Surveyor 28
2001 Mars Odyssey 29
2003 Mars Exploration Rovers 29
2005 Mars Reconnaissance Orbiter 30
Smart Lander and Long-Range Rover 30
Scout Missions 31
Sample Return and Other Missions 31
Getting to Mars 31
Escape velocity 31
Routes and travel time 33
Supplies: food, water, oxygen 35
Psychological needs/concerns 35
References 40
4
Mars as a Solar System Body Place in the Solar System
The Solar System. NASA/JPL.
This picture depicts the correct
relative sizes of the 9 planets of the Solar
System in the correct order. The planets
are Mercury, Venus, Earth, Mars, Jupiter,
Saturn, Uranus, Neptune, and Pluto.
Mars is the fourth planet from the Sun. It
is one of the four inner planets. Mars
orbits at a distance of 1.52 Astronomical
Units (227,940,000 km) from the Sun.
One Astronomical Unit is equal to 1.496
x 108 km, the average distance from the
Earth to the Sun. Astronomical Units are
abbreviated A.U. Its orbit is situated
between those of Earth and the Asteroid
Belt.
Sun and planets. NASA/JPL.
This picture depicts the four gas
giant planets (Jupiter, Saturn, Uranus,
and Neptune), Earth, and the Sun. Earth
is the tiny dot between Jupiter and the
Sun. The relative sizes of the objects
are to scale, with 3200 km corresponding
to one pixel of the image.
If the relative sizes of the planets
were shrunk to be one billionth of its
actual size, the Earth would be the size
of a large marble (2 cm diameter), Mars
would be the size of a pea (1 cm
diameter), Jupiter would be the size of a
grapefruit, Saturn would be the size of an
orange, Uranus and Neptune would each
be the size of lemons, and the Sun would
be the size of a tall man.
5
The relative sizes of the Mercury, Venus, Earth, and Mars. NASA/JPL.
While it is easy to compare the
relative sizes of the planets in an image,
it is more difficult to compare their
relative distances from the Sun. If the
Solar System was shrunk to one billionth
of its actual size, the Moon would be
about 30 centimeters away from the
Earth. The Sun would be 150 meters
(one and a half football fields) away from
the Earth. Mars would be 325 meters
away (three football fields), Jupiter would
be 750 meters away (5 city blocks),
Saturn would be 1500 meters away (10
city blocks), and the nearest star would
be more than 40,000 km away (twice the
circumference of the Earth!)
From the Earth, Mars looks like a
big, reddish star. A somewhat closer
view as in this image taken as the Mars
Climate Orbiter was approaching the
planet, shows the brightly lit side of Mars
that is facing the Sun.
Physical Properties and Composition
Mars has a mass of 6.4x1023 kg,
or about 100 times less than the mass of
Earth. It has a diameter of 6,000 km, or
about half that of Earth. The surface
area of Mars is about the same as the
land area of Earth. There is no evidence
of current plate tectonic activity or active
volcanism on Mars, although there is
evidence to suggest that such
phenomena have been present in the
past. Mars is made of an inner core with
a 1700 km radius, a molten mantle, and
a very thin crust that ranges from 80 km
to 30 km thick in places. The planet is
made mostly of iron. In fact, iron oxide
(rust) on the surface of Mars is what
makes the so-called “Red Planet” appear
red.
6
The interior of Mars. NASA/JPL.
The surface of Mars. NASA/JPL.
Because Mars is not very
massive, it can retain only a thin
atmosphere of mostly carbon dioxide.
Carbon dioxide makes up 95.3 percent of
the atmosphere, while nitrogen at 2.7
percent, argon at 1.6 percent, oxygen at
0.15 percent, and water at 0.03 percent
make up the remainder. The carbon
dioxide on Mars does produce a small
greenhouse effect that raises the
temperature on the planet about five
degrees. The atmosphere is thick
enough to produce very large dust
storms that can be seen from Earth.
A dust devil on Mars, taken by the Mars Global Surveyor. NASA/JPL.
A Martian sunset, taken by the Imager for Mars Pathfinder. NASA/JPL.
7
The red and blue colors in this
Martian sunset are caused by absorption
and scattering of light by dust in the
atmosphere.
Mars also has ice caps on both its
north and south poles. The ice caps
grow and shrink with the seasons, and
they are made of both carbon dioxide ice
(“dry ice”) and water ice. The ice caps
can be seen from Earth.
Martian North Polar Cap. NASA/JPL. The Moons of Mars
Mars has two moons named
Phobos and Deimos, Greek for fear and
panic. Phobos is the closer of the two,
orbiting Mars 9378 km above the planet’s
center. It is very small – the diameter of
the moon is only 22 km. It is very odd-
shaped, and has a mass of just 1.1x1016
kg. It is composed mostly of carbon-rich
rock and is heavily cratered. Most
astronomers think that Phobos is a
captured asteroid.
Phobos orbits Mars very quickly.
It usually rises, transverses the Martian
sky, and sets twice every Martian day.
The moon is also very close to Mars’
surface. Just as an airplane flying over
the Earth’s equator cannot be seen
above the horizon for an observer in the
United States, Phobos is so close to
Mars’ surface that it cannot be seen
above the horizon from all points on
Mars. As it orbits, it slowly spirals in
towards the Martian surface. Phobos
looses 1.8 meters of altitude per century,
and in 50 million years it will either crash
into the surface or be destroyed in the
atmosphere.
8
Phobos taken from the Viking 1 Orbiter. NASA/JPL.
Deimos orbits farther out than
Phobos, and it is even smaller, with a
diameter of only 12.6 km and a mass of
1.8E15 kg. In fact, Deimos is the
smallest known moon in the Solar
System. Like Phobos, Deimos is made
of mostly cratered carbon-rich rock, is
very amorphous, and is thought to be a
captured asteroid. Like our own Moon,
Deimos orbits far enough away from
Mars that it is being slowly pushed
farther and farther away from the planet.
Deimos, taken from the Viking 2 Orbiter. NASA/JPL. Mars Geography
Like Earth, the surface of Mars
has many kinds of landforms. Some of
Mars’ spectacular features include
Olympus Mons, the largest mountain in
the Solar System. The Tharsis Bulge is
a huge bulge on the Martian surface that
is about 4000 km across and 10 km high.
The Hellas Planitia is an impact crater in
the southern hemisphere over 6 km deep
and 2000 km in diameter. And the Valles
Marineris, the dark gash in Mars’ surface
shown in the picture below, is a system
9
of canyons 4000 km long and from 2 to 7
km deep.
Mars, taken by the Hubble Space Telescope. NASA/JPL.
The white patches in the map of
the Martian surface shown below are
clouds and storms in Mars’ atmosphere.
Mars with clouds and storms, taken by the Hubble Space Telescope. NASA/JPL.
Martian Topography. NASA/JPL.
This is a map of Martian
topography. In the left image, the
Tharsis Bulge can be seen in red and
white. The Valles Marineris is the long
blue gash through the middle. In the
right image, the blue spot is the Hellas
impact basin. Craters can also be seen
in the right image.
Mars Topography. NASA/JPL.
This image is a flat map of Mars,
made from data from an instrument
aboard the Mars Global Surveyor. There
10
are striking differences between the
northern and southern hemispheres.
The northern hemisphere (top) is
relatively young lowlands. It is about 2
billion years old. The southern
hemisphere (bottom) consists of ancient
and heavily cratered highlands, much
like the surface of the Moon. It is about 4
billion years old. There is a very clean
boundary between the two regions,
although the reason for this sharp break
is unknown. It might be due to a very
large impact that occurred just after the
planet’s formation. The Hellas impact
basin is visible as the bright blue region
on the left side of the image. The
Tharsis Bulge is the bright red region on
the right side. It is interesting to note that
these two features are located on exact
opposite sides of the planet from each
other. Olympus Mons is the white spot
to the left of the Tharsis Bulge.
Mountains
The picture below shows the
Libya Montes, examples of mountains on
Mars. The Libya Montes were formed by
a giant impact. The mountains and
valleys were subsequently modified and
eroded by other processes, including
wind, impact cratering, and flow of liquid
water to make the many small valleys
that can be seen running northward in
the scene. This picture covers nearly
122,000 square kilometers (47,000
square miles).
Mountains on Mars. NASA/JPL. Volcanoes
There is no known current active
volcanism on Mars. All of the volcanoes
on Mars appear to be extinct. Mars also
lacks plate tectonics. Both volcanic and
11
plate tectonic activity are caused by heat
flowing from the interior of a planet
toward the surface. Because Mars is
much smaller than the Earth (about half
its diameter), and is much less massive
(about 1/10 the mass of Earth), the
planet cooled off very quickly. There is
no more heat to escape from the interior
of the planet, and therefore all plate
tectonic and volcanic activity has
stopped.
The best known volcano on Mars
is Olympus Mons, which is the largest
volcano in the Solar System. It is a
shield volcano, meaning that it has
broad, gentle slopes that were formed
from the eruption of lava. It rises 24 km
(78,000 ft.) above the surrounding plains
– much higher than Mt. Everest here on
Earth. Its base is more than 700 km in
diameter, which is bigger than the state
of Missouri. It is rimmed by a cliff 6 km
(20,000 ft) high. The last time Olympus
Mons erupted was about one billion
years ago.
Olympus Mons. NASA/JPL.
Oblique view of Olympus Mons. NASA/JPL.
Elevation of Olympus Mons. Valleys
The following picture is an image
of the Valles Marineris, the great canyon
of Mars. It is like a giant version of the
12
Grand Canyon. The image shows the
entire canyon system, which is over
3,000 km long, stretching over about
one-third of the planet. The canyon
averages 8 km deep and might have
formed from a combination of plate
tectonics and erosion. Several craters
are also visible around the canyon.
Valles Marineris. NASA/JPL.
Oblique view of the Valles Marineris. NASA/JPL. Craters
Like the Earth and the Moon,
Mars also has impact craters. All three
bodies have experienced approximately
the same rate of cratering, but because
of erosion, the craters have different
appearances on each surface. Because
the Moon has little to no atmosphere,
most craters there look as fresh as the
day they were made. Mars does support
a thin atmosphere, so some erosion of
craters there does take place. However,
the extent of this erosion is very small
compared to the erosion of craters that
happens on Earth.
Craters on Mars. NASA/JPL. Earth: This crater was created by a
comet or asteroid that hit the Earth
13
several hundred million years ago. It is
located in the Sahara Desert in Chad,
and it is about 17 km wide. Erosion of
the crater is clearly visible.
Crater on Earth. NASA/JPL. Mars: This crater is located on the
surface of Mars. While not as eroded as
the craters on Earth, the rim of the crater
has been sculpted by ice that forms on
the ground.
Crater on Mars. NASA/JPL. Moon: These craters on the Moon are
located near the Sea of Tranquility.
Craters on the Moon show very little
erosion because the Moon has very little
atmosphere.
Craters on the Moon. NASA/JPL.
14
Surface rocks
In this image of the Martian
surface taken by the Imager for Mars
Pathfinder, the colors have been
exaggerated to help show differences
among the rocks and soils. It is clear
from the image that there are three
different types of rocks. The white
arrows point to flat white rocks of
unknown age. The red arrows point to
large rounded rocks that show
weathering on their surfaces, and so
have probably been at the site for some
time. The blue arrows point to smaller,
angular rocks. These rocks have not
been weathered, and so are thought to
have been deposited or placed at this
site recently, possibly by an asteroid
impact.
Rocks on the surface of Mars. NASA/JPL. The following images of rocks on the
surface of Mars were taken by the
cameras aboard the Mars Pathfinder.
Rocks on the surface of Mars. NASA/JPL.
Rocks on the surface of Mars. NASA/JPL.
15
Rocks on the surface of Mars. NASA/JPL.
Rocks on the surface of Mars. NASA/JPL.
Rocks on the surface of Mars. NASA/JPL.
Rocks on the surface of Mars. NASA/JPL.
Rocks on the surface of Mars. NASA/JPL.
Rocks on the surface of Mars. NASA/JPL.
16
Rocks on the surface of Mars. NASA/JPL.
Rocks on the surface of Mars. NASA/JPL.
Rocks on the surface of Mars. NASA/JPL.
Rocks on the surface of Mars. NASA/JPL. Crust composition
Mars' crust varies in thickness
across the planet. In the northern
hemisphere, the crust is only about 35
km thick, while in the southern
hemisphere, it is about 80 km thick. This
is probably caused by a period of uneven
cooling that the planet experienced. For
unknown reasons, Mars’ Northern
Hemisphere cooled more slowly than the
Southern Hemisphere, causing it to form
a smoother, thinner crust in that area.
This image shows a possible
configuration of soil and ice in the first
three feet of the surface of Mars.
17
Soil composition on Mars. NASA/JPL. Atmosphere composition
Mars’ atmosphere is composed
mostly of carbon dioxide, which accounts
for 96% of the total. The rest of the
atmosphere is nitrogen, and argon, with
very small amounts of oxygen. Mars has
a very thin atmosphere; it is 200 times
less massive than the atmosphere on
Earth. It would not be possible for
people to breathe on Mars – not only is
the atmosphere very, very thin, there is
not enough oxygen. However, it is thick
enough to allow a parachute to slow an
incoming spacecraft. Mars also has
clouds and dust storms, as visible in the
pictures below.
Clouds in the Martian atmosphere. NASA/JPL.
Clouds and Storms on Mars. NASA/JPL. Ice caps
See also the benchmark lesson on Water
on Mars.
Mars has ice caps at both its
northern and southern poles. The ice is
18
water ice and carbon dioxide ice (dry
ice). In ideal observing conditions, it is
possible to see the Martian ice caps from
a backyard telescope on Earth.
Mars with ice caps. NASA/JPL.
In the summer, the ice caps shrink as the
water ice evaporates, leaving behind the
carbon dioxide ice.
Martian North Polar Ice Cap. NASA/JPL.
Conditions on Mars Gravity, etc.
The acceleration due to gravity on
the surface of Mars is 3.72 m/s^2, or
about 0.38 times of Earth. The surface
magnetic field is about 800 times smaller
than that of Earth.
Atmosphere (content, density, sky
appearance)
Mars has a very thin atmosphere.
With a mass of only about 2.4E19 grams,
it is about 200 times less massive than
the atmosphere of the Earth. Of the
entire planet, only about 4 parts out of
100 million are in the atmosphere. The
surface pressure on Mars due to the
atmosphere is only 7 millibars, or about
0.007 times the pressure of one
atmosphere on Earth. Mars’ atmosphere
is made up of 95.3% carbon dioxide,
2.7% nitrogen, 1.6% argon, 0.13%
oxygen, 0.07% carbon monoxide, and
19
about 0.03% water vapor. Mars has 70
times more carbon dioxide than the
Earth.
It would not be possible for a
person to survive by breathing the
Martian atmosphere. The atmosphere is
too thin and does not contain enough
oxygen to sustain human life. Any
astronauts present on the surface would
need life support equipment such as
space suits to survive. Space suits
would also protect the astronauts from
harmful radiation that can reach the
surface through the thin atmosphere, and
from the extremely cold temperatures.
Sunset on Mars. NASA, JPL.
Weather, winds, storms
Storms and carbon dioxide clouds
do form on Mars. Evidence of winds on
Mars can be seen in this image of dunes
formed on the Martian surface. The wind
that formed these dunes was blowing
from the bottom left to the top right of the
image. The image was taken by a
camera on the Mars Global Surveyor,
and is about 3 km wide.
Unlike Earth, it does not rain on
Mars. It is possible for clouds to form in
the thin atmosphere, but temperatures
are too low to allow liquid water to form.
However, water ice fog is often created
in the bottoms of Martian canyons in
early morning, and frost can form in
many places on the surface.
20
Martian sand dunes. NASA/JPL.
Temperatures, seasons, climate
The average surface temperature
on Mars ranges from 180 to 270 K, or –
93 degrees C to –3 degrees C (-135
degrees F to 26 degrees F). Daytime
temperatures range from 216-226 K (-57
to -47 degrees C, or –71 to –53 degrees
F), and nighttime temperatures range
from 153-208 K (-120 to –65 degrees C,
or –184 to –85 degrees F).
Like Earth, Mars experiences
changes of seasons. On any planet,
changes of season are caused by the tilt
of the planet’s axis. As a result of a
planet’s axial tilt, the north pole of a
planet’s axis points toward the Sun at
times in its orbit around the Sun, and at
other times, it points away from the Sun.
As an example, when the north
pole of Earth’s axis is pointing toward the
Sun, the northern hemisphere receives
the most direct rays of sunlight. The Sun
travels very high in the sky during this
time, and the number of daylight hours
per day is increased. With longer days
and more direct sunlight, the northern
hemisphere is heated, causing summer.
At the same time, the opposite is true for
the southern hemisphere. That part of
the Earth receives the least amount of
direct rays of sunlight, the sun is very low
in the sky, and the days are very short.
This causes the southern hemisphere to
experience winter.
Conversely, when the north pole
of the Earth’s axis is pointing away from
the Sun, the northern hemisphere
receives the least direct rays of sunlight.
The Sun travels is very low in the sky
during this time, and the number of
daylight hours per day is decreased.
With shorter days and less direct
sunlight, the northern hemisphere is
cooled, causing winter. At the same
time, the opposite is true for the southern
21
hemisphere. That part of the Earth
receives the most amounts of direct rays
of sunlight, the sun is very high in the
sky, and the days are very long. This
causes the southern hemisphere to
experience summer.
The axial tilt of a planet causes seasons.
The length and severity of
seasons on a planet are determined by
the amount of the planet’s axial tilt. A
planet with no axial tilt would have no
seasons, while one with a 90 degree
axial tilt (such as Uranus!) would have
very extreme seasons. Seasons on
Earth are moderate because Earth’s axis
is tilted by 23.45 degrees. Mars has
seasons that are very similar to Earth’s
because Mars’ axis is tilted by 23.98
degrees.
On Earth, the axial tilt is the only
reason we have seasons. The Earth’s
orbit is very nearly circular, so the
seasons are not influenced by the small
amount that the Earth is closer to or
farther from the Sun over the course of a
year. (If Earth’s distance from the Sun
was what caused the seasons, the entire
Earth would experience the same
season at the same time, which, of
course, isn’t true!)
Seasons on Mars are a little more
complicated. Mars has a more elliptical
orbit than Earth, so the small amount that
the planet is closer to or farther from the
Sun over the course of a year do make a
difference in the amount of sunlight that
reaches Mars. However, for the most
part, the seasons are caused by the tilt of
Mars’ axis.
22
In terms of Mars’ climate history,
Mars is much colder now than it was in
its early days. More than 2 billion years
ago, Mars was much warmer, and
consequently, wetter.
Length of year
It takes Mars 1.88 Earth tropical
years to orbit the Sun once. This means
that one year on Mars is about 687 Earth
solar days long.
Length of day
It takes Mars 1.026 Earth solar
days to rotate once on its axis. This
means that one day on Mars is about 24
hours and 37 minutes long.
Water on Mars
Polar Ice Caps
Mars has ice caps on both its
north and south poles. The ice caps are
made of water ice and carbon dioxide ice
(dry ice). There are two kinds of ice caps
on Mars: seasonal ice caps and residual
ice caps. Seasonal ice caps accumulate
during the winter season, and evaporate
during the summer. The residual caps
remain during the entire year.
Martian North Polar Cap. NASA/JPL.
Mars’ seasonal ice caps are
entirely dry ice that is about 1 meter
thick. The southern seasonal cap
measures about 4000 km across when
its largest during southern winter, and
the northern cap measures about 3000
km across at its largest, during northern
winter. When summer temperatures rise
above 150K (-120 C), the ice sublimes
(passes directly from the solid state into
the gaseous state, bypassing the liquid
state) into the atmosphere. Large
23
seasonal changes in the amount of
carbon dioxide in the atmosphere cause
large seasonal changes, up to 30%
different, in the atmospheric pressure on
Mars.
Mars’ residual caps vary by
hemisphere. The northern cap is about
1000 km across and is made of mostly
water ice. In fact, it is the main
repository of water on Mars. The
southern cap is much smaller, only about
350 km across. It is made of carbon
dioxide ice.
Martian North Polar Cap. NASA/JPL.
Water channels
While there is no running water on
Mars today, there is plenty of evidence
that it once existed on the surface. Most
of this evidence is in the form of dry
channels in the ground that were formed
by running water. Water existed on the
surface of Mars several billion years ago,
when the atmosphere of the planet was
thicker and the temperature was warmer.
Water channels on Mars. NASA/JPL.
There are two kinds of channels
on Mars that have been left by water
flows: runoff channels and outflow
channels. Runoff channels are the
equivalent of dry river beds on Mars.
They are a series of meandering,
connecting pathways that are found only
in the southern highlands. They, like the
24
southern highlands, are thought to be
about 4 billion years old.
Outflow channels are channels
that were created during enormous flash
floods on Mars. After the time of free
flowing water, when the runoff channels
were formed, the climate on Mars
became very cold and much of the water
froze into ice caps or permafrost just
below the surface. About one billion
years later, volcanoes became active on
the planet and melted much of the water.
The melting water cascaded to lower
elevations in huge flash floods, carving
outflow channels as it went. Many
teardrop shaped “islands” were also
formed in the outflow channels. When
the volcanism ended, the water refroze
into the conditions that exist today.
Water channels on Mars. NASA/JPL.
25
Water channels on Mars. NASA/JPL.
Water channels on Mars. NASA/JPL.
Surface Water
The sizes of the outflow channels
indicate that there was once a great deal
of water present on the surface of Mars.
While some of it has frozen out into the
northern residual ice cap, the majority of
the water is trapped just below the
surface in permafrost.
Soil composition on Mars. NASA/JPL. Previous, Current, and Future Missions to Mars Mariner 4
Mariner 4 was a small robotic
spacecraft that was sent to Mars on
November 28, 1964 to complete one
flyby. It flew over Mars in July, 1965 and
took pictures of the surface with its digital
tape recorder. The images showed
26
lunar-type impact craters. After its flyby,
it continued in orbit around the Sun for
three years.
Mariner 6-7
Mariner 6 and Mariner 7 were
identical small robotic spacecraft that
were launched on July 31, 1969 and
August 5, 1969, respectively. They
arrived at Mars at about the same time
and completed one flyby. Mariner 6 flew
over the Martian equator, and Mariner 7
flew over the southern polar region. Both
had imaging equipment, and they sent
back hundreds of pictures. They also
analyzed the Martian atmosphere with
remote sensing equipment. The data
that Mariner 6 and Mariner 7 collected
confirmed that the dark lanes seen on
Mars from Earth were not canals, as was
previously thought.
Mariner 9
Mariner 9 was also a small robotic
spacecraft, and it was launched on May
30, 1971. Unlike Mariner 4, 6, and 7,
which simply flew by Mars, Mariner 9
was designed to establish an orbit
around the planet. It did so successfully,
and continued to orbit for almost a year.
Mariner 9 used its imaging instruments to
make a map of the entire surface of
Mars. As a result, many previously
unknown features of Mars were
discovered, including Olympus Mons and
Valles Marineris, and dry river beds.
Close up images were also taken of the
two Martian moons, Phobos and Deimos.
Mariner 9. NASA/JPL.
27
Viking 1-2
Viking 1 and 2 were identical
robotic spacecraft launched on August
20, 1975 and September 9, 1975
respectively. They were the first man-
made spacecraft to land on another
planet. Each Viking spacecraft consisted
of an orbiter and a lander. Each orbiter
and lander flew to Mars together, and
then decoupled in the Martian
atmosphere. The lander descended to
the ground and the orbiter continued to
orbit the planet. The entire mission was
designed to continue for 6 weeks after
landing, but all 4 components continued
to be active long after this deadline had
passed. The Viking 1 orbiter continued
to fly over the Martian surface for a full
three years, and the lander lasted 7
years on the surface of Mars. The Viking
2 orbiter and lander both lasted for four
years.
The Viking 1 and 2 landers
descended to two different parts of Mars,
but they carried out the same types of
experiments. While on the ground, they
performed tests of the Martian soil to
look for signs of life. However, no such
signs were detected. Both the landers
and the orbiters sent many hundreds of
images of the surface of Mars back to
Earth.
Viking Lander. NASA/JPL. Mars Pathfinder/Sojurner Rover
28
Mars Pathfinder was a robotic
spacecraft that was launched on
December 4, 1996. It landed on Mars on
July 4, 1997, using a parachute and
airbags to cushion the fall. Upon
landing, Pathfinder unfolded its
instruments and deployed a small mobile
robot called Sojurner Rover. The lander
was renamed the Carl Sagan Memorial
Station after successful setup on the
Martian surface.
Mars Pathfinder landed in an
outflow channel littered with many
different kinds of rocks. Cameras on the
lander sent back over 16,500 images of
the Martian surface, and cameras on the
Sojurner Rover sent back another 500
more. In addition, Pathfinder completed
more than 15 chemical analyses of the
rocks and soil, and it studied the wind
and weather of the planet.
Mars Pathfinder. NASA/JPL.
Airbags landing system for Mars Pathfinder. NASA/JPL. Mars Global Surveyor
Mars Global Surveyor is a robotic
spacecraft designed to study Mars while
in a polar orbit around the planet. It was
launched from Earth on November 7,
1996. Mars global Surveyor completed
its mission in January 2001, and as it is
still orbiting Mars today, it is currently in
an extended mission phase. The
satellite has returned more data about
Mars than all of the previous missions to
29
Mars combined. It has sent back
thousands of images including 3-D
images of the northern polar ice cap,
studied the magnetic field of Mars, found
possible locations for water, and studied
the Martian moons.
Mars Global Surveyor. NASA/JPL. 2001 Mars Odyssey
2001 Mars Odyssey is a robotic
spacecraft that was launched on April 7,
2001. It is currently in orbit around Mars,
collecting images and data to help
scientists determine the soil and rock
composition, the amount of water on
Mars, the history of the climate of Mars,
and the extent of radiation on the planet.
Mars Odyssey. NASA/JPL. 2003 Mars Exploration Rovers
Two identical rovers will be
launched between May and July 2003,
bound for Mars. The rovers will be much
like the Sojurner Rover, but they will be
much more powerful. Like Mars
Pathfinder, the Rovers will enter the
Martian atmosphere directly, slowed by
parachutes. Then airbags will shelter the
robots as they bounce approximately 12
times and roll to a stop. Upon landing,
30
the spacecraft will unfold and the Rover
will deploy. Unlike Pathfinder, the
Rovers will have all the scientific
instruments on board, and they will be
able to travel up to 100 yards each
Martian day. With no need to return to
the landing site, the Rovers will be able
to explore a comparatively large area of
the Martian surface. The Rovers, which
will land in different areas on Mars, will
send back images from their cameras
and data about the Martian soils, which
they will be able to analyze at very small
scales.
Mars Exploration Rover. NASA/JPL. 2005 Mars Reconnaissance Orbiter
This robotic spacecraft, planned for
launch in 2005, will be designed to
image the surface of Mars to even
smaller scales. It will map the
surface of the planet with sufficient
resolution to be able to see rocks the
size of beach balls. Hopefully the
data it collects will allow scientists to
understand better the location and
amount of water on Mars.
Mars Reconnaissance Orbiter. NASA/JPL.
Smart Lander and Long-Range Rover
31
The Smart Lander and Long-
Range Rover are planned for launch by
2007. They will be designed to use a
new precise landing method that should
allow landings in otherwise inaccessible
areas. The spacecraft will also be a
laboratory for even better surface
measurements.
Scout Missions
Scout Missions, which could be
small airborne craft or small landers, are
also planned for 2007 launch. They
would help increase the scale of airborne
observations or increase the number of
sites on Mars that have been visited by
human spacecraft.
Sample Return and Other Missions
NASA plans many other missions
to Mars after 2010. One type of mission
includes a spacecraft that would land on
Mars, collect samples of Martian soil,
and return those samples to Earth. This
type of mission might be underway as
soon as 2011, but for now the first
Sample Return mission is slated for
2014, and the second for 2016.
Getting to Mars Escape velocity
Launch of the Mars Pathfinder Mission.
NASA/JPL.
The first problem facing a
potential trip to Mars is leaving Earth.
Specifically, this problems deals with the
enormous amount of energy necessary
to break free from the Earth’s
gravitational field and start traveling
towards Mars, or anywhere else in the
Solar System. To find out what energy,
and therefore speed, is necessary to
32
escape Earth’s gravity, let us consider
the energy of a rocket at Earth’s surface:
E = ½ mrocket vinitial
2 – GMearthmrocket/Rearth Energy is the sum of kinetic and potential
energies. Here, vinitial is the initial
velocity, mrocket is the mass of the rocket,
and Mearth and Rearth are the mass of the
Earth and the radius of the Earth. Now,
because the energy of the rocket is
constant as it travels upward, we can
equate the energy of the rocket at the
surface to the energy of the rocket at its
maximum altitude:
½ mrocket vinitial
2 – GMearth mrocket /Rearth = ½ mvfinal
2 – GMearth mrocket /rmaximum. Here, vfinal is the final velocity and rmaximum
is the maximum height. However, at its
maximum height, vfinal = 0, so the
equation becomes
½ mrocket vinitial
2 – GMearth mrocket /Rearth = – GMearth mrocket /rmaximum. Solving for vi, we have vinitial
2 = 2GMearth(1/Rearth – 1/ rmaximum).
Setting rmaximum = 8, which is the
condition for gravitational escape, vinitial
becomes vescape and we have
vescape = sqrt(2GMearth/Rearth). The same logic can be applied to any
planet, so the equation for escape
velocity can be generalized to
vescape = sqrt(2GM/R). Thus, the escape velocity from any
planet depends on the mass of the
planet and the radius of the planet. For
example, let us assume that we have a
spacecraft on Earth that we are trying to
send into space. Mearth = 5.98x1024 kg,
and Rearth = 6.37x106 m, so we get:
vescape = sqrt (2GM/R)
vescape = sqrt (2(6.67x10-11 Nm2/kg2)(5.98x1024 kg)/(6.37x106 m)) vescape = 1.12 x104 m/s, or about 11 km/s. Now, let us assume astronauts have
successfully completed their mission on
33
Mars and need to calculate the escape
velocity on Mars so they can travel back
to Earth. Mmars = 6.42x1023 kg, and Rmars
= 3.397x106 m, so we get:
vescape = sqrt (2GM/R) vescape = sqrt (2(6.67x10-11 Nm2/kg2)(6.42x1023 kg)/(3.397x106 m)) vescape = 5.0 x103 m/s, or about 5 km/s. Routes and travel time
There are many different possible
routes to take when sending a spacecraft
to Mars. As each trip covers a different
distance, each takes different amounts of
time and fuel.
Perhaps the most familiar type of
route involves sending the spacecraft out
when Mars is about 45 degrees ahead of
Earth in its orbit. This happens once
every 26 months. The spacecraft
powers outward and catches up with
Mars in about 260 days. For the return
trip, which also takes 260 days, the
spacecraft simply leaves Mars when
Earth is slightly ahead in its orbit, and
spirals into Earth’s orbit, catching up with
the planet. In this scenario, a team
arriving on Mars would be able to spend
460 days there. The entire trip would
take about two and a half years. This
type of route is known as a conjunction
class route because the spacecraft
arrives on Mars or Earth when that
planet is in conjunction with where the
other planet was when the spacecraft
left.
The Sun, Earth, Mars configuration upon launch from Earth.
34
The Sun, Earth, Mars configuration upon arrival at Mars.
A different type of route is known
as an opposition class route, which is
similar in style to conjunction class
routes. It is called opposition class
because Earth and Mars make their
closest approach sometime during the
trip. A spacecraft would have to leave
Earth when Mars was significantly ahead
in its orbit, and the trip would take 220
days. During the return trip, the
spacecraft would spiral inside Earth’s
orbit and catch up to the planet from the
back. The return trip would take 290
days. To time the orbits correctly, there
would only be 30 days available to stay
on the surface of Mars.
Lower thrust rockets can also
travel to Mars using less direct means.
These types of spacecraft spiral out of
Earth’s gravitational field, and arrive at
Mars in 85 days. Part of the ship
detaches to drop off the astronauts and
their gear, and the return module
continues to fly by the planet. The return
module will rendezvous with Mars again
in 131 days, allowing the astronauts to
catch their ride home.
There are many other proposed
ways to get astronauts to and from the
red planet. For example, one scenario
envisions astronauts launching from
Earth and landing on one of Mars’
moons. The astronauts could then set
up a base of operation from which they
could make many trips to the surface of
the planet. In another proposal, a space
station that acts as a permanent ferry
35
could be put in orbit between the two
planets. Smaller spacecraft could then
taxi astronauts between Earth and the
space station and between the space
station and Mars. This situation would
allow many more frequent trips for many
more travelers back and forth between
the planets.
Supplies: food, water, oxygen.
Freeze dried ice cream.
Every person on board a
spacecraft bound for any Solar System
body needs to have access to a
minimum amount of food, water, and
other supplies. Some of these items,
such as air and water, can be filtered and
recycled, while others, such as food,
cannot. For one day on the spacecraft,
one person typically needs 1 kg of
oxygen, 0.5 kg of dry food and 1 kg of
whole food, 4 kg of drinking water, and
26 kg of wash water. Of these staples,
80% of the oxygen, 80% of the drinking
water, and 90% of the wash water can
be recycled. None of the food can be
recycled. For a one way flight lasting
200 days, this translates to 3,440 kg of
supplies needed. Once on the surface of
Mars, oxygen and water can be
manufactured by the astronauts. Food is
therefore the only supply to bring to the
surface, and for a 600 day stay for four
people, 1,200 kg of dry food and 2,400
kg of whole food will be needed.
Psychological needs/concerns
Taking a trip to Mars would be
unlike anything ever experienced by
humans before. As they travel away at
thousands of kilometers per hour in a tiny
capsule, the Earth would get smaller and
36
smaller until it was just a tiny dot. The
feeling of empty space all around would
be almost crushing, leaving no doubt of
the tiny insignificance of the speck of a
spacecraft. And how would people
handle living together, cramped in a tiny
space with no escape for three years?
Communication with Earth would take
longer and longer, eventually causing
there to be 20 minute delays between
messages. If problems aboard the
spacecraft emerged, there would be little
or no help available from Earth. The
threat of death would be woven into
everything the astronauts did. A tiny hull
breach by a small meteorite or a flare
from the Sun would pose fatal hazards
that the crew could not prepare for or fix.
What would be the psychological effects
of such a journey?
It is possible to get a glimpse of
what life might be like on such a journey
by looking at similar environments here
on Earth. Environments such as that on
board a submarine, the International
Space Station, or a remote scientific
camp in Antarctica mimic the
psychological problems that might be
present during a trip to Mars. Examples
of these psychological problems could
include concerns about a limited amount
of resources, the unchanging social
group, social isolation, limited
communication with the outside world, a
self-contained ecosystem, the constant
sense of danger, physical confinement,
lack of privacy, lack of separation
between work and non-work, limited
opportunity for variety and change,
limited sensory deprivation, and
dependence on machine-dominated
environment.
As a specific example, travelers to
Antarctica are very cut off from the
outside world, just as astronauts bound
for Mars would be. Neither would be
37
able to contact their loved ones
whenever they wished, and both would
be so far removed from the recognizable
world that no trace of it would remain.
Also, people in Antarctica must be very
careful with their equipment, food, and
supplies in order to stay alive in the
bitterly cold, harsh conditions.
Astronauts bound for Mars would share
these types of concerns. However,
people living in Antarctica would have
plenty of air to breathe and plenty of
water to drink. They would not have to
bring these supplies with them or be
concerned that they might run out. They
would also have plenty of space – if one
member of an Antarctica team got
annoyed with another, he or she would
have the whole continent to walk away
and be separate for a while. Astronauts,
however, would be very confined with no
escape from each other, and they would
be very worried about the supply of air
and water.
On the International Space
Station, astronauts deal with limited
supplies of air, water, and food every
day. They also live in very small
quarters and must be able to cooperate
in order to survive. These conditions
would be very similar to those
experienced by astronauts bound for
Mars. However, if astronauts aboard the
ISS ever got homesick or frightened,
they merely have radio down to Earth to
speak with their families or friends, or to
look out the window to see that Earth is
just a short flight away. In the event of a
major disaster that threatened the lives
of those aboard, emergency escape
vehicles are available to shuttle the men
and women back to their home planets.
However, aboard spacecraft bound for
Mars, no such quick communication or
emergency ride home would exist. As
38
the ship got farther and farther away
from the Earth, radio messages would
take longer and longer to reach them.
Also, the Earth itself would shrink to the
size of a tiny dot, similar to the other
stars. No one in human history has ever
been so far from our home planet, and
the psychological effects of seeing Earth
nearly disappear into the darkness of
space are much unknown.
Perhaps the best analogue
relating to travel to Mars would be that of
a person in a submarine. Living on a
submarine for an extended period of time
would certainly be similar to living in a
spaceship going to Mars. In both
situations, the people on board would be
living in very cramped, tight quarters, and
they would be forced to get along to
survive. They would be breathing filtered
air and drinking filtered water. All
necessary food and personal supplies
would have to be brought on board the
ship before it departed. In addition,
communication with the outside world
would be limited and delayed, resulting in
only sporadic contact with the crew’s
loved ones and friends at home.
Perhaps most similar would be the
dependence on machines for life and
safety and the imminent threat of death if
those machines fail. Just as all aboard
the submarine would be killed in the
event of a hull breach, or a fire, so would
all be killed in a spaceship bound for
Mars. However, it is important to note
that if a crew member became very ill or
if an emergency happened that was not
immediate, the submarine (unlike the
spacecraft) could always return to the
surface in a relatively short time to
secure help.
In order to alleviate some of these
potential problems that might arise
during a mission to Mars, studies are
being done to determine the types and
39
numbers of people that would best
handle the enormous stress and that
best get along in these types of
environments. Technology is also being
developed to help determine when an
astronaut is in psychological distress,
and to develop strategies for dealing with
the distress that do not involve returning
to the Earth. For example, computers
can now discern the emotional inflection
in a person’s voice to look for signs of
emotional trouble. If the computer does
find that someone is in need of help, it is
programmed to suggest ways to alleviate
the problem, such as recommending
extra rest, extra food, or possibly
medications.
40
The Benchmark Lessons were developed with the help of the following sources: Alpert, Mark. “How To Go To Mars.” Scientific American, March 2000, pp. 44-51. Bill Arnet’s “The Nine Planets” website, http://nineplanets.org Begley, Sharon. “The Search for Life.” Newsweek, December 6, 1999, pp. 54-61. Chaisson, Eric, and McMillan, Steve. Astronomy Today. Prentice Hall, Upper Saddle
River, New Jersey, 1999. “Cognitave States.” Discover, May 2001, pp. 35. Hayden, Thomas. “A Message, But Still No Answers.” Newsweek, December 6, 1999, pp. 60. JPL’s Mars for Teachers site, http://mars.jpl.nasa.gov/classroom/teachers.html JPL’s Mars Missions website, http://mars.jpl.nasa.gov/missions/ JPL’s Planetary Photojournal, http://photojournal.jpl.nasa.gov/ Mars Pathfinder Science Results Directory,
http://mars.jpl.nasa.gov/MPF/science/science-index.html Murr, Andrew and Giles, Jeff. “The Red Planet Takes a Bow.” Newsweek, December
6, 1999, pp. 61. The NASA Image Exchange, http://nix.nasa.gov/ NASA Goddard Space Flight Center
http://svs.gsfc.nasa.gov/stories/MOLA/index.html NASA Goddard Space Flight Center, Earth Science Gallery
http://www.gsfc.nasa.gov/gsfc/newsroom/tv%20page/g00-016_earth.html Oberg, James, and Aldrin, Buzz. “A Bus Between the Planets.” Scientific American, March 2000, pp. 58-60. Robinson, Kim Stanley. “Why We Should Go to Mars.” Newsweek, December 6, 1999, pp. 62. Serway, Raymond A. Principles of Physics. Saunders College Publishing, Harcourt Brace College Publishers, Austin, 1994.
41
Simpson, Sarah. “Staying Sane in Space.” Scientific American, March 2000, pp. 61-62. Singer, Fred S. “To Mars By Way of Its Moons.” Scientific American, March 2000, pp. 56-57. Weed, William Speed. “Can We Go To Mars Without Going Crazy.” Discover, May
2001, pp. 36. Wilford, John Noble. “Photos Bolster Idea of Water, and Possibly Life, on Mars.” New
York Times, 2/20/03 Yam, Philip. “Invaders from Hollywood.” Scientific American, March 2000, pp. 62-63. Zeilik, Michael, Gregory, Stephen A., and Smith, Elske v. P. Introductory Astronomy
and Astrophysics. Saunders College Publishing, Harcourt Brace Jovanovich College Publishers, Austin, 1992.
Zorpette, Glenn. “Why Go To Mars?” Scientific American, March 2000, pp. 40-43. Zurbin, Robert. “The Mars Direct Plan.” Scientific American, March 2000, pp. 52-55.