1) What is the Mars Rover made of?
The Mars Rover is built of a variety of different materials with
different functions. In some ways one can compare the rover with an
insect. This is mainly because the rover, like insects, has the
"skeleton" on the outside. The "skeleton" of the rover consists of the body-shell containing the
"guts" of the rover. This body shell is made of an aluminum alloy. The
computer (the "brain") of the rover and most of the teflon or Kapton
isolated copper cables (nervous system) resides in this body-shell
along with batteries that enable the rover to save energy for late
evening, night and morning activities. To charge the batteries the
rover relies on three panels of solar cells as energy collectors. The
interior of the body-shell is insulated from the exterior by an almost
perfect thermal insulator,
aerogel.
In this way the rover is able to
maintain a reasonable temperature of its interior. Added to this shell
are a lot of sensory organs (mostly eyes; cameras), the wheel
suspension for all six wheels, more antennae than most insects and the
one lonely arm. Both wheel suspension and wheels are made from
aluminum alloys with fittings made of titanium here and there. The top
of the body of the rover — called the rover equipment deck — has
hinges at the edges that carry the solar panels. The solar panels
consist of arrays of delicate elements that are mounted on plates of a
very strong and lightweight material with an interior that has a honeycomb
structure of thin aluminum walls.
2) How does the Mars Rover robotic arm function?
The Mars Rover robotic arm
works in some respects just like a human
arm. It consists of an upper arm, a forearm and a wrist with a rather
large hand with only four "fingers". The robotic arm has roughly the
same dimensions as the arm of grown man, i.e. around 80 cm from
shoulder to wrist. The shoulder joint can rotate from side to side and
move the upper arm up and down. The forearm moves by a single joint
just like a human elbow and the wrist also moves almost like a human
wrist. Only many of the joints are somewhat more flexible than the
corresponding human joints. And the last joint of the robotic arm is
quite different from anything human. The four fingers — really four
different scientific instruments — of the robotic arm all point in
different directions. And when the arm chooses which finger to engage
in a particular piece of work, it makes use of the last — the fifth
joint — that is unlike anything human. The fifth joint can rotate all
the way around, full 360 degrees, and more. Using the robotic arm it is possible to put any of the four
instruments carried by the arm on a chosen surface of a rock or on a
soil patch for detailed studies.
3) How did you choose where to place the magnets on the rover?
The magnets are there to catch magnetic dust suspended in the thin
air on Mars. Some of this dust is slowly "raining" out of the
atmosphere and therefore it was important to us that the magnets were
placed high on the rover rather than beneath a "shelf" like one of the
solar panels. Also important was to "angle" the magnets with respect
to horizontal high enough that they would be able NOT to attract – or
to loose – material that is less magnetic. This is particularly true
for the filter magnet that is designed to attract preferentially the
most magnetic particles from the airborne dust. And of course very
important too is to position the magnets so that they are accessible
by the instruments that will read the data from the magnets. This is
first the panoramic camera, Pancam, but the two magnets in front of
the camera mast are positioned there also so that they can be reached
by the arm instruments: the elemental particle analyzer (APXS) and the
mineral analyzer (Mössbauer spectrometer). Also the microscopic imager
will provide data on the dust captured on these magnets.
For the sweep magnet a position close to the calibration target was
important. This would allow regular monitoring of the dust build up on
this magnet and make it useful for the outreach work the
Planetary
Society is doing.
4) Why is Mars dust magnetic?
The dust on Mars is magnetic because (at least) some of the dust
particles contain a magnetic mineral. And this is about all we know
about why the dust is magnetic — for some people that might be enough
— but not for us.
There are many different ways the presence of
magnetic minerals could make dust magnetic: One possibility is that
each magnetic dust particle consists of one single little crystal of a
magnetic mineral. If this was the case then one would expect many of
the dust particles to be non-magnetic because we do know what elements
the dust particles are made up of on the average — and since the
chemical composition of the dust and soil cannot be accounted for by
iron-oxides alone, some dust particles would have to have other
compositions. Another possibility is that all the dust particles
consist of many very small crystals — in fact these are probably so
small that we would call them crystallites to emphasize how small they
are. In this way, it is possible that almost all the dust particles are
more or less magnetic. Only very few of them would be very strongly
magnetic — and probably only few would be non-magnetic. During the
Mars Pathfinder mission in 1997 we found that the dust particles did
not seem to be as strongly magnetic as they could have been if many of
the particles consisted of very magnetic minerals. On the other hand,
the magnets on Pathfinder relatively rapidly caught enough dust
particles that patterns of dust were visible on the magnets only a
few sols into the mission.
If we know exactly which mineral is
responsible for the magnetism of the dust, and the crystallite size of
the magnetic mineral, we can learn much about the processes under
which the dust formed, probably this will also tell us if the dust
formed many years ago or if the dust forming processes are still
active on Mars today. Some of the processes that can produce magnetic
dust require large volumes of liquid water.
5) How long is the Mars Rover mission scheduled to last?
The Mars Rover missions are scheduled to last 90 days. The
principal leader of the scientific payload of the rovers, Steve
Squyres, once reflected on the efficiency and lifetime of the 2003
Mars Exploration Rover mission and said that these robotic field
geologists would have roughly 90 days to do what an experienced field
geologist would probably be able to accomplish in about 90 minutes.
The limited capacity of these robotic rovers and the way we work the
rovers from Earth inevitably makes things much slower than if we had a
human being in place on Mars.
6) What is the size of Mars compared to the size of Earth? Does that
affect gravity?
The size of Mars is much smaller than the size of Earth. The
diameter of Mars is roughly half the diameter of Earth. We know that
the mass of Mars is about one tenth the mass of Earth. This is what is
expected if Mars is composed of (very) roughly the same constituents
as Earth. The combination of these facts means that gravity at the
surface of Mars is smaller than at the surface of Earth. Gravity is a
result of masses attracting one another and when the mass of Mars is
only about one tenth that of Earth, one could maybe expect gravity at
the surface to be very much smaller than it is on Earth. However,
because the diameter of Mars is only half that of Earth, if you stood on the
surface of Mars you would be so much closer to the center of Mars that
gravity amounts to 38 % of gravity at the surface of Earth. So in
principle you would be able to jump more than 2 times as high on the
surface of Mars as you can here (on Mars you would need to wear a
heavy space suit which would reduce the initial speed of your jump a
little).
