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| Putting Exploration in Context |
MRO and CRISM are vital pathfinders for human exploration of the Red Planet. Read about:
The first settlers in the New World asked fundamental
questions as they entered a new environment and faced "living off the
land." Where could they build a settlement near a supply of fresh water? What locations were
protected from flooding? Where was the fertile land to grow crops?
The
first human explorers on Mars will face some similar questions. Most
basically, they will need protection from the Martian environment. All
places on Mars are harsh by Earth standards, but some are less harsh
than others. For example, some regions are more prone to dust storms,
and some are colder.
The explorers' long journey will be more feasible if they
can use at least some resources on Mars and "live off the land."
Their most important resource will be water –to drink, to grow food,
and
to extract oxygen to breathe and hydrogen for fuel. Close behind will
be building materials. Mars' thin atmosphere provides little protection
from radiation and nighttime chill, and using local rock and soil to
shield buildings would
be vital.
The first explorers on Mars will want to visit a "safe" site, for
example, one not covered in boulders and one not too steeply sloped.
Less obviously, they will not want one where the soil is so weak that a spacecraft or
building would sink in and one where the soil is full of toxic chemicals. Ideally, they will want one at
which the soil could be brought into a pressurized, heated environment
and used to grow food plants.
In this artist's conception of a human base on Mars, the
interconnected buildings at lower right are banked in soil for
protection from the environment. This assumes that the soil can be easily moved. Greenhouses are using the local soil to
grow food. This assumes non-toxic soil with essential elements for
plants. The nozzle-shaped structures in the crater at the upper left are
inhaling the thin atmosphere and condensing and extracting its water. This assumes that the
base is in a relatively "humid" part of the planet. A landing vehicle
is descending on parachutes. Parachutes don't work at higher Martian
elevations – there is too little air – and a parachute landing would be risky in an area prone to high winds and dust storms.
So, constructing this base would require reconnaissance to find a
low-lying site with "humid" air (by Martian standards); safe, workable,
fertile soil; and mild weather.
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This
painting by space artist Mike Carroll shows a landing vehicle
descending to a Mars base complete with permanent dwellings and
greenhouses. (Image credit: The Mars Society)
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MRO's instrument suite is
exceptionally suited to begin the reconnaissance needed to find a
suitable site for landing or longer-term settlement. HiRISE's
super-high resolution can scout for hazards like boulders and identify
sites that are "trafficable" (meaning, safe to move around in). MARCI's daily global weather maps can identify areas prone to dust storms and high winds.
CRISM can help to address a half-dozen critical questions that need to be answered to support future human exploration: (1) (2) (3) (4) (5) (6)
(1)
What is the range of soil compositions that could affect the soil's
usefulness for construction or for possibly growing plants in pressurized
greenhouses?
Some soils on Mars have a high content of
sulfate, a salt that is easily dissolved in water, which would have to be removed
before plants could grow in them. Potentially those soils could
be cemented into a hardpan that would resist being worked for construction. CRISM is especially sensitive to sulfate and can map areas rich in it [more].
Food
plants raised by Martian settlers need essential elements for growth.
Mars is short of one of these elements, nitrogen. On Earth,
nitrogen in the atmosphere is converted by lightning and by some
biological processes into a form that can be used by plants.
Fertilizer, which supplements what nature provides, comes from nitrate
minerals. Either nitrogen
could be extracted from the thin Martian air and converted or nitrate
minerals could be used if the mineral deposits could be located. CRISM
is especialy sensitive to nitrate minerals and could detect them
at low concentrations.
CRISM's ability to detect and map sulfates and nitrates will help to
choose a landing site with soil that is easily moved for
construction and that would be suitable for indoor culture of food
plants.
(2) How much dust or ice haze is present in different locations and
seasons?
In areas of Mars where there is a lot of
suspended dust in the atmosphere, settling dust would cause problems
with
exposed machinery, for example, solar panels used to generate
electricity. Solar power is an ideal energy source on Mars, where rainy
days are not an issue. However, Martian dust coats solar panels and cuts
their power output dramatically. This has happened repeatedly on MER. Similarly, cloudy days – those with a lot of ice haze in the atmosphere – temporarily drop solar panels' output.
CRISM's strength among MRO's atmospheric instruments is its ability to
accurately measure the total amount of haze in the atmosphere. It will globally
map atmospheric dust and ice haze abundance every couple of weeks and build up a
history of abundances of water ice and dust in the atmosphere as a
function of
latitude, longitude, and season. These observations will build on earlier measurements from TES and THEMIS and show how atmospheric properties vary from Mars-year to
Mars-year. This will help to choose a landing site with the most
favorable cloud conditions and low dust fallout.
(3) Where are there usable sources of water?
Explorers on Mars can obtain water locally by condensing water vapor out
of the atmosphere, by mining ground ice, or by extracting it from rocks or soils that contain chemically bound water. The Gamma Ray Spectrometer on Mars Odyssey has begun to map where ground ice occurs, and MRO's SHARAD radar sounder will help to locate concentrations of ice more precisely.
CRISM will help locate water from the other two sources. Its systematic
measurements of the atmosphere will determine the total amount of water
vapor present in the atmosphere as a function of
latitude, longitude, and season. These observations will build on
earlier measurements from TES and show how repeatable high-humidity
areas are Mars-year to Mars-year. CRISM is also MRO's specialist for
finding chemically bound water, with an ability to detect and map
water-containing minerals [more]. This information will help to choose a landing site with accessible water.
(4) Are there poisons in Mars' dust or rocks that could affect human explorers?
There are a number of possible poisons on Mars' surface, and it will take a
variety of measurements to identify them. For example, when the Viking
Landers visited Mars' surface and tested the soil for microscopic organisms, some of the
results suggested the presence of strong, toxic chemicals called peroxides or superoxides.
Currently there is no information about hazardous rock and soil
material, but CRISM will begin to assemble that information. For
example, in some locations, Martian rocks have been altered by water into a type of mineral called phyllosilicate, or clay.
Another class of mineral that can form from alteration of Mars' rocks by water is serpentine, which can contain the
toxic substance asbestos. CRISM is able to detect and map these types of minerals so that human explorers could avoid them.
(5) Is there present-day liquid water that could harbor Martian organisms
or that could be contaminated with germs spread by human explorers?
Finding present-day liquid water would revolutionize our understanding of Mars. MRO's Context Imager can resolve features about 12 meters (40 feet) across, which is sufficient to detect a new gully if one formed today. SHARAD could detect liquid water while it is still below the surface, in the
upper few hundred meters (upper quarter-mile) of the subsurface.
CRISM has a role in detection of present-day water, too. The Context
Imager probably would not catch a gully in the act of forming and see
the flowing water that formed it. Other evidence would be needed to
prove that liquid water was involved. Most likely, this water would be
very salty, with a high concentration of sulfates and other minerals
that dissolve easily. They would be left behind when the water
evaporated in Mars' thin atmosphere. CRISM's mineral-mapping capability
would allow it to detect the mineral stain of sulfate salts left
behind.
(6) Do Mars' moons have water that could be utilized by human explorers?
The Apollo lunar missions used two spacecraft to land on the Moon and
return to Earth. A command and service module contained all of the fuel
needed to reach the Moon, go into lunar orbit, and then return to
Earth. But it never touched down on lunar soil. Instead, the lunar
module piggybacked to the Moon unpowered, then carried astronauts to
the lunar surface and back to lunar orbit, to meet up with their ride
home aboard the command and service modules. Its purpose fulfilled, the
lunar module was abandoned in lunar orbit and never saw Earth again.
Splitting the mission into two vehicles saved the tremendous amount of
fuel that would have been needed to land a single large craft on the
Moon and blast off again.
For a round trip to Mars, a similar two-spacecraft design is
likely, with an orbiter that returns to Earth and a lander that does
not. However, much more fuel will be needed than for a lunar
mission. An ability to refuel the Earth-return vehicle in Mars orbit
would be a huge asset.
Mars has two small moons, Phobos and Deimos, that some scientists and engineers have hoped might be a source of fuel for the return trip from Mars. The Mariner 9 and Viking spacecraft were the first to observe these two small
satellites from Mars orbit. They found that the bodies are dark and
somewhat resemble primitive outer solar system bodies thought to
contain chemically bound water.
Could water be extracted from Phobos' or Deimos' surfaces, split into
hydrogen and oxygen, and used as rocket fuel? Yes, but only if the
satellites actually contain water. Repeated attempts to detect that
water by analyzing the satellites' spectrum of reflected sunlight,
using Earth-based telescopes, have not found definitive evidence for
any water-containing minerals. But the satellites are difficult targets
at Earth's distance, dim and nearly lost in Mars' glare, and that makes
seeing them at all acutely difficult.
CRISM and the OMEGA spectrometer on Mars Express provide the best chance yet to find the sought-after water on Phobos
and Deimos. Both cover wavelengths with the strongest absorptions due
to water, and both are able to view the satellites free of Mars' glare.
Unless and until they find water, any thoughts about astronauts making
a refueling stop at Phobos or Deimos is just speculation.
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This
painting by space artist Pat Rawlings shows astronauts mining the
surface of Phobos for water, which is broken down into hydrogen and
oxygen for rocket fuel for the journey home. Although chemically bound water on
Phobos and Deimos has been conjectured, there is no actual evidence for
any water. (Image credit: The Mars Society)
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