8. Mars: the red planet
- Like the Earth, the planet Mars
has an atmosphere, white clouds, polar caps and seasons.
- Mars has a partially liquid core,
probably containing molten iron and perhaps surrounding a solid iron core, as
within the Earth.
Mars does not now have a global, dipolar magnetic field to deflect lethal
cosmic rays and energetic solar particles.
- The oldest terrain on Mars
exhibits bands of magnetized material with alternating polarity, most likely
originating about 4 billion years ago when the red planet might have had a
global, dipolar magnetic field.
- In the early 20th century it was thought that seasonal water melting from the polar caps in
spring and summer produced a dark band of vegetation on Mars, and that
intelligent Martian inhabitants had constructed canals to transport water
across the planet.
- The seasonal dark regions on Mars
are now attributed to winds, and the canals are now known to be an illusion
caused when the eye arranges small-disconnected features into lines.
- Mars now has a thin, cold and dry
atmosphere that is composed almost entirely of carbon dioxide, with a surface
pressure of about one hundred fifthtieth of the Earthís atmosphere and a mean
surface temperature that is well below the freezing temperature of water.
- Because of the low surface
pressure and temperature of the Martian atmosphere, it cannot now rain on Mars.
If any liquid water were now released on the planetís surface, it would
survive for just a brief time before freezing or evaporating.
- The Martian atmosphere contains
virtually no oxygen, so it has no ozone layer. The planetís surface is
therefore exposed to the full intensity of the Sunís ultraviolet rays.
- Powerful and pervasive winds roar
across Mars, sweeping up vast dunes of sand and fine-grained dust, creating
tornado-like dust devils, and occasionally producing global dust storms that
hide the entire planet from view.
- Seasonal polar caps of frozen
carbon dioxide, or dry ice, wax and wane with the seasons on Mars. They lie on
top of extensive caps of frozen water in both hemispheres. In the north, a residual or permanent
cap of water ice remains in the summer heat, but carbon dioxide ice also
remains in the southern winter.
- Layers in the polar caps of Mars
suggest climate changes on time scales of 10 thousand to 100 thousand years,
perhaps triggered by periodic variations in the planetís orbit and rotation
- Mars is divided into two
strikingly different hemispheres; in the south there are the older, elevated,
heavily cratered highlands that resemble the lunar highlands. In the north
there are the younger, lower-lying, smoother volcanic plains.
- Towering volcanoes and immense
canyons are found on Mars.
- The dry tracks of past flowing
water are etched into the surface of Mars, marking the site of ancient rivers
and floods that occurred 3 to 4 billion years ago. Water networks are found in
the heavily cratered southern highlands, and outflow channels are located in
the equatorial regions running downhill from the highlands to the northern
- Water might have once lapped the
shores of long-vanished lakes and seas on Mars.
- Instruments aboard orbiting
spacecraft have detected water-related minerals on the surface of Mars,
especially in the ancient southern highlands
- Landers and rovers have obtained
evidence for a watery past on Mars, but the Mars Pathfinder lander and its Sojourner
Rover found that their landing sites have been untouched by water since it
flowed across the region more than 2 billion years ago. The two Mars Exploration Rovers, Opportunity and Spirit, have found evidence of past water flow on Mars, but no
signs of recent running water.
- Huge amounts of water once flowed
on the Martian surface, but exactly where all that water came from and where it
all went are still uncertain. Colliding asteroids and comets could have
deposited the water in the early history of the planet, or Mars might have been
warmer long ago, with a thick, dense atmosphere, rain and flowing water. Most
of the water that once flowed on Mars is now frozen into ice on or below the
- Subsurface water ice is suggested
by flow-like patterns of material ejected from impact craters on Mars, and
substantial amounts of frozen water have been inferred from spectrometers
aboard the 2001 Mars Odyssey spacecraft.
- The Phoenix lander obtained evidence for subsurface water ice and past
water flow in the northern polar plains of Mars, and detected snow falling from
Martian clouds of water ice.
- Liquid water
may have been seeping out of the walls of canyons and craters on Mars in the
past few million years, creating small gullies and depositing the debris in
fanlike deltas. Some of the gullies have been attributed to landslides of sand
or loose dust.
- The lack of a global dipolar magnetic
field and a thick atmosphere with an ozone layer, which would respectively
divert cosmic rays or solar energetic particles and absorb ultraviolet rays,
suggest that Marsí surface is now a sterile place where life cannot survive.
If life did once exist there, it might have survived beneath the surface,
within rocks or deep underground in the possibly wet and more temperate part of
the planetís interior.
- Five spacecraft have successfully
landed on the reddish-brown Martian surface and revealed no signs of life on
- There are no detectable organic
molecules or cells in the Martian surface examined by the Viking 1 and 2 landers.
They found no unambiguous evidence for biological life at their landing sites.
The chemically reactive, highly oxidized soil will destroy cells, while also
rusting the Martian surface red.
- Cosmic impacts with Mars are
capable of ejecting surface rocks into space, and some of them eventually
arrive at the Earth. One such meteorite from Mars, named ALH 84001, was once
thought to exhibit evidence for ancient, microscopic bacteria-like fossils, but
non-biological explanations are now accepted for these features.
- The search for life on Mars is now focused on the hunt for
liquid water, which might indicate that Mars is habitable and could have
sustained life either in the remote past or recently.
- Methane has recently been found in the Martian atmosphere;
it could be due to geochemical processes or to bacteria-like microorganisms.
NASA has plans to launch a Mars Science
Laboratory that would analyze the surface material near its landing site on Mars for proteins,
amino acids and other molecules that are essential to life as we know it.
- Mars has two small moons, named Phobos and Deimos. Phobos
is heading towards eventual collision with Mars.
Copyright 2010, Professor Kenneth R. Lang, Tufts University