bringer of War) is also known as the 'Red Planet', due to its distinctive red appearance from Space.
It has also featured in many theories involving alien civilisations - there have been
stories about it being the home of a hostile civilisation, the base of an advanced species
of human and even the home of a dying civilisation! Some astronomers, such as
Percival Lowall, claimed that its 'canal-like' markings indicated that an advanced
alien species lived there. In 1964 however, the Mariner 4 space probe - to the disappointment of
many people - put a stop to all that and confirmed that, at present, there are no signs of any civilisation on the red planet,
though there do appear to be dried up riverbeds which implies that there was once water on Mars, so it may thus once have been capable of supporting life.
Mars was once thought of as being quite similar to Earth's moon - a small
dust-covered lifeless body, cold, dry and inhospitable. However, as our knowledge of this planet has very rapidly increased
over the past few decades - Mars being by far the most visited planet by terrestrial spacecraft - this notion has long since been shattered,
and has been replaced with one of a complex, intriguing planet, with many exciting secrets yet to be revealed.
One of the ways in which Mars has been able to deceive people into believing it to be a fairly dull, uninspiring place
is by being covered by dust. This very fine-grained material,
settled out of the atmosphere, is present throughout Mars, and forms a thick layer even on the highest volcanoes. The dustier
areas of Mars are in fact those which appear brightest to us.
As this dust settles on Mars, it can trap volatile materials, forming a mantle of icy dust. After some time, these volatile ices can turn to dust, leaving strange pits. This icy mantle, whose thickness varies throughout Mars (it is thickest at the poles)
is increasingly becoming the subject of scientific investigations. Evidence suggests that the mantle may once even have flowed
like a fluid, thus bearing some resemblances to glaciers here on Earth, and possibly explaining the presence of the canal-like markings and canyons.
Windy Weather, Climate and Atmosphere
Even though Mars' weak atmospheric pressure, averaging 7 millibars at the surface,
is less than 1% that of the Earth's, it nonetheless has a considerable impact on Mars, and can vary seasonally by up to 25%. Despite being thin,
the presence of dust and ice particles in the atmosphere give it some complex dynamics,
which explains why Martian weather contains such strong winds, in addition to variable low level fogs, seasonal frost,
high-level ice clouds and even dust storms. This atmosphere is also responsible for creating a weak greenhouse effect which warms the planet to the tune of around 5°C, much less than the Earth's 35°C, but by no means insignificant.
Although it may at first appear rather strange for a cloudless planet, Mars' thin atmosphere is capable of supporting wind, and wind is actually a
major characteristic of Mars, and it is this wind which has shaped the Martian landscape into what we see today.
Spacecraft visiting the planet have witnessed dust storms and avalanches, both seemingly caused by wind. In fact,
dust patterns behind some large objects can be observed to change over time, due to the varying wind conditions,
and sand dunes can be observed to move, due to dust deposition. Evidence of erosion can be found in craters.
Although Mars is smaller than the Earth, its much slower spin
means that a Martian day lasts 41 minutes longer. In addition,
Mars has a similar axial tilt as we do, so a Martian year is made up of four distinct seasons. The
years themselves however are 687 days long, so each season would last 6 of our months.
Data collected by the various spacecraft orbiting Mars seems to confirm the absence of any phenomena of horizontal plate tectonics on Mars, revealing an important difference with respect to the Earth. Rather, it appears that the Martian surface experiences a kind of 'vertical' plate tectonics, with hot lava pushing vertically upwards and thus shaping the planet's surface. This may go some way to explaining the thinness of the planet's atmosphere with respect to the Earth's, where a large part of the atmospheric gases comes from the Earth's interior, expelled through gaps in the Earth's crust at tectonic plate boundaries.
Is There Water on Mars?
A distinct physical feature of Mars is the presence of the two polar ice caps. Scientists have deduced that these are
composed of water ice and solid Carbon Dioxide. Recent discoveries have included discovering water ice below the Martian surface, present for most if not all of the Martian year.
In fact, Mars Odyssey detected the presence of a large quantity of water ice mixed into the soil over a wide area around the South pole at a depth of about 1 metre from the surface.
The Mars Global Surveyor spacecraft has also provided clues that further water reservoirs may exist underground, though seemingly not in quantities large enough to be responsible for the creation of Mars' great canyons and flood plains.
The Changing Face of Mars
Recent evidence however has showed that the Southern ice cap is being eroded at
a relatively high rate, prompting many theories about why this may be. It is thought that the Martian climate and weather is
changing over time and may follow regular variations in its orbit.
Indeed, there is evidence to suggest that Mars has changed significantly over time. For instance there's the fact that the
Southern hemisphere is high and heavily cratered, whereas the Northern hemisphere is both lower and flatter, a sign that it is younger.
In addition, certain features along the edge of the Southern highlands bear characteristics which could only have been formed by liquid water. So whilst today Mars may look more similar to the Moon than the Earth, the evidence suggests this was certainly not always the case.
Volcanoes and Valleys
Mars also has the largest volcanic mountain in the
Solar system - Olympus Mons, which is 27 kilometres high and massive 600 km across! Not only that
but it has a collection of Volcanoes in the north that are so big that they deformed the
planet's spherity. The absence of horizontal plate tectonics could go some way to explaining the large size of these volcanoes, as it means lava always pushes through the crust at the same places, creating fewer, larger volcanoes.
Mars also has large spaces going down - the Vallis Marineris canyon
system stretches for over 5,000 kilometres and is up to 7km deep - it's the dark patch you
can can see to the right on the picture above.
Mars has two natural satellites - Phobos
(meaning fear) which orbits at just 5982km and Deimos (meaning terror) which orbits at
23,000km and looks like a bright star from the Martian sky. Because of their size and
irregular shapes, scientists believe they are captured asteroids. To find out more about them, look at our Phobos & Deimos section.