ESA’s Mars Express is due to arrive at Mars in December 2003, and its Beagle 2
lander will be making a touchdown in the middle of the Martian winter. Will it
see a ‘white Christmas’ on the Red Planet? Also, if humans one day go to Mars,
would they need to take a sunscreen?

Over its four-year lifetime, Mars Express will be returning data to refine the
latest computer models of the Martian climate. It will be closely watching the
clouds, fog, dust devils, and storms, looking for clues to explain the climate
changes on Mars, now and in the past, and to better prepare us for future missions.

ESA scientists are already working to make sure that future missions to Mars
arrive safely, and that future human explorers know what kind of weather to
expect. They have developed a global atmospheric circulation model for Mars,
which uses the same principles as those used to predict weather on Earth.
Weather data sent back from Mars Express will help us to perfect these Martian
weather forecasts.

This winter, the weather will be similar to that of the Earth, but colder. Mars
Express will experience cold, cloudy mornings and cool, hazy afternoons. Some of
the clouds could be made of water-ice crystals, but most clouds are made of
crystals of carbon dioxide, or ‘dry ice’. Temperatures will fall below ñ125 C
but, because there is not enough moisture in the atmosphere to produce a
significant amount of snow, Beagle 2 itself will not see a ‘white Christmas’.

One of the main investigations carried out by Mars Express will be the global
study of the atmospheric circulation and composition. Its instruments will also
search for water, from just below the surface to the upper reaches of the
atmosphere. ESA scientists hope that the instruments on board Mars Express will
detect the presence of water below the surface, and may answer the question of
whether there has ever been life on Mars.

Like Earth, Mars has a summer season too, but this is very different from the
heatwaves that many of us are now experiencing in Europe. If you are on
vacation, spare a thought for a future holidaymaker on Mars. With maximum
temperatures reaching only 0 C, and plunging to ñ80 C at night, this is as cold
as Antarctica in winter.

However, the summer temperatures do melt the carbon dioxide ice that make up the
polar ice caps, and the atmosphere gets thicker. This raises the typical air
density to about that of Earth’s atmosphere at 25,000 metres where only the
highest-flying research aircraft have ventured.

However, even this atmosphere is still too thin to protect us from the incoming
radiation from space, such as ultraviolet light, X-rays and gamma rays, or
charged particles such as protons and electrons. On this dry, cold world, human
holidaymakers will have a different set of weather concerns, not least exposure
to these harshest elements of space weather.

Unlike Earth, which sits inside a protective magnetic shield called the
magnetosphere, Mars does not have a global magnetic field to protect it from
solar flares and cosmic rays. Solar protons pose the biggest threat to us
because they ionise molecules along their tracks. These can be very damaging
when passing through humans and they pose a long-term health risk.

Scientists do not yet know why Mars’s magnetic field disappeared about 4000
million years ago. Since then, the solar wind has gradually eroded the Martian
atmosphere so that today it is less than 1% as thick as that of the Earth.

With radiation hazards, tissue damage and sunburn, Mars sounds like a dangerous
place to go on holiday. You can leave your umbrella on Earth, but remember to
take your Geiger counter!

More about …

* Mars Express factsheet
http://www.esa.int/esaSC/SEM75G1A6BD_index_0.html

Related links

* Mars Express launch web site
http://www.esa.int/marsexpresslaunch

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/export/esaCP/SEM68PYO4HD_index_1.html]
Beagle 2 will descend to the surface, entering the atmosphere at more than
20,000 km/h. A heat-resistant front shield will protect it as friction with the
upper atmosphere slows it down. When its speed has fallen to about 1600 km/h,
parachutes will deploy to slow it further.

Credits: Illustration by Medialab, ESA 2001

[Image 2:
http://www.esa.int/export/esaCP/SEM68PYO4HD_index_1.html#subhead1]
The Beagle-2 lander, to be carried on ESA’s Mars Express, is equipped with a
suite of instruments designed to look for evidence of life on Mars.

Credits: ESA/Medialab

[Image 3:
http://www.esa.int/export/esaCP/SEM68PYO4HD_index_1.html#subhead2]
Frosty white water ice clouds and swirling orange dust storms above a vivid
rusty landscape reveal Mars as a dynamic planet in this sharpest view ever
obtained by an Earth-based telescope. The Earth-orbiting Hubble telescope
snapped this picture on June 26, when Mars was approximately 43 million miles
(68 million km) from Earth — its closest approach to our planet since 1988.
Hubble can see details as small as 10 miles (16 km) across. Especially striking
is the large amount of seasonal dust storm activity seen in this image. One
large storm system is churning high above the northern polar cap [top of image],
and a smaller dust storm cloud can be seen nearby. Another large duststorm is
spilling out of the giant Hellas impact basin in the Southern Hemisphere [lower
right].

Credits: NASA and The Hubble Heritage Team (STScI/AURA)