IT isn鈥檛 easy being Santa Claus. In his grotto at the North Pole he faces
freezing temperatures, howling snow storms and recalcitrant reindeer. But if
things seem bad now, just wait until we colonise the Solar System. When Santa
looks for a new base among the planets, the conditions are going to be much,
much worse. Still, if he chooses wisely, he could be in line for some of the
most spectacular views in the Solar System. So Santa, if you鈥檙e reading, here is
a quick guide to the poles on offer.
The north pole of any planet is defined by a trick known as the right-hand
screw rule. Make your right hand into a 鈥渢humbs up鈥� shape. If the planet鈥檚
direction of rotation matches the way your fingers curl, your thumb points
towards the north pole. Try it with the way the Earth rotates (the Earth鈥檚
rotation is from West to East, which is why the Sun appears to move from East to
West).
The north pole on Venus is underneath the planet as seen from Santa鈥檚 home on
Earth, because Venus spins in the opposite direction from every other planet in
the Solar System. Not that Santa or anybody else standing there would know the
difference. Venus has a dense atmosphere of carbon dioxide filled with
lemon-yellow clouds of highly concentrated sulphuric acid. The atmosphere would
allow only a murky yellow light to penetrate to the pole and Santa would never
see the Sun move across the sky. He would be able to see for several kilometres
at the surface, though, and pictures of Venus show a very flat rocky terrain.
鈥淚t鈥檚 a bit like the bottom of the ocean,鈥� says Andrew Ingersoll, professor of
planetary science at Caltech in Pasadena.
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There鈥檇 be no need for a heavy beard or thick red woollen clothing to keep
warm. At more than 450掳C, the temperature at the surface is hot enough to
melt lead and the pressure is almost 100 times that on Earth鈥檚 surface. The
weather patterns on Venus are likely to be very consistent throughout the
Venusian year, which lasts for roughly 224 Earth days. This is mainly because
the atmosphere is so thick and moves so fast that any heating or cooling gets
mixed around very quickly. 鈥淵ou鈥檇 hardly know whether it was summer or winter,鈥�
says Ingersoll.
A more spectacular place to set up base might be the north pole of Mercury.
Mercury is a small, barren planet pockmarked with craters and no atmosphere
worth mentioning. Conditions there are particularly harsh: because it is so
close to the Sun, the maximum temperature is around 400掳C. But the planet
has no atmosphere to retain the heat so the temperature is less than 鈭� 150掳C
in the shade. Most of the planet experiences both extremes of temperature during
each long `day鈥�, which lasts 176 Earth days. And yet the poles might be to
Santa鈥檚 liking.
Because of the way the Earth鈥檚 orbit is inclined relative to Mercury,
astronomers can sometimes see Mercury鈥檚 poles. 鈥淲e鈥檝e had a pretty clear look,鈥�
says Ingersoll. By bouncing radio waves off this part of the planet, they have
spotted signs of ice. Astronomers suggest that ice could only survive the fierce
daytime sunlight at the bottom of craters that are permanently in shadow鈥攁
situation that can only exist because Mercury spins with its axis almost
perpendicular to its orbital plane.
These craters would be extraordinary places, says Ingersoll. Deep inside
them, the sky would appear black but the landscape would not be entirely in the
dark. While the Sun鈥檚 body would be hidden from view, its outermost
atmosphere鈥攖he corona鈥攚ould still show above the mountain tops at
the crater鈥檚 edge. The shimmering corona would cast an eerie blue light across
the crater floor, and every now and then a huge arc of plasma known as a coronal
mass ejection would burst into view above the horizon.
The pale blue light would reveal a strange landscape. Nobody knows what form
the ice on Mercury takes but it is almost certainly left over from comets that
have collided with the surface. Ingersoll guesses that it could be in the form
of dirty boulders of frozen water, carbon dioxide and even noble gases such as
argon. The ice would not only provide a spectacular setting but would be a
useful resource for anybody setting up on the planet. A supply of water, for
example, would mean that Santa would not have to take his own.
The north pole of Mars is in some ways similar to Earth鈥檚. It is currently
pointing away from the Sun and so is in the middle of a harsh winter, much of it
spent in total darkness. It also has a polar cap consisting mainly of water ice.
If Santa wanted to reward his elves with a relaxing beach holiday at the end of
the season, Mars would have a distinct advantage. 鈥淭he permanent ice cap is
surrounded by sand dune fields like those in North Africa,鈥� says Ronald Greely,
a planetary geologist at Arizona State University in Tempe. The dunes range in
size from just a few metres across to 100 metres. In winter they become lightly
dusted by a bright frost of dry ice. And since dry ice turns directly from solid
to gas, this frost would disappear magically under the eyes of the elves when
they embarked on their summer break.
Possibly the most interesting place to set up a base would be Titan, Saturn鈥檚
largest moon. Titan鈥檚 atmosphere is so thick with methane and ammonia that
astronomers have difficulty seeing the surface. Methane exists as a liquid, gas
and a solid on Titan, just as water exists in all these forms on Earth. The few
tantalising glimpses astronomers have had of the surface indicate that it may
have oceans of liquid methane as well as solid land masses. Nobody is quite sure
what exists at the poles but it cannot be a floating mass of ice as it is around
Earth鈥檚 North Pole鈥攎ethane ice does not float on liquid methane.
Astronomers hope to get a better idea of what exists beneath the atmosphere on
Titan in 2004, when the Cassini spacecraft, now en route to Saturn, will drop a
probe onto this wintry moon.
If it鈥檚 seriously cold conditions that Santa is after, the outer Solar System
is by far the most promising destination. The north poles of Saturn, Neptune and
Pluto are all pointing away from the Sun and so these places are in the throes
of winter. 鈥淭he Solar System is a very wintry place at the moment,鈥� says
Ingersoll. Hear that, Santa? You鈥檒l be spoiled for choice.