Travelling at nearly 20 times the speed of sound, Europe's most adventurous spacecraft will still take six months to travel 250 million miles to its final destination--Mars. Five days before the European Space Agency's Mars Express goes into orbit around the Red Planet, it will split into two, ejecting a hitch-hiking space probe from the mother ship.

The probe, called Beagle 2, will then begin its hazardous journey to the Martian surface to search for evidence of extraterrestrial life.

If all goes to plan, this is what should happen next.

As Beagle 2 speeds towards the ground at more than 14,000mph, its heat shields become white hot as atmospheric friction begins to slow the space probe down. An explosive mortar fires at a given point above ground to deploy a small pilot parachute, which pulls the probe into two sections, releasing the bigger main chute from its stowed position so that it can take the strain and slow Beagle 2's descent still further.

Pyrotechnic bolts suddenly explode at just the right moment to release Beagle 2's cumbersome heat shield, which falls harmlessly to the ground. Moments before impact, three giant gas bags inflate around the clam-shaped probe to provide a protective cushion that guards against impact damage. Immediately on contact, the main chute is jettisoned to allow the probe to bounce and roll, safely cocooned within its pneumatic protection. A few agonising seconds later, it comes to a gentle halt, allowing the huge inflated balloons to roll away, so bringing Beagle 2 into direct contact with the cold, dry Martian surface.

That is how it should happen, but nothing is for sure when it comes to Mars. Even the best-laid plans of rocket scientists can fall apart when it comes to a Martian adventure; so much so that this part of space is dubbed the Bermuda Triangle of the solar system. Any one of dozens of points in the mission could go wrong.

If Beagle 2 fails to separate, for example, it cannot make its controlled descent to the planet's surface to look for signs of life. Nor will the mother ship be able to fulfil its mission of mapping the Martian landscape from orbit.

The separation depends on a small, 1.6kg device called the "spin-up and eject mechanism", which, like most components of this multi-nation mission, is contracted out to an individual company or consortium (in this case, the British aerospace and defence company, Hunting Engineering).

Over the years, fewer than ten of the 30 or so missions to Mars have been a success. Most, if not all, the failures have been down to some apparently trivial fault that led to a catastrophic failure.

In 1993, the Mars Observer probe disappeared as it approached the planet, possibly due to a minor electrical fault leading to a fuel-tank explosion. In 1999, a mix-up over the use of metric and imperial units sent the Climate Orbiter probe too close to the Martian surface, causing it to burn up in the atmosphere. Three months later, the Polar Lander crash-landed, probably because of a few silly errors in a line of software code.

In the past, the US and the former Soviet Union have dominated the race to Earth's closest planetary neighbour, but Mars Express represents the European third way, albeit with help from a Russian-built rocket.

Indeed, some of the Mars Express instruments are based on the remote-observation payload that was intended to be launched on the Russian Mars 96 programme -- another mission that ended in ignominy.

But the real coup for Britain was the decision of the European Space Agency to add a lander to search for signs of microscopic life.

The decision came after NASA said in August 1996 that a Martian meteorite in Antarctica possessed signs of life. The announcement led to a fierce row, in which data was questioned, claims ridiculed, and insults exchanged. …