The probe, Beagle 2, will be placed aboard a European Space Agencyspacecraft, Mars Express, which is scheduled to blast off from Russia's Baikonur launchpad in Kazakhstan next May 23.
If all goes well, exactly one year from now the mother ship will drop off its tiny golden baby as it finally nears the Red Planet.
The lander will then spin gently out into space, glide through the upper layers of the thin Martian atmosphere before descending to its surface by parachute, with the final bump being softened by airbags.
Onboard is an array of instruments which, by the time Beagle 2's electrical heart expires six months later, could tell us once and for all whether water, the stuff of terrestrial life, is present on Mars.
And it could indicate whether Mars's rocks contain the carbon isotopes or if its atmosphere has traces of methane, the calling cards of biological life past or present.
"This is a device which is built to try and answer a very fundamental question -- is there life elsewhere in the Solar System and more importantly is this the first step towards knowing whether we are alone in the Universe?" said Colin Pillinger, a professor of planetary science at Britain's Open University here who is the force behind Beagle 2.
The possibility that Mars could be or has been a haven for life has obsessed astronomers and science-fiction writers for at least a century.
On the face of it, the chances are not good.
The fourth planet from the Sun is cold and dim compared with our home; its temperatures range from 20 C (68 F) to a bleak minus 140 C (minus 220 C); its atmosphere is composed 95 percent of carbon dioxide; and its topography of spectacular mountains, rugged valleys and plains is swept by violent dust storms.
If Mars ever had oceans, they probably boiled off into the atmosphere aeons ago.
But the news is not all bad.
Images sent back by NASA's Mars Odyssey orbiter suggest there is a thin layer of water ice at the Martian poles, and water may have trickled down its surface or even now may lie abundantly just beneath the soil.
And, for some, Martian meteorites that were wacked off the planet millions of years ago by an asteroid impact and eventually plummeted to Earth hold enticing signs of having contained microbial life.
Beagle 2 -- named in honour of the Beagle, the sailing ship that took Charles Darwin on his voyage of discovery -- aims to answer the questions by being the first space lander to be in effect a high-powered geology lab in miniature.
Shown to journalists and project sub-contractors on Thursday during its final assembly phase in a germ-free unit, the Beagle is the equivalent of what is usually a whole room, containing half a tonne of equipment.
Just 65 centimetres (26 inches) across and weighing 68 kilospounds), it looks in Pillinger's words like "a tiny garden barbecue" -- the kind that looks like an opened-out clam shell.
Inside is a silvery robot arm, at the end of which is a camera, a microscope, an X-ray spectrometer and gamma-ray analyser, which are designed to sniff out a suitable rock sample. A "mole", a spring-loaded gadget, will then bury into the soil to grab the sample, which will then be burned in oxygen by a miniature gas spectrometer to see what kind of gas signatures emerge.
The Mars Express/Beagle 2 package, due to be hoisted into space by a Russian Soyuz-Fregat launcher, is ESA's attempt to do quick, cheap unmanned explorations of the Solar System.
The idea is to have probes that are half the cost and time-scale of mammoth spacecraft that take a decade to build and cost half a billion dollars. Three catastrophic losses by US and Russian spacecraft over the past six years shows how Mars has become an expensive graveyard of dreams.
Pillinger is leery about saying how much Beagle 2 costs, but acknowledges the price is "in the region" of 30 million pounds (45 million euros, dollars), although many services were provided free or at low cost by sub-contractors and colleagues in the space community