European robot probe Schiaparelli prepares for Mars landing
A small robot probe could make history by becoming the first European spacecraft to survive a landing on Mars.
Scientists will be crossing their fingers as Schiaparelli flies itself on autopilot through the Martian atmosphere.
After a descent lasting a nail-biting six minutes, the 2.4m-wide (8ft) disc-shaped lander will briefly fire its retro rockets before belly flopping on to a plain near the Martian equator at 3.48pm Wednesday, UK time.
The only previous European Space Agency (Esa) spacecraft to attempt a Mars landing was the ill-fated British-built Beagle 2 on Christmas Day 2003.
After separating from the Mars Express orbiter that carried it to the Red Planet, Beagle 2 was not heard from again.
It was not until 2015 that scientists discovered the Beagle had landed, but could not communicate after failing to deploy solar panels.
Mission controllers hope Schiaparelli, part of an ambitious joint European and Russian mission to search for evidence of life on Mars, will fare better but stress that landing on the planet is notoriously tricky.
British space scientist Dr Manish Patel, from the Open University, a member of the team that will be analysing data from the spacecraft, said: "It's certainly a tense time. I'm looking forward to an interesting night's sleep, or lack of it.
"The classic problem with Mars is its thin atmosphere. If you have a thick atmosphere, it naturally slows you down, and if there's no atmosphere, it's easy. But Mars has a very thin atmosphere that slows you down a bit, but can still cause a lot of problems. It varies a lot; you get waves and ripples which are unpredictable.
"Dust impacting on the heat shield can also be a hazard, but I'm told that's one that can be compensated for."
Schiaparelli hitched a ride to Mars on the ExoMars Trace Gas Orbiter (TGO) spacecraft, crossing a distance of 500 million km (310 million miles) on its seven-month journey from Earth.
The probe parted company with its mothership on Sunday. It is due to enter the Martian atmosphere at around 3.42pm on Wednesday, travelling at roughly 21,000 km/h (13,050 mph).
Although it carries some instruments, Schiaparelli's main job will be to test out the landing system for a future ExoMars rover mission due to be launched in 2020.
Initially slowed by the friction on its heat shield, the probe will deploy its parachute at altitude of about 11 km (6.8 miles). As it nears the ground, three clusters of retro rockets will fire, slowing the craft's speed to less than 7km/h (4.3 mph) two metres (6.5ft) from the surface. The rockets will then switch off, allowing the probe to drop the rest of the way.
A special crushable structure built into the spacecraft will cushion against the final shock.
During the descent Schiaparelli will take pictures of the approaching Martian terrain.
The landing site is Meridiani Planum, a flat region that interests scientists because it contains an ancient layer of haematite. On Earth, the iron oxide mineral almost always forms in a watery environment.
Schiaparelli will spend up to about four days gathering weather data before its batteries run out.
While the landing is taking place, TGO will settle itself in orbit around Mars.
Starting next year, the orbiter will sniff the Martian atmosphere for traces of methane and help scientists decide if it has a geological or biological origin. On Earth, methane is chiefly produced by billions of bacterial organisms, many of which live in the guts of animals such as cows.
ExoMars Rover will deploy a six-wheeled mobile laboratory to the surface of Mars to drill into the soil and look for definitive signs of past or present life.