Landing a robot spacecraft on Mars is notoriously difficult and there is a long history of failed missions.

To date, only the American space agency Nasa has succeeded in getting a handful of functioning probes and rovers onto the Martian surface.

Mars is tricky because of its thin, yet dynamic, atmosphere. It makes for a fast and bumpy ride that can have an unexpected outcome.

Open University space scientist Dr Manish Patel, a lead investigator with the ExoMars mission, explained: "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 thrown up from the Martian surface is another hazard.

The European probe Schiaparelli, whose fate still hangs in the balance after it broke off contact while attempting to land on Mars on Wednesday, was sent on its mission near the height of the Martian dust storm season.

Whether or not dust storms had anything to do with the loss of communication with the probe less than a minute before it was due to touch down remains to be seen.

Data streamed from the craft prior to that point suggests it may have jettisoned its parachute too soon, and its retro-rockets did not fire for long enough.

It was the Soviet Union which pioneered Mars landings - although every one of their attempts failed.

The first Soviet probe, Mars 2, burned up in the Martian atmosphere in November 1971. A month later Mars 3 landed on the surface and operated for all of 20 seconds before cutting out.

Two more craft from the same series, Mars 6 and Mars 7, respectively, crashed and missed the planet.

The first successful Mars landings were made by Nasa's Viking 1 and 2 probes in 1975. They controversially produced evidence of living microbes on the planet's surface which was later dismissed by independent experts. The findings could be explained by non-biological chemical effects, it was claimed.

In 1988 and 1996 two more Soviet missions - and one post-Soviet Russian mission - Phobos 1, Phobos 2, and Mars 96, all failed.

Nasa scored another hit with its Pathfinder mission which landed a base station and a rover, called Sojourner, on the planet in 1997.

Then came a set-back for the Americans. Mars Polar Lander, which reached Mars in December 1999, broke off contact with Earth and is thought to have crashed. Two penetrator probes released by the lander were also lost.

Another failure followed, this time European. British-built Beagle 2, which hitched a ride with the European Space Agency's Mars Express orbiter, vanished after heading for the planet on Christmas Day 2003.

In 2015 it was spotted on the Martian surface. Satellite images suggested it had failed to deploy two solar panels, leaving its radio antenna blocked.

Nasa meanwhile continued its run of successful rover missions. In 2004 two rovers, Spirit and Opportunity, arrived separately on Mars looking for geological clues that may indicate the presence of past life. Contact with Spirit was lost in March 2010, while Opportunity has continued to operate for more than 50 times longer than its intended lifespan.

The American agency's Phoenix Mars Lander successfully touched down in May 2008 and confirmed the presence of water ice beneath the Martian surface. Communication with the lander was lost in November 2008 after its solar panels were damaged by the harsh Martian winter.

In 2011 Russia launched an ambitious mission to return samples from Phobos, one of the two Martian moons. But Phobos-Grunt never even left Earth orbit. A crippling malfunction stranded the spacecraft, which eventually plummeted back to Earth and burned up in the atmosphere.

Nasa's most successful rover to date, the £2 billion Mars Science Laboratory (MSL) - also known as Curiosity - landed in Gale Crater near the Martian equator on August 5 2012. The rover has been investigating a mountain in the crater's centre whose exposed rock faces represent various periods of Martian geological history.

MSL used a sophisticated "Sky Crane" system to achieve a soft landing with the heavy rover.

Using four steerable engines, the craft's descent module hovered over the landing site before releasing the rover in a "bridle" that was lowered to the ground. When an on-board computer sensed that the touchdown was successful, the rover was cut free.