The six-wheeled robot last contacted Earth in June last year, just before it was enveloped in the darkness of a global dust storm.

Engineers hoped Opportunity would power back up when the skies cleared and sunlight hit its solar panels again - but there has not been a peep out of the rover.

The routine prompt commands that have been sent to Opportunity will now end. The mission has been declared over.

"We tried valiantly over these last eight months to recover the rover, to get some signal from it," explained project manager John Callas.

"We've listened every single day with sensitive receivers, and we sent over 1,000 recovery commands. We heard nothing and the time has come to say goodbye."

The decision brings the curtain down on one of Nasa's most successful ever ventures.

Opportunity and its twin robot, called Spirit, landed on Mars in January 2004 with the goal of investigating whether the planet ever had the conditions necessary to support life.

The mission team believed its "mobile geologists" would work for at least 90 Martian days and have the capability to travel up to 1km.

In the end, the golf-buggy-sized rovers surpassed all expectations.

Spirit worked for six years, logging a drive distance of almost 8km; and Opportunity trundled on for 45km over 14.5 years - a record for any wheeled vehicle off Earth.

Nasa is currently preparing a near-twin of Curiosity, which will be delivered to the planet in February 2021. It will be joined on the surface a month later by Europe's Rosalind Franklin rover, although at a very different location.