Opportunity has fallen silent as a gigantic dust storm envelops Mars and blots out the sun.

NASA experts have expressed concern over an unprecedented “massive Martian dust storm” that has engulfed the Opportunity rover mission.

The storm covers an area as large as North America and Russia combined – a quarter of the surface of Mars – and has left the golf-cart-sized rover temporarily unable to conduct science operations.

The US space agency’s rover runs on solar power and has entered low power mode to conserve energy.

Mission engineers believe it is unlikely the rover has enough sunlight to charge back up for at least the next several days, NASA said in a statement earlier this week.

A massive Mars dust storm is turning day-to-night, causing the solar-powered @MarsRovers Opportunity to have likely entered a low-power mode where all subsystems are off, except a mission clock that can wake the computer to check power levels. Info: https://t.co/lSOHSsu1Oc pic.twitter.com/jjjr6qs4cK — NASA (@NASA) June 13, 2018

The first indicators of the storm were reported on May 30 and it is nearly circling the planet, NASA scientist Rich Zurek said on Wednesday in a conference call.

The storm’s density was estimated at a record opacity level, of 10.8, said John Callas, project manager at NASA.

This reading is about twice as dense as any other storm that Opportunity has endured since landing on Mars in 2004.

It could also pose a threat to the Curiosity rover, which is monitoring the storm from the periphery.

Engineers are also concerned that freezing temperatures caused by the storm could damage the rover, as cold is thought to be what led to the breakdown of NASA’s Spirit rover – Opportunity’s twin – in 2010.

Mer-B

Opportunity is also known as MER-B (Mars Exploration Rover-B), and it was the second of the rovers launched on 2003, landing on January 25, 2004, three weeks after Spirit landed on the other side of the planet.

Spirit kept functioning until it got stuck in 2009 and stopped communications the next year. Each rover was designed to only last 90 days, yet Opportunity has exceeded its operating plan by 14 years and 48 days.

According to NASA since landing on Mars, the rover has made a number of discoveries about the Red Planet including showing evidence that long ago at least one area of Mars stayed wet for an extended period suggesting that conditions could have been favourable for sustaining microbial life.

The NASA team has used the rover more than 50 times longer than originally planned and it survived such a storm before in 2007. Opportunity has travelled a total of 45.09km.