NASA's Curiosity rover clicks last selfie on Mars’ Vera Rubin Ridge

NASA's Curiosity rover has taken its last selfie on the twisting ridge on Mars that has been the robotic explorer's home for more than a year, the US space agency said. After having collected new samples from the Vera Rubin Ridge, the car-sized rover will now descend toward a clay region of Mount Sharp. On December 15 last year, Curiosity drilled its 19th sample at a location on the ridge called Rock Hall. On January 15, the spacecraft used its Mars Hand Lens Imager (MAHLI) camera on the end of its robotic arm to take a series of 57 pictures, which were stitched together into a selfie.

The "Rock Hall" drill hole is visible to the lower left of the rover in the image. The scene is dustier than usual at this time of year due to a regional dust storm, NASA said. Curiosity has been exploring the ridge since September of 2017. It is now headed into the "clay-bearing unit," which sits in a trough just south of the ridge.

Clay minerals in this unit may hold more clues about the ancient lakes that helped form the lower levels on Mount Sharp. Curiosity, which landed on Mars in 2012, was designed to assess whether Mars ever had an environment capable to support microbes.

Meanwhile, NASA's golf-cart-sized Opportunity rover -- which recently completed 15 years on the surface of Mars -- may have 'died' after a massive global storm engulfed the Red Planet seven months ago, scientists say.

No signal from Opportunity has been received since June 10 last year, as a planet-wide dust storm blanketed the solar-powered rover's location on the western rim of Perseverance Valley, eventually blocking out so much sunlight that the rover could no longer charge its batteries.

Although the storm eventually abated and the skies over Perseverance cleared, the rover has remained silent despite the mission team's repeated attempts to contact it.

Since loss of signal, over 600 recovery commands have been radiated to the rover, NASA said in a statement.

"I haven't given up yet," said Steven W Squyres, the principal investigator of the Mars Exploration Rover Mission (MER), which involves two Mars rovers, Opportunity and its twin rover, Spirit.

"This could be the end. Under the assumption that this is the end, it feels good. I mean that," Squyres was quoted as saying by The New York Times.

The team is continuing to listen for the rover over a broad range of times, frequencies and polarizations using the Deep Space Network (DSN) Radio Science Receiver.

The six-wheeler rover landed in a region of Mars called Meridiani Planum on January 24, 2004, sending its first signal back to Earth from the surface of the Red Planet.

The rover was designed to travel 1,006 metres and operate on the Red Planet for 90 Martian days (sols), NASA said in a statement.

It has travelled over 45 kilometres and logged its 5,000th Martian day (or sol) back in February 2018.

Opportunity and its twin rover, Spirit, launched from Cape Canaveral, Florida, in 2003. Spirit landed on Mars in 2004, and its mission ended in 2011.