What was originally intended as a 90-day exploration of the Opportunity Rover has now reached 5,000 days. The longest-working explorer remains on Mars for 13 years.

On Feb. 16, NASA's Opportunity Rover celebrated its 5,000 sols or Martian days on the Red Planet. This milestone is the latest in the list of accomplishments of the golf-cart-size robotic field geologist.

Martian day or sol is about 40 minutes longer than a day on Earth while a year on Mars is equivalent to almost two Earth years.

Milestones On Mars

"We've reached lots of milestones, and this is one more," says John Callas, Opportunity Project Manager of NASA's Jet Propulsion Laboratory in Pasadena, California, who also noted that the exploration and scientific discoveries are the rover's more important achievements.

It has explored the Victoria and Endeavour craters. It survived sand traps, dust storms, and more importantly, it discovered multiples signs of water on the arid planet.

The rover has sent a total of 225,000 images to Earth. All the images captured by the rover's engineering and science cameras can be viewed online. Its built-in Panoramic Camera recorded its 4,999th day on Mars.

Many Years Of Opportunities

The solar-powered NASA Opportunity Rover landed on Mars on January 25, 2004. Since then, the rover had been trekking the planet's surface to provide significant revelations about the Red Planet.

"Five thousand sols after the start of our 90-sol mission, this amazing rover is still showing us surprises on Mars," Callas said.

At the start of the mission, NASA did not expect the rover to survive the harsh winter on Mars but in 2015, the rover achieved a driving milestone after reaching 42 kilometers of driving time on Mars, a distance equivalent to a full marathon.

The rover has traveled a total of 45 kilometers from its landings to its current location in a channel called Perseverance Valley.

Discovery Of Rock Stripes

Among the latest images that the rover sent back to Earth show streams of rocks and gravel, that resemble rock stripes in the Martian landscape. This discovery may point to possible sources of water on the Red Planet.

On Earth, rock stripes are formed when the wet soil freezes and thaws in repeating cycles.

"One possible explanation of these stripes is that they are relics from a time of greater obliquity when snow packs on the rim seasonally melted enough to moisten the soil, and then freeze-thaw cycles organized the small rocks into stripes," says Ray Arvidson, Deputy Principal Investigator for the Opportunity Rover.

The rover observed the rock stripes while investigating in the Perseverance Valley that drops on the inside slope of the western rim of the Endeavour Crater. It captured images of the textured rows on the ground using its Navigation Camera.

NASA said wind blowing up the Perseverance Valley could also be the reason for the rock stripes or a combination of dried moisture and wind creating ridges on the soil.

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