NASA's Mars Opportunity rover that was originally said to last for only 90 days is now celebrating its 12-year anniversary on the red planet.

Opportunity has made its way to 12 years because of the help of several factors, including helpful unforeseen surface conditions and few creative software changes. It landed in Mars back in January 2004 after a six-and-a-half-month journey from Earth. It made its successful entry to the Martian atmosphere through the aid of a parachute, retrorockets, and a cocoon of airbags.

As reported in TechCrunch, the extreme level of the dust on Mars is one of the factors why NASA believed the rover would only last for 90 Martian days. They further believed that these dust particles would "build up on Opportunity's solar panels and eventually, the rover would be unable to receive power."

Receiving solar power on Mars, which is 50 percent farther away from the Sun than Earth, was a known challenge even without the dust. NASA designed Opportunity's solar panels to be as wide as possible in order to collect as much sunlight as it could. Even so, the lifetime of Opportunity was measured in days, perhaps months, but certainly not years.

Luckily, a surprising thing happened: every once in a while, whirling columns of air, or "dust devils," swept over the rover and cleaned off the coating of dust from the solar panels.

Although dust build up would continue to be a challenge, NASA believes it also has helped keep the rover's lights on.

Throughout the years, Opportunity has faced a lot of challenges. For instance, it has found itself slightly buried in a sand dune. Thankfully, the hardworking engineers and scientists at NASA's Jet Propulsion Laboratory was able to come up with a sequence of wheel rotations that would ultimately set the rover free.

Another challenge faced by the team is the needed software upgrades. These upgrades have to be done remotely. "Remote software updates to improve the rover's visual detection, photography, and hazard detection capabilities."

The greatest challenge is the yearly cost of keeping the rover functional. It is estimated that NASA spends about $14 million annually to keep Opportunity operational. This is one of the reasons some believe Opportunity should no longer be kept functional, especially that it is no longer as capable as it once was.

As of present, the rover continues to accomplish useful scientific work, and after 12 years, Opportunity is believed to be moving onward.