LOS ANGELES, Jan. 25 (Xinhua) -- NASA's Opportunity rover marked the 15th anniversary of its touchdown on Mars on Thursday. But the special moment was a little bittersweet.

The spacecraft has not been heard from since a planet-wide dust storm in June last year. Although the storm eventually abated and the Martian skies cleared, the rover has not communicated with Earth since then.

"Fifteen years on the surface of Mars is testament not only to a magnificent machine of exploration but the dedicated and talented team behind it that has allowed us to expand our discovery space of the Red Planet," said John Callas, project manager for Opportunity at NASA's Jet Propulsion Laboratory in Pasadena, California.

"However, this anniversary cannot help but be a little bittersweet as at present we don't know the rover's status. We are doing everything in our power to communicate with Opportunity, but as time goes on, the probability of a successful contact with the rover continues to diminish," he said.

Opportunity's mission continues, in a phase where mission engineers at JPL are sending commands to as well as listening for signals from the rover. If engineers hear from the rover, they could attempt a recovery, said the team.

Opportunity landed on Mars on Jan. 24, 2004. The golf-cart-sized rover was designed to travel 1,006 meters and operate on the Red Planet for 90 Martian days. In fact, it has traveled over 45 kilometers and logged its 5,000th Martian day back in February 2018.