After more than six years roaming the surface of Mars, NASA's Mars rover Opportunity has spotted its first dust devil on the red planet.

Unlike its robotic twin on Mars Spirit ? a prolific dust devil photographer ? Opportunity's attempts to catch the tornado-like wind formations had repeatedly come up empty. That is, until now.

In a July 15 photo taken with its mast-mounted panoramic camera, Opportunity captured a tall column of swirling dust. [Opportunity rover's dust devil photo.]

"This is the first dust devil seen by Opportunity," said Mark Lemmon of Texas A&M University, College Station, a member of the rover science team, in a statement.

Opportunity took the photo while looking east-southeastward, following a drive that took the rover approximately 230 feet (70 meters). The photo's original use was to help plan for the next drive.

While this was the rover's first dust devil sighting, Opportunity's beleaguered twin Spirit has seen dozens of Mars dust devils from its location halfway around the planet.

The terrain at Spirit's exploration site inside Mars' Gusev Crater is rougher and dustier than the Meridiani Planum region where Opportunity is working, Lemmon explained. So, vortices of wind form more readily and raise more dust at Gusev, he added.

Spacecraft orbiting Mars have photographed tracks left by dust devils near Opportunity, but overall, they are scarcer at Meridiani than Spirit's location. It is also possible that swirling winds at Meridiani may be more common than visible signs of them, but that they occur where there is no loose dust to kick up, rover scientists said.

In fact, just a day before Opportunity photographed the dust devil, Martian wind helped clean some of the dust off of the rover's solar array, which increased electricity output from that array by more than 10 percent.

"That might have just been a coincidence, but there could be a connection," Lemmon said.

NASA's Phoenix Mars Lander also spotted dust devils in the Martian arctic during the lander's 2008 mission.

The Mars rover team is resuming systematic checks for afternoon dust devils, using Opportunity's navigation camera, for the first time in about three years.

Opportunity and Spirit arrived on the surface of Mars in 2004, for missions originally designed to last for three months. Opportunity landed on Mars on Jan. 25, 2004 (Eastern Time).

Spirit touched down ahead of Opportunity, but fell silent on March 22 of this year, when it skipped a planned communications session with controllers on Earth. Spirit has been out of communication since then, entering a low-power hibernation mode as the Martian winter set in and temperature dropped, leaving the rover with insufficient power to properly function.

However, Spirit may wake up with the arrival of the Martian spring, mission managers have said.