NASA says its Mars rover Curiosity has come across its first meteorite on the surface of the Red Planet, and reports it's a whopper.

The iron meteor scientists have dubbed "Lebanon" is almost 7 feet wide, and sits next to a smaller meteorite tagged as "Lebanon B," NASA's Jet Propulsion Laboratory in Pasadena, Calif., reported.

The photos of the meteorites were released this week although Curiosity discovered the twin space rocks in May, JPL scientists said.

"Heavy Metal! I found an iron meteorite on Mars," Curiosity's handlers wrote on the mission's Twitter page.

The two Lebanon meteorites and a third one seen nearby are the first Curiosity has discovered since its landing on Mars in August 2012.

Images captured by Curiosity's Chem-Cam and Remote Micro-Imager cameras showed strange sharp openings on the exterior surface of the largest meteorite, NASA reported.

"One possible explanation is that they resulted from preferential erosion along crystalline boundaries within the metal of the rock," NASA officials suggested. "Another possibility is that these cavities once contained olivine crystals, which can be found in a rare type of stony-iron meteorites called pallasites, thought to have been formed near the core-mantle boundary within an asteroid."

Such olivine crystals, being much softer than iron, would have long since eroded away leaving just the iron surviving, they said.

Meteorites have also been discovered on Mars by the two smaller twin NASA rovers Spirit and Opportunity that arrived on the Red Planet in 2004.

Spirit stopped working in 2011 but Opportunity is still alive and conducting scientific exploration.

Scientists admit to being puzzled as to why most of the meteorites found on the surface of the Red Planet are iron rich, in comparison to meteorites on Earth, where iron-rich examples are outnumbered by stony ones.

One possible explanation may be that large iron-rich specimens may be more resistant to erosion processes unique to Mars than stony varieties of space rocks, scientists speculate.

Curiosity has already uncovered evidence that Mars may once have possessed habitable conditions for primitive forms of life -- the mission's major goal -- and is currently on its way to Mount Sharp, rising from the middle of the rover's Gale Crater landing site.

On June 24, the rover completed a complete Martian year -- 687 Earth days -- of scientific observation and exploration.

Curiosity has traveled approximately three miles over the Martian surface since its arrival on Mars.