Curiosity rover discovers rare 'Egg Rock' on Mars

A globular, golf-ball-size object discovered by NASA's Curiosity rover on Mars has been confirmed as a rare iron-nickel meteorite fallen from the red planet's sky.

Iron-nickel meteorites are a common class of space rocks found on Earth, and previous examples have been seen on Mars, but this one, called "Egg Rock," is the first on Mars examined with a laser-firing spectrometer, NASA said. To do so, the rover team used Curiosity's Chemistry and Camera (ChemCam) instrument. Scientists of the Mars Science Laboratory (MSL) project, which operates the rover, first noticed the odd-looking rock in images taken by Curiosity's Mast Camera (Mastcam) at a site the rover reached by an October 27 drive.

"The dark, smooth and lustrous aspect of this target and its sort of spherical shape attracted the attention of some MSL scientists when we received the Mastcam images at the new location," said ChemCam team member Pierre-Yves Meslin, of National Centre for Scientific.

Research (CNRS) and the University of Toulouse in France. ChemCam found iron, nickel and phosphorus, plus lesser ingredients, in concentrations still being determined through analysis of the spectrum of light produced from dozens of laser pulses at nine spots on the object. The enrichment in both nickel and phosphorus at some of the same points suggests the presence of an iron-nickel-phosphide mineral that is rare, except in iron-nickel meteorites, Meslin said.

Iron meteorites typically originate as the core material of asteroids that melt, allowing the molten metal fraction of the asteroid's composition to sink to the centre and form a core. "Iron meteorites provide records of many different asteroids that broke up, with fragments of their cores ending up on Earth and on Mars," said ChemCam team member Horton Newsom of the University of New Mexico in the US.

"Mars may have sampled a different population of asteroids than Earth has," said Newsom. In addition, the study of iron meteorites found on Mars - including examples found previously by Mars rovers - can provide information about how long exposure to the Martian environment has affected them, in comparison with how Earth's environment affects iron meteorites.

Egg Rock may have fallen to the surface of Mars many millions of years ago, NASA said. Researchers will be analysing the ChemCam data from the first few laser shots at each target point and data from subsequent shots at the same point, to compare surface versus interior chemistry. Egg Rock was found along the rover's path up a layer of lower Mount Sharp called the Murray formation, where sedimentary rocks hold records of ancient lake-bed environments on Mars.