Egg Rock: What we learned from an iron meteorite on Mars

The Curiosity mission team is studying the so-called 'Egg Rock' – a metallic nickel iron-rich meteorite – glimpsed by the Mars rover.

The dark, golf-ball-size object in this composite, colorized view from the ChemCam instrument on NASA's Curiosity Mars rover is a nickel-iron meteorite, as confirmed by analysis using laser pulses from ChemCam on Oct. 30, 2016.

It's been more than four years since NASA's Curiosity rover landed on Mars, enabling researchers to study the shape and composition of the planet's landscape in a mission that had originally been planned to last less than two years. Even as the rover's instruments begin to show signs of wear and tear, however, scientists are still making discoveries.

For the first time on Mars, researchers used a spectrometer to zap an object the size of a golfball with a laser this week to confirm that it is an iron-nickel meteorite that fell to the planet's surface, according to NASA and the Jet Propulsion Laboratory. Although such objects are common on Earth and to be expected on the Red Planet as well, studying them in tandem with what we already know about the planet's atmosphere could reveal a wealth of new information about the history of the solar system.

Horton Newsom, a researcher from the University of New Mexico, Albuquerque, said the object, known as Egg Rock, could carry within its core information that differs from asteroids currently being studied.

"Iron meteorites provide records of many different asteroids that broke up, with fragments of their cores ending up on Earth and on Mars," Dr. Newsom, a member of the team that wields Curiosity's Chemistry and Camera (ChemCam) instrument, said in a statement. "Mars may have sampled a different population of asteroids than Earth has."

Egg Rock might have fallen to the Mars surface millions of years ago, so researchers will analyze ChemCam data to compare the chemistry of its surface to its interior, the statement noted.

Deborah Byrd, writing for EarthSky, noted that the latest samples could be in much better shape than those collected on Earth, thanks to atmospheric differences:

Mars would be a great place to look for meteorites. Rocks from outer space that fall to Mars’s surface are more likely than on Earth to remain in excellent condition for millions of years. That’s because moisture and oxygen – two of the main culprits that cause weathering in earthly rocks – are found in only very small amounts in the Red Planet’s surface soils.

Also, Mars is closer to the asteroid belt so more space rocks may find their way to Mars than Earth.

Those factors, combined with a thin atmosphere that provides less friction for incoming space rocks, may contribute to an abundance of meteorites on the surface of our neighboring planet.

Scientists first noticed the rock, which had stood out in contrast to the dusty soil in pictures taken late last week.

"The dark, smooth and lustrous aspect of this target, and its sort of spherical shape attracted the attention of some [Mars Science Laboratory] scientists when we received the Mastcam images at the new location," ChemCam team member Pierre-Yves Meslin said in a statement. He's with France's National Center for Scientific Research (CNRS) and the University of Toulouse, France.

Curiosity's second mission extension began last month and aims to investigate the ways in which ancient environmental conditions on Mars changed over time.

Egg Rock was discovered in an area where sedimentary rocks serve as evidence of an ancient lakebed on the Martian surface. At some point in the past, the region once had conditions that researchers suspect would be conducive to microbial life.

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