Astronomy - Curiosity Finds “Egg Rock” Iron Meteorite

NASA's intrepid Mars rover gets a close-up view of a bizarrely shaped space rock that landed on the slope of Mount Sharp.

Egg Rock on the Martian surface. The grid of spots on its surface are reflections from firings of Curiosity's ChemCam laser.
NASA / JPL / MSSS

It's strange, what you might find sitting on the surface of Mars. Scientists working on NASA's Mars Science Laboratory (MSL) mission got a close-up look at a meteorite on the surface of the Red Planet recently, courtesy of the Curiosity rover.

Mission personnel first noticed the intruder in images taken by the rover's Mast Camera (Mastcam) on October 27th. The rover got up close to examine the rock a few days later on October 30th. The team dubbed it "Egg Rock," borrowing the moniker from a 1,000-foot-long spit (with a lighthouse) off the coast of Bar Harbor, Maine, here on planet Earth. Curiosity is currently exploring the Bar Harbor plain of "Mount Sharp" (Aeolis Mons).

“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,” says Pierre-Yves Meslin (IRAP, University of Toulouse, France) in a recent press releasefrom NASA and the Jet Propulsion Laboratory.

Martian Rocks, But Not From Mars

The polished silvery-gray surface of the nodule first caught the eye of researchers, and it became the first Martian meteorite analyzed Curiosity's ChemCam, a spectrometer that fires brief but powerful laser pulses to vaporize tiny bits of rock. ChemCam's analysis confirms that Egg Rock is indeed an iron-nickel meteorite, whose outer surface momentarily melted and ablated during the meteorite's high-velocity plunge through Mars' tenuous atmosphere.

The golf ball-sized Egg Rock close up. The smooth, almost glassy surface resulted from momentary melting of the outer layer as this iron-nickel meteorite plunged through the Martian atmosphere.
NASA / JPL / LANL / CNES / IRAP / LPGNantes / CNRS / IAS / MSSS

Iron meteorites represent fragments of the cores of asteroids that differentiated — that is, molten material that sank to the cores of their parent bodies during formation. The composition of Egg Rock is particularly intriguing, as Curiosity's ChemCam instrument reveals an iron, nickel and phosphorus amalgamation sprinkled with lesser amounts of other elements. Analysis is still underway, but the presence of the phosphorus and nickel enrichment suggests the existence of an iron-nickel-phosphide mineral known as schreibersite that's almost exclusive to iron-nickel meteorites.

This isn't the first time a meteorite has been spotted on Mars. The Opportunity rover found the first meteorite on Mars back in 2005, named "Heat Shield Rock," followed by the 0.6-meter "Block Island" meteorite in 2009. Meanwhile, in May 2014, Curiosity spotted the enormous 2-meter-widerock named Lebanon, the largest meteorite found to date on Mars, along with two smaller-sized companions lying nearby.

Curiosity spotted this massive, half-buried meteorite (and a smaller fragment in the foreground) in 2014. The big one, about 2 meters (7 feet) across, was nicknamed Lebanon.
NASA / JPL / MSSS

Does Mars get hit more than Earth? It presents a smaller target, but perhaps the Red Planet gets pummeled by a different population of meteorites than we do, owing to its proximity to the asteroid belt. Such discoveries on Mars are also interesting, as more of the meteorite survives intact on impact, owing to the much thinner atmosphere on Mars. Looking at finds such as Egg Rock are also a testament to how weathering over time affects meteorites on Mars versus Earth.

“Iron meteorites provide records of many different asteroids that broke up, with fragments of their cores ending up on Earth and on Mars,” says ChemCam scientist Horton Newsom (University of New Mexico at Albuquerque) in the same NASA-JPL press release. “Mars may have sampled a different population of asteroids than Earth has.”

The tiny moons Deimos and Phobos are captured asteroids as well, and innermost Phobos is a massive "meteorite to be" that will smash into Mars 20 to 40 million years from now.

Martian meteorites have also been found on the Earth, including NWA 7034 (better known as "Black Beauty"), and Allan Hills (ALH) 84001, the asteroid that stirred up controversy in 1996 due to the discovery of supposed Martian micro-fossils in its interior. Mars has a much lower escape velocity than the Earth, and its much more likely that meteorites from Mars arrive at Earth than the other way around.

Launched on November 26, 2011, from Cape Canaveral Air Force Station, Curiosity arrived at Gale crater on the flanks of Mount Sharp on August 6, 2012. With 1513 sols on Mars and 8.8 miles (14.2 km) on its odometer, Curiosity is well over two years past warranty and still chugging along. The plutonium-238 in its power-producing MMRTG (Multi-Mission Radioisotope Thermoelectric Generator) has a half-life of 88 years, and there's a pretty good chance that the rover will be operational when its successor, NASA'sMars 2020 Rover, joins Curiosity in a few years.

We're starting to get a good sampling of the meteorites dotting the surface of Mars, some of which are rare specimens indeed. I wonder what a meteorite found on Mars might be worth?