Little is known about the population of metal-rich Near-Earth Asteroids (NEAs), their number, origin, and relationship with meteorites found on Earth. A new paper by Planetary Science Institute Associate Research Scientist Juan Sanchez explains how near-infrared spectroscopic data of two NEAs reveals new information about the composition and physical properties of these bodies.
“We find that both NEAs are composed of mostly metal and a small fraction of silicate minerals, similar to mesosiderites, a rare type of stony-iron meteorites found on Earth,” said Sanchez, lead author of the paper “Physical Characterization of Metal-rich Near-Earth Asteroids 6178 (1986 DA) and 2016 ED85” that appears in Planetary Science Journal. PSI Laboratory Technician Neil Pearson is also an author.
“Analysis of their orbits allows us to trace their origin to a region in the outer asteroid belt where the largest metal-rich asteroids reside,” Sanchez said. The asteroid belt is located between the orbits of Mars and Jupiter.
“According to some studies, there are more than 60 parent bodies represented among iron meteorites found on Earth; however, those parent bodies have not been identified so far. There are also stony-iron meteorites and metal-rich carbonaceous chondrites whose origin is unknown,” Sanchez said. “Because NEAs represent a direct link between meteorites found on Earth and their parent bodies throughout the Solar System, the identification of metal-rich NEAs get us closer to determining the specific origin of the meteorites that derive from them.”
The larger NEA, (1986 DA), is shown to be primarily metal by using radar data from an earlier study. Metal has a much higher radar reflectivity than rocky bodies composed of silicate minerals. The team’s new near-infrared spectra of 1986 DA confirmed that the asteroid surface is a mixture of about 85% metal and 15% pyroxene, a rock-forming silicate mineral found in igneous and metamorphic rocks.
For the other NEA, 2016 ED85, there is no radar data available, but Sanchez finds that its near-infrared spectrum is almost identical to the spectrum of 1986 DA and other metal-rich asteroids, suggesting that this object has a similar composition.
The paper’s findings are based on observations from the NASA Infrared Telescope Facility on the island of Hawaii. The work was funded by the NASA Near-Earth Object Observations Program, which also funds the NASA Infrared Telescope Facility.
Featured image: Photograph of stony-iron meteorite called mesosiderite showing iron-nickel metal mixed with silicate rocky material. Two metal-rich near-Earth asteroids observed by Planetary Science Institute astronomer Juan Sanchez are thought to be made of this rare class of meteorite. Credit: University of Arizona.
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