4.10.2021
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.
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.
An artist’s impression of a close flyby of the metal-rich near-Earth asteroid 1986 DA. Astronomers using the NASA Infrared Telescope Facility have confirmed that the asteroid is made of 85% metal.
Credit: Addy Graham/University of Arizona.
Quelle: PSI
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'Mini Psyches' Give Insights into Mysterious Metal-Rich Near-Earth Asteroids
Metal-rich near-Earth asteroids, or NEAs, are rare, but their presence provides the intriguing possibility that iron, nickel and cobalt could someday be mined for use on Earth or in Space.
New research, published in the Planetary Science Journal, investigated two metal-rich asteroids in our own cosmic backyard to learn more about their origins, compositions and relationships with meteorites found on Earth.
These metal-rich NEAs were thought to be created when the cores of developing planets were catastrophically destroyed early in the solar system's history, but little more is known about them. A team of students co-led by University of Arizona planetary science associate professor Vishnu Reddy studied asteroids 1986 DA and 2016 ED85 and discovered that their spectral signatures are quite similar to asteroid 16 Psyche, the largest metal-rich body in the solar system. Psyche, located in the main asteroid belt between the orbits of Mars and Jupiter rather than near Earth, is the target of NASA's Psyche mission.
"Our analysis shows that both NEAs have surfaces with 85% metal such as iron and nickel and 15% silicate material, which is basically rock," said lead author Juan Sanchez, who is based at the Planetary Science Institute. "These asteroids are similar to some stony-iron meteorites such as mesosiderites found on Earth."
Astronomers have been speculating as to what the surface of Psyche is made of for decades. By studying metal-rich NEAs that come close to the Earth, they hope to identify specific meteorites that resemble Psyche’s surface.
"We started a compositional survey of the NEA population in 2005, when I was a graduate student, with the goal of identifying and characterizing rare NEAs such as these metal-rich asteroids," said Reddy, principal investigator of the NASA grant that funded the work. "It is rewarding that we have discovered these 'mini Psyches' so close to the Earth."
"For perspective, a 50-meter (164-foot) metallic object similar to the two asteroids we studied created the Meteor Crater in Arizona," said Adam Battle, who is a co-author of the paper along with fellow Lunar and Planetary Laboratory graduate students Benjamin Sharkey and Theodore Kareta, and David Cantillo, an undergraduate student in the Department of Geosciences.
The paper also explored the mining potential of 1986 DA and found that the amount of iron, nickel and cobalt that could be present on the asteroid would exceed the global reserves of these metals.
Additionally, when an asteroid is catastrophically destroyed, it produces what is called an asteroid family – a bunch of small asteroids that share similar compositions and orbital paths.
The team used the compositions and orbits of asteroids 1986 DA and 2016 ED85 to identify four possible asteroid families in the outer region of the main asteroid belt, which is home to the largest reservoir of small bodies in the inner part of the solar system. This also happens to be the region where most of the largest known metallic asteroids including 16 Psyche reside.
"We believe that these two 'mini Psyches' are probably fragments from a large metallic asteroid in the main belt, but not 16 Psyche itself," Cantillo said. "It's possible that some of the iron and stony-iron meteorites found on Earth could have also come from that region in the solar system too."
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.