U.S. scientists have discovered that a meteorite that fell over El Dorado County in northern California this past spring was the rarest type known to have hit our planet – a carbonaceous chondrite.
A very fast-moving fireball was observed on April 22, 2012 over large parts of California and Nevada. Equivalent to 4 kilotons of TNT, the fireball was photographed, and recorded by video and by weather Doppler-radars.
The images and videos helped to trace back its orbit to the far reaches of the outer part of the asteroid belt. The radar data helped meteorite hunters to recover a total of 77 specimens, with the first ones found only two days after the fall.
The meteorite was named Sutter’s Mill, after the location where it fell.
A multinational group of scientists was assembled to study the meteorite. They learned that it formed about 4.5 billion years ago. It was knocked off its parent body, which may have been an asteroid or a Jupiter-family comet, roughly 50,000 years ago. As it flew toward Earth, it traveled an eccentric course through the Solar System, flying from an orbit close to Jupiter toward the sun, passing by Mercury and Venus, and then flying out to hit Earth.
According to the study published in the journal Science, the Sutter’s Mill meteorite entered the atmosphere at about 64,000 miles per hour.
“If this were a much bigger object, it could have been a disaster,” explained co-author Prof Qing-zhu Yin of the University of California Davis. “This is a happy story in this case.”
Before entering Earth’s atmosphere, the meteorite is estimated to have weighed roughly 100,000 pounds. Most of that mass burned away when the meteorite exploded. Scientists and private collectors have recovered about 2 pounds remaining.
The team studied the meteorite’s mineralogy, internal textures, chemical and isotopic compositions and magnetic properties. They also identified where hydrogen, and therefore water-rich fragments, resides in the meteorite without breaking it open.
“For me, the fun of this scientific gold rush is really just beginning,” Prof Yin said. “This first report based on the initial findings provides a platform to propel us into more detailed research.”
“Scientists are still finding new and exciting things in Murchison, a similar type of meteorite to Sutter’s Mill, which fell in Victoria, Australia, in 1969, the same year Apollo astronauts Neil Armstrong and Buzz Aldrin returned the first lunar samples to the Earth. We will learn a lot more with Sutter’s Mill.”
Bibliographic information: Peter Jenniskens et al. 2012. Radar-Enabled Recovery of the Sutter’s Mill Meteorite, a Carbonaceous Chondrite Regolith Breccia. Science, vol. 338, no. 6114, pp. 1583-1587; doi: 10.1126/science.1227163