SACRAMENTO — The meteorite fragments that crashed down in El Dorado County in April contain some of the best-preserved elements from the dawn of the solar system ever recovered, according to a study.
The Sutter's Mill meteorite entered Earth's atmosphere at about 8 a.m. on April 22 with the force of a 4-kiloton bomb. The explosion when it broke apart could be heard as far away as Washington state, and it produced a fiery streak seen across northern Nevada and California.
It weighed about 100,000 pounds and was as big as a minivan. The 77 fragments recovered on the ground weigh only about 2 pounds.
Yet those bits are proving to be among the most significant meteorite finds, according to the study in today's issue of the journal Science, which includes nine co-authors from the University of California at Davis.
The meteorite arrived at a record entry speed of nearly 18 miles per second, and it broke apart at a record altitude of about 34 miles above sea level.
"The entry was very violent," said Peter Jenniskens, a senior researcher at the Search for Extraterrestrial Intelligence Institute and the study's lead author. "We think that's why there were no big chunks, because this object came in with such a high speed."
It was called the Sutter's Mill meteorite because most of the fragments were found near Lotus and Coloma along the American River, where the Gold Rush began in California in 1848. Jenniskens found a piece in the parking lot of Marshall Gold Discovery State Historic Park.
The study, which includes 69 co-authors from around the globe, found that the meteorite fragments are the most pristine samples of a rare type of carbonaceous chondrite, an amalgam of minerals that formed about 4.5 billion years ago when the solar system itself was taking shape.
Doppler weather radar was used to track the meteorite's arrival, a relatively new technique. As a result, researchers know more about where this meteorite came from.
They believe it's from an asteroid belt with a highly eccentric orbit that passes between Jupiter and Mars, then swings close by the sun, and that it broke off from a larger object, likely an asteroid, 15,000 to 19,000 years ago, considered very recent in meteorites.
"Among the known asteroid orbits, this one might be the most eccentric," said Qing-Zhu Yin, a UC Davis geology professor and a study co-author. "As a result, its orbit may have had its outmost point all the way to Jupiter."
Through the solar system
The meteorite contained evidence of its travels through the solar system. Among the elements detected using specialized equipment at UC Davis was oldhamite, a sparkly brown crystalline mineral thought to have originated in the solar nebula when the solar system formed.
Oldhamite is very reactive and can disappear just from being breathed on. It often vanishes before it can be examined in recovered meteorites.
In this case, Jenniskens and a few area residents were able to recover and preserve fragments within hours of their falling from the sky. Rain that fell the next day would likely have erased the oldhamite. It marks the first time oldhamite has been detected on a recovered meteorite.
"We are suspecting that the oldhamite originated in a different type of meteorite, normally associated with Earth and Venus and not in an area of primitive asteroids from farther out ... ," said Jenniskens. "It's telling us a story about mixing in the early solar system."
The meteorite contains compounds picked up from different regions of the solar system: one that is relatively cold and wet, and another that is hot and dry. This is unusual, indicating that parts of the meteorite had different histories.
According to an accompanying article in Science, the researchers more recently found diamonds in the meteorite, which don't belong in either type of environment.
Analysis by UC Davis shows evidence that minerals in the meteorite once had contact with flowing water, possibly on a parent asteroid.
This is not unusual in meteorites, Yin said, but nevertheless fascinating. Earth is thought to have originally acquired a water supply from crashing meteorites.
"You can say with one little piece in your hand, you are holding the entire solar system," said Yin. "There's a lot of excitement with this meteorite."
NASA and the European and Japanese space agencies are planning to land probes on asteroids over the next decade. One goal is to look for water. The first of these is a NASA probe expected to launch in 2016, Yin said.
"It so happens the target they identified, based on remote sensing, resembles this meteorite," he said. "Basically, this material gives us an early glimpse of what we might find."