Forged at the dawn of the solar system, a fist-sized meteorite has ended its millions-mile journey, safe and secure, in the hands of Mountain View scientists.
An analysis of the glass-crusted black rock and its 600 siblings is revealing, for the first time, the life and death of meteors that streak across our nighttime skies.
“It’s like a little window into the earliest times of our solar system … before there was such a thing as Earth,” said meteor astronomer Peter Jenniskens of the SETI Institute and NASA Ames Research Center, who led the study published Aug. 8 in the journal Meteoritics and Planetary Science.
Since the dawn of humanity, the explosive streak of a meteor across the night sky has inspired fear and bewilderment.
Scientists believe that asteroids are the wreckage of destroyed would-be-planets, created in the first chaotic million years of the solar system.
Circling between what is now Mars and Jupiter, these planets collided – blown to smithereens – and created fields of debris, called asteroids. In an orbiting belt that’s been dubbed “the blood spatter of the solar system,” asteroids continue to collide — and sometimes chunks fall out of the belt, hit the Earth’s atmosphere and fall to the ground as meteorites.
The new research announced this week is notable because it tells a meteorite’s origin story.
That was possible because astronomers detected and tracked an 88-ton asteroid, called 2008-TC3, long before it actually hit us. They watched it enter Earth’s atmosphere, melt away, and then explode, showering the landscape with rock shards. These meteorites were recovered and the location of each piece was mapped. From the pattern, they could prove what part of the asteroid had survived to the ground.
It was the first time that rocks could be directly linked to an asteroid observed in space.
“What makes this work especially exciting is that the scientists were able to track the incoming meteoroid, to know where it would fall, and then go find the specific remains,” said science educator Andrew Fraknoi, emeritus chair of the Astronomy Department at Foothill College in Los Altos Hills.
In the dangerous “shooting gallery” of space, “the more we know about these cosmic ‘bullets,’ the better it is for us,” he said.
This story starts in 2008, when Richard Kowalski, working with the University of Arizona, noted a moving white dot on his computer screen at an observatory on Mount Lemmon outside Tucson, Arizona.
The flickering object looked as if it was hurtling directly toward Earth. For 20 hours, the computers in NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena tracked its trajectory.
The size of a small car, “it was coming into the Earth’s atmosphere at incredible speeds,” at 8 miles per second, said Jenniskens. That’s the speed it would take to travel from San Francisco to San Jose in just under 7 seconds.
Then, high above the Nubian Desert of northern Sudan, the asteroid collided with the atmosphere, releasing the energy of one to two kilotons of TNT.
The light was so bright that it woke up a train station attendant in the remote desert. KLM airplane pilots over Chad reported a distant flash. U.S. government satellites also documented the explosion; their recordings were released to scientists early this year.
Where did it land? With an explosion so high in the atmosphere, many scientists assumed that none of the asteroid had survived the scorching race through the Earth’s atmosphere.
But Jenniskens decided to investigate.
Born in the Netherlands, he had fallen in love with meteors at first sight when, as a graduate student, he witnessed a brilliant green-yellow streak across an inky black sky. He is now a global expert on the subject, investigating asteroid impacts in remote Russia and other distant locales.
To expand the search for meteorites, Jenniskens coordinates a network of cameras in California and Nevada and invites the public to join the meteor surveillance by reporting their own fireball sightings, post videos and scan the ground for anything that looks unusual. Jenniskens hopes to use his cameras to trace the origin of that meteorite all the way back to one of the debris fields in the asteroid belt.
“Peter Jenniskens is the Indiana Jones of meteorite hunters,” Fraknoi said.
Soon after 2008 TC3 fell to Earth, he flew to Sudan and joined University of Khartoum professor Muawia Shaddad and 40 students to search the desert in hopes of finding anything that survived. Walking side by side, they did a grid search over about 19 miles over sand plains, golden dunes and rocky hills and across long dried-out river beds. Eyes were peeled for anything out of the ordinary.
“There are lots of rocks in the desert,” said Jenniskens. “But we were looking for rocks covered in black glassy ‘fusion crust.'”
The very first meteorite was found only 2 1/2 hours into the search on a late afternoon. “Everybody started dancing and singing and shouting. We had a big party,” he recalled.
More were found in the days that followed. While all were covered in glassy crust, they had different colors and textures from different mixtures of olivines, pyroxenes, iron sulfides and other minerals, unexpectedly showing that asteroid 2008 TC3 spawned many types of meteorites.
The flickering of the asteroid on approach to Earth had revealed its shape, spin and orientation when it hit the atmosphere.
But the location of the meteorite falls were puzzling. The smaller shards had fallen along a narrow 0.7-mile wide corridor, the team found. The larger pieces, which fell farther downrange, were spread up to 4 miles apart.
To understand why, Darrel Robertson from NASA’s Asteroid Threat Assessment Project at NASA Ames performed computer modeling to decode this pattern.
As it soared, they found, the asteroid’s front side melted. Behind it was a vacuum-like wake. As small fragments broke and fell off the asteroid’s sides, they were swept into that wake and then fell to the ground in a narrow corridor along the asteroid’s path.
The last piece to survive was in the bottom-back of the asteroid, the team concluded. Then, under pressure, that piece suddenly collapsed and shattered. Shock waves ejected these pieces sideways – scattering them.
The mystery solved, the rocks are now preserved in plastic boxes and handled only with gloves.
“All these meteorites tell an incredible story,” said Jenniskens. “They’re little treasures.”
Did you see a fireball? Report it here to the American Meteor Society: https://amsmeteors.org/fireballs/
Learn more: http://fireball.seti.org/
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