About 66 million years ago, a 9-kilometer-wide chunk of rock collided with Earth, triggering the mass extinction of all dinosaurs except birds and leaving a huge impact crater off the coast of Mexico that still contains evidence of the cataclysmic event. However, little is known about where the space chunk came from or what it was made of.
To learn more about the Chicxulub impactor, a group of researchers analyzed samples from the crater and compared them with samples from other impact craters that were formed between 36 and 470 million years ago. They found traces of a rare element called ruthenium, which matched the composition of carbon-based asteroids in the asteroid belt between Mars and Jupiter. The new study, published in Sciencesuggests that the dinosaur-killing rock may have originated much further away, in the outer regions of the solar system. Around 4.5 billion years ago, it was pushed into the main asteroid belt by the extreme motions of Jupiter, and eventually met its fate on Earth.
“This was a cosmic coincidence 66 million years ago,” Mario Fischer-Gödde, a scientist at the Institute of Geology and Mineralogy at the University of Cologne and lead author of the study, told Gizmodo. “We don’t know exactly what triggered it, but it’s very likely that it came from the asteroid belt.”
The study suggests that the asteroid may have formed further out in the solar system and migrated toward the inner solar system due to a disruption in the orbits of the outer planets. Before it took its position as the fifth planet from the sun, Jupiter moved quite a bit, moving toward the center of the solar system, then back out, and at one point getting as close as Mars. Jupiter may have stopped its migration toward the sun due to Saturn’s gravitational field. But by then, the gas giant’s motion had already greatly affected the solar system, causing some faraway asteroids to migrate toward the inner planets.
Although the Chicxulub impact body was known to have come from our solar system, its exact origin was debated. Fischer-Gödde believed that ruthenium could help scientists figure this out, and developed a new technique that could break the chemical bonds of rock samples to find the rare element.
Ruthenium is one of the rarest metals on Earth. It originally formed in primordial stars and found its way into the building blocks of planetary objects throughout the universe. The element was buried deep inside the Earth long before the impact that wiped out the dinosaurs. The discovery of ruthenium in the samples from Chicxulub crater rules out other types of meteorites and supports the hypothesis that the Chicxulub asteroid came from the outer reaches of the solar system.
Asteroids in the inner solar system contain fewer ruthenium isotopes. This is probably because the inner solar system probably had higher temperatures when the planets were still forming. As a result, asteroids in the inner solar system are made of metal and silicates and contain less water, said Fischer-Gödde. The asteroids in the outer solar system, on the other hand, contain more volatile elements such as carbon, hydrogen and nitrogen.
The researchers behind the new study say these giant asteroid impacts are less likely today under the solar system’s current, more stable conditions. “So the good news is that there aren’t many bodies wandering around wildly in our solar system,” Fischer-Gödde said. “Everything is in a stable configuration; there would have to be some kind of disturbance, such as a collision, to create an asteroid that passes by Earth.”
For his next investigation, Fischer-Gödde wants to analyze samples from the moon to identify the culprits behind the craters that litter the lunar surface. “The lunar crust provides records of impacts from bodies that have struck both the moon and the Earth,” he said. “So if we want to know what kind of asteroid material hit the Earth in its early history, around 4 billion years ago, we need to go to the moon.”
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