Asteroid Shower Happened on Earth 800 Million Years Ago, Says Lunar Crater Study
A team of researchers using the Kaguya lunar orbiter say a gigantic asteroid roughly 62 miles (100 kilometers) in diameter slammed into Earth nearly 800 million years ago — after breaking up into meteoroids via the Earth-Moon gravitational system — according to a study recently published in the journal Nature Communications.
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Kaguya detects 800-million-year-old asteroid shower
Led via an Osaka University team, the researchers investigated the ages of formation for 59 lunar craters with diameters of roughly 12.4 miles (20 km) using the Kaguya lunar orbiter spacecraft's Terrain Camera (TC).
The Kaguya mission — formerly called SELENE, for SELenological and ENgineering Explorer) — falls under the purview of the Japanese Space Agency (JAXA).
More specifically, the researchers proved that an asteroid 62.1 miles (100 kilometers) in diameter experienced disruption 800 million years ago (800 Ma). It then broke down into at least 8 to 11 × 10^16 pounds (4 to 5 × 10^16 kilograms) of meteoroids — roughly 30 to 60 times more massive than the Chicxulub impact — and plunged into both the Earth and moon.
Asteroid impact sheds light on Cretaceous extinction
This discovery answers a long-held suspicion that a thin layer of iridium (Ir) enrichment (a rare element on Earth) — dating back 65.5 Ma and detected globally — suggests that a 6-to-9-mile (10-to-15-kilometer) in diameter asteroid slammed into the Earth, either causing or accelerating the Cretaceous mass extinction.
Of course, this is a rare occurrence in our planet's history. The probability of an asteroid impact of this scale is estimated at once every 100 Ma. Impact craters created on Earth before 600 Ma are long-erased from years of erosion, volcanic activity, and other geological processes. Hence, the researchers needed to look to the moon where erosion is practically non-existent to study that period in the history of the Earth-moon system.
The team investigated the age distribution of 59 large craters with diameters larger than roughly 12.4 miles (20 kilometers) — focusing on the density of 0.06-to-0.6-mile-(0.1-to-1-kilometer)-diameter craters within the ejecta of all 59 craters. For example, the Copernicus crater — roughly 57.7 miles (93 kilometers) in diameter — along with its surrounding craters were investigated. The density of 860 craters — each with a diameter of 0.06 to 0.6 miles (0.1 to 1 kilometer) — was examined to calculate the age of the Copernicus crater.
The researchers found 8 to 59 craters showed signs of forming at the same time — a record-setting discovery.
Earth, moon impact 30 to 60 times that of Chicxulub impact
Since crater scalding laws and the probabilities of collision with the Earth and moon, at least 8 to 11 × 10^16 pounds (4 to 5 × 10^16 kilograms) of meteoroids roughly 30 to 60 times more than the infamous Chicxulub impact must have slammed into our planet just before the Cryogenian (720 to 635 Ma) — known as a time of significant biological and environmental changes.
"Our research results have provided a novel perspective on earth science and planetary science," said the study's lead author Professor Terada, according to an early release. "They will yield a wide range of positive effects in various research fields."
It's difficult to investigate ancient asteroid impacts because of the Earth's natural erosion and volcanic activity. This is why to learn more about bad days long forgotten by the organisms and geological surface of the Earth, spacecraft like the lunar-orbiting Kaguya from JAXA are the best-known way to fill in the historical gaps — by taking a look at our satellite, the moon.
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