Asteroid breakup may explain inner solar system bombardment 800 million years ago

A Southwest Research Institute-led study has proposed a connection between a specific collision in the main asteroid belt and an inner-solar-system-wide bombardment episode that may have had measurable biological and geological consequences on Earth. The research suggests that the catastrophic breakup of the Eulalia parent body could be linked to an impact shower that struck the terrestrial planets about 800 million years ago. The work is published on the arXiv preprint server.

“The role impacts have played in shaping the origin and evolution of life in our solar system is poorly understood,” said Dr. William Bottke, an executive director in SwRI’s Solar System Science and Exploration Division in Boulder, Colorado. He also directs the Center for Lunar Origin and Evolution (CLOE), SwRI’s team in NASA’s Solar System Exploration Research Virtual Institute, and is lead author of a paper describing this research. “The heavily cratered surface of the moon serves as a reminder of the large impacts in Earth’s past, but so far, only the Chicxulub impact event 66 million years ago has been strongly linked to a specific effect on life, namely the mass extinction of the dinosaurs.”

Finding geological evidence of impacts older than 650 million years ago on Earth is challenging because of the constant renewal of our home planet’s surface. Earth’s landscape constantly changes as constructive forces such as volcanoes and plate tectonics build it up, while destructive forces such as weathering wear it down. One way researchers have searched for clues about Earth’s past is to study asteroid shower events.

“These rare events, triggered by large, well-positioned collisions in the main asteroid belt, bombard all inner solar system worlds,” Bottke said. “So, evidence preserved on the moon’s static surface can be used to infer what happened on Earth and Mars in ancient times.”

The moon preserves the record

Scientists have proposed that a substantial surge in large lunar impacts occurred approximately 800 million years ago, based on the ages of large lunar craters and the age distributions of impact glass materials found by the Apollo missions. The key challenge has been identifying and testing a plausible source for this impact spike.

“Our cosmic forensics team used collisional and dynamical models to link these to the formation of the Eulalia asteroid family, when a primitive carbonaceous chondrite-like object collided with another object,” Bottke said. “The location of the parent asteroid was key—it broke up on the brink of the gravitational 3:1 mean motion resonance with Jupiter.”

A breakup at Jupiter’s gateway

This orbital configuration, known as J3:1, describes when an asteroid completes three orbits around the sun for every orbit of Jupiter. The J3:1 resonance serves as a gravitational escape hatch for the asteroid belt, delivering objects into planet-crossing regions. Many present-day near-Earth asteroids have come from the J3:1 region.

The simulations indicated that half the collision fragments reached J3:1 almost immediately, spraying planetary shrapnel across the inner solar system and leading to elevated bombardment of the moon and terrestrial planets. Then, over the next 100–150 million years, another 25% of the fragments drifted into the J3:1 resonance because of nongravitational thermal forces in a process known as the Yarkovsky effect.

A barrage with planetary effects

The results demonstrate that the Eulalia breakup can plausibly account for the observed lunar craters formed around 800 million years ago and may have had widespread repercussions across the inner solar system. Research indicates that for every large impact that occurred on the moon, roughly 20 similar-sized or larger impacts occurred on Earth.

“Given that the peak of this barrage coincides with a period of widespread cooling and major shifts in our biosphere, it is tempting to suggest that the former produced the latter,” Bottke said. “On Mars, these impacts would have triggered substantial episodes of seismic shaking and can be linked in time with a surge in volcanic activity. Together, this showcases how certain catastrophic collisions in the main belt could have had far-reaching consequences for the history of the terrestrial planets.”

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