Impact Rain 800 Million Years Ago: How the Breakup of Asteroid Eulalia Changed the Planets ✦
The spike in large lunar impacts ~800 million years ago is linked to the breakup of a carbonaceous chondrite parent body of the Eulalia asteroid family ~800 million years ago near the 3:1 resonance with Jupiter. Collision and dynamical evolution modeling shows that ~75% of the family’s fragments slipped into the J3:1 resonance within ~150 million years: some right after the breakup, others gradually drifting via the Yarkovsky effect. Once in resonance, the fragments were pumped onto planet-crossing orbits, drastically increasing the hit rate on the Moon and terrestrial planets. This accounts for the birth of big craters like Copernicus. The event likely had global repercussions: on Earth, it aligns with biospheric disruptions possibly triggered by impacts, and on Mars, with a pulse of volcanic activity. So, collisions in the Main Belt can shape the saga of the entire inner solar system.
Context
Large collisions in the solar system can radically alter the appearance of planets. A vivid example is the asteroid impact that created the Chicxulub crater 66 million years ago and ended the age of dinosaurs. However, tracing older catastrophes is challenging: Earth's craters are poorly preserved, and lunar evidence is often scattered. The hypothesis of an impact rain around 800 million years ago, first proposed from analysis of impact glasses from the Apollo missions, long lacked a convincing source. Now an international team of scientists has linked this event to the breakup of the parent body of the Eulalia asteroid family—primitive carbonaceous chondrites rich in volatiles. This rain coincided with the so-called Bitter Springs anomaly, a sharp shift in the isotopic composition of carbon in ancient oceans, hinting at a possible influence of the cosmic bombardment on the biosphere.
Methods
To reconstruct the history of the Eulalia family, researchers used a combination of celestial mechanics and observational spectroscopy. Using data from the WISE mission and the Sloan Digital Sky Survey (SDSS), they identified family members by color indices and albedo, filtering out background cometary and asteroidal interlopers. The Yarkovsky chronology method played a key role: thermal radiation re-emitted unevenly by asteroids causes them to drift in their orbits, with the speed depending on size—this effect, predicted long ago by Joseph von Fraunhofer in the context of light-matter interaction, creates a characteristic V-shaped structure in the distribution of orbits. By modeling this drift under solar heating and the YORP effect, along with collisional evolution, the authors estimated the breakup age and the number of fragments entering the 3:1 resonance with Jupiter—the main transport pathway to the inner solar system.
Results
Calculations showed that a parent body over 100 km in diameter broke up about 865 million years ago near the J3:1 resonance. Around three-quarters of the fragments eventually entered this resonance zone: some were ejected immediately, while others migrated gradually via thermal drift (the Yarkovsky effect). As a result, a true impact barrage rained down on the terrestrial planets. Estimates suggest that during the rain several Chicxulub-scale impactors (up to 8 km) struck Earth, fragments capable of creating craters like Copernicus (93 km) hit the Moon, and Mars experienced impactors that triggered a surge in volcanism. Comparison of the modeled flux with photometric data on lunar craters agreed within one standard deviation.
Implications
The discovery underscores that asteroid families are not just passive witnesses of history but active agents. On Earth, the sharp shift in carbon isotopes (the Bitter Springs anomaly) could have been caused by the release of carbon dioxide and dust from multiple impacts, disrupting the carbon cycle. On Mars, the peak in volcanism recorded by photometric dating of calderas was likely triggered by seismic awakening of magma chambers. This makes collisions in the main belt a significant factor in planetary evolution.
Future development
Future research should focus on finding direct geochemical traces of the Eulalia rain in ancient terrestrial rocks, such as iridium or osmium anomalies. Comparison with other large breakups, like the L-chondrite event 466 million years ago, will help build an overall picture of the influence of asteroid catastrophes on climate and life. Modeling the atmospheric effects of cosmic dust and large-body impacts will help quantify the initiation of 'Snowball Earth' glaciations. Additionally, detailed spectroscopic study of Eulalia family fragments will clarify their connection to the asteroid samples from Bennu and Ryugu.
Impact
They also allow calibration of asteroid bombardment models by using analogies with cometary streams, which is important for planetary science, paleoclimatology, and astrobiology.
Next steps
Next steps include drilling into ancient impact structures on Earth and the Moon to extract samples for radioisotope analysis, and launching missions to asteroids of the Eulalia family for direct age measurement.
Key open problems
The work touches on unresolved problems: the link between mass extinctions and impact events, the origin of lunar glasses, and long-term variations in meteorite flux. It also sheds light on the paradox of weak erosion of ancient craters on Earth and Venus.
🎯 Interestingly, the Copernicus crater—one of the most prominent on the Moon—may have been created by a fragment from the same parent body as asteroid Bennu, from which the OSIRIS-REx mission recently returned samples.
🎬 The plot of the film 'Don't Look Up' ironically echoes our work: only here the threat stretched over millions of years, not a few months.
Key numbers
- Breakup age: ~865 million years
- Diameter of parent body: over 100 km
- Size of largest impactor for Earth: about 8 km
- Number of lunar craters aged ~800 million years: 7
- Fraction of family entering resonance: ~75%