Planetary Flybys May Have Triggered Earth's Worst Mass Extinctions

Life on Earth underwent a long evolutionary journey that eventually gave rise to us, the purportedly intelligent species that dominates the planet.

But there was no grand plan or design, only happenstance, nature, and luck.

Life on Earth suffered multiple extinctions, but got back up, dusted itself off, and continued its long march toward complexity.

The Chicxulub impact that wiped out the dinosaurs and set the stage for the ascension of mammals grabs plenty of headlines. But there may have been more subtle events that also led to extinctions.

Gravitational tides generated by the flybys of planetary-mass objects or dwarf planets may have played a role, according to a new preprint paper.

Illustration of a massive tidal wave created by the flyby of a planetary-mass object. (Fargion, arXiv, 2026)

Daniele Fargion, a theoretical physicist from Rome University, points out that there is ample evidence for a population of dwarf-planet-sized objects in the outer Solar System, of which Pluto may be the most well-known member.

There could be thousands or tens of thousands of these objects on elliptical orbits. Gravitational perturbations could send some of these objects into the inner Solar System, where collisions like the one between Earth and Theia created the Moon.

But far more likely than head-on collisions are flybys.

“Such passages may have left strong tidal signatures: giant waves, large volcanic episodes, sea regressions, coherent meteor showers, and major climatic perturbations,” Fargion writes.

“These mechanisms could have contributed to several major biological mass extinctions over the past 600 million years, as suggested by peculiar correlations in the geological record.”

Fargion says that collisions with planetary-mass objects could have created the planets’ off-axis spins. (Fargion, arXiv, 2026)

Extinctions Without a Smoking Crater

Fargion explains that Earth’s major mass extinctions coincide with major changes in planetary climate, meteoric impacts, and enormous volcanic eruptions. Correlation is one thing, but finding the definitive links between them is more difficult.

While there is plenty of evidence, including the iridium anomaly, that an impact wiped out the dinosaurs and created a mass extinction about 64 million years ago, the causes of other mass extinctions are not so clear.

“But, neither an iridium anomaly nor a large meteoritic crater has been dated back to the Permian/Triassic mass extinction, 251 million years ago, which was the largest known extinction in the history of life, where global species extinction ranged between 80% and 95%,” the author explains.

“Here we suggest that tidal effects of planetary-mass objects which pass near Earth could have caused all of these and can explain the complex geological records of the major biological mass extinctions.”

There are many anomalies in the inner Solar System that can be attributed to flybys of, collisions with, or captures of planetary-mass objects from the outer Solar System. Uranus is tilted on its side, which could be due to a collision. Triton, Neptune’s largest moon, appears to be a captured Kuiper Belt Object.

And the Late Heavy Bombardment may have been caused by perturbations from a planetary-mass flyby. The Solar System also features several retrograde-orbit moons, a phenomenon that still awaits an explanation.

“Passage of such objects near Earth could have generated on it gigantic tidal waves, large volcanic eruptions and drastic changes in global climate and sea level,” writes Fargion.

Evidence in Fossil Coral

Some evidence for past flybys can be seen in the Earth-Moon system, according to the new paper.

“Fossil corals show that the rate of decrease in the number of diurnal rings during annual cycles, i.e. the rate of decrease in the number of days in a year, has changed suddenly into a slower rate at the end of the Devonian,” Fargion writes.

“Since the lengthening of the day is due to slowing of the rotation of Earth by the well-understood Moon’s tidal forces, it implies that at the end of the Devonian the moon-Earth distance increased suddenly by a significant fraction.”

A collision couldn’t do that because it’s so sudden and would create an instantaneous change. But a flyby could.

“Such an increase could have been induced by a tidal pull in a nearby passage of a visiting planet/moon,” Fargion explains.

Some of the planetary-mass objects in our Solar System. During flybys, objects with this much mass could have triggered extinctions on Earth. (Fargion, arXiv, 2026)

That tidal pull could also generate global tsunamis and powerful tides that lasted years. It would also deform the crust and generate tidal heating in the planet’s interior, which could have triggered massive volcanic eruptions.

Jupiter as a Reference Point

These events were all a long time ago, and it’s challenging to estimate how many flybys there were and how massive the objects were.

But Jupiter may provide a way to understand. Jupiter is slightly tilted on its axis, and also seems to have an unaccounted-for energy source that contributes to its high surface temperature. Fargion calculates that Jupiter has suffered 16 collisions with objects of 0.5 Earth masses in its history.

The Solar System’s history is a puzzle, and Earth’s history is likewise puzzling. Ongoing discoveries of massive objects in the outer Solar System show that they are a part of that puzzle too. If they visited the inner Solar System, they could have triggered extinctions.

And if it happened before, it could happen again.

A Warning for the Future

“The consequent lessons for us humans, to overcome such an eventual extinction are: deep sky inspection to seek weakest far dwarf planet sources, once found, alert the incoming events as soon as possible,” the author writes.

If the incoming object is larger than an asteroid and is a planetary-mass object, the required preparation would be fundamentally different. The main danger, according to Fargion, would be from massive tidal waves that swept around the planet and persisted for years.

“The tidal mass extinction, its rate and form, may also explain the famous Fermi Paradox,” Fargion concludes.

“Where is everybody, or, why they are not yet here? The answer could be that life is unstable and short.”

The paper was presented at the Multi-frequency Behaviour of High Energy Cosmic Sources conference in June 2025. A preprint is available at ArXiv.

This article was originally published by Universe Today. Read the original article.