Researchers from the Planetary Science Institute in Arizona report that some of the sharp climate shifts in Earth’s deep past may have been sparked by the gravitational pull of nearby stars moving through our galactic neighborhood. The findings appear in the Astrophysical Journal Letters, a respected venue for concise, impactful astronomy research.
The team built models to observe how the Sun would behave as it orbits the Milky Way while coming into proximity with other luminous bodies. By simulating these encounters, they explored how extra stellar gravity could influence the stability of the solar system and, in particular, the path of Earth around the Sun. The results suggest that even distant stellar passings can nudge planetary orbits sufficiently to affect climate over long timescales.
In the model, the Sun experiences close approaches to neighboring stars roughly once every million years, with a distance around 50,000 astronomical units. To put that into perspective, one astronomical unit equals about 150 million kilometers, the mean distance from the Earth to the Sun. The simulations also indicate that a more distant but still relatively nearby star comes within about 20,000 AU on cycles of about 20 million years. These timings and distances describe a long, slow dance of stars relative to our system that could imprint subtle but meaningful changes on planetary motions.
When a passing star exerts its gravity, the orbits of major planets can be perturbed. Even small shifts in orbital geometry can translate into shifts in the Earth’s climate due to variations in insolation, orbital eccentricity, and the distribution of solar energy across the globe. The researchers emphasize that these perturbations are not abrupt events but gradual adjustments that unfold over tens of thousands to millions of years, aligning with the timescales of long term climate fluctuations noted in geological records.
As an example, the team highlights a Paleocene-Eocene climate interval from roughly 56 million years ago, during which global temperatures rose by several degrees Celsius. Such warming episodes are typically associated with complex mechanisms, yet the new work suggests that external gravitational nudges from stellar neighbors could contribute to orbital configurations favorable to warmer climates. The approach provides a complementary perspective to internal Earth system processes and volcanic activity that have long been considered primary drivers of ancient climate swings.
The analysis also points out that the most recent similar gravitational influence from another star would have occurred several million years in the past, continuing a pattern that has persisted over the solar system’s history. This ongoing external forcing underscores the idea that Earth’s climate is shaped by a combination of internal dynamics and the broader galactic environment in which the planet resides.
Beyond Earth, the study notes that the gravitational reach of passing stars can alter the evolution of planets throughout the solar system. The results imply that some orbital configurations we observe today might owe part of their origin to historical stellar flybys, which could also affect the delivery of comets and the long term stability of distant icy bodies in the outer solar system. In other words, the solar system is not a closed, isolated system but a dynamic part of a larger cosmic neighborhood that leaves fingerprints on planetary histories.
Earlier work by other researchers revealed traces of colossal collisions between large exoplanets that, in at least one scenario, produced a vast cloud of gas after the impact. The current investigation builds on that sense of scale by considering how gravitational interactions with nearby stars could shape planetary orbits before or after such dramatic events. Taken together, these lines of inquiry help illuminate how Earth’s climate and planetary architecture reflect a history of gravitational influences that extend far beyond our Sun alone.