2025AJ....170...71Z

Passing stars (also called stellar flybys) have notable effects on the solar system's long-term dynamical evolution, injection of Oort cloud comets into the solar system, properties of trans-Neptunian objects, and more. Based on a simplified solar system model, omitting the Moon and the Sun's quadrupole moment J₂, it has recently been suggested that passing stars are also an important driver of paleoclimate before ∼50 Myr ago, including a climate event called the Paleocene-Eocene Thermal Maximum (∼56 Myr ago). In contrast, using a state-of-the-art solar system model, including a lunar contribution and J₂, and random stellar parameters (>400 simulations), we find no influence of passing stars on paleoclimate reconstructions over the past 56 Myr. Even in an extreme flyby scenario in which the Sun-like star HD 7977 (m = 1.07M_⊙) would have passed within ∼3900 au about 2.8 Myr ago (with 5% likelihood), we detect no discernible change in Earth's orbital evolution over the past 70 Myr, compared to our standard model. Our results indicate that a complete physics model is essential to accurately study the effects of stellar flybys on Earth's orbital evolution.