Star HD 7977 Can Alter Earth’s Orbit

These are simulations predicting the Earth’s past orbital evolution under the influence of the other planets, 5 of the largest asteroids, and Pluto. 100 simulations are run on both the right and the left side. Earth’s orbit in each simulation is sampled every 1000 years for 300,000-year spans. Each simulation’s sample series has a unique color, but all colors lie nearly right on top of each other for the first ~half of the animation. Among the 100 simulations, the only difference is that the planets’ starting positions differ by random amounts less than 2 cm. The simulations on the left side are subjected to the passage of Sun-like star HD 7977 at 2.8 Myrs in the past, while the right side simulations are not. HD 7977 is assumed to come within 4000 au of the Sun. There is a large amount of uncertainty in this star’s closest approach distance. The approach distance we use has a 5% likelihood (within current observational uncertainties), and significantly larger approach distances are more likely. However, this encounter illustrates the role that stellar passages can play in altering the long-term orbital evolution of Earth and the other planets.