Title: "The Sagittarius Dwarf Galaxy Impact on 'Snowball Earth' Events and the History of Life in the Solar System"
Abstract:
Geological evidence confirms that our planet’s surface has undergone two distinct “snowball Earth” periods, during which the polar ice sheets extended toward the equatorial latitudes, dramatically affecting the entire biosphere and causing mass extinction of species. Astronomical evidence has shown that these two events coincided with episodes of increased star formation rates in the Milky Way, indicating that Galactic dynamics could play an integral role in planetary evolution and perhaps also in the history of biodiversity. We simulate the ongoing encounter between the Milky Way and the Sagittarius dwarf galaxy at very high resolution, using state-of-the-art meshless magnetohydrodynamical N-body methods, and we find that the recent pericentric passages of that merger have induced global starbursts throughout the Galactic disk during the epochs in question. We measure the simulated local densities in neutral atomic gas as well as the cosmic ray fluid as a function of time for many possible solar neighborhoods, demonstrating that this galactic collision has been responsible not only for the large negative radiative-forcing necessary to cause the observed “snowball Earth” events, but also for sea-level radiation dose-rate increases large enough to incite massive genomic instability, potentially giving rise to the subsequent explosions of aerobic and then multi-cellular life on Earth during the Cambrian era.