The Heliosphere, a case of a Habitable Astrosphere (Merav Opher, 11/7/2023)
Channel: Academy of Athens
Date: 09/11/2023

Merav Opher
Astronomy Department, Boston University, Boston, MA, United States

Abstract:
Most stars generate winds and move through the interstellar medium that surrounds them. This movement creates a cocoon formed by the deflection of these winds that envelops and protects the stars. We call these ‘cocoons’ astrospheres. The Sun has its own cocoon, the heliosphere. The heliosphere is an immense shield that protects the solar system from harsh, galactic radiation. The radiation that enters the heliosphere affects life on Earth as well as human space exploration. Galactic cosmic rays are the dominant source of radiation and principal hazard affecting space missions within our solar system. Current global heliosphere models do not successfully predict the radiation environment at all locations or under different solar conditions. To understand the heliosphere’s shielding properties, we need to understand its structure and large-scale dynamics. A fortunate confluence of missions (e.g. Voyagers, New Horizons, Cassini, IBEX) has provided the scientific community with a treasure of heliospheric data. However, fundamental features concerning the physics of our solar bubble remain unknown. In this talk I will review some of the advances that the new NASA Drive Center Hydrogen Ion charge Exchange and Large-Scale Dynamics (SHIELD;https://shielddrivecenter.com/, Director: M. Opher, Project Manager: J. D. Richardson) is making in understanding the heliosphere; the only known habitable astrosphere.

I will review the Sun’s Trajectory in the last 10 million years and possible terrestrial implications on Climate and Biological Evolution. Until recently, the primary focus with respect to astronomical impacts on Earth’s climate and biota have centered around those arising from changes in the tilt of the Earth axis, spin and rotation. The Sun moves large distances (~19pc/Myr) through the variable Interstellar Medium and recent analyses present geological evidence from 60Fe and 244Pu isotopes that Earth received interstellar material about 2-3 Myr ago and 7 Myr ago. I will discuss our new research indicating the encounter of Earth with a massive cold cloud in the Local Ribbon of Cold Clouds 3 Myr ago, and with the edge of the Local Bubble 7 Myr ago. Both encounters shrinked the Sun’s protective bubble—the heliosphere —to within Earth’s orbit exposing Earth to a cold dense interstellar medium. I will discuss the possible terrestrial consequences to climate and to biological evolution.