Earth's Mesosphere During Possible Encounters With Massive Interstellar Clouds 2 and 7 Million Years Ago

TL;DR

This study uses a modern atmospheric chemistry model to analyze Earth's mesospheric response during past encounters with dense interstellar clouds, revealing confined noctilucent clouds, ozone depletion, and significant changes in sunlight and radiation.

Contribution

It provides a detailed re-evaluation of Earth's atmospheric response during interstellar cloud encounters using advanced modeling techniques.

Findings

Noctilucent clouds remained polar and short-lived during cloud crossings.

Polar ozone was significantly depleted, but total ozone increased.

Densest clouds reduced surface sunlight by up to 7% and halved outgoing longwave radiation.

Abstract

Our solar system's path has recently been shown to potentially intersect dense interstellar clouds 2 and 7 million years ago: the Local Lynx of Cold Cloud and the edge of the Local Bubble. These clouds compressed the heliosphere, directly exposing Earth to the interstellar medium. Previous studies that examined climate effects of these encounters argued for an induced ice age due to the formation of global noctilucent clouds (NLCs). Here, we revisit such studies with a modern 2D atmospheric chemistry model using parameters of global heliospheric magnetohydrodynamic models as input. We show that NLCs remain confined to polar latitudes and short seasonal lifetimes during these dense cloud crossings lasting $\sim10^5$ years. Polar mesospheric ozone becomes significantly depleted, but the total ozone column broadly increases. Furthermore, we show that the densest NLCs lessen the amount of sunlight reaching the surface instantaneously by up to 7% while halving outgoing longwave radiation.