# Was the Sun a Slow Rotator? -- Sodium and Potassium Constraints from the Lunar Regolith

## TL;DR

This study suggests that paleo space weather caused the loss of sodium and potassium from the lunar surface, indicating the Sun was likely a slow rotator in its early history, impacting planetary evolution and habitability.

## Contribution

It introduces a novel link between lunar volatile depletion and the Sun's primordial rotation state, providing new constraints on early solar activity.

## Key findings

- Lunar sodium and potassium depletion is influenced by space weather.
- The Sun was likely a slow rotator in its early history.
- Solar activity impacts lunar surface composition and early planetary environments.

## Abstract

While the Earth and Moon are generally similar in composition, a notable difference between the two is the apparent depletion in moderately volatile elements in lunar samples. This is often attributed to the formation process of the Moon and demonstrates the importance of these elements as evolutionary tracers. Here we show that paleo space weather may have driven the loss of a significant portion of moderate volatiles, such as sodium and potassium from the surface of the Moon. The remaining sodium and potassium in the regolith is dependent on the primordial rotation state of the Sun. Notably, given the joint constraints shown in the observed degree of depletion of sodium and potassium in lunar samples and the evolution of activity of solar analogues over time, the Sun is highly likely to have been a slow rotator. Since the young Sun's activity was important in affecting the evolution of planetary surfaces, atmospheres, and habitability in the early Solar System, this is an important constraint on the solar activity environment at that time. Finally, since solar activity was strongest in the first billion years of the Solar System, when the Moon was most heavily bombarded by impactors, evolution of the Sun's activity may also be recorded in lunar crust and would be an important well-preserved and relatively accessible record of past Solar System processes.