Obliquity Variability of a Potentially Habitable Early Venus

TL;DR

This study explores how the obliquity of a hypothetical early Venus, with rapid rotation and low-mass atmosphere, would have varied over time, revealing simpler dynamics and unexpected long-term variability compared to Earth.

Contribution

It provides new insights into the obliquity dynamics of early Venus under different rotational and atmospheric conditions, highlighting differences from Earth's obliquity behavior.

Findings

Obliquity variation structure is simpler than Earth's without a large Moon.

Unexpected long-term variability of up to ±7° for retrograde Venuses.

Low-obliquity Venuses exhibit minimal obliquity variability over billion-year timescales.

Abstract

Venus currently rotates slowly, with its spin controlled by solid-body and atmospheric thermal tides. However, conditions may have been far different 4 billion years ago, when the Sun was fainter and most of the carbon within Venus could have been in solid form, implying a low-mass atmosphere. We investigate how the obliquity would have varied for a hypothetical rapidly rotating Early Venus. The obliquity variation structure of an ensemble of hypothetical Early Venuses is simpler than that Earth would have if it lacked its large Moon (Lissauer et al., 2012), having just one primary chaotic regime at high prograde obliquities. We note an unexpected long-term variability of up to $\pm7^\circ$ for retrograde Venuses. Low-obliquity Venuses show very low total obliquity variability over billion-year timescales -- comparable to that of the real Moon-influenced Earth.