The Faint Young Sun Problem Revisited

Abstract

Earth and Mars should have been frozen worlds in their early history because of lower solar luminosity but were not, which challenges our understanding of early atmospheres and surface conditions and/or our understanding of solar evolution. This is known as the "faint young Sun problem." One resolution to the problem is that the Sun was more massive and luminous in its youth before blowing off mass. Astrophysical studies of stellar evolution and behavior, however, including recent analysis of Kepler space-telescope data, indicate that mass loss is both insufficient and occurs too early to allow for a more luminous Sun after ca. 4 Ga. Alternatively, greenhouse gases were surprisingly effective at warming young Earth and Mars. High concentrations of CO 2 with the possible addition of biogenic CH 4 are likely dominant factors promoting open-water conditions on Archean Earth. Evidence of precipitation and flowing water on young Mars, including river valleys thousands of kilometers long, is more problematic. Recent studies indicate that 3-4 Ga river valleys and delta deposits in crater lakes could have been produced in <~10 7 years. Highly transient warm periods during times of favorable orbital parameters possibly led to brief melting under otherwise icy conditions. Seasonal melting and runoff would be more likely with ~1%-10% atmospheric H 2 and CH 4 , perhaps derived from serpentinization of olivine in the martian crust and released from frozen ground by impacts and volcanism, and/or derived directly from volcanic outgassing. The recently recognized effectiveness of hydrogen and methane at absorbing infrared radiation in a thick CO 2 -dominated atmosphere, in a process known as "collision-induced absorption," is probably essential to the solution to the faint young Sun problem for Mars.

Venusian Habitable Climate Scenarios: Modeling Venus Through Time and Applications to Slowly Rotating Venus‐Like Exoplanets

“…There is still debate in the ancient Earth GCM community about the actual composition and thus temperature of early Earth's atmosphere given observational proxies for CO 2 that span orders of magnitude, though models suggest that the range encompasses several viable scenarios (e.g., Charnay et al, , ; Krissansen‐Totton et al, ; Kunze et al, ; Le Hir et al, ; Wolf & Toon, ). These GCM studies and most proxies (e.g., Spencer, ) are from the Archean rather than the late Hadean, but there is some evidence that habitable surface conditions existed well back into the Hadean (e.g., Arndt & Nisbet, ; Harrison, ).…”

Venusian Habitable Climate Scenarios: Modeling Venus through time and applications to slowly rotating Venus-Like Exoplanets

“…There is still debate in the ancient Earth GCM community about the actual composition and thus temperature of early Earth's atmosphere given observational proxies for CO 2 that span orders of magnitude, though models suggest that the range encompasses several viable scenarios (e.g., Charnay et al, 2013;Wolf & Toon, 2013;Kunze et al, 2014;Le Hir et al, 2014;Charnay et al, 2017;Krissansen-Totton et al, 2018). These GCM studies and most proxies (e.g., Spencer, 2019) are from the Archean rather than the late Hadean, but there is some evidence that habitable surface conditions existed well back into the Hadean (e.g., Harrison, 2009;Arndt & Nisbet, 2012).…”

Croll, feedback mechanisms, climate change and the future

“…During this long period of time solar luminosity steadily increased by 30%. Yet, the early Earth provides ample geological evidence of abundant liquid water, erosion and sediment recycling as early as 4.35 billion years ago and consequently of surface temperatures not vastly different to today's (Watson & Harrison 2005;Spencer 2019). Accordingly, a negative feedback is needed to counter the increasing solar energy and to explain what has become known as the 'Faint young Sun paradox'.…”