We investigate the role which clouds could play in resolving the Faint Young Sun Paradox (FYSP). Lower solar luminosity in the past means that less energy was absorbed on Earth (a forcing of -50 Wm-2 during the late Archean), but geological evidence points to the Earth being at least as warm as it is today, with only very occasional glaciations. We perform radiative calculations on a single global mean atmospheric column. We select a nominal set of three layered, randomly overlapping clouds, which are both consistent with observed cloud climatologies and reproduce the observed global mean energy budget of Earth. By varying the fraction, thickness, height and particle size of these clouds we conduct a wide exploration of how changed clouds could affect climate, thus constraining how clouds could contribute to resolving the FYSP. Low clouds reflect sunlight but have little greenhouse effect. Removing them entirely gives a~forcing of +25 Wm-2 whilst more modest reduction in their efficacy gives a forcing of +10 to +15 Wm-2. For high clouds, the greenhouse effect dominates. It is possible to generate +50 Wm-2 forcing from enhancing these, but this requires making them 3.5 times thicker and 14 K colder than the standard high cloud in our nominal set and expanding their coverage to 100% of the sky. Such changes are not credible. More plausible changes would generate no more that +15 Wm-2 forcing. Thus neither fewer low clouds nor more high clouds can provide enough forcing to resolve the FYSP. Decreased surface albedo can contribute no more than +5 Wm-2 forcing. Some models which have been applied to the FYSP do not include clouds at all. These overestimate the forcing due to increased CO2 by 20 to 25% when CO2 is 0.01 to 0.1 bar.
The Sun was fainter when the Earth was young, but the climate was generally at least as warm as today; this is known as the `faint young Sun paradox'. Rosing et al. [1] claim that the paradox can be resolved by making the early Earth's clouds and surface less reflective. We show that, even with the strongest plausible assumptions, reducing cloud and surface albedos falls short by a factor of two of resolving the paradox. A temperate Archean climate cannot be reconciled with the low level of CO2 suggested by Rosing et al. [1]; a stronger greenhouse effect is needed.
The purpose of this paper is to explore a resolution for the Faint Young Sun Paradox that has been mostly rejected by the community, namely the possibility of a somewhat more massive young Sun with a large mass loss rate sustained for two to three billion years. This would make the young Sun bright enough to keep both the terrestrial and Martian oceans from freezing, and thus resolve the paradox. It is found that a large and sustained mass loss is consistent with the well observed spin-down rate of Sun-like stars, and indeed may be required for it. It is concluded that a more massive young Sun…
Solar models suggest that four billion years ago the young Sun was about 25% fainter than it is today, rendering Earth's oceans frozen and lifeless. However, there is ample geophysical evidence that Earth had a liquid ocean teeming with life 4 Gyr ago. Since ${\cal L_\odot} \propto G^7M_\odot^5$, the Sun's luminosity ${\cal L_\odot}$ is exceedingly sensitive to small changes in the gravitational constant $G$. We show that a percent-level increase in $G$ in the past would have prevented Earth's oceans from freezing, resolving the faint young Sun paradox. Such small changes in $G$ are consistent…
The Faint Young Sun Paradox comes from the fact that solar luminosity (2-4)x10^9 years ago was insufficient to support the Earth's temperature necessary for the efficient development of geological and biological evolution (particularly, for the existence of considerable volumes of liquid water). It remains unclear by now if the so-called greenhouse effect on the Earth can resolve this problem. An interesting alternative explanation was put forward recently by M.Krizek (New Ast. 2012, 17, 1), who suggested that planetary orbits expand with time due to the local Hubble effect, caused by the unif…
Faint young Sun paradox (FYSP) is one of the unsolved problem in solar physics. The present study aims to get a possible solution for the FYSP through sun-like G stars and their exoplanetary systems. Using physical properties of exoplanetary data, an empirical relationship between the rate of mass loss ($\frac{dM}{dt}$) with stellar mass (M$_{\star}$) and age ({\em t}) is obtained. We found mass loss rate varies with stellar mass as $\propto$ $(M_{\star}/M_\odot)^{-3.788}$ and proportional to the age as $\propto$ t$^{-1.25}$, which indicates rate of mass loss is higher during early evolutionar…
For more than four decades, scientists have been trying to find an answer to one of the most fundamental questions in paleoclimatology, the `faint young Sun problem'. For the early Earth, models of stellar evolution predict a solar energy input to the climate system which is about 25% lower than today. This would result in a completely frozen world over the first two billion years in the history of our planet, if all other parameters controlling Earth's climate had been the same. Yet there is ample evidence for the presence of liquid surface water and even life in the Archean (3.8 to 2.5 billi…
Different solutions have been proposed to solve the "faint young Sun problem", defined by the fact that the Earth was not fully frozen during the Archean despite the fainter Sun. Most previous studies were performed with simple 1-D radiative convective models and did not account well for the clouds and ice-albedo feedback or the atmospheric and oceanic transport of energy. We apply a global climate model (GCM) to test the different solutions to the faint young Sun problem. We explore the effect of greenhouse gases (CO2 and CH4), atmospheric pressure, cloud droplet size, land distribution, and …
Stellar evolution models predict that the solar luminosity was lower in the past, typically 20-25 % lower during the Archean (3.8-2.5 Ga). Despite the fainter Sun, there is strong evidence for the presence of liquid water on Earth's surface at that time. This "faint young Sun problem" is a fundamental question in paleoclimatology, with important implications for the habitability of the early Earth, early Mars and exoplanets. Many solutions have been proposed based on the effects of greenhouse gases, atmospheric pressure, clouds, land distribution and Earth's rotation rate. Here we review the f…
Geological evidence suggests liquid water near the Earth's surface as early as 4.4 billion years ago when the faint young Sun only radiated about 70% of its modern power output. At this point, the Earth should have been a global snowball if it possessed atmospheric properties similar to those of the modern Earth. An extreme atmospheric greenhouse effect, an initially more massive Sun, release of heat acquired during the accretion process of protoplanetary material, and radioactivity of the early Earth material have been proposed as reservoirs or traps for heat. For now, the faint-young-sun par…
Models of the Sun's long-term evolution suggest that its luminosity was substantially reduced 2-4 billion years ago, which is inconsistent with substantial evidence for warm and wet conditions in the geological records of both ancient Earth and Mars. Typical solutions to this so-called "faint young Sun paradox" consider changes in the atmospheric composition of Earth and Mars, and while attractive, geological verification of these ideas is generally lacking-particularly for Mars. One possible underexplored solution to the faint young Sun paradox is that the Sun has simply lost a few percent of…
Given a solar luminosity L_Ar = 0.75 L_0 at the beginning of the Archean 3.8 Gyr ago, where L_0 is the present-day one, if the heliocentric distance r of the Earth was r_Ar = 0.956 r_0, the solar irradiance would have been as large as I_Ar = 0.82 I_0. It would allowed for a liquid ocean on the terrestrial surface which, otherwise, would have been frozen, contrary to the empirical evidence. By further assuming that some physical mechanism subsequently displaced the Earth towards its current distance in such a way that the irradiance stayed substantially constant over the entire Archean from 3.8…
Earth's earliest sedimentary record contains evidence that surface temperatures were similar to, or perhaps even warmer than modern. In contrast, standard Solar models suggest the Sun was 25% less luminous at this ancient epoch, implying a cold, frozen planet-all else kept equal. This discrepancy, known as the Faint Young Sun Paradox, remains unresolved. Most proposed solutions invoke high concentrations of greenhouse gases in the early atmosphere to offset for the fainter Sun, though current geological constraints are insufficient to verify or falsify these scenarios. In this work, we examine…
A 2000-2017 set of long-period comets with high-quality orbits of perihelion distance <1 AU is used to show that the objects that perish shortly before perihelion are nearly exclusively the Oort Cloud comets, especially those with perihelia within 0.6 AU of the Sun, intrinsically fainter, and dust poor. Their propensity for disintegration is much higher than predicted by Bortle's perihelion survival rule, prompting the author to propose a new synoptic index to be tested in future prognostication efforts. By their susceptibility to demise near the Sun, the nuclei of Oort Cloud comets differ dra…
The faint young Sun paradox remains an open question. Presented here is one possible solution to this apparent inconsistency, a more massive early Sun. Based on conditions on early Earth and Mars, a luminosity constraint is set as a function of mass. We examine helioseismic constraints of these alternative mass-losing models. Additionally, we explore a dynamic electron screening correction in an effort to improve helioseismic agreement in the core of the an early mass-losing model.
Despite their importance for determining the evolution of the Earth's atmosphere and surface conditions, the evolutionary histories of the Earth's atmospheric CO$_2$ abundance during the Archean eon and the Sun's activity are poorly constrained. In this study, we apply a state-of-the-art physical model for the upper atmosphere of the Archean Earth to study the effects of different atmospheric CO$_2$/N$_2$ mixing ratios and solar activity levels on the escape of the atmosphere to space. We find that unless CO$_2$ was a major constituent of the atmosphere during the Archean eon, enhanced heating…
In this thesis, I explore two topics in exoplanet science. The first is the prevalence of Earth-size planets in the Milky Way Galaxy. To determine the occurrence of planets having different sizes, orbital periods, and other properties, I conducted a survey of extrasolar planets using data collected by NASA's Kepler Space Telescope. This project involved writing new algorithms to analyze Kepler data, finding planets, and conducting follow-up work using ground-based telescopes. I found that most stars have at least one planet at or within Earth's orbit and that 26% of Sun-like stars have an Eart…
We investigate mass losses via stellar winds from sun-like main sequence stars with a wide range of activity levels. We perform forward-type magnetohydrodynamical numerical experiments for Alfven wave-driven stellar winds with a wide range of the input Poynting flux from the photosphere. Increasing the magnetic field strength and the turbulent velocity at the stellar photosphere from the current solar level, the mass loss rate rapidly increases at first owing to the suppression of the reflection of the Alfven waves. The surface materials are lifted up by the magnetic pressure associated with t…
