Despite being pivotal to the habitability of our planet, the process by which Earth gained its present-day hydrogen budget is unclear. Due to their isotopic similarity to terrestrial rocks across a range of elements, the meteorite group that is thought to best represent Earth's building blocks is the enstatite chondrites (ECs). Because of ECs' nominally anhydrous mineralogy, these building blocks have long been presumed to have supplied negligible hydrogen to the proto-Earth. However, recent bulk compositional measurements suggest that ECs may unexpectedly contain enough hydrogen to readily explain Earth's present-day water abundance. Together, these contradictory findings mean the contribution of ECs to Earth's hydrogen budget is currently unclear. As such, it is uncertain whether appreciable hydrogen is a systematic outcome of Earth's formation. Here, we explore the amount of hydrogen in ECs as well as the phase that may carry this element using sulfur X-ray absorption near edge structure (S-XANES) spectroscopy. We find that hydrogen bonded to sulfur is prevalent throughout the meteorite, with fine matrix containing on average almost 10 times more H-S than chondrule mesostasis. Moreover, the concentration of the H-S bond is linked to the abundance of micrometre-scale pyrrhotite (Fe1-xS, 0<x<0.125). This sulfide can sacrificially catalyse a reaction with H2 from the disk at high temperatures to create H2S, which could be dissolved in adjoining molten silicate-rich material. Upon rapid cooling, this assemblage would form pyrrhotite encased in submicron silicate-rich glass that carries trapped H2S. These findings indicate that hydrogen is present in ECs in higher concentrations than previously considered and could suggest that this element may have a systematic, rather than stochastic, origin on our planet.
We examine how water is produced globally over the lunar surface as it orbits in/out of the magnetotail. Due to the interaction of the solar wind (SW) with Earth's magnetic field, upstream the magnetic field is compressed down to ~10 Earth radii. However, the diverted stream of SW around Earth's magnetic field results in an extended depleted region of SW protons (positively charged hydrogen) out to 1000's of Earth radii, referred to as the magnetotail. The Moon orbits at a distance of ~40 Earth radii; therefore, upstream it is within the SW, but downstream it is partially shielded while in the…
In this work we generalize the notion of convective inhibition to apply in cases where there is an infinite reservoir of condensible species (i.e., an ocean). We propose a new model for the internal structure and thermal evolution of super-Earths with hydrogen envelopes. We derive the criterion for convective inhibition in a generalizes phase mixture from first principles thermodynamics. We then investigate the global ocean case using a water-hydrogen system, for which we have data, as an example. We then extend our arguments to apply to a system of hydrogen and silicate vapor. We then employ …
Hydrogen in rocky planet atmospheres has been invoked in arguments for extending the habitable zone via N2-H2 and CO2-H2 greenhouse warming, and providing atmospheric conditions suitable for efficient production of prebiotic molecules. On Earth and Super-Earth-sized bodies, where H2-rich primordial envelopes are quickly lost to space, volcanic outgassing can act as a hydrogen source, provided it balances with the loss rate from the top of the atmosphere. Here, we show that both Earth-like and Mars-like planets can sustain atmospheric H2 fractions of several percent across relevant magmatic fO2…
Super-Earths and sub-Neptunes are commonly thought to have accreted hydrogen/helium envelopes, consisting of a few to ten percent of their total mass, from the primordial gas disk. Subsequently, hydrodynamic escape driven by core-powered mass-loss and/or photo-evaporation likely stripped much of these primordial envelopes from the lower-mass and closer-in planets to form the super-Earth population. In this work we show that after undergoing core-powered mass-loss, some super-Earths can retain small residual H/He envelopes. This retention is possible because, for significantly depleted atmosphe…
Recent observations of the Earth's exosphere revealed the presence of an extended hydrogenic component that could reach distances beyond 40 planetary radii. Detection of similar extended exospheres around Earth-like exoplanets could reveal crucial facts in terms of habitability. The presence of these rarified hydrogen envelopes is extremely dependent of the planetary environment, dominated by the ionizing radiation and plasma winds coming from the host star. Radiation and fast wind particles ionize the uppermost layers of planetary atmospheres, especially for planets orbiting active, young sta…
Oxygen and hydrogen ion abundance in the near-Earth magnetosphere: Statistical results on the response to the geomagnetic and solar wind activity conditions
The formation of the solar system's terrestrial planets concluded with a period of giant impacts. Previous works examining the volatile loss caused by the impact shock in the moon-forming impact find atmospheric losses of at most 20-30 per cent and essentially no loss of oceans. However, giant impacts also result in thermal heating, which can lead to significant atmospheric escape via a Parker-type wind. Here we show that H2O and other high-mean molecular weight outgassed species can be efficiently lost through this thermal wind if present in a hydrogen-dominated atmosphere, substantially alte…
By plotting empirical chemical element abundances on Earth relative to the Sun and normalized to silicon versus their first ionization potentials, we confirm the existence of a correlation reported earlier. To explain this, we develop a model based on principles of statistical physics that predicts differentiated relative abundances for any planetary body in a solar system as a function of its orbital distance. This simple model is successfully tested against available chemical composition data from CI chondrites and surface compositional data of Mars, Earth, the Moon, Venus, and Mercury. We s…
The Oxygen Valve on Hydrogen Escape Since the Great Oxidation Event
Institute of Astronomy, University of Cambridge（剑桥大学天文学研究所）；School of Physics and Astronomy, University of Leeds（利兹大学物理与天文学院）；Center for Space and Habitability, University of Bern（伯尔尼大学太空与宜居性中心）
Direct detection of hydrogen reveals a new macroscopic crustal water reservoir on early Mars
Technical University of Denmark（丹麦技术大学）；University of Copenhagen（哥本哈根大学）；Paul Scherrer Institut（保罗谢勒研究所）；European Synchrotron Radiation Facility（欧洲同步辐射装置）
We investigate equilibrium chemistry between molten metal and silicate, and a hydrogen-rich envelope using 18 independent reactions among 25 phase components for sub-Neptune-like exoplanets. Both reactive metal and unreactive metal sequestered in an isolated core are modeled. The overarching effects of equilibration are oxidation of the envelope and reduction of the mantle and core. Hydrogen and oxygen typically comprise significant fractions of metal cores at chemical equilibrium, leading to density deficits that offer a possible alternative explanation for the low densities of the Trappist-1…
Materials at high pressures and temperatures are of great interest for planetary science and astrophysics, warm dense matter physics, and inertial confinement fusion research. Planetary structure models rely on our understanding of the behaviour of elements (and their mixtures) at exotic conditions that do not exist on Earth, and at the same time planets serve as natural laboratories for studying materials at extreme conditions. In this review we discuss the connection between modelling planetary interiors and high-pressure physics of hydrogen and helium. First, we summarise key experiments fo…
Volatile molecules containing hydrogen, carbon, and nitrogen are key components of planetary atmospheres. In the pebble accretion model for rocky planet formation, these volatile species are accreted during the main planetary formation phase. For this study, we modelled the partitioning of volatiles within a growing planet and the outgassing to the surface. The core stores more than 90\% of the hydrogen and carbon budgets of Earth for realistic values of the partition coefficients of H and C between metal and silicate melts. The magma oceans of Earth and Venus are sufficiently deep to undergo …
Recent detection of exoplanets with Earth-like insolation attracts growing interest in how common Earth-like aqua planets are beyond the solar system. While terrestrial planets are often assumed to capture icy or water-rich planetesimals, a primordial atmosphere of nebular origin itself can produce water through oxidation of the atmospheric hydrogen with oxidising minerals from incoming planetesimals or the magma ocean. Thermodynamically, normal oxygen buffers produce water comparable in mole number to or more than hydrogen. Thus, the primordial atmosphere would likely be highly enriched with …
