Chemical Differentiation of Planets: A Core Issue

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 show, moreover, that deviations from the proposed law for a given planet correspond to later surface segregation of elements driven both by gravity and chemical reactions. We thus provide a new picture for the distribution of elements in the solar system and inside planets, with important consequences for their chemical composition. Particularly, a 4 wt% initial hydrogen content is predicted for bulk early Earth. This converges with other works suggesting that the interior of the Earth could be enriched with hydrogen.

Laboratory Investigations Coupled to VIR/Dawn Observations to Quantify the Large Concentrations of Organic Matter on Ceres

Organic matter directly observed at the surface of an inner planetary body is quite infrequent due to the usual low abundance of such matter and the limitation of the infrared technique. Fortuitously, the Dawn mission has revealed, thanks to the Visible and InfraRed mapping spectrometer (VIR), large areas rich in organic matter at the surface of Ceres, near Ernutet crater. The origin of the organic matter and its abundance in association with minerals, as indicated by the low altitude VIR data, remains unclear, but multiple lines of evidence support an endogenous origin. Here, we report an experimental investigation to determine the abundance of the aliphatic carbon signature observed on Ceres. We produced relevant analogues containing ammoniated-phyllosilicates, carbonates, aliphatic carbons (coals), and magnetite or amorphous carbon as darkening agents, and measured their reflectance by infrared spectroscopy. Measurements of these organic-rich analogues were directly compared to the VIR spectra taken from different locations around Ernutet crater. We found that the absolute reflectance of our analogues is at least two orders of magnitude higher than Ceres, but the depths of absorption bands match nicely the ones of the organic-rich Ceres spectra. The choices of the different components are discussed in comparison with VIR data. Relative abundances of the components are extrapolated from the spectra and mixture composition, considering that the differences in reflectance level is mainly due to optical effects. Absorption bands of Ceres’ organic-rich spectra are best reproduced by around 20 wt.% of carbon (a third being aliphatic carbons), in association with around 20 wt.% of carbonates, 15 wt.% of ammoniated-phyllosilicate, 20 wt.% of Mg-phyllosilicates, and 25 wt.% of darkening agent. Results also highlight the pertinence to use laboratory analogues in addition to models for planetary surface characterization. Such large quantities of organic materials near Ernutet crater, in addition to the amorphous carbon suspected on a global scale, requires a concentration mechanism whose nature is still unknown but that could potentially be relevant to other large volatile-rich bodies.

Expansion-Oriented View On Origin of Oceans

Both the concepts of plate tectonics and continental drift conceive that the planet earth’s dimension, associated with its oceans, has remained unchanged throughout the past geological periods. In contrast, Hilgenberg’s model of earth expansion endorses that initially the planet was considerably small and devoid of oceans [1]. Based on earth expansion theory the author has pointed out that since the primordial condensed or small earth was devoid of oceans, initially the ocean-forming water must have been associated with the mantle, thereby turning that geosphere considerably fluid and pre-eminently suitable for planetary expansion. Expansion of the planet appears to have been caused owing to swelling up of the semi-fluid mantle in response to an external gravitational pull caused by an extra-terrestrial planetary body, probably the Moon. The primordial earth was completely covered with a relatively thin granitic crust, which, due to swelling up of the mantle developed a number of long and sinuous expansion cracks. Through these expansion cracks widespread eruption of molten magma took place spreading on both sides of the cracks to form rudimentary oceans basins. With continued expansion, the dimension of the oceans was broadened while the expansion cracks turned in to mid-oceanic ridges. Associated with expulsion of molten lava, large quantum of volatiles, chiefly constituted of water was released from the mantle that formed the ocean water while due to desiccation of the mantle, the process of expansion was eventually stopped.

The Global Body Size Biomass Spectrum is Multimodal

Recent research provides an unprecedented account of the diversity and biomass of life, but the data also suggest unexplained patterns such as the co-dominance of very different life forms. We compile the planetary body size biomass spectrum across all taxa and investigate possible underlying forces. We find that small (10-14 g) and large (106 g) organisms vastly outweigh other sizes. The global spectrum reveals an allometric power exponent close to zero, with the marine spectrum in particular showing multiple closely packed modes that are compatible with metabolic food webs. All habitat realms share two distinct size modes that correspond well to the evolutionary innovations of unicellular and complex multicellular life forms, plus a smaller third mode representing unicellular endosymbiotic life. Each mode contains both producers and consumers. These findings show both differences and similarities across habitat realms and point to a size-based synthesis of microevolution, macroevolution, and macroecology.

Steam Atmospheres and Magma Oceans on Planets

A magma ocean is a global layer of partially or fully molten rocks. Significant melting of terrestrial planets likely occurs due to heat release during planetary accretion, such as decay heat of short-lived radionuclides, impact energy released by continuous planetesimal accretion, and energetic impacts among planetary-sized bodies (giant impacts). Over a magma ocean, all water, which is released upon impact or degassed from the interior, exists as superheated vapor, forming a water-dominated, steam atmosphere. A magma ocean extending to the surface is expected to interact with the overlying steam atmosphere through material and heat exchange. Impact degassing of water starts when the size of a planetary body becomes larger than Earth’s moon or Mars. The degassed water could build up and form a steam atmosphere on protoplanets growing by planetesimal accretion. The atmosphere has a role in preventing accretion energy supplied by planetesimals from escaping, leading to the formation of a magma ocean. Once a magma ocean forms, part of the steam atmosphere would start to dissolve into the surface magma due to the high solubility of water into silicate melt. Theoretical studies indicated that as long as the magma ocean is present, a negative feedback loop can operate to regulate the amount of the steam atmosphere and to stabilize the surface temperature so that a radiative energy balance is achieved. Protoplanets can also accrete the surrounding H2-rich disk gas. Water could be produced by oxidation of H2 by ferrous iron in the magma. The atmosphere and water on protoplanets could be a mixture of outgassed and disk-gas components. Planets formed by giant impact would experience a global melting on a short timescale. A steam atmosphere could grow by later outgassing from the interior. Its thermal blanketing and greenhouse effects are of great importance in controlling the cooling rate of the magma ocean. Due to the presence of a runaway greenhouse threshold, the crystallization timescale and water budget of terrestrial planets can depend on the orbital distance from the host star. The terrestrial planets in our solar system essentially have no direct record of their earliest history, whereas observations of young terrestrial exoplanets may provide us some insight into what early terrestrial planets and their atmosphere are like. Evolution of protoplanets in the framework of pebble accretion remains unexplored.

Conflicts of Planetary Proportion – A Conversation

The introduction of the long-term history of the Earth into the preoccupations of historians has triggered a crisis because it has become impossible to keep the “planet” as one single entity outside of history properly understood. As soon as the planetary intruded into history, it became impossible to keep it as one naturalized background. By problematizing the planetary, Dipesh Chakrabarty has forced philosophers, historians and anthropologists to extend pluralism to the very ground on which history was supposed to unfold. Hence Bruno Latour’s attempt at counting the number of “planets” whose attractions are simultaneously being felt today on any political question. Each of his eight planets are defined by the disconnect between where they are situated and where they are imagined to be moving, which means that each planet is led by a different and incommensurable philosophy of history. Such a “fictional planetology” is then discussed by Chakrabarty, who reviews the difficulties historians have had in taking the nonhuman (and hence the planet) as a historical agent and then adds to Latour’s count a new planetary body which further complicates the geopolitical situation. The result of their joint effort is to shift questions of philosophy of history to philosophy of geography.

Nano to Mini satellite and dedicated instruments: a new opportunity for planetary exploration

<p>Large planetary science missions carry a suite of instruments that must negotiate observations and priorities to fulfill their scientific objectives.  A new paradigm of mission brings use of deployable nano-spacecraft as independent operating observers to provide added science.  As in the case of the Hera mission, the Hera mothercraft will carry through the cruise phase two small CubeSats and deploy them once in the vicinity of the Didymos asteroid system.  These small CubeSats are able to navigate relative to the observing planetary body and conduct meaningful science through 1-2 miniaturized instruments.  </p> <p>The Juventas CubeSat for Hera will be discussed along with presentation of its low frequency radar, JuRa.  Its scientific objectives and contribution to the Hera and AIDA objectives will be presented.</p>