Current Earth Research Articles

GENERAL THEORY OF THE ROTATION OF THE NON-RIGID EARTH AT THE SECOND ORDER. I. THE RIGID MODEL IN ANDOYER VARIABLES

This paper is the first part of an investigation where we will present an analytical general theory of the rotation of the non-rigid Earth at the second order, which considers the effects of the interaction of the rotation of the Earth with itself, also named as the spin-spin coupling. Here, and as a necessary step in the development of that theory, we derive complete, explicit, analytical formulae of the rigid Earth rotation that account for the second-order rotation-rotation interaction. These expressions are not provided in this form by any current rigid Earth model. Working within the Hamiltonian framework established by Kinoshita, we study the second-order effects arising from the interaction of the main term in the Earth geopotential expansion with itself, and with the complementary term arising when referring the rotational motion to the moving ecliptic. To this aim, we apply a canonical perturbation method to solve analytically the canonical equations at the second order, determining the expressions that provide the nutation-precession, the polar motion, and the length of day. In the case of the motion of the equatorial plane, nutation-precession, we compare our general approach with the particular study for this motion developed by Souchay et al., showing the existence of new terms whose numerical values are within the truncation level of 0.1 μas adopted by those authors. These terms emerge as a consequence of not assuming in this work the same restrictive simplifications taken by Souchay et al. The importance of these additional contributions is that, as the analytical formulae show, they depend on the Earth model considered, in such a way that the fluid core resonance could amplify them significatively when extending this theory to the non-rigid Earth models.

Atmospheric Dynamics of Earth‐Like Tidally Locked Aquaplanets

We present simulations of atmospheres of Earth‐like aquaplanets that are tidally locked to their star, that is, planets whose orbital period is equal to the rotation period about their spin axis, so that one side always faces the star and the other side is always dark. Such simulations are of interest in the study of tidally locked terrestrial exoplanets and as illustrations of how planetary rotation and the insolation distribution shape climate. As extreme cases illustrating the effects of slow and rapid rotation, we consider planets with rotation periods equal to one current Earth year and one current Earth day. The dynamics responsible for the surface climate (e.g., winds, temperature, precipitation) and the general circulation of the atmosphere are discussed in light of existing theories of atmospheric circulations. For example, as expected from the increasing importance of Coriolis accelerations relative to inertial accelerations as the rotation rate increases, the winds are approximately isotropic and divergent at leading order in the slowly rotating atmosphere but are predominantly zonal and rotational in the rapidly rotating atmosphere. Free‐atmospheric horizontal temperature variations in the slowly rotating atmosphere are generally weaker than in the rapidly rotating atmosphere. Interestingly, the surface temperature on the night side of the planets does not fall below ∼240 K in either the rapidly or slowly rotating atmosphere; that is, heat transport from the day side to the night side of the planets efficiently reduces temperature contrasts in either case. Rotational waves and eddies shape the distribution of winds, temperature, and precipitation in the rapidly rotating atmosphere; in the slowly rotating atmosphere, these distributions are controlled by simpler divergent circulations. Both the slowly and rapidly rotating atmospheres exhibit equatorial superrotation. Systematic variation of the planetary rotation rate shows that the equatorial superrotation varies non‐monotonically with rotation rate, whereas the surface temperature contrast between the day side and the night side does not vary strongly with changes in rotation rate.

DETECTING PLANETARY GEOCHEMICAL CYCLES ON EXOPLANETS: ATMOSPHERIC SIGNATURES AND THE CASE OF SO2

We study the spectrum of a planetary atmosphere to derive detectable features in low resolution of different global geochemical cycles on exoplanets - using the sulphur cycle as our example. We derive low resolution detectable features for first generation space- and ground- based telescopes as a first step in comparative planetology. We assume that the surfaces and atmospheres of terrestrial exoplanets (Earth-like and super-Earths) will most often be dominated by a specific geochemical cycle. Here we concentrate on the sulphur cycle driven by outgassing of SO2 and H2S followed by their transformation to other sulphur-bearing species which is clearly distinguishable from the carbon cycle which is driven by outgassing of CO2. Due to increased volcanism, the sulphur cycle is potentially the dominant global geochemical cycle on dry super-Earths with active tectonics. We calculate planetary emission, reflection and transmission spectrum from 0.4 to 40 micrometer with high and low resolution to assess detectable features using current and Archean Earth models with varying SO2 and H2S concentrations to explore reducing and oxidizing habitable environments on rocky planets. We find specific spectral signatures that are observable with low resolution in a planetary atmosphere with high SO2 and H2S concentration. Therefore first generation space and ground based telescopes can test our understanding of geochemical cycles on rocky planets and potentially distinguish planetary environments dominated by the carbon and sulphur cycle.

Partitioning of Si and O between liquid iron and silicate melt: A two‐phase ab‐initio molecular dynamics study

The magma ocean process in the early history of the Earth has a great influence on the light element identities and contents of the core which subsequently affect the energy of the geodynamo provided by the compositional convection and the inner core growth through their effect on the phase diagram of iron alloy. In the present work, a two‐phase ab‐initio molecular dynamics method is established to study the solubility of silicon and oxygen in liquid iron in equilibrium with silicate melt. The ab‐initio results are found to be in close agreement with experimental data. At the base of a deep magma ocean (39 GPa and 3116 K), liquid iron contains 2.7 wt% silicon and 0.5 wt% oxygen at the current bulk Earth composition. The oxygen content is low compared with its current estimate in the core, indicating a deeper magma ocean may need to be invoked.

A satellite observation system simulation experiment for carbon monoxide in the lowermost troposphere

We demonstrate the feasibility of using observing system simulation experiment (OSSE) studies to help define quantitative trace gas measurement requirements for satellite missions and to evaluate the expected performance of proposed observing strategies. The 2007 U.S. National Research Council Decadal Survey calls for a geostationary (GEO) satellite mission for atmospheric composition and air quality applications (Geostationary Coastal and Air Pollution Events Mission (GEO‐CAPE)). The requirement includes a multispectral (near‐infrared and thermal infrared) measurement of carbon monoxide (CO) at high spatiotemporal resolution with information on lowermost troposphere concentration. We present an OSSE to assess the improvement in surface CO characterization that would result from the addition of a GEO‐CAPE CO measurement to current low Earth orbit (LEO) thermal infrared‐only measurements. We construct instrument simulators for these two measurement scenarios and study the case of July 2004 when wildfires in Alaska and Canada led to significant CO pollution over the contiguous United States. Compared to a control experiment, an ensemble‐based data assimilation of simulated satellite observations in a global model leads to improvements in both the surface CO distributions and the time evolution of CO profiles at locations affected by wildfire plumes and by urban emissions. In all cases, an experiment with the GEO‐CAPE CO measurement scenario (overall model skill of 0.84) performed considerably better than the experiment with the current LEO/thermal infrared measurement (skill of 0.58) and the control (skill of 0.07). This demonstrates the advantages of increased sampling from GEO and enhanced measurement sensitivity to the lowermost troposphere with a multispectral retrieval.

An “Inverse Conglomerate” Paleomagnetic Test and Timing of In Situ Terra Rossa Formation at Bloomington, Indiana

Directions of remanent magnetism in an ∼2-m interval of terra rossa claystone at Bloomington, Indiana, cluster around the current Earth magnetic field direction, a fact consistent with authigenic formation of the terra rossa over the last 0.78 m.yr., the date of the latest earth’s magnetic field reversal, and suggesting a minimum terra rossa formation rate of ∼2: 5m =m:yr: Paleomagnetic directions in limestone “floaters” within the terra rossa are indistinguishable from directions of the bedrock Mississippian Harrodsburg Limestone, indicating that the floaters are in situ and perfectly preserve their original stratigraphic position. Thus, the red claystone containing the floaters is interpreted as an authigenic, isovolumetric replacement of the Harrodsburg—the replacement of which the floaters escaped—and precludes the possibility that the floaters and the surrounding claystone are a mudflow that had carried limestone blocks in it. The implication that the claystone is authigenic independently confirms the petrographic observations reported previously that the red clay grew in situ, replacing the underlying limestone at a moving metasomatic front. Rock magnetic studies of the terra rossa clays show evidence of both goethite and maghemite as main magnetic carriers of this remanence. Both minerals are independently known to occur in pisolites of the terra rossa. The ferric-ironbearing red clays also are weakly magnetic.

The Earth as an extrasolar planet: the vegetation spectral signature today and during the last Quaternary climatic extrema

AbstractThe so-called vegetation red-edge (VRE), a sharp increase in the reflectance around 700 nm, is a characteristic of vegetation spectra, and can therefore be used as a biomarker if it can be detected in an unresolved extrasolar Earth-like planet integrated reflectance spectrum. Here, we investigate the potential for the detection of vegetation spectra during the last Quaternary climatic extrema, the Last Glacial Maximum (LGM) and the Holocene optimum, for which past climatic simulations have been made. By testing the VRE detectability during these extrema, when Earth's climate and biomes maps were different from today, we are able to test the vegetation detectability on a terrestrial planet different from our modern Earth. Data from the Biome3.5 model have been associated to visible Global Ozone Monitoring Experiment (GOME) spectra for each biome and cloud cover to derive Earth's integrated spectra for given Earth phases and observer positions. The VRE is then measured. Results show that the vegetation remains detectable during the last climatic extrema. Compared to the current Earth, the Holocene optimum, with a greener Sahara, slightly increases the mean VRE on one hand, while on the other hand, the large ice cap over the northern hemisphere during the LGM decreases vegetation detectability. We finally discuss the detectability of the VRE in the context of recently proposed space missions.

Evolution of the Theory of the Earth: A Contextualized Approach for Teaching the History of the Theory of Plate Tectonics to Ninth Grade Students

Current high school Earth Science curricula and textbooks organize scientific content into isolated “units” of knowledge. Within this structure, content is taught, but in the absence of the context of fundamental understandings or the process of how the science was actually done to reach the conclusions. These are two key facets of scientific literacy. I have developed curriculum from a historical perspective that addresses two particular units of study in Earth Science (“geologic time” and “plate tectonics”). The curriculum traces the evolution of the theory of plate tectonics. It includes contextualized experiences for students such as telling stories, utilizing original historical texts, narratives, and essential questions, to name a few. All of the strategies are utilized with the goal of building understanding around a small set of common themes. Exploring the historical models in this way allows students to analyze the models, while looking for limitations and misconceptions. This methodology is used to encourage students to develop more scientifically accurate understandings about the way in which the world and the process of scientific discovery work. Observations of high student engagement during the utilization of this contextualized approach has demonstrated that a positive effect on student understanding is promising.

Lunar-forming collisions with pre-impact rotation

Abstract Prior models of lunar-forming impacts assume that both the impactor and the target protoearth were not rotating prior to the Moon-forming event. However, planet formation models suggest that such objects would have been rotating rapidly during the late stages of terrestrial accretion. In this paper I explore the effects of pre-impact rotation on impact outcomes through more than 100 hydrodynamical simulations that consider a range of impactor masses, impact angles and impact speeds. Pre-impact rotation, particularly in the target protoearth, can substantially alter collisional outcomes and leads to a more diverse set of final planet–disk systems than seen previously. However, the subset of these impacts that are also lunar-forming candidates—i.e. that produce a sufficiently massive and iron-depleted protolunar disk—have properties similar to those determined for collisions of non-rotating objects [Canup, R.M., Asphaug, E., 2001. Nature 412, 708–712; Canup, R.M., 2004a. Icarus 168, 433–456]. With or without pre-impact rotation, a lunar-forming impact requires an impact angle near 45 degrees, together with a low impact velocity that is not more than 10% larger than the Earth's escape velocity, and produces a disk containing up to about two lunar masses that is composed predominantly of material originating from the impactor. The most significant differences in the successful cases involving pre-impact spin occur for impacts into a retrograde rotating protoearth, which allow for larger impactors (containing up to 20% of Earth's mass) and provide an improved match with the current Earth–Moon system angular momentum compared to prior results. The most difficult state to reconcile with the Moon is that of a rapidly spinning, low-obliquity protoearth before the giant impact, as these cases produce disks that are not massive enough to yield the Moon.

Origin of the ocean on the Earth: Early evolution of water D/H in a hydrogen-rich atmosphere

The origin of the Earth's ocean has been discussed on the basis of deuterium/hydrogen ratios (D/H) of several sources of water in the Solar System. The average D/H of carbonaceous chondrites (CC's) is known to be close to the current D/H of the Earth's ocean, while those of comets and the solar nebula are larger by about a factor of two and smaller by about a factor of seven, respectively, than that of the Earth's ocean. Thus, the main source of the Earth's ocean has been thought to be CC's or adequate mixing of comets and the solar nebula. However, those conclusions are correct only if D/H of water on the Earth has remained unchanged for the past 4.5 Gyr. In this paper, we investigate evolution of D/H in the ocean in the case that the early Earth had a hydrogen-rich atmosphere, the existence of which is predicted by recent theories of planet formation no matter whether the nebula remains or not. Then we show that D/H in the ocean increases by a factor of 2–9, which is caused by the mass fractionation during atmospheric hydrogen loss, followed by deuterium exchange between hydrogen gas and water vapor during ocean formation. This result suggests that the apparent similarity in D/H of water between CC's and the current Earth's ocean does not necessarily support the CC's origin of water and that the apparent discrepancy in D/H is not a good reason for excluding the nebular origin of water.

The Quaternary in French secondary school: its disappearance today in light of the sociocultural stakes of its introduction during the 19th century

The Quaternary in French secondary school: its disappearance today in light of the sociocultural stakes of its introduction during the 19th century

Is it possible to find a solar signature in the current climatic warming?

This paper investigates whether it is possible to find a solar signature in the current Earth’s climatic warming. The attempt seems audacious as, on one hand, solar output variability on the atmosphere is far to be understood, and on the other hand, there is evidence that most of the warming observed over the last 50 years can be attributed to human activities. However, series of the annual global average temperature, from 1861 up to now are available, showing periods of warming and cooling that are statistically significant. From recent findings, it is also known that solar irradiance shows a variability and can be modeled today with a good accuracy over the last century. The idea was to compare the likelihood linear trends shown in the climatic data with those of the irradiance, during same well defined time ranges. Changes from 1861 to 1975 show an unexpected remarkable correlation, whereas the period 1976–2000 completely deviates from the previous analysis. The 1861–1975 set of data supports the suggestion of an influence of solar irradiance on global climate, which was checked as a natural forcing: the response is found to be λ = 0.46 °C/W m −2, a quite reasonable value, bearing in mind the imprecision in the irradiance modeling. This analysis is also discussed in the scope of other forcings and uncertainties in the data.

Early tides: Response to Varga et al.

Tidal cycling has been causally implicated at the origin of life, but the speed of early tides has not been established. The rotation period of the Earth is the dominant parameter, and a length of day (LOD) of under 6 h at 3.9 Ga was inferred by regression from present values [Lathe, R. 2004. Icarus 168, 18–22]. However, this would imply critical lunar proximity at that time; in their commentary Varga et al. instead argue for a more distant Moon, proposing LOD = 16.8 h . The debate is accentuated because regression from current values requires an Earth–Moon juxtaposition at around 2 Ga, for which there is no evidence. A smooth retreat from a Moon-forming impact at 4.5 Ga is also irreconcilable with the weight of paleotidal evidence. An inflection in the lunar recession curve is required to reconcile current and recent Earth–Moon values with a 4.5 Ga origin, requiring a change in tidal friction during the evolution of the Earth–Moon system. Depending on whether this took place at ∼ 2 – 2.5 Ga before present, or more recently ( ∼ 0.8 – 0.2 Ga ), LOD values are estimated at between 12 and 16 h, suggesting a compromise figure of LOD = ∼ 14 h , with tides every ∼7 h, at 3.9 Ga.

An ‘entry level’ mission to a near Earth object

Near Earth Objects (NEOs) are comets or asteroids that intersect or pass near to our planet posing a real and underestimated danger to mankind. While the probability of impact is low, the consequences of such an impact could be apocalyptic. Various programs are underway to discover these kilometer-sized objects from Earth. However, once targets of interest have been identified a fly-by or orbiting spacecraft is required to understand the objects’ mass, morphology and composition. Fly-past NEO missions represent the simplest interplanetary missions and need not be high cost. An ‘entry level’ mission has been conceptually designed able to deliver a 10 kg science ‘reference’ payload to NEO fly-by for a total mission cost (including launch and operations) of € 20 million (FY2003). This paper outlines the platform architecture, cost and cost drivers, and describes the key technology trades to be performed and the developments required to extend current Low Earth Orbit (LEO) technology to a deep space mission. It concludes by identifying the top-level trade-offs to be made in order to enhance the science return of the mission.

Terra Cognita: Using Earth Observing Systems to Understand Our World

Who would believe that a butterfly, by flapping its wings in Peru, could set off a chain of events leading to a monsoon thousands of miles away? This familiar notion from chaos theory may seem absurd even as it raises a worthy point: Everything around us is intimately connected. And by studying how broad forces in nature interact, we can construct predictions that offer great benefits to society. Now a global effort is under way to revolutionize our understanding of the Earth as an interconnected whole. The effort aims to integrate Earth observing capabilities based on satellites and in situ or ground-based sensors into a Global Earth Observation System of Systems (GEOSS). By uniting these systems, scientists hope to take the pulse of the planet, and in so doing, generate a range of environmental, economic, and health benefits. For instance, should the effort yield even a 1°F improvement in weather forecasting, power utilities can plan their daily output needs more accurately, resulting in an annual $1 billion electricity savings for consumers in the United States alone, according to the U.S. Environmental Protection Agency (EPA). Likewise, improved monitoring of air pollution, or better satellite mapping of habitats that harbor malaria, cholera, or West Nile virus, could save many lives by establishing warning systems for at-risk populations that might reduce exposure. A total of 54 countries, the European Union, and 33 international organizations have joined the GEOSS thus far, providing a welcome boost to the environmental reputation of its sponsor: the United States. The project is also the first project of its kind to get such high-level support, says Steve Goodman, chief of the Earth and Planetary Science Branch at the National Aeronautics and Space Administration (NASA) Marshall Space Flight Center. “I’ve never seen a program move at a pace like this with such a sustained effort,” says Gary Foley, who is director of the EPA National Exposure Research Laboratory. “It seems to be the right thing at the right time with the right leadership. It was what everyone seemed to be looking for.”

アンコール遺跡基壇の消石灰改良土による修復と土質特性

This paper describes the restoration project done on Angkor complex in Cambodia by JSA (Japanese Government Team for Safeguarding Angkor), which is started 1994. Especially it focuses on laterite block tower's original geotechnical structure and the current earth mound of foundation using slaked lime stabilized soil as a test result of the reconstruction project. Angkor ruins have been damaged to go to deteriorate by the geographical natural cycle of dry season and rainy season. Such environmental factor have been causing deformation and making foundation harder. Hence, the seasonal change of soil characteristics had to be taken account, and accommodated for improving mound stability even with slaked lime stabilized soil which is arranged for filing. This paper shows the soil properties of the original foundation, N-value distribution in soil layers, and the relation between additive content of slaked lime and the change in the foundation property, whose strength was our goal for the laterite block tower foundation.

NASA announces organizational shake‐up affecting Earth and space science programs

On 24 June, the National Aeronautic and Space Administration announced major organizational changes that will affect the agency's Earth and space science programs.NASA Administrator Sean O'Keefe announced that a “streamlining” of the agency's functions into four mission offices will involve combining the current Earth science and space science enterprises into one all‐encompassing science mission directorate.

3-Axes Attitude Estimation Experiments Using CCD Earth Sensor

The CCD Earth Sensor (CCDESA) is an attitude sensor that estimates three-axis attitude angles using the Earth's images. Current Earth sensors detect infrared rays radiated by CO2, however, the CCDESA detects the Earth by acquiring visible rays with a Charge Coupled Device (CCD). This CCDESA is a mission sensor of μ-LabSat which was launched by H-IIA as a piggyback satellite in December 2002. This paper discusses the CCDESA and the results of the on-orbit experiments.

Simulations of a late lunar-forming impact

Results of about 100 hydrodynamic simulations of potential Moon-forming impacts are presented, focusing on the “late impact” scenario in which the lunar forming impact occurs near the very end of Earth's accretion (Canup and Asphaug, 2001, Nature 412, 708–712). A new equation of state is utilized that includes a treatment of molecular vapor (“M-ANEOS”; Melosh, 2000, in: Proc. Lunar Planet. Sci. Conf. 31st, p. 1903). The sensitivity of impact outcome to collision conditions is assessed, in particular how the mass, angular momentum, composition and origin (target vs. impactor) of the material placed into circumterrestrial orbit vary with impact angle, speed, impactor-to-target mass ratio, and initial thermal state of the colliding objects. The most favorable conditions for producing a sufficiently massive and iron-depleted protolunar disk involve collisions with an impact angle near 45 degrees and an impactor velocity at infinity <4 km/sec. For a total mass and angular momentum near to that of the current Earth–Moon system, such impacts typically place about a lunar mass of material into orbits exterior to the Roche limit, with the orbiting material composed of 10 to 30% vapor by mass. In all cases, the vast majority of the orbiting material originates from the impactor, consistent with previous findings. By mapping the end fate (escaping, orbiting, or in the planet) of each particle and the peak temperature it experiences during the impact onto the figure of the initial objects, it is shown that in the successful collisions, the impactor material that ends up in orbit is primarily that portion of the object that was heated the least, having avoided direct collision with the Earth. Using these and previous results as a guide, a continuous suite of impact conditions intermediate to the “late impact” (Canup and Asphaug, 2001, Nature 412, 708–712) and “early Earth” (Cameron, 2000, in: Canup, R.M., Righter, K. (Eds.), Origin of the Earth and Moon, pp. 133–144; 2001, Meteorit. Planet. Sci. 36, 9–22) scenarios is identified that should also produce iron-poor, ∼ lunar-sized satellites and a system angular momentum similar to that of the Earth–Moon system. Among these, those that leave the Earth >95% accreted after the Moon-forming impact are favored here, implying a giant impactor mass between 0.11 and 0.14 Earth masses.

The Visibility of Earth Transits

The recent photometric detection of planetary transits of the solar-like star HD 209458 at a distance of 47 parsecs suggest that transits can reveal the presence of Jupiter-size planetary companions in the solar neighborhood (Charbonneau et al. 2000; Henry et al. 2000). Recent space-based transit searches have achieved photometric precision within an order of magnitude of that required to detect the much smaller transit signal of an earth-size planet across a solar-size star. Laboratory experiments in the presence of realistic noise sources have shown that CCDs can achieve photometric precision adequate to detect the 9.6 E-5 dimming of the Sun due to a transit of the Earth (Borucki et al. 1997; Koch et al. 2000). Space-based solar irradiance monitoring has shown that the intrinsic variability of the Sun would not preclude such a detection (Borucki, Scargle, Hudson 1985). Transits of the Sun by the Earth would be detectable by observers that reside within a narrow band of sky positions near the ecliptic plane, if the observers possess current Earth epoch levels of technology and astronomical expertise. A catalog of solar-like stars that satisfy the geometric condition for Earth transit visibility are presented.