Ground-based optical telescopes suffer from a blind zone surrounding the Sun. In this article, two telescopes were proposed to be deployed on an Earth‑leading heliocentric orbit approximately 10 ...million kilometers ahead of the Earth to warn of asteroids approaching Earth from the sunward direction. Considering the initial orbit determination, a discovery model for asteroids was established. Based on Granvik's impactor and near-Earth asteroid (NEA) populations, the warning efficiency of the Earth‑leading heliocentric orbiting telescopes for asteroids approaching Earth from the sunward direction was simulated. The simulation results show that under the designed search strategy, with a limiting apparent magnitude of 24, the warning efficiency of two Earth‑leading heliocentric orbiting telescopes for impactors and NEAs approaching Earth from the sunward direction reaches 99.0% and 94.3% (with 0.4% and 0.8% uncertainty, respectively) within 6 years, which is 95.8% and 57.5% (with 0.7% and 1.7% uncertainty, respectively) for one telescope deployed on an Earth‑leading heliocentric orbit and 22.1% (with 1.5% uncertainty) for two telescopes deployed on a Sun-Earth L1 orbit. Earth‑leading heliocentric orbiting telescopes thus provide a possible option to cover the blind zone of ground-based optical telescopes.
•ELHO was used to cover the blind zone of ground-based optical telescopes.•“Discovery” was defined by initial orbit determination condition.•Survey telescope and follow-up telescope work cooperatively to discover asteroids.•Warning efficiency for asteroids approaching Earth from the sunward direction is more than 94%.
We used nearly 4 years of data from the Mars Atmosphere and Volatile EvolutioN orbiter to map the distribution and motion of energetic O+ ions (2.3–30 keV) in the Martian environment. Our analysis ...reveals two typical features: a strong plume of energetic O+ ions in the +E hemisphere at dayside, driven by the convective electric field, and a less strong tailward gathering flow of energetic O+ ions in the –E hemisphere at nightside. Based on previous studies, this study reveals more details on energetic O+ ion escape: (a) velocities for energetic O+ ions between bow shock and induced magnetic boundary have much larger Y‐axis component, indicating that energetic O+ ions may not only escape along +Z‐axis but also slip away on the Y‐axis in MSE coordinates; (b) energetic O+ ions at low altitude in the –E hemisphere have little component along Y‐axis, and energetic O+ ions at nightside in the –E hemisphere “gather” along the tail and finally escape from the planet, driven by the convective electric field and the Martian current system. Comparing the fluxes and escape rates of energetic O+ at different distances away from the Sun and under different solar activities, we found that the heliocentric radial distance of Mars plays a more important role in ion escape than the solar activity level.
Plain Language Summary
The answer to how does the water escape from unmagnetized planets like Mars is debated. Due to lack of an intrinsic global magnetic field, the Martian upper atmosphere can be easily eroded by the solar wind, which is an effective way for the water to escape after being ionized to H+ and O+. The motion of energetic O+ ions can be used as a probe of the escape of heavy ions. In present study, we report a global map of energetic O+ ions outflows for the first time using nearly 4 years of data from the Mars Atmosphere and Volatile EvolutioN orbiter. Our analysis reveals two typical features: a strong radial plume of energetic O+ ions in the northward dayside, driven by the convective electric field, and a less strong tailward gathering flow of energetic O+ ions in the southward nightside. In addition, we found that the heliocentric radial distance of Mars plays a more important role in ion escape than the solar activity level. These results are helpful to understand where and how the water escape from the unmagnetized planets to the space.
Key Points
A global map of energetic O+ ions (from 2.3 to 30 keV) outflows is built using 4 years data from Mars Atmosphere and Volatile EvolutioN
Energetic O+ ions are able to slip away along Y‐MSE direction in the plume and "gather" along the tail in the −E hemisphere
The heliocentric radial distance of Mars plays a more important role in ion escape than the solar activity level
This paper investigates the problem of multiple solar sail-based spacecraft formation flying in which the chief follows a heliocentric displaced orbit, whereas each deputy adjusts the sail propulsive ...acceleration so as to track a desired (relative) trajectory with respect to the chief. In particular, coordinated control strategies are presented for both the full state feedback case and the relative velocity unavailability case, respectively. The developed consensus-based algorithms rely on the protocols formulated on an undirected communication topology with information link couplings, utilizing every available neighbor-to-neighbor information data such that the reliability of the formation system can be enhanced. Illustrative examples show the validity the proposed method.
•Multiple solar sail formation flying around a heliocentric displaced orbit is investigated.•Two distributed cooperative control laws are designed via consensus algorithms.•The control strategies take into account the full state feedback case and the relative velocity-free case, respectively.
This paper analyzes the possibility of maintaining a circular displaced non-Keplerian orbit around the Sun by means of a Sun-facing diffractive sail. With the goal of monitoring the Earth’s ...high-latitude regions, the spacecraft is required to track its displaced orbit at an angular velocity equal to the mean motion of the planet. In doing so, the spacecraft keeps a constant average phase shift with respect to Earth’s angular position along its orbit, allowing the objectives of the scientific mission to be achieved. The diffractive sail, recently proposed by Swartzlander and chosen in this paper as the spacecraft’s primary propulsion system, is a special photonic solar sail in which the membrane film is covered by an advanced diffractive metamaterial. In particular, a Sun-facing diffractive sail with a grating at normal incidence generates radial and transverse thrust components of equal magnitude; that is, the thrust vector is tilted 45 degrees from the Sun-spacecraft line. This peculiarity enables the diffractive sail to maintain a family of circular displaced non-Keplerian orbits, each of which is characterized by unique values of radius and a lightness number for an assigned value of spacecraft displacement relative to the Ecliptic. A comparison with the ideal reflecting sail shows that the diffractive sail performs better because for the same overall spacecraft mass, the latter needs about 30% less surface area exposed to the Sun. Finally, this paper discusses the classical stability problem, assuming an error in orbit insertion of the diffractive sail-based spacecraft. In this context, extensive numerical simulations show that such displaced orbits are marginally stable.
We present SHINeS, a space simulator which can be used to replicate the thermal environment in the immediate neighborhood of the Sun down to a heliocentric distance r ∼ 0.06 au. The system consists ...of three main parts: the solar simulator which was designed and constructed in-house, a vacuum chamber, and the probing and recording equipment needed to monitor the experimental procedures. Our motivation for building this experimental system was to study the effect of intense solar radiation on the surfaces of asteroids when their perihelion distances become smaller than the semi-major axis of the orbit of Mercury. Comparisons between observational data and recent orbit and size-frequency models of the population of near-Earth asteroids suggest that asteroids are super-catastrophically destroyed when they approach the Sun. Whereas the current models are agnostic about the disruption mechanism, SHINeS was developed to study the mechanism or mechanisms responsible. The system can, however, be used for other applications that need to study the effects of high solar radiation on other natural or artificial objects.
•An experimental system that simulates the thermal environment at small heliocentric distances.•Experimental investigation of the mechanisms by which low perihelion NEAs are destroyed.•Evidence of desiccation cracking and discoloration on asteroid analogue materials.
Solar wind controls on Mercury's magnetospheric cusp He, Maosheng; Vogt, Joachim; Heyner, Daniel ...
Journal of geophysical research. Space physics,
June 2017, 2017-06-00, 20170601, Letnik:
122, Številka:
6
Journal Article
Recenzirano
This study assesses the response of the cusp to solar wind changes comprehensively, using 2848 orbits of MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) observation. The ...assessment entails four steps: (1) propose and validate an approach to estimate the solar wind magnetic field (interplanetary magnetic field (IMF)) for MESSENGER's cusp transit; (2) define an index σ measuring the intensity of the magnetic disturbance which significantly peaks within the cusp and serves as an indicator of the cusp activity level; (3) construct an empirical model of σ as a function of IMF and Mercury's heliocentric distance rsun, through linear regression; and (4) use the model to estimate and compare the polar distribution of the disturbance σ under different conditions for a systematic comparison. The comparison illustrates that the disturbance peak over the cusp is strongest and widest extending in local time for negative IMF Bx and negative IMF Bz, and when Mercury is around the perihelion. Azimuthal shifts are associated with both IMF By and rsun: the cusp moves toward dawn when IMF By or rsun decrease. These dependences are explained in terms of the IMF Bx‐controlled dayside magnetospheric topology, the component reconnection model applied to IMF By and Bz, and the variability of solar wind ram pressure associated with heliocentric distance rsun. The applicability of the component reconnection model on IMF By indicates that at Mercury reconnection occurs at lower shear angles than at Earth.
Plain Language Summary
Mercury's magnetosphere was suggested to be particularly sensitive to solar wind conditions. This study investigates the response of the magnetospheric cusp to solar wind conditions systematically. For this purpose, we analyze the statistical predictability of interplanetary magnetic field (IMF) at Mercury, develop an approach for estimating the solar wind magnetic field (IMF) for MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER's) cusp transit, construct an indicator for the activity level of the cusp, build an empirical model for the indicator as a function of solar wind variables from 3 years of the MESSENGER measurements, and compare the cusp activity under different conditions. Results demonstrate that the azimuthal location, horizontal extension, and the internal magnetic disturbance are dependent on all IMF components as well as on Mercury's heliocentric distance. These results provide evidence and clues to fundamental processes of solar wind and magnetosphere interactions.
Key Points
IMF predictability and IMF estimation at Mercury, magnetic disturbances as indicators of the cusp, and a new empirical modeling of the cusp
The horizontal location and extension of the cusp are susceptible to all IMF components and Mercury's heliocentric distance
The IMF By dependence is opposite to that at Earth, revealing that reconnections occur at lower shear angles at Mercury than at Earth
•A unique historical approach.•A useful transition technique from Heliocentric to geocentric system and vice versa.•Simulation which could be extended in various celestial objects leading to useful ...conclusions.•How the free interactive computing tool GeoGebra can be used in astronomical calculations.
The word ’Geocentric’ comes from the Greek word Γεωκεντρικό which is a compound word composed from two words: “γεω” means Earth and “κεντρικό” means centric. Geocentric aspect, appears for the first time in ancient Greece. Pythagoras had formulated the geocentric system with the Earth at the center of the Universe surrounded by the orbiting planets with Sun included. Later Greek ancient astronomers, trying to explain the weird planetary motion in the sky, introduced the epicyclic theory.33The epicyclic theory was well formulated by Hipparchus and Apollonius. Using this theory the two famous Greek astronomers managed to explain the weird planetary motion on the sky. This theory states that the geocentric planetary motion could be considered as a combination of circular motions. Today this idea is quite sensible if we consider that the geocentric motion could be perceived as synthesis of two independent motions; one is the rotation of the planet around the Sun and the other is the apparent rotation of the Sun around the Earth. Someone could say that the heliocentric motion is hidden inside the geocentric planetary path as one of two superimposed motions. This logical conclusion is supported by F. Hoyle Hoyle (1975) who states “We know that the difference between a heliocentric theory and a geocentric theory is one of relative motion only, and that such a difference has no physical significance.” In other words Geocentrism isn’t completely wrong excluding only the arbitrary claim that the Earth is fixed and immobile at the center of the Universe.
Geocentrism lasted many years until Nicolaus Copernicus at the middle of 15th century, proposed the heliocentric system by transferring the reference origin from Earth to Sun. Although Copernican model was capable explaining the geocentric orbits of planets with negligible eccentricity, it failed to give a convincing explanation in cases of planets with considerable eccentricity like Mars. The lack of symmetry in Mar’s trajectory led Kepler to discover that planet’s orbits weren’t circular, as it was already believed, but elliptical. According to (Evans, 1998, p.431) Kepler said “I therefore once again think it to have happened by divine arrangement, that I arrived at the same time in which he was intent upon Mars, whose motions provide the only possible access to the hidden secrets of astronomy, without which we would remain forever ignorant of those secrets.” In this article we are trying to simulate the process followed by Kepler, studying the apparent geocentric Mar’s orbit which triggered him to discover elliptical planetary orbits.
The relation between heliocentrism and geocentrism is highlighted during this study. Besides, this aspect is mentioned by David R. Topper...But this fact is then sometimes generalized to positing that geocentrism and Heliocentrism are equivalent, that they are the same geometrically or mathematically or even exactly the same; in a phrase, there is an isomorphism between them... Topper (2007) The methodology which was used, in the whole process, relies on mathematical modeling. This approach is based mainly on dynamic position change over time, which the interactive mathematic software GeoGebra can generously provide. The end of this historical approach shows that the heliocentric view was revealed throughout a geocentric model, proving the equivalence of these two different aspects. Finally the theoretical numerical results of this study seem to be in full agreement with the astronomical records of that era with minimal discrepancies.
This article discusses Zhuangzi’s metaphysical theory from the standpoint of a form of structural ontology that was developed by neurophilosopher Northoff and which differs from typical studies of ...Zhuangzi’s metaphysics. According to Nossoff’s world–brain relationship, a structural positivism based on relationships, the body is nested in the world and the brain is nested in the body. Northoff contends that elements of Eastern philosophy support this viewpoint. I have examined three aspects of Zhuangzi’s philosophy by interpreting his texts: the existence of a world independent from the subject and mind, the subject and mind dependent on the world, and the coexistence of differentiation and inclusiveness between the world and the subject. The problem this article attempts to address is how Zhuangzi achieved a Copernican revolution within the framework of non-reductive neurophilosophy, bringing about a shift away from non-anthropocentrism.
In the seventeenth century, science and religion clashed over cosmology. The relationship between science and religion was at extreme odds at the Galileo trials but softened in the twentieth century ...when the Catholic Church accepted the new science. Meanwhile, the evolutionary theory proposed in the nineteenth century lowered the status of humans to animals and damaged faith in biblical inspiration. The Scopes Trial in the southern United States in the 1920s was the result of the defiance of the Protestants, who insisted on a literal interpretation of the Bible. "Creation science," which began to thrive in the western United States in the 1960s, insisted on equal time in schools alongside evolutionary theory. After re-peated defeat in court, creation science is desperately trying to get its footing in science with a new name: intelligent design. The creation science movement that came Korea in the 1980s joined hands with Christian obscurantism and is running amok. When creationism pretends to be science, it is an unfair interference of religion in science. Creation science is a pseudoscience that cannot be accepted as science.
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