A cometary mechanism for the formation of tektites

1963 ◽  
Vol 272 (1351) ◽  
pp. 467-480 ◽  
Keyword(s):  
Small Eccentricity ◽  
The Earth ◽  
Short Period ◽  
Cometary Material ◽  
General Order ◽  
Order Of Magnitude

Passage of the Earth through a comet must occur on average every million years approximately and last for a time of a few hours. A proportion of short-period comets will have had sufficiently small eccentricity (less than about 0.6) for accretion of cometary material to occur during such passages and produce a narrow jet of material falling vertically down-wards through the atmosphere. The orbits of these comets are such that the jet would be most likely to fall within lower latitudes, as is found for tektite fields. The temperature within the accretion-stream would be sufficiently great to vaporize most materials, and the tektites are regarded as forming from the most refractory substances within the stream, so that they are not characteristic of cometary compositions. The speeds of entry into the atmosphere are high enough for ablation to occur, and the dimensions of the resulting fields and their total masses agree in general order of magnitude with those estimated for actual fields.

The Origin of the Moon and its Relationship to the Origin of the Solar System

1962 ◽  
Vol 14 ◽  
pp. 133-148 ◽  
Author(s):  
Harold C. Urey
Keyword(s):  
Solar System ◽  
The Moon ◽  
The Past ◽  
The Earth ◽  
Short Period ◽  
Origin Of The Moon

During the last 10 years, the writer has presented evidence indicating that the Moon was captured by the Earth and that the large collisions with its surface occurred within a surprisingly short period of time. These observations have been a continuous preoccupation during the past years and some explanation that seemed physically possible and reasonably probable has been sought.

scholarly journals New Tools for the Optimized Follow-Up of Imminent Impactors

Universe ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 10
Author(s):  
Maddalena Mochi ◽  
Giacomo Tommei
Keyword(s):  
Orbit Determination ◽  
Main Belt ◽  
Impact Monitoring ◽  
The Earth ◽  
Current Observation ◽  
Short Period ◽  
Fly Eye ◽  
Near Earth Asteroids ◽  
Near Earth Objects

The solar system is populated with, other than planets, a wide variety of minor bodies, the majority of which are represented by asteroids. Most of their orbits are comprised of those between Mars and Jupiter, thus forming a population named Main Belt. However, some asteroids can run on trajectories that come close to, or even intersect, the orbit of the Earth. These objects are known as Near Earth Asteroids (NEAs) or Near Earth Objects (NEOs) and may entail a risk of collision with our planet. Predicting the occurrence of such collisions as early as possible is the task of Impact Monitoring (IM). Dedicated algorithms are in charge of orbit determination and risk assessment for any detected NEO, but their efficiency is limited in cases in which the object has been observed for a short period of time, as is the case with newly discovered asteroids and, more worryingly, imminent impactors: objects due to hit the Earth, detected only a few days or hours in advance of impacts. This timespan might be too short to take any effective safety countermeasure. For this reason, a necessary improvement of current observation capabilities is underway through the construction of dedicated telescopes, e.g., the NEO Survey Telescope (NEOSTEL), also known as “Fly-Eye”. Thanks to these developments, the number of discovered NEOs and, consequently, imminent impactors detected per year, is expected to increase, thus requiring an improvement of the methods and algorithms used to handle such cases. In this paper we present two new tools, based on the Admissible Region (AR) concept, dedicated to the observers, aiming to facilitate the planning of follow-up observations of NEOs by rapidly assessing the possibility of them being imminent impactors and the remaining visibility time from any given station.

scholarly journals Radar Observations of Comet Nuclei and Comae

2005 ◽  
Vol 13 ◽  
pp. 763-763
Author(s):  
Donald B. Campbell ◽  
John K. Harmon ◽  
Micael C. Nolan ◽  
Steven J. Ostro
Keyword(s):  
Cross Sections ◽  
Cometary Nucleus ◽  
Size Distributions ◽  
Radar Systems ◽  
The Earth ◽  
Radar Cross Sections ◽  
Short Period ◽  
Grain Size Distributions ◽  
Resolution Imaging

Nine comets have been detected with either the Arecibo (12.6 cm wavelength) or Goldstone (3.5 cm) radar systems. Included are six nucleus detections and five detections of echoes from coma grains. The radar backscatter cross sections measured for the nuclei correlate well with independent estimates of their sizes and are indicative of surface densities in the range of 0.5 to 1.0 g cm-3. Like most asteroids, comets appear to have surfaces that are very rough at scales much larger than the radar wavelength. Coma echo models can explain the radar cross sections using grain size distributions that include a substantial population of cm-sized grains. A long term goal of the cometary radar program has been the high resolution imaging of a cometary nucleus. Eleven short period comets are potentially detectable over the next two decades a few of which may be suitable for imaging. We are always waiting for the arrival of a new comet with an orbit that brings it within 0.1 AU of the earth.

The Propagation of Short Period Air Pressure Micro-Oscillations

1954 ◽  
Vol 35 (1) ◽  
pp. 20-25
Author(s):  
W. H. Roschke
Keyword(s):  
Wind Speed ◽  
Air Pressure ◽  
Saint Louis ◽  
Short Period ◽  
Order Of Magnitude

Air pressure micro-oscillations of the impulse-type (period: 10–25 seconds) as recorded by Macelwane Electromagnetic Microbarographs in a small tripartite arrangement at Florissant, Missouri (near Saint Louis) are propagated in the direction and with a speed that is of the same order of magnitude as the wind speed in the lower layers of the atmosphere but not necessarily at the surface.

scholarly journals 42. Solar cosmic radiation and the interstellar magnetic field

1958 ◽  
Vol 6 ◽  
pp. 404-419 ◽  
Author(s):  
A. Ehmert
Keyword(s):  
Magnetic Field ◽  
Solar Radiation ◽  
Cosmic Radiation ◽  
The Sun ◽  
High Latitudes ◽  
Narrow Angle ◽  
The Earth ◽  
Order Of Magnitude ◽  
The Impact ◽  
Impact Zones

The increase of cosmic radiation on 23 February 1956 by solar radiation exhibited in the first minutes a high peak at European stations that were lying in direct impact zones for particles coming from a narrow angle near the sun, whilst other stations received no radiation for a further time of 10 minutes and more. An hour later all stations in intermediate and high latitudes recorded solar radiation in a distribution as would be expected if this radiation fell into the geomagnetic field in a fairly isotropic distribution. The intensity of the solar component decreased at this time at all stations according to the same hyperbolic law (~t–2).It is shown, that this decreasing law, as well as the increase of the impact zones on the earth, can be understood as the consequence of an interstellar magnetic field in which the particles were running and bent after their ejection from the sun.Considering the bending in the earth's magnetic field, one can estimate the direction of this field from the times of the very beginning of the increase in Japan and at high latitudes. The lines of magnetic force come to the earth from a point with astronomical co-ordinates near 12·00, 30° N. This implies that within the low accuracy they have the direction of the galactic spiral arm in which we live. The field strength comes out to be about 0·7 × 10–6gauss. There is a close agreement with the field, that Fermi and Chandrasekhar have derived from Hiltner's measurements of the polarization of starlight and the strength of which they had estimated to the same order of magnitude.

scholarly journals Investigation of the Orbital Stability of Minor Planets with Cometary Eccentricities

1972 ◽  
Vol 45 ◽  
pp. 431-436 ◽  
Author(s):  
G. A. Chebotarev ◽  
N. A. Belyaev ◽  
R. P. Eremenko
Keyword(s):  
Orbital Stability ◽  
Minor Planets ◽  
The Earth ◽  
Short Period ◽  
Account Information

The evolution of the orbits of 19 asteroids of particular interest has been studied over the interval 1660–2060, perturbations by Venus to Pluto being taken into account. Information was obtained about the encounters with Venus, the Earth, and Mars. A few approaches of Hidalgo to Jupiter were noted. In distinction to the orbits of short-period comets, the orbits of the 19 asteroids are stable throughout the 400-yr interval.

scholarly journals Comparative Measurements of Local Seismic Rotations by Three Independent Methods

Sensors ◽  
2020 ◽  
Vol 20 (19) ◽  
pp. 5679
Author(s):  
Johana Brokešová ◽  
Jiří Málek
Keyword(s):  
Seismic Source ◽  
Medium Size ◽  
Period Range ◽  
Small Aperture ◽  
Technical Problems ◽  
Rotation Rates ◽  
Active Experiment ◽  
Short Period ◽  
Order Of Magnitude ◽  
The Given

A comparative active experiment that is aimed at collocated measurement of seismic rotation rates along three orthogonal axes by means of three different methods is described. The rotation rates in a short-period range of 6–20 Hz were obtained using three different methods: the 6C Rotaphone sensor system developed by the authors, the commercial R-1 rotational sensor by Eentec, and a small-aperture array of twelve standard velocigraphs in a rectangular arrangement. Those three methods are compared and discussed in detail. A medium-size quarry blast was used as a seismic source. At a distance of approximately 240 m, the rotation rates reached an amplitude of the order of magnitude of 10−4–10−5 rad/s. The array derived rotation rates displayed serious limitations, as clearly documented. The R-1 instruments have shown certain technical problems that partly limit their applicability. The measured rotation rates were compared to the relevant acceleration components according to rotation-to-translation relations. Out of all the three methods, the records best matching the acceleration components were made by Rotaphone. The experiment also revealed that rotation rates in the given short-period range noticeably changed over a distance as short as 2 m.

scholarly journals Earth as a Gravitational-Wave Interferometr

2019 ◽  
Vol 224 ◽  
pp. 03012
Author(s):  
Vadim Il’chenko
Keyword(s):  
Gravitational Wave ◽  
Upper Mantle ◽  
Oscillatory System ◽  
Average Depth ◽  
Lunar Tide ◽  
Crust And Upper Mantle ◽  
The Earth ◽  
Order Of Magnitude ◽  
Gravitational Wave Interferometer ◽  
Gravitational Influence

Based on the principle of Equivalence of Gravitating Masses (EGM) and tectonostratigraphic model of the Earth outer shell structure (the Earth crust and upper mantle), the average depth of the lunar mass gravitational influence on the Earth was calculated as ~1600 km. The developed model is based on the mechanism of rocks tectonic layering of the Earth crust-mantle shell as an oscillatory system with dynamic conditions of a standing wave, regularly excited by the lunar tide and immediately passing into the damping mode. After comparing the average depth of solid lunar tide impact of ~1600 km with the height of the solid lunar tide “hump” on the Earth surface of 0.5 m, a “tensile strain” was calculated with an amplitude only one order of magnitude larger than the amplitude of the gravitational wave recorded by the Advanced LIGO interferometer: A≈10-18 m (the merger result of a black holes pair ca 1.3 Ga ago). The results of the present study suggest that the crust-mantle shell of the Earth may be used as a gravitational-wave interferometer.

scholarly journals The Visibility of Earth Transits

2004 ◽  
Vol 202 ◽  
pp. 445-447 ◽  
Author(s):  
T. Castellano ◽  
L. Doyle ◽  
D. McIntosh
Keyword(s):  
Laboratory Experiments ◽  
Ecliptic Plane ◽  
Solar Neighborhood ◽  
Geometric Condition ◽  
The Sun ◽  
Intrinsic Variability ◽  
Noise Sources ◽  
Photometric Detection ◽  
The Earth ◽  
Order Of Magnitude

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.

scholarly journals International VLBI Satellite (IVS)

1990 ◽  
Vol 123 ◽  
pp. 255-262
Author(s):  
R. T. Schilizzi
Keyword(s):  
Radio Telescope ◽  
First Generation ◽  
Angular Resolution ◽  
Radio Sources ◽  
Microwave Background ◽  
High Quality ◽  
The Earth ◽  
Order Of Magnitude ◽  
Radio Band ◽  
Magnitude Increase

AbstractIVS is under study in ESA as a second generation space VLBI observatory. The mission concept calls for a 25 m diameter radio telescope in space funded by the principal space agencies. Orbiting the Earth and observing in concert with the established ground-based VLBI arrays in Europe, USA, USSR and Australia, IVS will provide high quality images of galactic and extragalactic radio sources at wavelengths spanning the radio band from decimetres to millimetres with resolution as high as 10 micro arcseconds and sensitivity equal to those of ground-based images. New features of IVS compared to the first generation missions are: a more than order of magnitude increase in sensitivity; an order of magnitude increase in maximum angular resolution; extension of the wavelength range to the millimetre band; and the capability to operate as a stand-alone radio telescope enabling it to explore new frontiers in spectral line and microwave background research, in particular the distribution of galactic molecular oxygen and Compton scattering of the microwave background by foreground cluster gas.

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