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.

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.

Evolution of Comets into Asteroids?

1971 ◽  
Vol 12 ◽  
pp. 413-421 ◽  
Author(s):  
B.G. Marsden
Keyword(s):  
Solar Radiation ◽  
Solar Nebula ◽  
Oort Cloud ◽  
Original Version ◽  
Terrestrial Planets ◽  
Minor Planets ◽  
The Sun ◽  
Physical Difference ◽  
Short Period ◽  
The One

There has long been speculation as to whether comets evolve into asteroidal objects. On the one hand, in the original version of the Oort (1950) hypothesis, the cometary cloud was supposed to have formed initially from the same material that produced the minor planets; and an obvious corollary was that the main physical difference between comets and minor planets would be that the latter had long since lost their icy surfaces on account of persistent exposure to strong solar radiation (Öpik, 1963). However, following a suggestion by Kuiper (1951), it is now quite widely believed that, whereas the terrestrial planets and minor planets condensed in the inner regions of the primordial solar nebula, icy objects such as comets would have formed more naturally in the outer parts, perhaps even beyond the orbit of Neptune (Cameron, 1962; Whipple, 1964a). Furthermore, recent studies of the evolution of the short-period comets indicate that it is not possible to produce the observed orbital distribution from the Oort cloud, even when multiple encounters with Jupiter are considered (Havnes, 1970). We must now seriously entertain the possibility that most of the short-period orbits evolved directly from low-inclination, low-eccentricity orbits with perihelia initially in the region between, say, the orbits of Saturn and Neptune, and that these comets have never been in the traditional cloud at great distances from the Sun.

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.

scholarly journals The Role of Observation With Horizontal Meridian Circle in China for Establishing an Inertial Frame

1990 ◽  
Vol 141 ◽  
pp. 142-142
Author(s):  
Li Zhi-gang ◽  
Qi Guan-Rong
Keyword(s):  
Inertial Frame ◽  
Minor Planets ◽  
Meridian Circle ◽  
Horizontal Meridian ◽  
Proper Motions ◽  
The Earth ◽  
The Future ◽  
History Of ◽  
Radio Stars

While HIPPARCOS is expected to measure positions and proper motions with more accuracy than those obtained by ground-based instruments, what can we do in the future for ground-based instruments? The observations with them still are important for establishing an inertial frame because of the long history of observations with them and improvements in the instruments. Moreover, it is necessary to have data of observations from them for research on problems related to the Earth. The horizontal meridian circle in China (DCMT) is expected to have advantage over the classical meridian circles. The DCMT will be assembled and tested this year. It should work in the following fields: (1) observing radio stars, (2) observation of minor planets, (3) absolute determinations of IRS.

scholarly journals Four-billion year stability of the Earth–Mars belt

2020 ◽  
Vol 500 (1) ◽  
pp. 1151-1157
Author(s):  
Yukun Huang (黄宇坤) ◽  
Brett Gladman
Keyword(s):  
Semimajor Axis ◽  
Orbital Stability ◽  
Terrestrial Planet ◽  
Small Bodies ◽  
Mean Motion Resonances ◽  
Mean Motion ◽  
The Earth ◽  
Steady State Model ◽  
Near Earth Objects

ABSTRACT Previous work has demonstrated orbital stability for 100 Myr of initially near-circular and coplanar small bodies in a region termed the ‘Earth–Mars belt’ from 1.08 < a < 1.28 au. Via numerical integration of 3000 particles, we studied orbits from 1.04–1.30 au for the age of the Solar system. We show that on this time-scale, except for a few locations where mean-motion resonances with Earth affect stability, only a narrower ‘Earth–Mars belt’ covering a ∼ (1.09, 1.17) au, e < 0.04, and I < 1° has over half of the initial orbits survive for 4.5 Gyr. In addition to mean-motion resonances, we are able to see how the ν3, ν4, and ν6 secular resonances contribute to long-term instability in the outer (1.17–1.30 au) region on Gyr time-scales. We show that all of the (rather small) near-Earth objects (NEOs) in or close to the Earth–Mars belt appear to be consistent with recently arrived transient objects by comparing to a NEO steady-state model. Given the <200 m scale of these NEOs, we estimated the Yarkovsky drift rates in semimajor axis and use these to estimate that a diameter of ∼100 km or larger would allow primordial asteroids in the Earth–Mars belt to likely survive. We conclude that only a few 100-km sized asteroids could have been present in the belt’s region at the end of the terrestrial planet formation.

scholarly journals The Reference Frame Determined From the Observation of Minor Planets by Hipparcos

1990 ◽  
Vol 141 ◽  
pp. 329-336
Author(s):  
B. Morando ◽  
A. Bec-Borsenberger
Keyword(s):  
Reference Frame ◽  
High Precision ◽  
Reference System ◽  
Initial Position ◽  
Minor Planet ◽  
Minor Planets ◽  
The Moon ◽  
Phase Effect ◽  
The Earth ◽  
A Minor

The observation of minor planets by Hipparcos offers the opportunity to obtain high precision positions for some minor planets. About fifty minor planets are on the programme. Their ephemerides had to be improved in order to reach a precision of 1 arsec and occultations by the Earth and the Moon had to be predicted.From the position of a minor planet on reference great circles at different times better values of the initial position and velocity will be deduced but the reduction of the observations of the minor planets have to take into account the displacement of the photocentre relative to the centre which is due to the shape, the phase effect and the scattering properties of the surface. For some very small planets considered as star like this diplacement will be small and the precise positions obtained will allow to position the dynamical reference system relative to the Hipparcos system. For the bigger minor planets the observations by Hipparcos may give informations on the shape and scattering properties of the surface.

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.

scholarly journals Further measurements on wireless waves received from the upper atmosphere

1927 ◽  
Vol 116 (775) ◽  
pp. 682-693 ◽  
Keyword(s):  
Closed Loop ◽  
Wave Length ◽  
Direct Proof ◽  
Relative Magnitude ◽  
Upper Atmosphere ◽  
Circle Plane ◽  
The Earth ◽  
Direction Finder ◽  
Short Period ◽  
Attention To Detail

In previous papers the authors have described the development of experimental methods of measuring the directions and relative intensities of both the electric and magnetic forces in wireless waves received at the earth’s surface from a distant transmitting station. In this work it was seen that the detection of the arrival of waves deflected from the upper atmosphere, and polarised with their electric force in a horizontal plane, was rendered difficult owing to the relatively great reflecting powTer of the earth resulting from its high conductivity. By a suitable choice of wave-length and careful attention to detail in the design and construction of the apparatus, however, the methods employed enabled measurements to be made on both vertically and horizontally polarised waves. The results of such measurements enabled a direct proof to be given of the fact that the fading of wireless signals on a vertical aerial and the variations of bearings experienced on the closed-loop type of wireless direction-finder are due to the reception respectively of vertically and horizontally polarised waves deflected from the upper atmosphere in their passage from the transmitter to the receiver. On arrival at the receiver, these indirect or atmospheric waves interfere with the direct or ground waves, in a manner determined by their relative magnitude and phase, and produce the intensity and apparent direc­tional variations mentioned above. The results of such interference phenomena have been investigated experimentally by Appleton and Barnett and by Holling-worth. In a more recent publication the present authors have provided experimental evidence showing that the path of the indirect waves is confined to the great circle plane between the transmitter and receiver. The measurements of the quantities in the received waves as previously described by the authors were confined to observations on the transmissions from the Bournemouth broadcasting station over a short period. The object of the present paper is to describe the continuation of these measurements and their extension to the transmissions from other stations.

scholarly journals Jupiter – friend or foe? II: the Centaurs

2008 ◽  
Vol 8 (2) ◽  
pp. 75-80 ◽  
Author(s):  
J. Horner ◽  
B.W. Jones
Keyword(s):  
Solar System ◽  
Kuiper Belt ◽  
Giant Planet ◽  
Mass Extinctions ◽  
The Earth ◽  
Impact Rate ◽  
Short Period ◽  
Impact Risk ◽  
Life On Earth ◽  
The Impact

AbstractIt has long been assumed that the planet Jupiter acts as a giant shield, significantly lowering the impact rate of minor bodies upon the Earth, and thus enabling the development and evolution of life in a collisional environment which is not overly hostile. In other words, it is thought that, thanks to Jupiter, mass extinctions have been sufficiently infrequent that the biosphere has been able to diversify and prosper. However, in the past, little work has been carried out to examine the validity of this idea. In the second of a series of papers, we examine the degree to which the impact risk resulting from objects on Centaur-like orbits is affected by the presence of a giant planet, in an attempt to fully understand the impact regime under which life on Earth has developed. The Centaurs are a population of ice-rich bodies which move on dynamically unstable orbits in the outer Solar system. The largest Centaurs known are several hundred kilometres in diameter, and it is certain that a great number of kilometre or sub-kilometre sized Centaurs still await discovery. These objects move on orbits which bring them closer to the Sun than Neptune, although they remain beyond the orbit of Jupiter at all times, and have their origins in the vast reservoir of debris known as the Edgeworth–Kuiper belt that extends beyond Neptune. Over time, the giant planets perturb the Centaurs, sending a significant fraction into the inner Solar System where they become visible as short-period comets. In this work, we obtain results which show that the presence of a giant planet can act to significantly change the impact rate of short-period comets on the Earth, and that such planets often actually increase the impact flux greatly over that which would be expected were a giant planet not present.

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