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1.
NASA’s Meteoroid Environment Office has implemented a program to monitor the Moon for meteoroid impacts from the Marshall Space Flight Center. Using off-the-shelf telescopes and video equipment, the Moon is monitored for as many as 10 nights per month, depending on weather. Custom software automatically detects flashes which are confirmed by a second telescope, photometrically calibrated using background stars, and published on a website for correlation with other observations. Hypervelocity impact tests at the Ames Vertical Gun Range facility have begun to determine the luminous efficiency and ejecta characteristics. The purpose of this research is to define the impact ejecta environment for use by lunar spacecraft designers of the Constellation manned lunar program. The observational techniques and preliminary results will be discussed. The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.  相似文献   

2.
The occurrence and visibility of meteoroid impacts on the moon as seen from the earth were little more than speculation prior to November 1999. The best evidence of present-day impact activity came from the seismic experiments left on the Moon during the Apollo era. Past systematic attempts at earth-based observations to document lunar impacts revealed nothing conclusive. However, during the Leonid storms of 1999 and 2001, lunar impact events were for the first time confirmed by multiple independent observers. A total of 15 meteoritic impact flash events have been verified during these storms, with an additional 12 unconfirmed but likely events awaiting confirmation. Estimates of the mass of these meteoroids range from less than one gram for the faintest flashes to more than 10 kg for the brightest observed flash. The fraction of visible light to total energy produced by these events, a quantity known as luminous efficiency, averages about 0.001 for the established events. The confirmation of lunar meteoritic events on the Moon opens a new avenue in lunar and planetary research, one which could help bridge the gap between atmospheric sampling of the smallest components of meteoroid streams and interplanetary debris to the larger scale objects accessible to ground-based telescopes.  相似文献   

3.
The National Aeronautics and Space Administration (NASA) continues to make progress toward long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment. A subject for further definition is the lunar impact ejecta environment. The document NASA SP-8013 was developed for the Apollo program and is the latest definition of the ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar ejecta environment. NASA’s Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface ejecta environment. This paper reports the results of experiments on projectile impact into powered pumice targets, simulating unconsolidated lunar regolith. The Ames Vertical Gun Range (AVGR) was used to accelerate spherical Pyrex projectiles of 0.29g to velocities ranging between 2.5 and 5.18 km/s. Impact on the pumice target occurred at normal incidence. The ejected particles were detected by thin aluminum foil targets placed around the pumice target in a 0.5 Torr vacuum. A simplistic technique to characterize the ejected particles was formulated. Improvements to this technique will be discussed for implementation in future tests.  相似文献   

4.
The first confirmed lunar impact flash due to a non-Leonid meteoroid is reported. The observed Perseid meteoroid impact occurred at 18h28m27s on August 11, 2004 (UT). The selenographic coordinates of the lunar impact flash are 48±1° N and 72±2° E, and the flash had a visual magnitude of ca. 9.5 with duration of about 1/30 s. The mass of the impactor is estimated to have been 12 g based on a nominal model with conversion efficiency from kinetic to optical energy of 2×10−3. Extrapolation of a power law size-frequency distribution fitting the sub-centimeter Perseid meteoric particles to large meteoroids suggests that several flashes should have been observed at this optical efficiency. The detection of only one flash may indicate that the optical efficiency for Perseid lunar impact is much lower, or that the slope of the size distribution differs between large meteoroids and typical sub-centimeter meteoric particles.  相似文献   

5.
Abstract— We report on two surveys conducted during the times of Perseid shower maximum in 1997 and 1998. The first survey entailed the video monitoring of the Moon's disk with the intent of recording the optical flashes that should result when large meteoroids strike the lunar surface. The second survey consisted of a combination video camera and very low frequency (VLF) radiowave receiver system capable of detecting electrophonic meteors during their ablation in the Earth's atmosphere. Using standard ablation theory, we find that for a Perseid meteoroid to be capable of generating electrophonic sounds, it must have an initial mass in excess of 495 kg. We also find, as a result of the surveys, an upper limit of 2 × 10?17 m?2 s?1 to the flux of electrophonic Perseid meteors entering the Earth's atmosphere. Although our study indicates that large, meter-sized meteoroids must, at best, be sparsely distributed within the Perseid stream, we briefly discuss some tantalizing lines of evidence, found from within the astronomical literature, that hint at their true existence.  相似文献   

6.
An analysis of radar and photographic meteor data and of spacecraft meteoroid penetration data indicates that there probably has not been a large increase in meteoroid impact rates in the last 104 yr. The solar flare tracks observed in the glass linings of meteoroid impact pits on lunar rock 15205 are therefore reanalyzed assuming a meteoroid flux that is constant in time. Based on this assumption, the data suggest that the production rate of Fe-group solar flare tracks may have varied by as much as a factor of 50 on a time scale of about 104 yr. No independently obtained data are known to require conflict with this interpretation. Confidence in this conclusion is somewhat qualified by the experimental and analytical uncertainties involved, but the conclusion nevertheless remains the present “best” explanation for the observed data trends.  相似文献   

7.
In a small hypervelocity impact, superheated gas and particles glow brightly with thermal emission for a brief time interval at short wavelengths; this phenomenon is referred to as an impact flash. Over the past decade, impact flashes have been observed on the Moon and in the laboratory in both the IR and visible portions of the spectrum. These phenomena have been used to constrain impactor parameters, such as impact size, velocity and composition. With the arrival of the Cassini spacecraft at Saturn, we embarked on a study of impact flashes in Saturn's rings. We present results on the feasibility of observing impact flashes and therefore estimating the flux of meteoroids impacting Saturn's rings using Cassini's Ultraviolet Imaging Spectrograph (UVIS). Our modeling effort is two-fold. We start by simulating impacts using the CTH hydrodynamical code. Impacts involve an icy ring particle and a serpentine meteoroid, modeled with the ANEOS equation of state. The objects are centimeters to meters in diameter and collide at 30 to 50 km s−1. We then use the resulting temperatures and densities of the impact plumes in a radiative transfer calculation. We calculate bound-free, free-free, electron scattering and negative ion opacities along a line-of-sight through the center of each impact plume. Our model has shown that impact flashes will not be seen with the UVIS because (1) the plumes are optically thick when their central temperatures are high, with photosphere temperatures too cool to emit observable UV flux and (2) when the plumes become optically thin, even the hottest region of the plume is too cool to observe in the UV. This corroborates the lack of UVIS impact flash detections to date. Impact flashes are not likely to be seen by other Cassini instruments because of the short lifetimes of the plumes.  相似文献   

8.
The cometary meteoroid ejection model of Jones and Brown [Physics, Chemistry, and Dynamics of Interplanetary Dust, ASP Conference Series 104 (1996b) 137] was used to simulate ejection from comets 55P/Tempel-Tuttle during the last 12 revolutions, and the last 9 apparitions of 109P/Swift-Tuttle. Using cometary ephemerides generated by the Jet Propulsion Laboratory’s (JPL) HORIZONS Solar System Data and Ephemeris Computation Service, two independent ejection schemes were simulated. In the first case, ejection was simulated in 1 h time steps along the comet’s orbit while it was within 2.5 AU of the Sun. In the second case, ejection was simulated to occur at the hour the comet reached perihelion. A 4th order variable step-size Runge–Kutta integrator was then used to integrate meteoroid position and velocity forward in time, accounting for the effects of radiation pressure, Poynting–Robertson drag, and the gravitational forces of the planets, which were computed using JPL’s DE406 planetary ephemerides. An impact parameter (IP) was computed for each particle approaching the Earth to create a flux profile, and the results compared to observations of the 1998 and 1999 Leonid showers, and the 1993 and 2004 Perseids.  相似文献   

9.
The orbital distributions of dust particles in interplanetary space are revised in the ESA meteoroid model to incorporate more observational data and to comply with the constraints due to the long-term particle dynamics under the planetary gravity and Poynting–Robertson effect. Infrared observations of the zodiacal cloud by the COBE Earth-bound observatory, flux measurements by the dust detectors on board Galileo and Ulysses spacecraft, and the crater size distributions on lunar rock samples retrieved by the Apollo missions are fused into a single model. Within the model, the orbital distributions are expanded into a sum of contributions due to a number of known sources, including the asteroid belt with the emphasis on the prominent families Themis, Koronis, Eos and Veritas, as well as comets on Jupiter-encountering orbits. An attempt to incorporate the meteor orbit database acquired by the Advanced Meteor Orbit Radar at Christchurch is also discussed. Work was done during D. Galligan’s stay at the University of Canterbury.  相似文献   

10.
The authors have developed an observation procedure to determine the nature of detected lunar radio flux variations. The possibility to detect spacecraft SMART-1 impact radio flash is estimated. The upper limit of intensity is assessed for radio flashes produced by collisions of sporadic meteoroids with the moon as 10−7 Jy J−1 at 3.6 cm.  相似文献   

11.
Recent work on the gravitational focusing of meteoroid streams and their threat to satellites and astronauts in the near-Earth environment has concentrated on Earth acting as the gravitational attractor, totally ignoring the Moon. Though the Moon is twelve-thousandths the mass of the Earth, it too can focus meteors, albeit at a much greater distance downstream from its orbital position in space. At the Earth–Moon distance during particular phases of the Moon, slower speed meteoroid streams with very compact radiant diameters can show meteoroid flux enhancements in Earth’s immediate neighborhood. When the right geometric alignment occurs, this arises as a narrowed beam of particles of approximately 1,000 km width. For a narrow radiant of one-tenth degree diameter there is a 10-fold increase in the level of flux passing through the near-Earth environment. Meteoroid streams with more typical radiant sizes of 1° show at most two times enhancement. For sporadic sources, the enhancement is found to be insignificant due to the wide angular spread of the diffuse radiant and thus may be considered of little importance.  相似文献   

12.
Abstract— Using a dust flux model and experimental data on the efficiency of light emission upon impact, the number of impact flashes visible on the Moon by a camera on a lunar orbiter is estimated.  相似文献   

13.
Confirmed observations of meteoroids from the Leonid stream impacting the Moon in 1999 and 2001 have opened up new opportunities in observational and theoretical astronomy. These opportunities could help bridge the gap between the ground-based (atmospheric) sampling of the smallest meteoroids and the larger objects observable with ground-based telescopes. The Moon provides a laboratory for the study of hypervelocity impacts, with collision velocities not yet possible in ground-based laboratories. Development of automatic detection software removes the time-intensive activity of laboriously reviewing data for impact event signatures, freeing the observer to engage in other activities. The dynamics of professional-amateur astronomer collaboration have the promise of advancing the study of lunar meteoritic phenomenon considerably. These three factors will assist greatly in the development of a systematic, comprehensive program for monitoring the Moon for meteoroid impacts and determining the physical nature of these impacts.  相似文献   

14.
During the few days centered about new Moon, the lunar surface is optically hidden from Earth-based observers. However, the Moon still offers an observable: an extended sodium tail. The lunar sodium tail is the escaping “hot” component of a coma-like exosphere of sodium generated by photon-stimulated desorption, solar wind sputtering and meteoroid impact. Neutral sodium atoms escaping lunar gravity experience solar radiation pressure that drives them into the anti-solar direction forming a comet-like tail. During new Moon time, the geometry of the Sun, Moon and Earth is such that the anti-sunward sodium flux is perturbed by the terrestrial gravitational field resulting in its focusing into a dense core that extends beyond the Earth. An all-sky camera situated at the El Leoncito Observatory (CASLEO) in Argentina has been successfully imaging this tail through a sodium filter at each lunation since April 2006. This paper reports on the results of the brightness of the lunar sodium tail spanning 31 lunations between April 2006 and September 2008. Brightness variability trends are compared with both sporadic and shower meteor activity, solar wind proton energy flux and solar near ultra violet (NUV) patterns for possible correlations. Results suggest minimal variability in the brightness of the observed lunar sodium tail, generally uncorrelated with any single source, yet consistent with a multi-year period of minimal solar activity and non-intense meteoric fluxes.  相似文献   

15.
Measurements of meteoroid velocities and decelerations have been obtained from post-t 0 diffraction patterns present in echo signatures obtained from the multi-site AMOR radar operated at the University of Canterbury’s research facility. The system allows the sampling of a meteoroid’s velocity at separated points along the body’s trajectory to yield decelerations. The technique has potential value in providing data on the relation between trajectory behaviour, drag characteristics, the physical structure of meteoroids and stream membership or orbit type.  相似文献   

16.
This paper presents a review of research findings on the various forms of water on the Moon. First, this is the water of the Moon’s interior, which has been detected by sensitive mass spectrometric analysis of basaltic glasses delivered by the Apollo 15 and Apollo 17 missions. The previous concepts that lunar magmas are completely dehydrated have been disproved. Second, this is H2O and/or OH in a thin layer (a few upper millimeters) of the lunar regolith, which is likely a result of bombardment of the oxygen contained in the lunar regolith with solar wind protons. This form of water is highly unstable and quite easily escapes from the surface, possibly being one of the sources of the water ice reservoirs at the Moon’s poles. Third, this is water ice associated with other frozen gases in cold traps at the lunar poles. Its possible sources are impacts of comets and meteorites, the release of gas from the Moon’s interior, and solar wind protons. The ice trapped at the lunar polars could be of practical interest for further exploration of the Moon.  相似文献   

17.
A daylight bolide was observed over Galicia (NW Spain) and Minho (N. Portugal) on March 1, 2005 at 15 h10 min ± 3 min UTC. We interviewed 23 eyewitnesses of the event in order to obtain the azimuth, altitude, and slope of the fireball’s trajectory. Reports suggest an atmospheric ending height below 20 km, indicating that meteorite survival was likely. From the reconstructed trajectory and the fireball’s duration, we obtained the approximate heliocentric orbits for the meteoroid. Assuming an entry velocity higher than 20 km s−1 which is consistent with its estimated duration, the meteoroid originated in the asteroid belt.  相似文献   

18.
In an attempt to overcome some of the deficiencies of existing meteoroid models, NASA’s Space Environments and Effects (SEE) Program sponsored a 3 year research effort at the University of Western Ontario. The resulting understanding of the sporadic meteoroid environment – particularly the nature and distribution of the sporadic sources – were then incorporated into a new Meteoroid Engineering Model (MEM) by members of the Space Environments Team at NASA’s Marshall Space Flight Center. This paper discusses some of the revolutionary aspects of MEM which include (a) identification of the sporadic radiants with real sources of meteoroids, such as comets, (b) a physics-based approach which yields accurate fluxes and directionality for interplanetary spacecraft anywhere from 0.2 to 2.0 astronomical units (AU), and (c) velocity distributions obtained from theory and validated against observation. Use of the model, which gives penetrating fluxes and average impact speeds on the surfaces of a cube-like structure, is also described along with its current limitations and plans for future improvements.  相似文献   

19.
The lunar cratering rate is known reasonably well from comparison of observed crater frequencies with radiometric ages. Attempts to obtain a cratering rate for Mars have usually been based on calculation of the relative flux of asteroidal and cometary bodies on Mars and the Moon.The asteroidal flux on Mars cannot be obtained in a simple way from the observed number of Mars-crossing asteroids, i.e. those asteroids with perihelia within the orbit of Mars. Calculations of the secular perturbations of these asteroids by several authors, particularly williams, has shown that most of these bodies rarely come near even to Mars' aphelion when they are in the vicinity of the ecliptic plane, and their contribution to the Martian meteoroid flux is much smaller than has been commonly stated. Ring asteroids in the vicinity of the secular resonances discovered by Williams, high velocity fragments of asteroids on the inner edge of the asteroid belt, and possibly objects obtained from the 2:1 Kirkwood gap by a process described by Zimmerman and Wetherill are probably of greater importance in the 103-106 g meteoroid size range but are much less important in the production of large craters. Calculations of the Martian asteroidal and cometary impact rate are made, but the present unavoidable uncertainties in the results of these calculations result in their being of little value in establishing a Martian chronology. Suggestions for improving this situation are discussed.Paper presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.  相似文献   

20.
B.A. Ivanov 《Icarus》2006,183(2):504-507
Published data for global impact rate of bolides are compared with the cratering rate on the Moon in the past 100 Ma (assumed to be constant). The comparison shows, that in the limits of used models accuracy, the current meteoroid flux in the Earth-Moon system is approximately the same as in the last 100 Ma, provided most of the small (D<200 m) craters counted on the young (?100 Ma) lunar surface are primary, not secondary craters.  相似文献   

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