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1.
The known close approach of Asteroid (99942) Apophis in April 2029 provides the opportunity for the case study of a potentially hazardous asteroid in advance of its encounter. The visible to near-infrared (0.55 to 2.45 μm) reflectance spectrum of Apophis is compared and modeled with respect to the spectral and mineralogical characteristics of likely meteorite analogs. Apophis is found to be an Sq-class asteroid that most closely resembles LL ordinary chondrite meteorites in terms of spectral characteristics and interpreted olivine and pyroxene abundances, although we cannot rule out some degree of partial melting. A meteorite analog allows some estimates and conjectures of Apophis' possible range of physical properties such as the grain density and micro-porosity of its constituent material. Composition and size similarities of Apophis with (25143) Itokawa suggest a total porosity of 40% as a “current best guess” for Apophis. Applying these parameters to Apophis yields a mass estimate of 2×1010 kg with a corresponding energy estimate of 375 Mt for its potential hazard. Substantial unknowns, most notably the total porosity, allow uncertainties in these mass and energy estimates to be as large as factors of two or three.  相似文献   

2.
Optimal deflection of NEOs en route of collision with the Earth   总被引：1，自引：0，他引：1  
Ralph Kahle  Gerhard Hahn 《Icarus》2006,182(2):482-488
Recently, a method for the n-body analysis of the velocity change required to deflect a hazardous near-Earth object (NEO) was presented by Carusi et al. [Carusi, A., Valsecchi, G.B., D'Abramo, G., Boattini A., 2002. Icarus 159, 417-422]. We extent this method in order to optimize the velocity change vector instead of its along-track magnitude. From an application of both methods to a fictitious NEO we find Carusi's parallel approach to be reasonable for phases of unperturbed two-body motion. But, for orbit phases inhering third-body perturbations, i.e., for planetary close approaches or prior to a collision, the results obtained from the new method show the radial component of deflection impulse to play a major role. We show that a fivefold greater efficiency can be achieved by a deflection impulse being non-parallel to orbital velocity. The new method is applied to two possible 99942 Apophis impact trajectories in order to provide constraints for future Apophis deflection mission analysis.  相似文献   

3.
This paper is the third in a series. Paper 1 presented the results of numerical modeling of deflections of NEOs in route of collision with the Earth. The model was applied to a variety of dynamical cases including both asteroidal and cometary NEOs. Paper 2 introduced the concept of “distributed deflection,” i.e., the possibility to provide the ΔV necessary to deflect an object with a succession of maneuvers each of which would have been insufficient per se to obtain the desired result. In both papers no assumptions were made on the physical composition and structure of the NEO, nor on the details of the possible deflection maneuvers from the point of view of mission analysis. Moreover, ΔV-plots were computed assuming only along-track impulses (both in the positive and negative directions), because it is easy to demonstrate that in general this is energetically the most favorable configuration. Also in the present paper no assumptions were made on the physical composition and structure of the NEO, even if order of magnitude considerations are made on the physical feasibility of a deflection, in terms of the internal strength of the NEO. We present here the results of an investigation on the mission requirements necessary to deflect an object (or contribute to a succession of deflecting maneuvers) in terms of accessibility of the spacecraft terminal orbit from Earth with the current launchers.  相似文献   

4.
The paper refers to the current status of asteroid hazard in Russia and abroad. The authors emphasize the relevance of a sober assessment of its real state and specific circumstances working from the principle of reasonable sufficiency. The paper presents a practical approach to the asteroid hazard problem. It consists of a proposal for a mission to the Apophis asteroid and to define the main parameters of this hazardous celestial body. The article also considers how the spacecraft would look, as well as its mission profile for the period of 2012–2014.  相似文献   

5.
This paper presents a novel approach to the robust design of deflection actions for near Earth objects (NEO). In particular, the case of deflection by means of solar-pumped laser ablation is studied here in detail. The basic idea behind laser ablation is that of inducing a sublimation of the NEO surface, which produces a low thrust thereby slowly deviating the asteroid from its initial Earth threatening trajectory. This work investigates the integrated design of the space-based laser system and the deflection action generated by laser ablation under uncertainty. The integrated design is formulated as a multi-objective optimisation problem in which the deviation is maximised and the total system mass is minimised. Both the model for the estimation of the thrust produced by surface laser ablation and the spacecraft system model are assumed to be affected by epistemic uncertainties (partial or complete lack of knowledge). Evidence Theory is used to quantify these uncertainties and introduce them in the optimisation process. The propagation of the trajectory of the NEO under the laser-ablation action is performed with a novel approach based on an approximated analytical solution of Gauss’ variational equations. An example of design of the deflection of asteroid Apophis with a swarm of spacecraft is presented.  相似文献   

6.
Comets in the near-Earth object population   总被引：1，自引：0，他引：1  
Francesca DeMeo 《Icarus》2008,194(2):436-449
Because the lifespan of near-Earth objects (NEOs) is shorter than the age of the Solar System, these objects originate elsewhere. Their most likely sources are the main asteroid belt and comets. Through physical observations we seek to identify potential dormant or extinct comets among “asteroids” catalogued as NEOs and thereby determine the fraction of “comet candidates” within the total NEO population. Both discovery statistics and dynamical models indicate that candidate cometary objects in near-Earth space are predominantly found among those having a jovian Tisserand parameter Tj<3. Therefore, we seek to identify comet candidates among asteroid-like NEOs using three criteria: Tj<3, spectral parameters (C, D, T, or P taxonomic types), and/or low (<0.075) albedos. We present new observations for 20 NEOs having Tj<3, consisting of visible spectra, near-infrared spectra, and/or albedo measurements obtained using the NASA Infrared Telescope Facility, the Kitt Peak National Observatory 4 m, and the Magellan Observatory 6.5-m. Four of our “asteroid” targets have been subsequently confirmed as low activity comets. Thus our sample includes spectra of the nuclei of Comets 2002 EX12 = 169P (NEAT), 2001 WF2 = 182P (LONEOS), 2003 WY25 = D/1891 W1 (Blanplain), and Halley Family Comet 2006 HR30 = P/2006 HR30 (Siding Spring). From the available literature, we tabulate physical properties for 55 NEOs having Tj<3, and after accounting for possible bias effects, we estimate that 54±10% of NEOs in Tj<3 orbits have “comet-like” spectra or albedos. Bias corrected discovery statistics [Stuart, J.S., Binzel, R.P., 2004. Icarus 170, 295-311] estimate 30±5% of the entire NEO population resides in orbits having Tj<3. Combining these two factors suggests that 16±5% of the total discovered “asteroid-like” NEO population has “comet-like” dynamical and physical properties. Outer main-belt asteroids typically have similar taxonomic and albedo properties as our “comet candidates.” Using the model of Bottke et al. [Bottke, W.F., Morbidelli, A., Jedicke, R., Petit, J.M., Levison, H., Michel, P., Metcalfe, T.S., 2002. Icarus 156, 399-433] to evaluate source region probabilities, we conclude that 8±5% of the total asteroid-like NEO population have the requisite orbital properties, physical properties, and dynamical likelihood to have originated as comets from the outer Solar System.  相似文献   

7.
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8.
The emulsion chamber detector on board the “ShiJian-8” satellite is the first one in China designed especially for observing in space the highenergy electrons and γ-rays. In this paper, the principle of the detector design, the method of data processing and the preliminary results of observations are introduced. The design lifetime of the detector is 15 days on the orbit, and the energy range of detectable particles is 100GeV∼5TeV.  相似文献   

9.
A topical task for astronautics is to prepare a mission to the asteroid Apophis that is approaching the Earth. Determination of energetically favorable trajectories for a spacecraft involved in this mission with a return to the Earth has been considered. Two possible variants of engines for this mission are analyzed. The first variant employs electric engines with low jet thrust, while the second variant employs a spacecraft accelerated and controlled by only high-thrust engines. It is shown that both variants can be used in the mission to Apophis, but the use of electric engines with low thrust allows the project characteristics to be significantly improved.  相似文献   

10.
The surface of Mars is covered by weathered material. Mars' rusty red colour in particular is commonly ascribed to ferric iron-bearing minerals. The planet's surface is generally iron rich. Mössbauer spectroscopy is a powerful tool for quantitative mineralogical analysis of Fe-bearing minerals. Consequently, the miniaturized Mössbauer spectrometer MIMOS II is part of the payload of NASA's twin Mars Exploration Rovers “Spirit” and “Opportunity”, and ESA's ill-fated Mars Express lander “Beagle 2”. Both Mars Exploration Rovers are currently conducting successful surface operations on Mars. In this paper, we give a brief insight into mission operations with respect to the reconstruction of local weathering scenarios at the landing sites, which in turn will help to illuminate the climatic history of the planet. Mössbauer spectra obtained in preparation of the mission from the SNC meteorites Nakhla, Dar al Gani 476, and Sayh al Uhaymir, show weathering and other alteration features. Preliminary results of laboratory weathering experiments on Fe-bearing minerals (olivine and pyroxene) show the importance of analysing individual minerals to understand weathering of more complex mineral assemblages like, e.g., basalt.  相似文献   

11.
C.L Dandy  A Fitzsimmons 《Icarus》2003,163(2):363-373
We present the results of BVRIZ photometry of 56 near-Earth objects (NEOs) obtained with the 1-m Jacobus Kapteyn telescope on La Palma during 2000 and 2001. Our sample includes many NEOs with particularly deep 1-μm pyroxene/olivine absorption bands, similar to Q-type asteroids. We also classify three NEOs with particularly blue colors. No D-type asteroids were found, placing an upper limit of ∼2% on the fraction of the NEO population originating in the outer main belt or the Trojan clouds. The ratio of dark to bright objects in our sample was found to be 0.40, significantly higher than current theoretical predictions. As well as classifying the NEOs, we have investigated color trends with size and orbit. We see a general trend for larger silicate objects to have shallower absorption bands but find no significant difference in the distribution of taxonomic classes at small and large sizes. Our data clearly show that different taxonomic classes tend to occupy different regions of (a, e) space. By comparing our data with current model predictions for NEO dynamical evolution we see that Q-, R-, and V-type NEOs tend to have orbits associated with “fast track” delivery from the main belt, whereas S-type NEOs tend to have orbits associated with “slow track” delivery. This outcome would be expected if space weathering occurs on time scales of >106 years.  相似文献   

12.
The Mission MAGIA (Missione Altimetrica Geofisica GeochImica lunAre) was proposed in the framework of the ??Bando per Piccole Missioni?? of ASI (Italian Space Agency) in 2007. The mission was selected for a phase A study by ASI on February 7th 2008. The tight budget allocation, combined with quite ambitious scientific objectives, set challenging requirements for the satellite design. The paper gives a fast overview of the payloads complement and of the mission-constrained design drivers, including cost minimization, risk reduction, and AIT flexibility. The spacecraft architecture is then outlined, along with an overview of the key subsystems and trade-offs. Some details are given of a Moon gravitometric experiment based on a mother?Cdaughter satellite configuration with the daughter being a subsatellite released from the MAGIA satellite and intended to circle the Moon at a very low altitude. Budgets are appended at the end of the paper showing the key study results.  相似文献   

13.
Photometric and spectral analysis of data from the Cassini Visual and Infrared Mapping Spectrometer (VIMS) has yielded significant results regarding the properties and composition of the surface of Saturn's satellite Enceladus. We have obtained spectral cubes of this satellite, containing both spatial and spectral information, with a wavelength distribution in the infrared far more extensive than from any previous observations and at much higher spatial resolution. Using a composite mosaic of the satellite, we map the distribution of crystalline and amorphous ices on the surface of Enceladus according to a “crystallinity factor” and also the depth of the temperature- and structure-dependent 1.65 micron water-ice band. These maps show the surface of Enceladus to be mostly crystalline, with a higher degree of crystallinity at the “tiger-stripe” cracks and a larger amorphous signature between these stripes. These results suggest recent geological activity at the “tiger stripe” cracks and an intriguing atmospheric environment over the south pole where amorphous ice is produced either through intense radiative bombardment, flash-freezing of cryovolcanic liquid, or rapid condensation of water vapor particles on icy microspherules or on the surface of Enceladus.  相似文献   

14.
In 2001, NASA began assembling the Aerocapture Systems Analysis Team, a team of scientists and engineers from multiple NASA centers. Their charter is to perform high-fidelity analyses of delivering scientifically compelling orbital missions that use aerocapture for orbit insertion at their destinations. After establishing scientific credibility, studies focus on aerocapture systems design and performance, including approach navigation, flight mechanics, aerothermodynamics, and thermal protection. The team's October 2001-September 2002 study examined a mission to explore the organic environment of Titan and its chemical, geological, and dynamical context. Its architecture includes a Titan polar orbiter that would complete and extend Cassini's soon-to-begin global mapping, aiding global extrapolation of findings from a mobile in situ element (rover, blimp, etc.). The in situ element would perform remote sensing and in situ investigations, for analysis and characterization of Titan's surface, shallow subsurface, atmosphere, processes occurring there, and energy sources driving it all. The study concentrated on the orbiter and orbit insertion, largely treating the in situ element as a black box with data relay requirements. October 2002-September 2003 the team studied a mission to perform Cassini/Huygens-level exploration of the Neptune system. Before aerocapture this mission would deploy and support multiple Neptune atmospheric entry probes. After aerocapture the orbiter uses Triton as a “tour engine”, in much the same manner as Cassini uses Titan, to provide many Triton flybys and orbit evolution for detailed investigation of Neptune's interior, atmosphere, magnetosphere, rings, and satellites.This presentation summarizes the missions’ science objectives, instrumentation, and data requirements that served as the foundations for the studies, and describes mission design requirements and constraints that affect the science investigations.  相似文献   

15.
Ground-based observations of faint satellites nearby their planets with 1-2 m class telescopes usually do not allow for high quality astrometry and photometry, due to saturation by the primary or to poor S/N ratio on the satellite images, generally embedded on the scattered light of the planet. Earth-based observations of the Uranus satellites’ upcoming mutual events in 2007-2008 are no exception. In most cases, the event will take place at 4 arcs or less from the planet, with “planet minus satellite” brightness differences of 10 magnitudes. So as to make feasible the observations of these important phenomena, we have developed a prototype of a coronagraph of simple design making use of good quality commercial optical systems. Pilot tests made with this coronagraph with a telescope of show that it is possible to obtain S/N ratios of 50 or higher for 10 s exposures, for satellites as close as 2 Uranus radii from the planet center. We have also developed numerical algorithms which perform digital coronagraphy in the images, with the elimination of the influence of the planets’ scattered light. This procedure considerably improves the S/N ratio of the satellite images (with or without a coronagraph instrument) and shall be applied in the reduction of the observations of the Uranus events so as to achieve the highest possible photometric and astrometric quality.  相似文献   

16.
We examine the shape of a “rubble pile” asteroid as it slowly gains angular momentum by YORP torque, to the point where “landsliding” occurs. We find that it evolves to a “top” shape with constant angle of repose from the equator up to mid-latitude, closely resembling the shapes of several nearly critically spinning asteroids imaged by radar, most notably (66391) 1999 KW4 [Ostro, S.J., Margot, J.-L., Benner, L.A.M., Giorgini, J.D., Scheeres, D.J., Fahnestock, E.G., Broschart, S.B., Bellerose, J., Nolan, M.C., Magri, C., Pravec, P., Scheirich, P., Rose, R., Jurgens, R.F., De Jong, E.M., Suzuki, S., 2006. Science 314, 1276-1280]. Similar calculations for non-spinning extremely prolate or oblate “rubble piles” show that even loose rubble can sustain shapes far from fluid equilibrium, thus inferences based on fluid equilibrium are generally useless for inferring bulk properties such as density of small bodies. We also investigate the tidal effects of a binary system with a “top shape” primary spinning at near the critical limit for stability. We find that very close to the stability limit, the tide from the secondary can actually levitate loose debris from the surface and re-deposit it, in a process we call “tidal saltation.” In the process, angular momentum is transferred from the primary spin to the satellite orbit, thus maintaining the equilibrium of near-critical spin as YORP continues to add angular momentum to the system. We note that this process is in fact dynamically related to the process of “shepherding” of narrow rings by neighboring satellites.  相似文献   

17.
Apostolos A. Christou 《Icarus》2005,178(1):171-178
The upcoming crossing of the Sun and the Earth through the equatorial plane of the planet Uranus presents an opportunity to observe mutual eclipses and occultations of the uranian satellites. We present predictions for 321 such events from 2006 to 2010. 230 of these events are “nominal” i.e. they are predicted to occur based on the currently available ephemeris while a further 91 “grazing” events are allowable given the positional uncertainties of the satellites. Taking into account the statistical frequency of events that occur too close to the planet, during solar conjunction or are too “shallow” to observe, we conclude that about 150 events should be detectable from different longitudes around the world. We argue that a worldwide campaign of photometric observations of these events will yield, as in the case of the jovian and saturnian systems, high-precision astrometric information on the satellites toward improving their ephemerides as well as the system constants (satellite masses, uranian zonal harmonics, etc.). In addition, mathematical inversion of the lightcurves should permit, subject to the photometric quality and number of observed events, mapping of albedo variegations over the satellite hemispheres that were in darkness during the Voyager 2 encounter with the uranian system in 1985/1986.  相似文献   

18.
We provide an overview of features indicative of the interaction between water and lava and/or magma on Mars as seen by the High Resolution Imaging Science Experiment (HiRISE) camera during the Primary Science Phase of the Mars Reconnaissance Orbiter (MRO) mission. The ability to confidently resolve meter-scale features from orbit has been extremely useful in the study of the most pristine examples. In particular, HiRISE has allowed the documentation of previously undescribed features associated with phreatovolcanic cones (formed by the interaction of lava and groundwater) on rapidly emplaced flood lavas. These include “moats” and “wakes” that indicate that the lava crust was thin and mobile, respectively [Jaeger, W.L., Keszthelyi, L.P., McEwen, A.S., Dundas, C.M., Russel, P.S., 2007. Science 317, 1709-1711]. HiRISE has also discovered entablature-style jointing in lavas that is indicative of water-cooling [Milazzo, M.P., Keszthelyi, L.P., Jaeger, W.L., Rosiek, M., Mattson, S., Verba, C., Beyer, R.A., Geissler, P.E., McEwen, A.S., and the HiRISE Team, 2009. Geology 37, 171-174]. Other observations strongly support the idea of extensive volcanic mudflows (lahars). Evidence for other forms of hydrovolcanism, including glaciovolcanic interactions, is more equivocal. This is largely because most older and high-latitude terrains have been extensively modified, masking any earlier 1-10 m scale features. Much like terrestrial fieldwork, the prerequisite for making full use of HiRISE’s capabilities is finding good outcrops.  相似文献   

19.
The method applied since 1996 for the analysis of the orbital residuals of the LAGEOS satellites in order to measure the Lense-Thirring effect has been the subject of the present work. This method, based on the difference between the orbital elements of consecutive arcs, is explained and analysed also from the analytical point of view. It is proved that this “difference method” works well for the determination of the secular effects, as in the case of the relativistic precession induced by the Earth's angular momentum, but also very useful for the determination and study of the long-term periodic effects. Indeed, the only limitation in the determination of the periodic effects is the possibility of the reduction of their amplitude by a factor which depends from the periodicity of the given perturbation and from the orbital arc length chosen for the satellite during the data analysis. In the case of the Yarkovsky-Schach effect, the main non-gravitational perturbation seen in the LAGEOS satellites orbital residuals, in particular in its perigee rate and eccentricity vector excitation residuals, we show that the “difference method” is quite good also for the determination of the long-period perturbations induced by this subtle non-conservative force.  相似文献   

20.
We report unusual and somewhat unexpected observations of the jovian satellite Io, showing strong methane absorption bands. These observations were made by the Cassini VIMS experiment during the Jupiter flyby of December/January 2000/2001. The explanation is straightforward: Entering or exiting from Jupiter's shadow during an eclipse, Io is illuminated by solar light which has transited the atmosphere of Jupiter. This light, therefore becomes imprinted with the spectral signature of Jupiter's upper atmosphere, which includes strong atmospheric methane absorption bands. Intercepting solar light refracted by the jovian atmosphere, Io essentially becomes a “mirror” for solar occultation events of Jupiter. The thickness of the layer where refracted solar light is observed is so large (more than 3000 km at Io's orbit), that we can foresee a nearly continuous multi-year period of similar events at Saturn, utilizing the large and bright ring system. During Cassini's 4-year nominal mission, this probing technique should reveal information of Saturn's atmosphere over a large range of southern latitudes and times.  相似文献   

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