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At least 127 records · Page 7
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NASA NTRS2016

Unveiling Clues from Spacecraft Missions to Comets and Asteroids through Impact Experiments

The Deep Impact Spacecraft mission was the first to boldly face the challenge of impacting the surface of a comet, 9P/Tempel 1, to investigate surface and subsurface 'pristine' materials. The Stardust mission to Comet 81P/Wild 2 brought back an exciting surprise: shocked minerals which were likely altered during the comet's lifetime. Signatures of shock in meteorites also suggest that the violent past of the solar system has left our small bodies with signatures of impacts and collisions. These results have led to the question: How have impacts affected the evolutionary path taken by comets and asteroids, and what signatures can be observed? A future planetary mission to a near-Earth asteroid is proposing to take the next steps toward understanding small bodies through impacts. The mission would combine an ESA led AIM (Asteroid Impact Mission) with a JHU/APL led DART (Double Asteroid Redirect Mission) spacecraft to rendezvous with binary near-Earth asteroid 65803 Didymus (1996 G2). DART would impact the smaller asteroid, 'Didymoon' while AIM would characterize the impact and the larger Didymus asteroid. With these missions in mind, a suite of experiments have been conducted at the Experimental Impact Laboratory (EIL) at NASA Johnson Space Center to investigate the effects that collisions may have on comets and asteroids. With the new capability of the vertical gun to cool targets in the chamber through the use of a cold jacket fed by liquid nitrogen, the effects of target temperature have been the focus of recent studies. Mg-rich forsterite and enstatite (orthopyroxene), diopside (monoclinic pyroxene) and magnesite (Mg-rich carbonate) were impacted. Target temperatures ranged from 25 deg to -100 deg, monitored by connecting thermocouples to the target container. Impacted targets were analyzed with a Fourier Transform Infrared Spectrometer (FTIR) and Transmission Electron Microscope (TEM). Here we present the evidence for impact-induced shock in the minerals through both spectra and TEM imaging and compare with unshocked samples.

Lederer, Susan M.↗
NASA NTRS2017

PHYS: Division of Physical Chemistry 258 - Properties and Origins of Cometary and Asteroidal Organic Matter Delivered to the Early Earth

Comets and asteroids may have contributed much of the Earth's water and organic matter. The Earth accretes approximately 4x10(exp 7) Kg of dust and meteorites from these sources every year. The least altered meteorites contain complex assemblages of organic compounds and abundant hydrated minerals. These carbonaceous chondrite meteorites probably derive from asteroids that underwent hydrothermal processing within the first few million years after their accretion. Meteorite organics show isotopic and chemical signatures of low-T ion-molecule and grain-surface chemistry and photolysis of icy grains that occurred in cold molecular clouds and the outer protoplanetary disk. These signatures have been overprinted by aqueously mediated chemistry in asteroid parent bodies, forming amino acids and other prebiotic molecules. Comets are much richer in organic matter but it is less well characterized. Comet dust collected in the stratosphere shows larger H and N isotopic anomalies than most meteorites, suggesting better preservation of primordial organics. Rosetta studies of comet 67P coma dust find complex organic matter that may be related to the macromolecular material that dominates the organic inventory of primitive meteorites. The exogenous organic material accreting on Earth throughout its history is made up of thousands of molecular species formed in diverse processes ranging from circumstellar outflows to chemistry at near absolute zero in dark cloud cores and the formative environment within minor planets. NASA and JAXA are currently flying sample return missions to primitive, potentially organic-rich asteroids. The OSIRIS-REx and Hayabusa2 missions will map their target asteroids, Bennu and Ryugu, in detail and return regolith samples to Earth. Laboratory analyses of these pristine asteroid samples will provide unprecedented views of asteroidal organic matter relatively free of terrestrial contamination within well determined geological context. Studies of extraterrestrial materials and returned samples are essential to understand the origins of Solar System organic material and the roles of comets and asteroids to providing the starting materials for the emergence of life.

Messenger, Scott↗
NASA NTRS2015

BILLIARDS: Baseline Instrumented Lithology Lander, Inspector and Asteroid Redirection Demonstration System

BILLIARDS Baseline Instrumented Lithology Lander, Inspector, and Asteroid Redirection Demonstration System Proposed demonstration mission for Billiard-Ball concept Select asteroid pair with natural close approach to minimize cost and complexity Primary Objectives Rendezvous with a small (10m), near Earth (alpha) asteroid Maneuver the alpha asteroid to a collision with a 100m (beta) asteroid Produce a detectable deflection or disruption of the beta asteroid Secondary objectives Contribute knowledge of asteroid composition and characteristics Contribute knowledge of small-body formation Opportunity for international collaboration

Asteroid Redirection↗
NASA NTRS2020

Exogenic Basalt on Asteroid (101955) Bennu

When rubble-pile asteroid 2008 TC3 impacted Earth on October 7, 2008, the recovered rock fragments indicated that such asteroids can contain exogenic material. However, spacecraft missions to date have only observed exogenous contamination on large, monolithic asteroids that are impervious to collisional disruption. Here we report the presence of meter-scale exogenic boulders on the surface of near-Earth asteroid (101955) Bennu - the 0.5-km, rubble-pile target of the OSIRIS-REx mission which has been spectroscopically linked to the CM carbonaceous chondrite meteorites. Hyperspectral data indicate that the exogenic boulders have the same distinctive pyroxene composition as the howardite-eucrite-diogenite (HED) meteorites that come from (4) Vesta, a 525-km diameter asteroid that has undergone differentiation and extensive igneous processing. Delivery scenarios include the infall of Vesta fragments directly onto Bennu or indirectly onto Bennu’s parent body, where the latter’s disruption created Bennu from a mixture of endogenous and exogenic debris. Our findings demonstrate that rubble-pile asteroids can preserve evidence of inter-asteroid mixing that took place at macroscopic scales well after planetesimal formation ended. Accordingly, the presence of HED-like material on the surface of Bennu provides previously unrecognized constraints on the collisional and dynamical evolution of the inner main belt.

Asteroids↗
NASA NTRSDate not supplied

Identification of Additional Ceres-Like Asteroids in the Main Belt

Primitive (i.e., low-albedo and water-rich) asteroids are remnants from the early formation of the solar system. They offer insight into the physical and chemical processes that took place during this early period. Previous research has shown that many large primitive asteroids (with a diameter greater than 100 km) have similar spectral characteristics to the dwarf planet Ceres. These asteroids are found in a specific region beyond Ceres' orbit, between approximately 3.0 AU and 3.4 AU from the Sun. These Ceres-like asteroids have highly porous interiors, formed relatively late (1.5-3.5 million years after the formation of calcium-aluminum-rich inclusions), and experienced maximum interior temperatures of less than 900K. We have obtained new spectra of additional large primitive asteroids with similar spectral characteristics to Ceres, such as asteroid (168) Sibylla, some of which are located beyond 3.4 AU. The new spectra were measured at the NASA Infrared Telescope Facility in Hawai'i, using the prism (0.7-2.5 μm) and the long-wavelength cross-dispersed (LXD: 1.9–4.2-μm) modes of the SpeX spectrograph/imager. We will also discuss the implications of these new results on the mechanisms responsible for implanting Ceres-like asteroids into the Main Belt, such as dynamical instability.

Asteroids↗
NASA NTRS1975

Surface properties of asteroids - A synthesis of polarimetry, radiometry, and spectrophotometry

Surface compositions of 110 asteroids are analyzed using data obtained by polarimetry and visible and near-IR spectrophotometry. A comparison of albedos and diameters determined by polarimetry and radiometry indicates that a slight upward revision of the radiometric albedo scale is necessary. Reliable adopted albedos and diameters are presented for 56 objects, and rough diameters are obtained for 52 additional objects. More than 90% of the asteroids are shown to fall into two broad groups (C and S) which are compositionally similar to carbonaceous and stony meteorites, respectively. C-type asteroids are found to predominate in the asteroid belt, and the largest of these (Ceres, Pallas, Hygiea, Davida) may be metamorphosed. It is shown that Vesta may be the only differentiated asteroid remaining intact in the belt. The results support the conclusions that asteroids and meteorites have similar classes of mineral assemblages, but the distribution of asteroid types contrasts with the distribution of major meteorite types found on earth.

Chapman, C. R.↗
NASA NTRS1976

Radiometric diameters for an additional 22 asteroids

Ten-micron radiometry of 24 asteroids, 22 of which have not previously had their diameters and albedos determined, is presented. The magnitudes of the objects ranged from -0.35 to +5.35 and 13 of them had diameters smaller than 100 km. They ranged in albedo from 0.024 to 0.28, and the 22 previously unstudied objects included 10 C asteroids, seven S asteroids, three U asteroids, and two unknown. In the diameter-albedo plane, ten of the asteroids studied clustered near albedo 0.03 and diameter 100-200 km, in a region previously occupied by only seven asteroids but where Chapman et al. (1975) predicted many objects would be identified upon sampling those fainter than V equals about 12. The new data suggest that there are substantial numbers of S asteroids with diameter less than 100 km in the inner part of the belt.

Morrison, D.↗
NASA NTRS1977

Radiometric diameters of 84 asteroids from observations in 1974-1976

Diameters and geometric albedos are derived from 10- and 20-micron infrared photometry for 84 asteroids, 68 of them not previously observed in this program of asteroid radiometry. All but three of the 30 brightest asteroids are included in the total sample of 131 objects, and all asteroids with diameters greater than 250 km can now be identified. The albedos are strongly bimodal, with the great majority of asteroids (class C) having visual geometric albedos between 0.025 and 0.050. The albedos of the second most numerous class, the S asteroids, are primarily between 0.10 and 0.16. The third largest class appears to be the M objects, of which seven are now identified. Apparently, the M objects are very rare for semimajor axes of less than 2.4 AU. The unusual asteroids with albedos greater than 0.20 are also discussed.

Morrison, D.↗
NASA NTRS1978

Visual and infrared photometry of asteroids

Results are reported for a survey of asteroids at 0.56, 1.6, and 2.2 microns. The observations of 30 asteroids are reduced to relative reflectances at 1.6 and 2.2 microns (such that the relative reflectance at 0.56 micron is scaled to unity). These relative reflectances have important implications for the classification of asteroids. Low-albedo asteroids show a significant range in their infrared relative reflectances, but carbonaceous chondritic-type material remains a good candidate for their surface composition. Many S-type asteroids are found to have significantly brighter infrared relative reflectances than M-type asteroids. Lunarlike dark glass on the surfaces of these objects is probably ruled out. A metallic phase is the most plausible candidate, which implies a multiple-component surface composition perhaps similar to certain stony-iron meteorites. The data suggest that such a metallic phase may be common in the inner asteroid belt.

Veeder, G. J.↗
NASA NTRS1979

Round-Trip Missions to Low-Delta-V Asteroids and Implications for Material Retrieval

Low-delta-V asteroids are to be found among those which have perihelia near 1 AU. From the 50 known asteroids with perihelia less than 1.5 AU, 10 candidates for asteroid retrieval missions were selected on the basis of low eccentricity and inclination. To estimate the ranges of orbital elements for which capture in earth orbit may be feasible, a survey was made of 180 deg transfer from a set of orbits having elements near those of the earth to the earth. For 2 of the 10 low-delta-V asteroids and for an additional one with elements more earth-like than any yet known, direct ballistic round trips in the 1980's were computed. A stay time of several months at the asteroid was used. The results show that the total delta V, including that for rendezvous with earth upon return, for the known asteroids is above 14 km/sec. But if asteroids are found similar to the strawman considered, the total delta V could be as low as 10 km/sec.

David F Bender↗
NASA NTRS1979

Multiple asteroid rendezvous missions

Asteroid missions, centered on multiple asteroid rendezvous missions to main belt asteroids, are discussed and the required solar electric propulsion for these missions as well as the current performance estimates are examined. A brief statistical analysis involving asteroid availability transfer requirements and propulsion system capabilities is given, leading to a prediction that 5 to 8 asteroids can be encountered with a single launch. Measurement techniques include visual imaging, radio tracking, magnetometry, and in the case of landers, seismometry. The spacecraft will be propelled by a solar electric system with a power level of 25 kW to 40 kW and tour possibilities for 13 different asteroids have been developed. Preliminary estimates of asteroid triaxiality are made to calculate the effect of close orbits.

Bender, D. F.↗
NASA NTRS1979

Earth-crossing asteroids - Orbital classes, collision rates with earth, and origin

Asteroids that can intersect the orbit of the earth are discussed, which include Aten asteroids (semimajor axis (a) less than 1 AU, aphelion greater than 0.983 AU), Apollo asteroids (a greater than 1 AU, perihelion less than 1.017 AU), and Amor asteroids (perihelion distance between 1.017 and 1.3 AU). The principal sources of earth-crossing asteroids appear to be extinct comet nuclei and collision fragments from regions in the main asteroid belt. The total population of earth-crossers is estimated at 13,000, of which approximately 8% are Atens, 50% are Apollos, and 40% are Amors,and the present collision rate of such asteroids with the earth is estimated at about 3.5 objects, to absolute magnitude 18, per million years.

Shoemaker, E. M.↗
NASA NTRS1980

Infrared reflectance spectra of asteroids - A search for water of hydration

Infrared reflectance spectra have shown the presence of an absorption feature in the 3-4 micron region for seven C and U asteroids. By comparison with laboratory spectra of terrestrial silicates and meteorites, it is concluded that this band is probably due to water in the form of hydrated salts and silicates (clay minerals), implying that the surface material of these asteroids may be analogous to the CI and CM carbonaceous chondritic meteorites. The presence of other hydrated minerals, however, cannot be ruled out. The depths of the water bands in the spectra vary from asteroid to asteroid, though no asteroid spectrum shows a band as deep as was detected on 1 Ceres. On four other C asteroids, no water band was detected. The implications of these observations for the mineralogy of these asteroids are discussed

Lebofsky, L. A.↗
NASA NTRS1985

Asteroid Collisional Evolution Studies

Understanding asteroid collisional evolution is important for characterizing the physical state of asteroids today and for learning about the processes that acted in this region of the solar system early in its history. The collisional outcome algorithm in the numerical simulation of asteroid evolution was revised to reflect pressure-strengthening. Asteroid collisions are now treated as a distribution of oblique impacts rather than as only head-on collisions. The initial and evolved size distribution of a plausible asteroid population is compared with the observed size distribution. Asteroid accretion times and reconstruction of the primordial solar nebula suggest that there was significantly more mass in this part of the solar system when the asteroids were accreting.

Davis, D. R.↗
NASA NTRS1986

Studies of asteroids and comets

About 3000 accurate positions of asteroids and comets were measured concentrating particularly on close-Earth approachers, but also targeting asteroids in need for follow-up observations because of unusual orbital characteristics or poor observational history. In 1985, 36 of the discoveries were numbered. Very accurate + or - 0.1 arcsec?) positional measurements were made of P/Halley on four nights in November and December 1985 in support of Giotto mission navigation. The asteroid orbit files were maintained, and ephemeris data for observational planning were supplied to colleagues worldwide. Considerable progress was made in understanding how information on asteroid shapes, surface albedo variegation, and rotational states can be derived from lightcurve and phase curve data. The analytical formulation was completed of a new asteroid magnitude system for the International Astronomical Union; the system was adopted at the New Delhi General Assembly by IAU Commission 20. Photographic photometry of about 10000 images of faint asteroids observed during the course of the United Kingdom Schmidt-CalTech Asteroid Survey in 1981 was continued, completing the microdensitometric scanning and all process of software development for data handling.

Bowell, E. L. G.↗
NASA NTRS1986

Speckle interferometry applied to asteroids and other solar system objects

Speckle interferometry is a high angular resolution technique that allows study of resolved asteroids. By following the changing size, shape, and orientation of minor planets, and with a few general assumptions (e.g., geometric scattering, triaxial ellipsoid figures, no albedo features), it is possible to directly measure an asteroid's true dimensions and the direction of its spin axis in one or two nights. A particular subset of triaxial ellipsoid figures are equilibrium shapes, and would imply that some asteroids are thoroughly fractured. Such shapes if they exist among the asteroids would allow a determination of bulk density since there is a unique relation among spin period, size, shape, and density. The discovery of even a single rubble pile, (just as the finding of even one binary asteroid by speckle interferometric techniques) would drastically alter the notion of asteroids as small solid planets. The Pluto/Charon system was studied to aid in improving the orbital elements necessary to predict the eclipse/occultation season currently in progress. Four asteroids were reduced to their size, shape, and pole direction: 433 Eros, 532 Herculina, 511 Davida, and 2 Pallas.

Drummond, J. D.↗
NASA NTRS1986

Asteroid team

Work on asteroid classification continued was rewarded with the discovery of two Earth-approaching M asteroids. The M class is rare and these are the first found among the near-Earth asteroids to have the spectral albedo characteristic of this class. The two asteroids are newly discovered 1986 DA and 1986 EB which were observed at N and Q bandpasses (i.e., 10 and 20 microns) with the 3 m IRTF telescope and at five wavelengths from 0.36 to 0.85 microns from Kitt peak National Observatory's 0.36 m telescope. The derived diameters are about 2 km for both objects. In the asteroid radiometry program N or Q photometry was obtained for more than 40 asteroids in Feb. 1986. Radiometric diameter calibration support were provided for stellar occultations of stars by 230 Athamantis and 129 Antigone. The data were reduced but not analyzed. Infrared spectra (0.8 to 2.6 microns) of 60 asteroids were reduced and are now ready for compositional analysis.

Matson, D. L.↗
NASA NTRS1987

Asteroid lightcurve inversion

One of the most fundamental physical properties of any asteroid is its shape. Lightcurves provide the only source of shape information for most asteroids. Unfortunately, the functional form of a lightcurve is determined by the viewing/illumination geometry and the asteroid's light scattering characteristics as well as its shape, and in general it is impossible to determine an asteroid's shape from lightcurves. A technique called convex-profile inversion (CPI) that obtains a convex profile, P, from any lightcurve is introduced. If certain ideal conditions are satisfied, then P is an estimator for the asteroid's mean cross section, C, a convex set defined as the average of all cross sections C(z) cut by planes a distance z above the asteroids's equatorial plane. C is therefore a 2-D average of the asteroid's 3-D shape.

Ostro, Steven J.↗