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NASA NTRS1976

J, H, K photometry of 433 Eros and other asteroids

Results are reported for IR photometry of nine bright asteroids, including 433 Eros, which was conducted in the J, H, K, and (for Eros) L bands with an InSb photometer on the 1.3-m Kitt Peak telescope. It is found that the J-H and H-K color indices of all nine asteroids are slightly redder than those of the sun and that three C-type objects are somewhat redder in the same color indices than four S-types and an E-type. Eros is shown to have an unusually red J-K index; the shape of its IR spectral reflectance curve is attributed in part to the presence of the weak 2-micron pyroxene absorption band in the spectrum. The results show that JHK photometry is less diagnostic of asteroidal composition than higher-resolution IR spectrophotometry.

Chapman, C. R.↗
NASA NTRS1976

Spectrophotometry /0.33 to 1.07 microns/ of 433 Eros and compositional implications

The spectral reflectance (0.33-1.07 micrometers) for the asteroid 433 Eros was determined as a function of rotational phase during January 28-30, and February 15, 1975. Interpretation of absorption features suggests Eros is composed of an undifferentiated assemblage of moderate to high temperature minerals (iron, pyroxene, and olivine, but no carbon). H-type ordinary chondrites are such assemblages, but it would be premature to conclude that Eros is like an H chondrite meteorite in composition until a better understanding is reached of possible physical differences between laboratory powders and asteroid regoliths for metal-bearing assemblages. There are no large-scale major compositional variations on the different sides of Eros.

Pieters, C.↗
NASA NTRS1976

Polarization of the reflected light of asteroid 433 Eros

Linear polarizations measured for asteroid 433 Eros at various wavelengths and at solar phase angles ranging from 9 to 53 deg are presented. The polarization results are entirely typical of main-belt S asteroids, and indicate a dusty surface with geometric albedo 0.20. The derived effective diameter at photometric maximum is 21 km. Eros is quite uniform polarimetrically; no dependence on aspect is detected, and the polarization is shown to be constant during a single rotation with a precision of one part in forty.

Zellner, B.↗
NASA NTRS1979

X-ray observations of H1908+050 /=SS 433/

The X-ray source H1908+050 (=4U 1908+05 = A1909+04) was observed for three 6 day periods in 1977 and 1978 with the HEAO A-2 experiment. Because of the positional error box and variability of the source, the unusual emission-line object and variable radio source SS 433 has been suggested as the optical counterpart. The X-ray luminosity of the source varied by a factor of about 2 on a time scale of 6 months, and the spectrum of the object is consistent with either a power law of photon index of 2.1 or with 14.3 KeV thermal bremsstrahlung emission with an about 575 eV equivalent-width iron line. These X-ray characteristics argue against the source being extragalactic, but do not uniquely identify the type of source. The measurements are consistent with emission from a white dwarf with 100 million gauss magnetic field, but are also similar to the X-ray emission sometimes seen from Cir X-1. A search has been made for X-ray emission from similar radio sources, but no new X-ray sources were detected. A previously known source, A1850+00, is a possible counterpart for one of these radio sources.

Marshall, F. E.↗
NASA NTRS1979

Thermal properties of 433 Eros

Radiometric and reflected light observations of 433 Eros at high time resolution, high accuracy, and broad spectral coverage are reported. A thermal inertia model is used to estimate the thermal inertia, albedo, and size of Eros. An albedo of 0.125 plus or minus 0.025 with axes of 39.3 plus or minus 2.0 x 16.1 plus or minus 0.8 km is found. The estimate of the albedo is about 30% lower than previous estimates.

Lebofsky, L. A.↗
NASA NTRS1980

Acceleration, radiation and precession in SS 433

Some theoretical problems posed by the observations of SS 433 are considered. The monoenergetic beams point toward a gas-dynamic acceleration process. In this model the collimation implies that the acceleration occurs in a region of slab symmetry, possibly the surface layers of an accretion disk. The 164 day rotation of the beam pattern may be explained as a precession period.

Katz, J. I.↗
NASA NTRS1981

Optical photometry of SS 433 - 200 nights of data 1979-1980

Results from over 200 nights of optical photoelectric photometry of SS 433 during the period July 1979-October 1980 are presented. The data, taken in unfiltered light, the V band, an interference filter band centered on stationary H-alpha and a far-red band, provide evidence for an underlying 164-day light variation of peak-to-peak amplitudes 0.50 magnitude in V and 0.7 magnitude at 6567 A, and a binary-like variation with period 13.074 days and peak-to-peak amplitudes 0.50 and 0.60 magnitudes, respectively. The 13-day light curves are found to change slightly as a function of phase in the 164-day cycle, while seemingly erratic light fluctuations of up to 1 magnitude in 1 day and about 2 magnitudes in 3-4 days are imposed on both cyclic variations. It is noted that a conventional close-binary model is incapable of accounting for all the observed features, and alternatives involving some sort of luminous, rapidly changing extended low-mass envelope or screen in the binary system must be sought.

Kemp, J. C.↗
NASA NTRS1981

Intrinsic polarization of SS 433 - An electron scattering model

A model for the generation of the observed intrinsic linear polarization in the optical radiation from SS 433 due to scattering from free electrons in highly ionized material in a jet or inclined disk is examined and compared with observational data. Expressions for the Stokes parameters of the linear polarization as a function of phase are obtained for a simple jet model in which continuum light from a point source is singly scattered by free electrons located along the jets resulting in strikingly different relations between Q and U at different values of model parameters. Comparison of 30 broadband linear polarization measurements with the model indicates a mean value of rotation axis inclination to the line of sight of 63 deg, which is not inconsistent with X-ray and radio data. The measurements are also compatible with models invoking highly inclined disks or rings with emission arising in regions on opposite sides of a diameter.

Mclean, I. S.↗
NASA NTRS1984

Line locking and SS 433

The general problem of acceleration by line locking in an optically thin medium is considered. Analytic solutions to the coupled equations of radiation transfer and matter motion are presented. Using these solutions, restrictions on the physical conditions of the accelerated matter are derived. By applying these conditions to SS 433, it is found that if the absorbing ion is light (hydrogen or helium), the matter must be highly clumped, and the acceleration has to begin at approximately 10 to the 12th cm. Line-locking acceleration with a hydrogen-like heavy ion such as iron demands higher than solar ion abundance.

Pekarevich, M.↗
NASA NTRS1984

On the bizarre gamma-ray spectrum of SS 433

Lamb et al. (1983) have announced the discovery of a pair of gamma-ray lines interpretable as emission of the 1.368 MeV line of Mg-24 in the two oppositely directed relativistic jets of SS 433. The mass loss rate related to the Mg-24 and the kinetic energy flux of the Mg-24 are considered. In the present investigation, it is shown that the mass loss flux must be well in excess of 0.00001 solar mass per yr, while the abundance of the gamma-emitting nucleus is extremely high. Attention is given to the calculation of the gamma-ray production efficiency factor, the size of the emitting region, reaction processes, and X-ray luminosity. It is concluded that for plasma beam models, there must be a substantial overabundance, by a factor of 100 to approximately 1000, of the gamma-line producing nucleus. The association of the gamma-ray lines with Mg-24 is reasonable but not secure.

Helfer, H. L.↗
NASA NTRS1986

On the dust jet model of SS 433

The dust jet model for production of narrow gamma-ray lines from SS 433 is examined and shown to be implausible. Sputtering rates at disk temperatures are high, and self-absorption rates in the disk and jet are important; both imply that dust particles would easily be destroyed. The energy deposited in the dust jet particles by collisions with the ambient protons should be radiated in the optical and infrared in amounts greatly exceeding that observed. The dust momentum pumps ambient gas out of the beam at rates which imply that for the steady state, the ambient gas has to have an initial temperature exceeding one million K. The ambient medium is also required to have densities exceeding those postulated for the H-alpha-emitting gas jet, and the interaction within the gas jet material would result in appreciable broadening of the H-alpha emission lines. At present, there is no viable model for the steady state production of the gamma-ray line radiation.

Helfer, H. L.↗
NASA NTRS1986

Synchrotron and inverse Compton emission from expanding sources in jets - Application to SS 433

The formalism for an expanding source is extended to include continuous injection of electrons and the production of X-rays by inverse Compton scattering of external photons and synchrotron-self-Compton scattering. The model is applied to the expanding nonthermal sources entrained in the jets of SS 433. These sources are found capable of producing both the flaring radio component and the X-ray fluxes only if the relativistic electrons and the magnetic field are far out of equipartition. If the expanding source in the jets is in equipartition, the X-rays may originate from a stationary source within the binary system, which is self-absorbed at radio frequencies and produces X-rays by inverse Compton scattering of optical photons from the binary.

Band, David L.↗
NASA NTRS1990

Hollow conical jet models for SS 433 - A paradigm lost?

A precessing jet such as that in SS 433 may be approximated as an axisymmetric flow, if the precession time is short by comparison to the propagation time. A series of simulations has been conducted for precessing jets using an axisymmetric finite-difference hydrodynamics code. Examinations are made of hollow cylindrical jets, which lack the complication of a growing interior volume, and conical jets, which model the behavior of a precessing jet propagating on the surface of its precession cone.

Kochanek, Christopher S.↗
NASA NTRS1999

Bulk Compositional Trends in Meteorites: A Guide for Analysis and Interpretation of NEAR XGRS Data from Asteroid 433 EROS

The Near Earth Asteroid Rendezvous (NEAR) spacecraft is to orbit the S-class asteroid 433 Eros for about one year beginning on February 14, 2000. The X-ray/gamma-ray O, Mg, Al, Si, Fe, and K; possibly H, Ca, S, Ti, and Th) of Eros with a spatial resolution ranging from a few km for X-rays to approx. 25% of the asteroid's surface for gamma-rays. The major scientific goals for the NEAR XGRS are to relate the composition of Eros to known classes of meteorites, to assess compositional heterogeneity and to identify geological processes that have occurred on the asteroid. Comparing remote-sensing data from asteroids to laboratory data from meteorites requires that the latter be well determined and understood. How well particular classes of meteorites can be identified as analogues of Eros depends not only on the error of the XGRS measurement, but also on the spread in abundances observed among different members of a given meteorite class. To prepare for the return of XGRS data from Eros, we have compiled a large database of bulk elemental compositions of meteorites, using data from a wide variety of published and unpublished sources. Custom software was developed to easily extract statistical information and make plots of data from different meteorite classes. Here, we use the meteorite compositional database to investigate which abundances and abundance ratios, of those measureable by the NEAR XGRS, are most diagnostic for distinguishing meteorite classes and identifying geological processes that have occurred on the samples' parent asteroids.

Nittler, Larry R.↗
NASA NTRS1999

Preliminary Planning for NEAR's Low-Altitude Operations at 433 Eros

On February 14, 2000, an orbit insertion burn will place NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft (S/C) into orbit around asteroid 433 Eros. NEAR will initially orbit Eros with distances ranging from 500 to 100 km in order to characterize the shape, gravity and spin of Eros. Once the physical parameters of Eros are determined reasonably well, the plan is to establish an orbit of the NEAR S/C with increasingly lower altitudes as the one year orbital mission progresses while further characterizing the gravity and shape of Eros. Towards the end of the NEAR mission, after the shape, gravity and spin of Eros have been well characterized, the scientific interest of obtaining very close observations (< 5 km) can be realized. The navigation during this phase relies on a combination of NASA's Deep Space Network (DSN) radio metric tracking, laser ranging (LIDAR) data from the S/C to the surface of Eros, and onboard optical imaging of landmarks on Eros. This paper will provide preliminary plans for mission design and navigation during the last two months of the orbit phase, where several close passes to the surface will be incorporated to enhance the science return. The culmination of these close passes will result in the eventual landing of the S/C on the surface of Eros. Several considerations for these plans are given by Antreasian, et at. [1998]. The objective for the end of the mission will be to land the S/C autonomously using the surface relative information obtained from the onboard LIDAR instrument. The goal will be to soft land the S/C in such a way as to keep it operational. With the use of an onboard LIDAR landing algorithm as discussed by Antreasian et at. [1998], it is believed that the S/C impact velocity can be kept well under 7 m/s which is a requirement for allowing the S/C to remain operational.

Antreasian, P. G.↗
NASA NTRS2000

Orbit Operations at 433 Eros: Navigation for the NEAR Shoemaker Mission

NASA's Near Earth Asteroid Rendezvous Mission began its record-setting exploration of the asteroid 433 Eros by inserting the spacecraft into orbit about Eros on February 14, 2000. This is the first spacecraft from any country to orbit an asteroid. The mission has overcome a failed insertion burn attempt on December 20, 1998, an event that would have ended most planetary missions, to return to the same target and successfully begin its science mapping a little more than a year later. Shortly after the successful insertion into orbit, the mission was renamed NEAR Shoemaker (NEAR) in memory of the late astronomer and geologist Eugene Shoemaker. NEAR will gather science data at Eros until February 14, 2001, which is the nominal end of mission. The NEAR mission is managed by the Johns Hopkins University, Applied Physics Laboratory in Laurel, Maryland. Since the initial mission concept in 1992, the design and implementation of the NEAR navigation system have been the responsibility of the Jet Propulsion Laboratory, California Institute of Technology. This presentation will show some of the unique features of navigation and mission design related to orbiting an asteroid and to designing a robust navigation system for the NEAR spacecraft. The problem of navigating a spacecraft about an asteroid is made difficult by the relative uncertainty in the asteroid physical properties which perturb the orbit: i.e., the mass, gravity field, and spin state. To help solve this problem, the navigation system for NEAR uses traditional DSN radio metric Doppler and range tracking, along with new technologies of optical landmark tracking and laser ranging to the asteroid surface. The experiences to date for each of these data types in the navigation solutions will be presented. Plans for the remainder of the NEAR mission will be presented, which include low orbits (down to 35 km radius circular orbits), and close flybys that may pass within 1 km of the surface. In addition, at the end of mission, NASA has approved a controlled descent and hovering phase that will culminate with the spacecraft impacting the surface. The maneuver planning for this final phase will also be presented.

Williams, B. G.↗
NASA NTRS2001

Could 433 Eros have a Primitive Achondritic Composition?

One of the goals of the NEAR (Near Earth Asteroid Rendezvous) mission to 433 Eros is to determine if it has a meteoritic analog. We are currently investigating if primitive achondrites have bulk compositions and spectral properties similar to Eros. Additional information is contained in the original extended abstract.

Burbine, T. H.↗