Showing papers by "Jet Propulsion Laboratory published in 1996"

Hubble Space Telescope Observations of the Disk and Jet of HH 30

Abstract: HH 30 in Taurus has been imaged with the Hubble Space Telescope WFPC2. The images show in reflected light a flared disk with a radius of about 250 AU that obscures the protostar. The disk resembles detailed accretion disk models that constrain its density distribution and show that its inclination is less than 10 degrees. There are bipolar emission-line jets perpendicular to the disk, a very clear demonstration of the standard paradigm for accretion disk and jet systems. However, asymmetries in the light distribution show that the disk has not completely settled into a quasi-equilibrium accretion state, or that some of the observed scattering is from an asymmetric envelope. The emission-line jet itself is resolved into a number of knots with typical lengths and separations of 0".4, much smaller and more numerous than indicated by lower resolution ground-based studies. There are indications of still finer structures in the jet all the way to the resolution limit of 0".1. The knots have proper motions ranging from 100 to 300 km s^(-1) and are therefore generated at the surprisingly high rate of about 0.4 knots per jet per year. The jet appears to be collimated within a cone of opening angle 3o and can be seen to within 30 AU of the star. Both single- and multiple-scattering disk models have a range of possible solutions, but by requiring pressure support and temperature equilibrium, a self-consistent model emerges. There is evidence for pressure support because the disk appears to have a Gaussian height profile. The temperature at each point in the disk is determined by the disk geometry, which in turn fixes the temperature in a self-consistent manner. The extinction to the protostar is unknown but constrained to be greater than 24 mag. The optical properties of the scattering grains in the disk are determined and found to imply a large scattering asymmetry, but they seem to follow the interstellar reddening law. The absolute magnitude and colors of the unseen protostar, which has a brightness in the I bandpass of about 0.16 times solar and is very red, are obtained. The disk mass is about 0.006 times solar and has an expected lifetime of about 10^5 yr.

Discovery of Ganymede's magnetic field by the Galileo spacecraft

Abstract: THE Galileo spacecraft has now passed close to Jupiter's largest moon—Ganymede—on two occasions, the first at an altitude of 838 km, and the second at an altitude of just 264 km. Here we report the discovery during these encounters of an internal magnetic field associated with Ganymede (the only other solid bodies in the Solar System known to have magnetic fields are Mercury, Earth and probably lo1). The data are consistent with a Ganymede-centred magnetic dipole tilted by ∼10° relative to the spin axis, and an equatorial surface-field strength of ∼750 nT. The magnetic field is strong enough to carve out a magnetosphere with clearly defined boundaries within Jupiter's magnetosphere. Although the observations require an internal field, they do not indicate its source. But the existence of an internal magnetic field should in itself help constrain models of Ganymede's interior.

Postseismic Rebound in Fault Step-Overs Caused by Pore Fluid Flow

Abstract: Near-field strain induced by large crustal earthquakes results in changes in pore fluid pressure that dissipate with time and produce surface deformation. Synthetic aperture radar (SAR) interferometry revealed several centimeters of postseismic uplift in pull-apart structures and subsidence in a compressive jog along the Landers, California, 1992 earthquake surface rupture, with a relaxation time of 270 ± 45 days. Such a postseismic rebound may be explained by the transition of the Poisson's ratio of the deformed volumes of rock from undrained to drained conditions as pore fluid flow allows pore pressure to return to hydrostatic equilibrium.

Cassini plasma spectrometer investigation

Abstract: Cassini/Huygens is a joint project of NASA and the European Space Agency designed to explore the Saturnian system in depth during its four-year mission. Cassini, the orbiter spacecraft, will carry twelve hardware investigations while Huygens, the Titan atmospheric probe, will carry an additional six. The Cassini Plasma Spectrometer (CAPS), one of 12 orbiter investigations, includes 3 plasma sensors designed to cover the broadest possible range of plasma energy, composition, and temporal variation. It is conservatively estimated that CAPS will provide a factor of ten or more improvement in measurement capabilities over those of the Voyager spacecraft at Saturn.

Radii and Effective Temperatures for G, K, and M Giants and Supergiants

Abstract: Interferometrically determined angular diameters obtained at the Palomar Testbed Interferometer (PTI) for 80 giant and supergiant stars are presented in this paper.

The tidally induced warping, precession and truncation of accretion discs in binary systems: three-dimensional simulations

Abstract: We present the results of non linear, hydrodynamic simulations, in three dimensions, of the tidal perturbation of accretion discs in binary systems where the orbit is circular and not necessarily coplanar with the disc mid–plane. The accretion discs are assumed to be geometrically thin, and of low mass relative to the stellar mass so that they are governed by thermal pressure and viscosity, but not self–gravity. The parameters that we consider in our models are the ratio of the orbital distance to the disc radius, D/R, the binary mass ratio, Ms/Mp, the initial inclination angle between the orbit and disc planes, �, and the Mach number in the outer parts of the unperturbed disc, M. Since we consider non self-gravitating discs, these calculations are relevant to protostellar binaries with separations below a few hundred astronomical units. For binary mass ratios of around unity and D/R in the range 3 to 4, we find that the global evolution of the discs is governed primarily by the value of M. For relatively low Mach numbers (i.e. M = 10 to 20) we find that the discs develop a mildly warped structure, are tidally truncated, and undergo a near rigid body precession at a rate which is in close agreement with analytical arguments. For higher Mach numbers (M ≈ 30), the evolution is towards a considerably more warped structure, but the disc none the less maintains itself as a long–lived, coherent entity. A further increase in Mach number to M = 50 leads to a dramatic disruption of the disc due to differential precession, since the sound speed is too low to allow efficient communication between the disc’s constituent parts. Additionally, it is found that the inclination angle between the disc and orbital angular momentum vectors evolves on a longer timescale which is probably the viscous evolution timescale of the disc. The calculations are relevant to a number of observed astrophysical phenomena, including the precession of jets associated with young stars, the high spectral index of some T Tauri stars, and the light curves of X–ray binaries such as Hercules X-1 which suggest the presence of precessing accretion discs.

Converting light into spectrally pure microwave oscillation.

Abstract: We present theoretical and experimental results for a novel oscillator that converts continuous light energy into stable and spectrally pure microwave signals. This optoelectronic oscillator can generate ultrastable spectrally pure microwave reference frequencies as high as 75 GHz with a phase noise lower than 2140 dBcyHz at 10 kHz, independent of oscillation frequency.

Far-Ultraviolet Imaging of Jupiter's Aurora and the Io “Footprint”

Abstract: Far-ultraviolet images of Jupiter from the Hubble Space Telescope Wide Field Planetary Camera 2 reveal polar auroral emissions at 300 kilometer resolution and three times higher sensitivity than previously achieved. Persistent features include a main oval containing most of the emission and magnetically connected to the middle magnetosphere, diffuse and variable emissions poleward of the main oval, and discrete emission from Io's magnetic footprint equatorward of the oval. The auroral emissions are variable, exhibit magnetic conjugacy, and are visible above the planet limb. All emissions approximately co-rotate with Jupiter except the Io “footprint,” which is fixed along Io's magnetic flux tube.

Io's Interaction with the Plasma Torus: Galileo Magnetometer Report

Abstract: Galileo magnetometer data at 0.22-second resolution reveal a complex interaction between Io and the flowing plasma of the Io torus. The highly structured magnetic field depression across the downstream wake, although consistent with a magnetized Io, is modified by sources of currents within the plasma that introduce ambiguity into the interpretation of the signature. Highly monochromatic ion cyclotron waves appear to be correlated with the local neutral particle density. The power peaks in the range of molecular ion gyrofrequencies, suggesting that molecules from Io can remain undissociated over a region of more than 15 Io radii around Io.

Detection of Ozone on Ganymede

Abstract: An absorption band at 260 nanometers on the trailing hemisphere of Ganymede, identified as the Hartley band of ozone (O3), was measured with the Hubble Space Telescope. The column abundance of ozone, 4.5 × 1016 per square centimeter, can be produced by ion impacts or by photochemical equilibrium with previously detected molecular oxygen (O2). An estimated number density ratio of [O3]/[O2] ≈ 10−4 to 10−3 requires an atmospheric density orders of magnitude higher than upper limits from spacecraft occultation experiments. Apparently, this O2-O3 “atmosphere” is trapped in Ganymede9s surface ice, an inference consistent with the shift and broadening of the band compared with the gas-phase O3 band.

Evidence for a magnetosphere at Ganymede from plasma-wave observations by the Galileo spacecraft

Abstract: ON 27 June 1996 the Galileo spacecraft1,2 made the first of four planned close fly-bys of Ganymede, Jupiter's largest moon. Here we report measurements of plasma waves and radio emissions, over the frequency range 5 Hz to 5.6 MHz during the first encounter. Intense plasma waves were detected over a region of space nearly four times Ganymede's diameter, which is much larger than would be expected for a simple wake arising from Ganymede's passage through Jupiter's rapidly rotating magneto-sphere. The types of waves detected (whistler-mode emissions, upper hybrid waves, electrostatic electron cyclotron waves and escaping radio emission) strongly suggest that Ganymede has a large, extended magnetosphere of its own. The data indicate the presence of a strong (B > 400 nT) magnetic field, and show that Ganymede is surrounded by an ionosphere-like plasma with a maximum electron density of about 100 particles cm−3 and a scale height of about 1,000km.

ATMOS stratospheric deuterated water and implications for troposphere‐stratosphere transport

Abstract: Measurements of the isotopic composition of stratospheric water by the ATMOS instrument are used to infer the convective history of stratospheric air. The average water vapor entering the stratosphere is found to be highly depleted of deuterium, with delta-D(sub w) of -670 +/- 80 (67% deuterium loss). Model calculations predict, however, that under conditions of thermodynamic equilibrium, dehydration to stratospheric mixing ratios should produce stronger depletion to delta-D(sub w) of -800 to 900 (80-90% deuterium loss). Deuterium enrichment of water vapor in ascending parcels can occur only in conditions of rapid convection; enrichments persisting into the stratosphere require that those conditions continue to near-tropopause altitudes. We conclude that either the predominant source of water vapor to the uppermost troposphere is enriched convective water, most likely evaporated cloud ice, or troposphere-stratosphere transport occurs closely associated with tropical deep convection.

Detection of acetylene in the infrared spectrum of comet Hyakutake

Abstract: Comets are rich in volatile materials, of which roughly 80% (by number) are water molecules. Considerable progress is being made in identifying the other volatile species, the abundances of which should enable us to determine whether comets formed primarily from ice-covered interstellar grains, or from material that was chemically processed in the early solar nebula. Here we report the detection of acetylene (C2H2) in the infrared spectrum of comet C/1996 B2 (Hyakutake). The estimated abundance is 0.3-0.9%, relative to water, which is comparable to the predicted solid-phase abundance in cold interstellar clouds. This suggests that the volatiles in comet Hyakotake may have come from ice-covered interstellar grains, rather than material processed in the accretion disk out of which the Solar System formed.

Galileo Plasma Wave Observations in the Io Plasma Torus and Near Io

Abstract: The Galileo plasma wave instrument detected jovian radio emissions, narrowband upper hybrid waves, and whistler-mode emissions during the inbound pass through the Io torus. The upper hybrid waves provided an accurate profile of electron density through the Io torus and in the vicinity of Io. These measurements show that the torus density has increased by about a factor of 2 since the Voyager 1 flyby in 1979. A well-defined peak in the electron density was observed in the wake of Io, with densities as high as about 4 × 104 per cubic centimeter.

Hubble space telescope spectroscopic evidence for A 1 × 109 M⊙ black hole in NGC 4594

Abstract: The discovery by Kormendy of a M• 109 M☉ massive dark object (MDO) in NGC 4594 is confirmed with higher resolution spectroscopy from the Canada-France-Hawaii Telescope (CFHT) and the Hubble Space Telescope (HST). CFHT measurements with the Subarcsecond Imaging Spectrograph improve the resolution from σ* = 040 to 027 Gaussian dispersion radius of the point-spread function (PSF). The apparent central velocity dispersion rises from σ = 250 ± 7 km s-1 to σ = 286 ± 7 km s-1. As observed with the COSTAR-corrected HST, the Faint Object Spectrograph, and a 021 aperture, σ = 321 ± 7 km s-1 is still higher, and the central rotation curve is very steep. The highest-M• published dynamical model fits the new observations reasonably well when "observed" at HST resolution. The spatial resolution has now improved by a factor of ~5 since the discovery measurements, and the case for a black hole (BH) has strengthened correspondingly. We confirm that NGC 4594 has a Seyfert spectrum; Hα is ~5200 km s-1 wide at zero intensity. However, gas velocities are lower than the circular velocities implied by the stars, so they cannot be used to test the BH case in NGC 4594. The gas may be in a ring, or it may be associated with patchy dust. HST images with the Wide Field and Planetary Camera 2 show dust at some aperture positions. NGC 4594 appears to have a bright point nucleus. However, the central absorption-line strengths are low, consistent with dilution by enough nonthermal light to explain the "nucleus." There is no evidence for a distinct nuclear star cluster. NGC 4594 is similar to M87, which also has a nonthermal nuclear source, and not to M31 and NGC 3115, which have quiescent BHs and nuclear star clusters.

Cassini infrared Fourier spectroscopic investigation

Abstract: The composite infrared spectrometer (CIRS) is a remote sensing instrument to be flown on the Cassini orbiter. CIRS will retrieve vertical profiles of temperature and gas composition for the atmospheres of Titan and Saturn, from deep in their tropospheres to high in their stratospheres. CIRS will also retrieve information on the thermal properties and composition of Saturn's rings and Saturnian satellites. CIRS consists of a pair of Fourier Transform Spectrometers (FTSs) which together cover the spectral range from 10-1400 cm-1 with a spectral resolution up to 0.5 cm-1. The two interferometers share a 50 cm beryllium Cassegrain telescope. The far-infrared FTS is a polarizing interferometer covering the 10-600 cm-1 range with a pair of thermopile detectors, and a 3.9 mrad field of view. The mid-infrared FTS is a conventional Michelson interferometer covering 200-1400 cm-1 in two spectral bandpasses: 600-1100 cm- 1100-1400 cm(superscript -1 with a 1 by 10 photovoltaic HgCdTe array. Each pixel of the arrays has an approximate 0.3 mrad field of view. The HgCdTe arrays are cooled to approximately 80K with a passive radiative cooler.

A Magnetic Signature at Io: Initial Report from the Galileo Magnetometer

Abstract: During the inbound pass of the Galileo spacecraft, the magnetometer acquired 1 minute averaged measurements of the magnetic field along the trajectory as the spacecraft flew by Io. A field decrease, of nearly 40 percent of the background jovian field at closest approach to Io, was recorded. Plasma sources alone appear incapable of generating perturbations as large as those observed and an induced source for the observed moment implies an amount of free iron in the mantle much greater than expected. On the other hand, an intrinsic magnetic field of amplitude consistent with dynamo action at Io would explain the observations. It seems plausible that Io, like Earth and Mercury, is a magnetized solid planet.

Residual Circulation in the Stratosphere and Lower Mesosphere as Diagnosed from Microwave Limb Sounder Data

Abstract: Results for the residual circulation in the stratosphere and lower mesosphere between September 1991 and August 1994 are reported. This circulation is diagnosed by applying an accurate radiative transfer code to temperature, ozone, and water vapor measurements acquired by the Microwave Limb Sounder (MLS) onboard the Upper Atmosphere Research Satellite (UARS), augmented by climatological distributions of methane, nitrous oxide, nitrogen dioxide, surface albedo, and cloud cover. The sensitivity of the computed heating rates to the presence of Mt. Pinatubo aerosols is explored by utilizing aerosol properties derived from the measurements obtained by the Improved Stratospheric and Mesospheric Sounder instrument, also onboard UARS. The computed vertical velocities exhibit a Semiannual oscillation (SAO) around the tropical stratopause, with the region of downward velocities reaching maximum spatial extent in February and August. This behavior reflects the semiannual oscillation in temperature and ozone and mimics that seen in past studies of the October 1978–May 1979 period based on data from the Limb Infrared Monitor of the Stratosphere onboard the Nimbus 7 satellite. The SAO vertical velocities are stronger during the northern winter phase, as expected if planetary waves from the winter hemisphere are involved in driving the SAO. A possible quasi-biennial oscillation (QBO) signal extending from the middle into the upper stratosphere is also hinted at, with the equatorial vertical velocities in the region 10–1 hPa significantly smaller (or even negative) in 1993/94 than in 1992/93. Despite the short data record, the authors believe that this pattern reflects a QBO signal rather than a coincidental interannual variability, since the time–height section of vertical velocity at the equator resembles that of the zonal wind. Wintertime high-latitude descent rates are usually greater in the Northern Hemisphere, but they also exhibit significant variability there. In the three northern winters analyzed in this study, strong downward velocities are diagnosed in the lower stratosphere during stratospheric warmings and are associated with enhanced wave forcing (computed as the momentum residual) in the mid- and upper stratosphere. The implications of the computed circulation for the distribution of tracers are illustrated by the example of the “double-peaked” structure in the water vapor distribution measured by MLS.

Rate of left-lateral movement along the easternmost segment of the Altyn Tagh fault, east of 96°E (China)

Abstract: SUMMARY Field work carried out in Gansu province and complemented with analysis of SPOT panchromatic scenes allows us to characterize the deformations along the eastern segment of the Altyn Tagh fault and to place bounds on its Holocene left slip rate. East of 96°E, the long-term, left-lateral offset of stream channels, alluvial fans, and terrace edges is about 50 m. These offsets are most probably of Holocene age (12 ± 2 ka) and imply that the corresponding derived slip rate is 4 ± 2 mm yr−1. This observation is consistent with a north-eastward along-strike decreasing slip rate on the Altyn fault due to partitioning of slip on multiple, more easterly trending splays.

Atmospheric Parameters and Iron Abundances of Low-Mass Pre-Main-Sequence Stars in Nearby Star Formation Regions

Abstract: High-resolution echelle spectra have been obtained for low-mass pre-main-sequence stars in the Taurus-Auriga, Orion, Chamaeleon, Ophiuchus, and other star formation regions. Using temperature-sensitive individual metallic line ratios, new effective temperatures are determined for a sample of 30 G and K pre-main-sequence stars in nearby star-forming clouds to an accuracy of ± 200 K or better in most cases. Comparison of these values with previous spectral classifications using low-resolution spectra reveals occasional large discrepancies in spectral type. Microturbulences derived for 23 "weak line" T Tauri stars range as high as 3.1 ± 0.4 km s–1. The mean microturbulent velocity of the sample is 1.6 ± 0.6 km s–1. Using these new effective temperatures and microturbulences, iron abundances have been determined for 30 pre-main-sequence stars in several northern and southern sky star-formation regions. By determining the mean [Fe/H] for at least five stars in each cloud, bulk metallicities have been derived for the Taurus-Auriga, Orion, Chamaeleon, and Ophiuchus molecular clouds. [Fe/H] is approximately solar in all the regions surveyed.

Temperature and emissivity separation from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images

Abstract: The ASTER scanner on NASA's EOS-AM1 satellite (launch: 1998) will collect five channels of TIR data with an NE(Delta) T of less than or equal to 0.3 degrees Kelvin to estimate surface kinetic temperatures and emissivity spectra, especially over land, where emissivities are not known in advance. Temperature/emissivity separation (TES) is difficult because there are five measurements but six unknowns. Various approaches have been used to constrain the extra degree of freedom. ASTER's TES algorithm hybridizes three established algorithms, first estimating the temperature by the normalized emissivity method, and then using it to calculate emissivity band ratios. An empirical relationship predicts the minimum emissivity from the spectral contrast (min-max difference: MMD) of the ratioed values, permitting recovery of the emissivity spectrum. TES uses an iterative approach to remove reflected sky irradiance. Based on numerical simulation, TES can recover temperatures within about plus or minus 1.5 degrees Kelvin, and emissivities within about plus or minus 0.015. Limitations arise from the empirical relationship between emissivity values and spectral contrast, compensation for reflected sky irradiance, and ASTER's precision, calibration and atmospheric correction. Improvements of TES before launch will focus on refining the MMD relationship.

Time-Resolved Observations of Jupiter's Far-Ultraviolet Aurora

Abstract: Simultaneous imaging and spectroscopic observations of Jupiter's far-ultraviolet aurora covering half a jovian rotation were made on 31 May 1994. The Hubble Space Telescope Wide Field Planetary Camera 2 images revealed dramatic and rapidly changing auroral features, including discrete longitudinal structures along the auroral ovals, with variable contrast; a poleward offset in a north oval sector, showing equatorward motion near dusk; emissions polewards of the ovals, apparently co-rotating; and a bright event developing near the dawn limb. Viewing geometry effects explain the rotational intensity modulation observed by the International Ultraviolet Explorer, without intrinsic longitudinal asymmetries.

An isotopic study of soils in chronological sequences of alluvial deposits, Providence Mountains, California

Abstract: The carbon ({sup 14}C and {sup 13}C) and oxygen isotopic composition of pedogenic carbonate was determined for two soil chronosequences on limestone and granitic alluvium in the Providence Mountains area in the Mojave Desert, California. The measured {sup 14}C ages of pedogenic carbonate coating on clasts were interpreted in the light of a diffusion-reaction model developed in our recent studies. Model ages of soil formation calculated from the measured {sup 14}C ages of pedogenic carbonate are in correct relative order as determined by geomorphic evidence, and are also consistent with model ages from the measured {sup 14}C ages of soil organic matter. {sup 14}C model ages suggest that the order geomorphic surfaces we studied are of late Pleistocene age (ca. 47-17 ka) and the younger surfaces formed during the Holocene (ca. 11-4 ka). These age estimates of the geomorphic surfaces are older than the previously assigned ages based on a combination of soil development, geomorphic relationships, and several infrared-stimulated luminescence dates, but they are within a few thousand years of these other age estimates. Stable carbon isotopic composition of the soil carbonate indicates either a slight increase in C{sub 4} or CAM (crassulacean acid metabolism) plants or a decrease inmore » plant density in this area during the Holocene. Both the carbon and oxygen isotopic composition of soil carbonates suggests that the climate in the eastern Mojave Desert has, in general, become warmer and drier during the Holocene. 57 refs., 9 figs., 5 tabs.« less

Surface expression of the Chicxulub crater

Abstract: Analyses of geomorphic, soil, and topographic data from the northern Yucatan Peninsula, Mexico, confirm that the buried Chicxulub impact crater has a distinct surface expression and that carbonate sedimentation throughout the Cenozoic has been influenced by the crater. Late Tertiary sedimentation was mostly restricted to the region within the buried crater, and a semicircular moat existed until at least Pliocene time. The topographic expression of the crater is a series of features concentric with the crater. The most prominent is an approximately 83-km-radius trough or moat containing sinkholes (the Cenote ring). Early Tertiary surfaces rise abruptly outside the moat and form a stepped topography with an outer trough and ridge crest at radii of approximately 103 and approximately 129 km, respectively. Two discontinuous troughs lie within the moat at radii of approximately 41 and approximately 62 km. The low ridge between the inner troughs corresponds to the buried peak ring. The moat corresponds to the outer edge of the crater floor demarcated by a major ring fault. The outer trough and the approximately 62-km-radius inner trough also mark buried ring faults. The ridge crest corresponds to the topographic rim of the crater as modified by postimpact processes. These interpretations support previous findings that the principal impact basin has a diameter of approximately 180 km, but concentric, low-relief slumping extends well beyond this diameter and the eroded crater rim may extend to a diameter of approximately 260 km.

Constraints from Galileo observations on the origin of Jovian dust streams

Abstract: THE Ulysses spacecraft detected streams of sub-micrometre-sized dust particles as it approached Jupiter in 19921,2. Although interplanetary space was known to contain dust, the presence of discrete streams was completely unexpected. The directions from which the dust grains struck the spacecraft strongly suggested that the source lay somewhere within the Jupiter system. Three origins were proposed, the comet Shoemaker–Levy 9 (ref. 3), Jupiter's gossamer ring4, and the volcanoes on Io5, but there was no definitive evidence for or against any of the options. Here we report the detection by the Galileo spacecraft of even more intense dust streams—including three intense dust storms of month-long duration, with impact rates up to 10 times higher than those observed by Ulysses. Our analysis of the data confirms that the dust streams originate near Jupiter; we are able to rule out a cometary origin, but cannot yet determine conclusively whether the dust comes from Io or the ring.

A new telerobotic application: remote laparoscopic surgery using satellites and optical fiber networks for data exchange

Abstract: This article describes the significance in human, scientific, and technical terms of the first experiment in telerobotic surgery carried out between the NASA Jet Propulsion Laboratory in Pasadena, California, and the Telerobotics Laboratory of the Politecnico di Milano on 7 July 1993.An Italian robot in the Telerobotics Laboratory was remotely controlled by an Italian surgeon in the United States. The robot's task was to perform a surgical operation on a model containing a pig's organs, involving execution of a biopsy, aspi ration of organic material, and two incisions in preparation of laparoscopy. Transmission was effected by means of a double satellite link, with three transceiver stations: one in Italy, one close to New York, and one in Pasadena, and two geostation ary satellites, the first over the Atlantic and the second over the United States. The route length of the signals was 150,000 km in each direction, and the two centers are 10,000 km apart.