J. E. Blamont

The VEGA Venus balloon experiment

In June 1985, two instrumented balloons were placed in the atmosphere of Venus as part of the VEGA mission. Each balloon traveled about 30 percent of the way around the planet at a float altitude near 54 kilometers. In situ sensors measured pressure, temperature, vertical wind velocity, cloud particle backscatter, ambient light level, and frequency of lightning. A ground-based network of 20 radio antennas tracked the balloons by very long baseline interferometry (VLBI) techniques to monitor the Venus winds. The history, organization, and principal characteristics of this international balloon experiment are described.

Comet Halley: Nucleus and jets (results of the VEGA mission)

Abstract The VEGA-1 and VEGA-2 spacecraft made their closest approach to Comet Halley on 6 and 9 March, respectively. In this paper those results of the onboard imaging experiment which were obtained around closest approach are discussed. The nucleus of the comet was clearly identifiable as an irregularly shaped object, with overall dimensions of (16±1)×(8±1)×(8±1) km. The nucleus rotates in the prograde sense about an axis nearly perpendicular to the orbital plane with a period of 53±2 hours. Its albedo is only 0.04± 0.02 0.01 Many of the jet features observed during the second fly-by have been spatially reconstructed. Their sources form a quasi-linear structure on the surface. The dust above the surface is shown to be generally optically thin with the exception of certain specific dust jets. Brightness features on the surface are clearly seen. Correlating our data with other measurements, we conclude that the dirty snow-ball model will probably need to be revised.

Spectrophotometry of comet P/Halley at wavelengths 275—710 nm from Vega 2

Spectrophotometric observations of the inner coma of comet Halley in the range 275-710 nm were conducted from Vega 2 on March 8, 9, 10, 11, 1986. During the encounter session, when the impact parameter was minimum, p = 120 km, the gaseous emissions were still present, superimposed on an intense continuum. In the inner coma, C2 and C3 emissions steadily increase when the impact parameter decreases. The emissions of OH at 309 nm and CN in its band head at 388 nm show a plateau between 1500 and 600 km. The decrease in OH emission when the impact parameter is less than 500 km is interpreted in terms of high optical thickness of water vapor at Lyman-alpha. Pixel-to-pixel ratios of spectra show that the color of dust continuum presents small fluctuations which might be produced by a discontinuous emission of icy grains.

Vega project — Three channel spectrophotometer for the Halley's comet investigation

Abstract A spectrometer for the Halleys Comet Investigation after the VEGA Project is described in the present work. It consists of a telescope and three spectral channels: UV (120 – 290 nm), resolution Δ λ / λ = 170; VIS (280 – 710 nm), resolution Δ λ / λ = 170; IR (950 – 1900 nm), resolution Δ λ / λ = 70. With the help of two-coordinate scanner, the secondary mirror of the telescope allows spatial scanning of the Comet with a frame 2°×1,5° with 105 different pixels.

VEGA three-channel spectrometer experiment: Spectroscopy of comet Halley in the visible and near-ultraviolet ranges

Abstract A total of 3600 spectra of Comet Halley in the 275–710 nm were obtained on March, 8, 9, 10 and 11, 1986, from the VEGA 2 spacecraft. The emissions of OH, NH, CN, C 3 , CH, C 2 , NH 2 and H 2 O + are identified. From the OH intensity in the (0,0) band: 1.1 Megarayleigh at 5400 km from the nucleus, it can be inferred that the OH production rate was (1.4 ± 0.5)×10 30 molecules s −1 . The NH, C 3 , CH and NH 2 bands became comparatively more intense at distances from the nucleus shorter than 3000km. At 06:40 U.T. when the instrument field of view was 6000×4500 km, two jets were observed. Spectra from the jets show significant differences with other spectra. Inside a jet NH, C 3 and NH 2 are comparatively more intense and the rotational distributions of OH, CN and C 2 are strongly distorted. This shows that part of the observed emissions probably comes from radicals directly produced in the excited state during the initial process of photolysis of the parent molecules.

Near infrared observations of comet Halley from Vega 2

Abstract Spatial distribution of the continuum radiation in the range of 0.95–1.9 μ m presumes total dust production rate of the comet of 10 ρ tonne s −1 ( ρ is the dust material density) and its angular distribution proportional cos ϕ . Observations of the water vapor band at 1.38 μ m reveal strong jets, their time shift from the dust jet measured in situ is consistent with gas velocity of 0.82±0.1 km s −1 and dust velocity of 0.55±0.08 km s −1 . The OH vibrational-rotational bands observed are excided directly via photolysis of water vapor. Water vapor production rate deduced from the H 2 O band and OH band intensities is 8×10 29 s −1 . Intensity of the CN(0,0) band result in the CN column density of 9×10 12 cm −2 , i.e. larger by a factor of 3 than given by the violet band.