The Halley Mission
After their encounters, the Vegas' motherships were redirected by Venus' gravity to intercept Halley's Comet.
Images started to be returned on March 4, 1986, and were used to help pinpoint Giotto's close flyby of the comet. The early images from Vega that showed two bright areas on the comet, which were initially interpreted as a double nucleus. The bright areas would later turn out to be two jets emitting from the comet. The images also showed the nucleus to be dark, and the infrared spectrometer readings measured a nucleus temperature of 300 K to 400 K, much warmer than expected for an ice body. The conclusion was that the comet had a thin layer on its surface covering an icy body.
Vega 1 made its closest approach on March 6 at around 8,889 kilometers (at 07:20:06 UT) of the nucleus. It took more than 500 pictures via different filters as it flew through the gas cloud around the coma. Although the spacecraft was battered by dust, none of the instruments were disabled during the encounter.
The data intensive examination of the comet covered only the three hours around closest approach. They were intended to measure the physical parameters of the nucleus, such as dimensions, shape, temperature and surface properties, as well as to study the structure and dynamics of the coma, the gas composition close to the nucleus, the dust particles' composition and mass distribution as functions of distance to the nucleus and the cometary-solar wind interaction.
The Vega images showed the nucleus to be about 14 km long with a rotation period of about 53 hours. The dust mass spectrometer detected material similar to the composition of carbonaceous chondrites meteorites and also detected clathrate ice.
After subsequent imaging sessions on 7 and 8 March 1986, Vega 1 headed out to deep space. In total Vega 1 and Vega 2 returned about 1500 images of Comet Halley. Vega 1 ran out of attitude control propellant on 30 January 1987, and contact with Vega 2 continued until 24 March 1987.
Vega 1 and Vega 2 are currently in heliocentric orbits.
Read more about this topic: Vega 1
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