Gaseous CN, C 2, and C 3 jets in the inner coma of Comet P/Halley observed from the Vega 2 spacecraft

Abstract

Composite images of the inner coma of Comet P/Halley are constructed by superposing the monochromatic charts transmitted by the three-channel spectrometer of Vega 2 during the final approach session on March 9, 1986. The images have a moderate spatial resolution. They cover a sector of angle 50° converging to the nucleus. The scale of the images is 40,000 km. A solar type spectrum is adjusted separately to each cometary spectrum. Images of the CN, C 3 C 2 ( Δν = 1), and C 2 ( Δν = 0) emissions corrected of the continuum are presented. They show evidence of two well contrasted jets; one in the direction of the Sun and the other in the perpendicular direction. The jets are separated by a low-intensity radial zone having the shape of a valley. At a cometocentric distance of 25,000 km, the contrast is equal to 2 for C 2 and 3 for C 3. There is no evidence that the jets directly take their source at the nucleus surface. Radial and transverse profiles of the emissions are presented. The Δν = 1/ Δν = 0 intensity ratio of the Swan bands of C 2 is compared with published values deduced from theoretical calculations of the C 2 spectrum. The hypothesis of an extended source in the 10,000–30,000 km radius range is examined in connection with a possible second source of carbon-bearing radicals in the CHON particles.