The probe is "turned on" (meaning that its instruments were activated) when it was 1 000 000 kilometers from the comet. Everything was working to perfection, there were no dust particles, and soon the Earth began to receive the first pictures that were computer color-enhanced to highlight even minimum luminosity variations. First the comet appeared as a weak luminous halo and then, slowly, as Giotto got closer, it completely filled the monitors: the interior of a large irregular spot glowed with shaded coloured bands towards a more brilliant "heart". It seemed to be the nucleus, but it wasn't: the large colored spot was the gas jet and particles emitted by Halley which, because of its brilliance, obscures everything else; and it is also the most dangerous enemy for Giotto because it will certainly attack the probe when it passes close by. Instead, the nucleus is a dark spot, almost invisible, that can be seen just between the margins of the jet: only subsequent processing, which electronically "screens out" the luminous jet, will make it possible to see it with even unexpected precision. The probe continued to approach, sending pictures every four seconds (the time that the probe takes to revolve around itself), but in the meantime, at 250 000 kilometers from the nucleus, the particles began to strike the probe; first just barely noticed as isolated "clicks" transmitted by the on-board instruments, and then more frequently. It was immediately calculated that their weight was around one hundred millionth of a gram: not very serious yet for Giotto, but what would happen when the probe would move alongside the nucleus? Just when everyone feared the worst (especially for the television camera mirror on which a small crater was made with each impact that would compromise the quality of the image), the number of particles began to decrease up to about 70 000 kilometers from the nucleus: Giotto had been lucky to encounter the comet during a relatively "calm" moment, without those violent explosions of gas and dust that had damaged the other probes prematurely. All the instruments continued to operate perfectly and the nucleus got closer and closer. 10 000, 6 000 and 4 000 kilometers: the fateful moment almost arrived and by now the Esa scientists knew that Giotto would reach the objective, passing within 605 kilometers from the nucleus. But the television camera didn't make it to that point: at a distance of about 1 500 kilometers, the frequency of the impacts reduced the mirror to a "strainer", but the pictures that it had been able to transmit to that point went far beyond the wildest expectations. According to scientists, it will take years to study all the pictures (2 000, of which 69 of the nucleus) and to compare them with the enormous quantity of data transmitted by the other instruments of the "comet fleet". However, it can already be stated that such data will make it possible to write a new chapter in the history of the solar system.
The probe is "turned on" (meaning that its instruments were activated) when it was 1 000 000 kilometers from the comet. Everything was working to perfection, there were no dust particles, and soon the Earth began to receive the first pictures that were computer color-enhanced to highlight even minimum luminosity variations. First the comet appeared as a weak luminous halo and then, slowly, as Giotto got closer, it completely filled the monitors: the interior of a large irregular spot glowed with shaded coloured bands towards a more brilliant "heart". It seemed to be the nucleus, but it wasn't: the large colored spot was the gas jet and particles emitted by Halley which, because of its brilliance, obscures everything else; and it is also the most dangerous enemy for Giotto because it will certainly attack the probe when it passes close by. Instead, the nucleus is a dark spot, almost invisible, that can be seen just between the margins of the jet: only subsequent processing, which electronically "screens out" the luminous jet, will make it possible to see it with even unexpected precision. The probe continued to approach, sending pictures every four seconds (the time that the probe takes to revolve around itself), but in the meantime, at 250 000 kilometers from the nucleus, the particles began to strike the probe; first just barely noticed as isolated "clicks" transmitted by the on-board instruments, and then more frequently. It was immediately calculated that their weight was around one hundred millionth of a gram: not very serious yet for Giotto, but what would happen when the probe would move alongside the nucleus? Just when everyone feared the worst (especially for the television camera mirror on which a small crater was made with each impact that would compromise the quality of the image), the number of particles began to decrease up to about 70 000 kilometers from the nucleus: Giotto had been lucky to encounter the comet during a relatively "calm" moment, without those violent explosions of gas and dust that had damaged the other probes prematurely. All the instruments continued to operate perfectly and the nucleus got closer and closer. 10 000, 6 000 and 4 000 kilometers: the fateful moment almost arrived and by now the Esa scientists knew that Giotto would reach the objective, passing within 605 kilometers from the nucleus. But the television camera didn't make it to that point: at a distance of about 1 500 kilometers, the frequency of the impacts reduced the mirror to a "strainer", but the pictures that it had been able to transmit to that point went far beyond the wildest expectations. According to scientists, it will take years to study all the pictures (2 000, of which 69 of the nucleus) and to compare them with the enormous quantity of data transmitted by the other instruments of the "comet fleet". However, it can already be stated that such data will make it possible to write a new chapter in the history of the solar system.
