|THE LAST OF THE GIANTS|

To arrive at an appointment with only a one-second delay would seem to be rather difficult for anyone. But this amazing feat was accomplished by a 900-kilogram probe, not much larger than a compact car, after having traveled more than 7 billion kilometers in twelve years. This is exactly what happened on the night between August 24 and 25, 1989. In the control center of the Nasa Jet Propulsion Laboratory in Pasadena, California, hundreds of scientists had been sitting in front of their monitors for days nervously waiting for the last great event of the longest and most successful planetary mission in the history of astronomy: a fly-by by Voyager 2 just 4 950 kilometers from the south pole of Neptune, the last of the giant planets in our solar system. As pointed out by Edward Stone, the mission project leader, "This is the same as hitting a golf ball from New York and putting it in the hole in San Francisco, on the other side of the United States". Thirty-eight large radio-telescopes around the Earth were linked with the Pasadena control center and took turns pointing their antennas towards a unique, invisible point in the sky: Voyager's position. It was crossing a region of space 4 and a half billion kilometers away from our planet. Over there, in what is considered to be "solar Siberia", the Sun is nothing but a point that is barely brighter than the other stars. This is where Neptune, the eighth planet, is located. Its discovery was even more interesting than that of its closet "twin", Uranus. The first person to imagine that there might be another planet beyond Uranus was an English astronomy student, named John Couch Adams, in 1843. He had noted that Uranus followed a rather strange orbit around the Sun. In his opinion, these strange phenomena could only be justified by assuming that there was another planet, even farther away, that disturbed Uranus' orbit through gravitational attraction. Thus, he made the necessary calculations, on paper, of the dimension, distance and position of this hypothetical celestial body, which he himself could not search for directly in the sky because he could not use a large telescope. Then he asked for help from other astronomers, but no one took him seriously, and also because a very long and tedious search would be required. In the meantime, another young and very brilliant French astronomer, Urbain Le Verrier, made a series of calculations which led him to the same conclusions reached by Adams: he sent them to the Berlin observatory and had the good fortune of having his suspicions confirmed. The same evening he received the confirmation, the astronomer Johann Gottfried Galle compared them with an accurate star map kept at the observatory and, pointing the telescope towards the sky, was able to identify Neptune almost exactly where the calculations had indicated it should have been. It was the first time that a planet had been discovered thanks to mathematics: and Adams and Le Verrier deserve all the credit. Prior to Voyager's arrival, it was known that Neptune was a gaseous sphere whose volume is 57 times that of the Earth and takes 165 Earth years to complete an orbit around the Sun (in fact, when it was discovered, it had not yet completed an entire revolution). Since it is difficult to identify points of reference on the surface because of the great distance involved, astronomers could not determine its speed of rotation even if, by analogy with the other outer planets, they assumed that it was around 18 hours. In reality, Voyager would show that the rotation is exactly 16 hours and 3 minutes. The history behind the discovery of Neptune's two satellites, Nereide and Triton, is also quite interesting. Nereide, discovered only in 1919 by the Anglo-American astronomer Gerard Kuiper during a systematic search for the unknown moons of the outer planets, is very far away and rather small, with a diameter of just 300 kilometers. Its most unusual feature is that it has the most elliptical orbit of any other satellite in the solar system: at the closest point in its orbit, Nereide is slightly less than 1 500 000 kilometers away from the planet, while it is almost ten million away at the farthest point. On the other hand, Triton, which was identified in 1846, is much larger and orbits very close to the planet.
To arrive at an appointment with only a one-second delay would seem to be rather difficult for anyone. But this amazing feat was accomplished by a 900-kilogram probe, not much larger than a compact car, after having traveled more than 7 billion kilometers in twelve years. This is exactly what happened on the night between August 24 and 25, 1989. In the control center of the Nasa Jet Propulsion Laboratory in Pasadena, California, hundreds of scientists had been sitting in front of their monitors for days nervously waiting for the last great event of the longest and most successful planetary mission in the history of astronomy: a fly-by by Voyager 2 just 4 950 kilometers from the south pole of Neptune, the last of the giant planets in our solar system. As pointed out by Edward Stone, the mission project leader, "This is the same as hitting a golf ball from New York and putting it in the hole in San Francisco, on the other side of the United States". Thirty-eight large radio-telescopes around the Earth were linked with the Pasadena control center and took turns pointing their antennas towards a unique, invisible point in the sky: Voyager's position. It was crossing a region of space 4 and a half billion kilometers away from our planet. Over there, in what is considered to be "solar Siberia", the Sun is nothing but a point that is barely brighter than the other stars. This is where Neptune, the eighth planet, is located. Its discovery was even more interesting than that of its closet "twin", Uranus. The first person to imagine that there might be another planet beyond Uranus was an English astronomy student, named John Couch Adams, in 1843. He had noted that Uranus followed a rather strange orbit around the Sun. In his opinion, these strange phenomena could only be justified by assuming that there was another planet, even farther away, that disturbed Uranus' orbit through gravitational attraction. Thus, he made the necessary calculations, on paper, of the dimension, distance and position of this hypothetical celestial body, which he himself could not search for directly in the sky because he could not use a large telescope. Then he asked for help from other astronomers, but no one took him seriously, and also because a very long and tedious search would be required. In the meantime, another young and very brilliant French astronomer, Urbain Le Verrier, made a series of calculations which led him to the same conclusions reached by Adams: he sent them to the Berlin observatory and had the good fortune of having his suspicions confirmed. The same evening he received the confirmation, the astronomer Johann Gottfried Galle compared them with an accurate star map kept at the observatory and, pointing the telescope towards the sky, was able to identify Neptune almost exactly where the calculations had indicated it should have been. It was the first time that a planet had been discovered thanks to mathematics: and Adams and Le Verrier deserve all the credit. Prior to Voyager's arrival, it was known that Neptune was a gaseous sphere whose volume is 57 times that of the Earth and takes 165 Earth years to complete an orbit around the Sun (in fact, when it was discovered, it had not yet completed an entire revolution). Since it is difficult to identify points of reference on the surface because of the great distance involved, astronomers could not determine its speed of rotation even if, by analogy with the other outer planets, they assumed that it was around 18 hours. In reality, Voyager would show that the rotation is exactly 16 hours and 3 minutes. The history behind the discovery of Neptune's two satellites, Nereide and Triton, is also quite interesting. Nereide, discovered only in 1919 by the Anglo-American astronomer Gerard Kuiper during a systematic search for the unknown moons of the outer planets, is very far away and rather small, with a diameter of just 300 kilometers. Its most unusual feature is that it has the most elliptical orbit of any other satellite in the solar system: at the closest point in its orbit, Nereide is slightly less than 1 500 000 kilometers away from the planet, while it is almost ten million away at the farthest point. On the other hand, Triton, which was identified in 1846, is much larger and orbits very close to the planet.