After 26 years speeding through the void at 16km a second, the spacecraft Voyager 1 has boldly gone where no spacecraft has gone before — to the edge of the solar system.
Nasa scientists report today that the craft has buffeted into a region known as the termination shock, where the sun’s wind slams into the radiation from distant stars.
Voyager 1 and its sistership Voyager 2 are the stuff of stardom and stardoom. They are both headed for the far-off stars and both carry messages from Earth — and even a gold-plated disc carrying the calls of whales and the sound of rock’n’roll — to any extraterrestrial civilisations they might meet.
But both will fall silent long before they reach the nearest stars. They were launched in 1977, with missions to explore Jupiter and Saturn, and then fly by Uranus and Neptune and finally head out of the solar system. In February, 1998, Voyager 1, travelling at 56 000 kph, overtook the first great solar system explorer, Pioneer, to become the most far-reaching man-made thing.
Now, according to a team of scientists whose report features today in the journal Nature, Voyager 1 has passed another milestone. Far beyond the orbit of Pluto, the one-ton spacecraft has begun to explore the last outposts of the ”kingdom of the sun”.
This is where the solar magnetic field begins to fade into insignificance, where the blasts of solar wind –electrified particles blown off the sun’s outer envelope — have slowed down from a million miles an hour to less than the speed of sound. Some time in the next few years, Voyager 1 will be the first to pass another invisible boundary called the heliopause, where the sun’s influence wanes, and true interstellar space begins.
Stamatios Krimigis, of the Johns Hopkins University in Baltimore, reports in Nature that on August 1 last year an instrument on Voyager 1 registered evidence of a strange frontier crossing as it entered a region where solar wind-speeds dropped abruptly. Then, 200 days later, it met a fresh blast of the solar wind travelling at supersonic speed — as if the empire of the sun had jagged boundaries, or as if from time to time it invaded and then abandoned the territory on its fringe.
Dr Krimigis and his colleagues interpret this as a landmark in Voyager 1’s pilgrimage to the distant stars.
A second team, led by Frank McDonald, of the University of Maryland, says in the journal that Voyager 1 may be close to the termination shock zone of the solar system, though it has not got there yet.
Either way, Voyager 1 and its sister ship, now moving out of the solar system in a different plane, have broken all records. The double mission cost about $865-million and 11 000 work-years just to get as far as Neptune. The two spacecraft have sent back enough data to fill 6 000 complete sets of Encyclopaedia Britannica, with onboard computers far less powerful than the chip in a modern microwave oven, and an electronic signal which, when it reaches us, is now about 20-billion times weaker than a digital wristwatch.
Between them the spacecraft were the first to relay at close hand the marvels of the solar system — the giant volcano on Jupiter’s moon Io, ejecting sulphur 30 times the height of Mt Everest, the dazzling 10 000-strand necklace of icicles that make up Saturn’s rings, and the dark mysteries of Uranus.
After the spacecraft pass the heliopause, they will enter the region known as the Oort cloud, a nursery of comets. It could take them 20 000 years or more to get through this region but both will have fallen silent by 2020.
In about 40 000 years, Voyager 1 will be going towards a star in the constellation Camelopardalis. In 296 000 years Voyager 2 will pass within four light-years of Sirius. And both may be destined to wander the galaxy forever. – Guardian Unlimited Â