A spaceprobe called Ulysses made the polar pass at about midday as it continued to collect data on the solar wind, a stream of high-energy sub-atomic particles travelling at about 400 kilometres a second.
After years of delay, Ulysses was launched in 1990 from a space shuttle with the help of a battery of rockets that propelled it faster than any other spacecraft towards Jupiter.
In order to break out of the Earth's orbit around the Sun's equator, Ulysses had to use Jupiter's gravity to sling it into a right-angled turn that took it into trajectory over both poles of the Sun.
Ulysses is taking measurements of the solar winds coming from the polar regions in order to assess the impact that the Sun's activity is having on the magnetic field of Earth. It is due to pass over the Sun's north pole between June and September next year.
Scientists from the European Space Agency hope that the spaceprobe can help them to predict magnetic storms on Earth, which can disrupt electrical transmissions, television reception and cause power black- outs.
Little is known of the physical activity at the Sun's poles. A mission to collect data from the polar regions of the Sun is considered crucial to building a three-dimensional image of the solar wind.
Richard Marsden, the Ulysses project scientist at the agency, said: 'In the broadest sense studying the Sun will give us a better clue of how long-term solar changes will have an impact here on Earth.'
One of the more exotic goals for the probe is to search for the mysterious 'gravitational waves' predicted by Albert Einstein's general theory of relativity. According to the agency, such waves, which travel at the speed of light, are 'ripples in the curvature of space-time'. Ulysses provides the first real opportunity for scientists to detect them.
The agency says the results of the polar mission of Ulysses should be ready for analysis by the end of the week. Only then will the spaceprobe have fulfilled the mission of the Ulysses in Greek mythology, as outlined in Dante's Inferno: 'To venture the uncharted distances . . . of the uninhabited world behind the Sun.'
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