快猫短视频

Double Star, a joint Chinese-European space mission to study the Earth鈥檚 magnetic environment, is up and running.

鈥淚t鈥檚 doing great,鈥� says Philippe Escoubet, the mission鈥檚 project scientist at the European Space Agency. 快猫短视频s have begun analysing its first data and already it has made the longest-ever measurement of the turbulent region where the solar wind first encounters the Earth鈥檚 magnetic field.

The first of the mission鈥檚 twin satellites, TC-1, was launched from China in December 2003 and will be joined by its partner in July. Double Star will operate for 18 months alongside a four-satellite mission launched in 2000, called Cluster.

TC-1 takes 27 hours to orbit Earth and has a highly elliptical orbit. Its closest approach to Earth comes within 570 kilometres 鈥� just one tenth of the Earth鈥檚 radius 鈥� while at its furthest it is about 13 Earth radii away.

At that distance, the satellite moves relatively slowly as it begins to swing back round towards the Earth. This means it spends about 10 minutes 鈥� about twice as long as previous satellites 鈥� taking measurements from within a one-kilometre-wide 鈥渂ow shock鈥� zone.

This zone is the U-shaped boundary where the solar wind鈥檚 charged particles first hit the Earth鈥檚 magnetic field and are deflected around it, rather like water streaming around a pebble.

Bounce back

The bow shock shifts its position in response to changes in the Sun鈥檚 activity. As it fluctuated around TC-1, the spacecraft observed ions from the solar wind being bounced off the bow shock and back towards the Sun.

鈥淭his has been seen before, but because the Double Star spacecraft stays there for a long time, we see the way these ions are organised very well,鈥� Escoubet told 快猫短视频.

Double Star is intended to provide a long-range complement to ESA鈥檚 Cluster mission. Cluster studies Earth鈥檚 magnetosphere on relatively small scales with the four satellites spaced 250 kilometres apart. But Double Star will take measurements up to 40,000 km away from Cluster.

Already scientists are comparing the two missions鈥� measurements of the effects of a large eruption of gas from the Sun鈥檚 corona, called a coronal mass ejection, that occurred in January. Such events have in the past affected the operation of satellites and even knocked out power grids on Earth.

Direct influence

Escoubet also hopes both missions working in unison will be able to map the magnetopause, the boundary between the solar wind and region under the direct influence of the Earth鈥檚 magnetic field. This lies inside the bow shock.

Most of TC-1鈥檚 eight scientific instruments are working better than expected, but the mission鈥檚 two magnetometers need extra calibration. That is because the spacecraft鈥檚 own magnetic field turned out to be larger than predicted, so mission scientists are working on software that subtracts this effect.

The craft鈥檚 magnetic field decreases with distance and because the two magnetometers lie at different points long a three-metre boom, they will measure slightly different fields. This discrepancy will allow scientists to compute the effect of the craft鈥檚 own magnetic field, allowing them to subtract it.