麻豆淫院

As far as endings go, this one鈥檚 a real heart breaker. NASA鈥檚 Polar satellite concludes its successful mission at the end of April with a breathtaking visible-light image of the colorful dancing lights of the aurora. The Polar team has dubbed this final image "The Broken Heart."

When the Polar satellite launched February 24, 1996, the plan was for a two-year science mission to study the lights that form a ring around Earth鈥檚 north and south magnetic poles, known as the Northern and Southern Lights, or auroras. Polar has exceeded expectations by a decade.

鈥淲e鈥檝e gone well beyond our original plan and into our dreams,鈥� says John Sigwarth of NASA鈥檚 Goddard Space Flight Center in Greenbelt, Md., of Polar鈥檚 amazing 12-year run.

Polar orbits from Earth鈥檚 North Pole to its South Pole to study how solar wind particles and their energy enter Earth鈥檚 magnetosphere, the area surrounding Earth dominated by its magnetic field. Polar also revealed how those particles and their energy end up in Earth鈥檚 atmosphere, and how the radiation belts form and dissipate.

The satellite completes an orbit every 17陆 hours, passing over one pole at a maximum altitude of about 32,000 miles and diving past Earth鈥檚 equator to the opposite pole at a minimum distance of only about 3,200 miles. As Polar flies over the north and south poles, three of the satellite鈥檚 12 instruments capture images of auroras in ultraviolet, X-ray, and visible light. The other nine instruments take measurements of charged particles and Earth鈥檚 electric and magnetic fields throughout its journey around Earth.

鈥淧olar ran out of fuel during its final maneuver in February,鈥� says Sigwarth, project scientist for the Polar spacecraft. 鈥淏ut even after the fuel was exhausted, we continued to maneuver on the cold helium gas that was left in the tank,鈥� he explains.

Sigwarth likens the satellite鈥檚 post-fuel feat to 鈥渦sing the force of your breath as you breathe out to propel yourself backwards鈥� if you happen to be traveling through space like a satellite. But now Polar has run out of breath.

The plan is to turn off the satellite April 28 slightly ahead of a likely fatal encounter with the sun. From its current orientation, Polar will drift slowly, allowing the energy from our nearest star to quickly overwhelm the satellite. If Polar were left on, first to go would be its radiators, batteries, and transmitters. These would overheat and probably fail. The satellite鈥檚 planned turn off at the end of April will allow controllers to send the final commands before Polar meets its fate.

During its lifetime, Polar has had many accomplishments. Observations of energetic neutral atoms have provided the first-ever global images of substorm injections that are the sequence of events that lead to energetic auroral displays. These neutral atom images clearly show the broad extent in space of these energetic atoms and their instantaneous nature in time.

Polar observations have also revealed that solar storms deposit so much energy into Earth鈥檚 ionosphere that it expands to fill the magnetosphere all the way out to its boundaries, yielded the first-ever global X-ray images of auroras, and shown how dynamic pressure pulses, or 鈥済usts鈥� in the solar wind, influence the magnetosphere, ionosphere, and auroral ovals, rings around Earth鈥檚 magnetic poles where auroras are seen.

Source: by Laura Layton, NASA's Goddard Space Flight Center