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Magnetic "ropes" tying the Earth to the sun have been discovered by Nasa scientists exploring the mysterious energy that powers the spectacular displays of Northern Lights that illuminate the night sky over the Arctic region.
The giant ropes are made from twisted magnetic fields that act as invisible superhighways for solar particles to travel from the sun to the outer atmosphere, where they trigger immense displays of light for up to several hours at a time.
The discovery was made with the help of a fleet of Nasa satellites launched this year that have been monitoring the Northern Lights, or the aurora borealis, from space at the same time as scientists on the ground take measurements from underneath the atmosphere.
David Sibeck, a Nasa project scientist from the Goddard Space Flight Centre in Maryland, said the Themis satellites might have answered the question of where all the energy comes from that powers the Northern Lights.
The magnetic fields are organised much like the twisted hemp of a mariner's rope.
Although spacecraft have detected these invisible ropes before, it was the five micro satellites of Themis that allowed scientists to visualise their three-dimensional structure.
"Themis encountered its first magnetic rope on May 20. It was very large, about as wide as the Earth, and located approximately 40,000 miles above Earth's surface in a region called the magnetopause," Dr Sibeck said.
The magnetopause is where the solar wind from the Sun meets the magnetic field of the Earth.
At this point they push against each other like two cosmic Sumo wrestlers locked in combat, Dr Sibeck explained.
It was here that the rope was seen to form and then unravel in the space of just a few minutes, providing a brief but significant conduit for the solar wind to conduct energy from the Sun to the Earth.
Analysis of the nature of the aurora borealis began last March when a spectacular eruption of the Northern Lights, called a substorm, occurred over Alaska and Canada.
As the satellites monitored it from space, cameras on the ground photographed its development, said Vassilis Angelopoulos of the University of California at Los Angeles, the mission's principal investigator.
"The substorm behaved quite unexpectedly. The auroras surged westward twice as fast as anyone thought possible, crossing 15 degrees of longitude in less than a minute, " Professor Angelopoulos said.
Calculations suggest the total energy of the two-hour event amounted to the equivalent of that released during an earthquake of magnitude 5.5 on the Richter scale.
- Independent
