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Nasa to reveal details of hotly anticipated mission to the sun

The Guardian logo The Guardian 31/05/2017 Nicola Davis
Nasa is set to make an announcement today about its hotly anticipated mission to send a spacecraft into the sun's outer atmosphere. © Getty Images Nasa is set to make an announcement today about its hotly anticipated mission to send a spacecraft into the sun's outer atmosphere.

Nasa is set to make an announcement today about its hotly anticipated mission to send a spacecraft, the Solar Probe Plus, into the sun’s outer atmosphere.

The size of a car, shaped like the business end of a torch, and built to withstand temperatures of more than 1400C (2552F), the probe is set to be launched next summer in an unprecedented attempted to get up close to our star, coming within 4m miles of its surface.

“It is just extraordinary - it is something that people have wanted to do from the beginning of the space age,” said Tim Horbury, professor of physics at Imperial College London.

Scientist say the mission, costing in the region of $1.5bn, could radically change our understanding of the sun, while offering vital insights into space weather - phenomena including coronal mass ejections that trigger geomagnetic storms that not only damage satellite systems but can knock out power grids on Earth.

“It is just a hugely important and scientifically fascinating mission,” said David McComas, vice president of the Princeton University plasma physics laboratory and principal investigator for the probe’s “Integrated Science Investigation of the sun”, research that will probe how electrons, protons and other charged particles are accelerated in the sun’s atmosphere.

An artist’s impression of the Solar Probe Plus spacecraft approaching the sun. Photograph: Johns Hopkins University Applied/PA

“It is far closer than anything ever built by humanity has ever gotten to the sun,” McComas said.

Instruments for a suite scientific investigations on board the spacecraft will probe myriad solar phenomena from the electric and magnetic properties of the sun’s plasma to counting and catching the components of solar wind - a stream of charged particles, or plasma, that flows from the sun out into space.

“The sun is obviously very hot - its outer atmosphere is at hundreds of thousands of degrees Kelvin, and as a result it blows a bubble into interstellar space,” said Horbury. “We live in that bubble, we live in the heliosphere, and it is the solar wind that blows that bubble.”

The goal of the Solar Probe Plus is to understand how the sun makes the solar wind, and explore the physical process that are occurring. A member of the science team for the probe’s Fields instrument, Horbury plans to study turbulence within the solar wind.

“When we first started [looking at the sun from space] that we realised the sun is not a boring yellow sphere, it is an incredibly dynamic, active plasma object,” he said.

But the challenges have been immense, Horbury adds, describing the mission as “just on the edge of achievable”. The major difficulty was designing the probe to prevent it being toasted by the sun’s immense heat - as part of the solution the probe boasts a large heat-shield that is actively cooled by radiator systems.

“There is a tiny spacecraft cowering behind this big heat shield,” Horbury said. “It is just extreme - everything is different when you are that close in [to the sun].”

The Solar Probe Plus will travel far closer to the sun that any previous probe. While 4m miles might sound like a sizeable distance from the sun, it corresponds to under 10 solar radii. “[The Earth is] about 250-odd solar radii away, so it is really close,” said Horbury.

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The distance is crucial. Solar wind accelerates away from the sun, but at about 10 solar radii something remarkable happens. “[The solar wind] accelerates away until eventually goes effectively supersonic and at that point it is disconnected from the sun – the sun can never get it back,” said Hornbury. “That happens at about 10 solar radii. The point about the probe is it is going to get within that critical point.”

McComas’s part of the mission will explore in detail how certain particles in the solar atmosphere end up with very high energies. “They are really interesting and important particles because for example they can cause radiation damage in space to spacecraft, they can be a threat to astronauts in space,” he said.

The mission is not only expected to offer unprecedented insights into the physics of the sun - an endeavour that will shed light on processes happening in stars across the universe - but will also yield vital information about space weather, that could help scientists to predict major events before they affect Earth.

The stakes for the mission are high, admits Horbury.

“The thing about space is everyone has done the easy stuff- we are only left with the difficult things so by definition this is risky,” he said. “They are really pushing the limits of what is possible. But that is the way you make progress.”

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