Inouye’s moment of truth

America’s new Daniel K Inouye Solar Telescope has produced the most detailed solar images ever taken, showing structures as small as 30 kilometres. 

To put that in perspective, says its director, Thomas Rimmele, the best prior images had resolutions of only 160 kilometres. The new ones are “a factor of five better”. 

What they show are zones of churning plasma, each about the size of Texas. But within them are a plethora of smaller features, now revealed in intricate detail. 

Eventually, scientists hope, these will increase our understanding of how heat rises from the Sun’s interior to its surface.

But that’s only part of what they hope the $US16 million solar telescope will eventually see. 

One of the biggest questions about the Sun is why its corona is heated to millions of degrees, while its surface is only about 6000 degrees. 

“This is counterintuitive,” Rimmele says. “As you move your hand away from a hot plate, you expect it to get cooler. But the Sun does the exact opposite.”

The answer probably lies in energy originating from the Sun’s powerful magnetic field, something the Inouye will be able to study in great detail once it is fully online, probably in June. 

The telescope, which uses a four-metre primary mirror and an adaptive optics system that adjusts the image 2000 times a second to compensate for distortions from the Earth’s atmosphere, sits atop Hawaii’s 3100-metre Haleakala Volcano, on the island of Maui. 

The image, Rimmele says, represents the project’s “first engineering light” – meaning it’s the first test-run, not quite the same as the more carefully calibrated scientific images that will eventually follow. 

“First light is the moment of truth,” Rimmele says, adding that as the first images appeared, the atmosphere in the observatory “was similar to a rocket launch”.

One of the problems in designing such a large space telescope, he adds, was dealing with the amount of heat it produced. 

“Imagine a four-metre magnifying glass,” he says. Then imagine using that magnifying glass to focus light from the Sun. If the result sounds like a solar furnace, you wouldn’t be far off. At the focus, Rimmele says, the temperature is hot enough to melt metal. 

“To deal with these problems we make the equivalent of a swimming pool of ice every night to provide cooling,” he says. “[We also] have 7.5 miles [12 kilometres] of piping to distribute the coolant. The fact this complex machine delivered images of such quality right out of the box is amazing. 

Meanwhile, the goal is to connect results from Inouye with those from space missions, such as NASA’s Parker Solar Probe or the joint NASA/ESA Solar Orbiter, in order to study the Sun from two different perspectives, with an eye to determining how it produces flares and “space weather”. 

These are potentially dangerous on Earth, where they can knock out power grids, interfere with GPS, upset communications, or otherwise disrupt modern technology.

For example, says Valentin Pillet, of the US National Science Foundation, the day Hurricane Irma made landfall in the Virgin Islands in 2017, communications between first responders and their central command were interrupted for eight hours by a space-weather event — in this case, a flare. 

“So there we have an event on Earth, and an event on the Sun, which combined to make a clear threat.”

Image details: The picture above was taken at 789 nanometres (nm) and shows a pattern of turbulent “boiling” gas that covers the entire Sun. The cell-like structures are the signature of violent motions that transport heat from inside the Sun to its surface.

Hot solar material (plasma) rises in the bright centres of cells, cools off, then sinks below the surface in dark lanes in a process known as convection. In these dark lanes can also be seen the tiny, bright markers of magnetic fields. These are thought to channel energy up into the outer layers of the solar atmosphere called the corona.

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