NASA-funded rocket to see Sun with X-ray vision

Without special instrumentation, the sun seems calm and inert. But beneath this placid facade are innumerable miniature explosions called nanoforms.

These small, but intense, eruptions are born when magnetic field lines in the Sun 's atmosphere tangled and stretched until they broke like a band of rubber. The energy they release accelerates the particles at a speed close to that of light and, according to some scientists, warms the solar atmosphere up to a temperature of millions of degrees Fahrenheit.

All of this happens in such extreme light colors that the human eye can not see them. The nanoforms are not visible, at least not to the naked eye.

The search for nanoform traces requires X-ray vision and scientists have worked hard to develop the best tools for this work. The latest breakthrough in this project is represented by NASA's Focusing Optics X-ray Imager, or the FOXSI mission, which is expected to soon make its third flight from the White Sands Missile Range to White Sands, New Mexico, at the earliest on September 7th.

FOXSI is a sound rocket mission. Derived from the nautical term "sounding", which means measuring, sounding rockets make brief trips of 15 minutes over the Earth's atmosphere to take a look into the space before to fall back to the ground. Smaller, cheaper and faster to develop than large-scale satellite missions, sounding rockets allow scientists to test their latest ideas and instruments and obtain fast results.

FOXSI will travel 190 miles above the Earth's atmosphere shield to look directly at the Sun and search for nanoforms with X-ray vision.

"FOXSI is the first instrument specifically designed to image high-energy X-rays by focusing them directly," said Lindsay Glesener, a physicist at the University of Minnesota in Minneapolis and principal investigator for the mission. "Other instruments have made it for other astronomical objects, but FOXSI is up to now the only instrument to optimize specifically for the sun."

The Sun tells its story in layers of light, each revealing what is happening at different temperatures. For example, the sunlight that our eyes can see comes mainly from the photosphere of the sun, which is about 10,000 degrees Fahrenheit. But much more is happening outside the limits of human vision. X-ray light, in particular, reveals processes that heat the plasma to millions of degrees Fahrenheit, such as the most violent explosions on the nanoform cores.

But the high-quality views of the sun's X-rays are not easy. Unlike visible light, X-rays are difficult to focus. they are largely unaffected by the lenses and mirrors used in conventional telescopes. Previous X-ray missions had to do without concentrated light.

"In the past, we typically used carefully selected masks to block some of the incoming X-rays," said Säm Krucker, a space physicist at the University of California at Berkeley and principal investigator of the two previous FOXSI flights. "This does not result in very high quality images, but it has nevertheless provided us with crucial information about the most energetic part of solar flares."

To focus X-rays, the FOXSI team used extremely hard and smooth surfaces angled at a small angle (less than half a degree) that gently correct incoming X-ray light toward a focus point.

"With these telescopes, we can now make targeted X-ray images of our Sun," said Krucker. "These images have a much improved image quality with much higher sensitivity."

This will be FOXSI's third flight – its first in 2012, during which it successfully watched a small solar flare underway, and the second in 2014, when it detected the best evidence at the time of the X-ray emission by nanoforms. The third mission follows this discovery, but this time it also includes a new telescope designed for low-power, flexible X-ray imaging.

"The inclusion of the flexible X-ray telescope gives us more accurate temperatures," said Glesener, allowing the team to spot the nanoflare signatures that would be missed with hard X-ray telescopes alone. In addition, several other performance improvements have been made to produce more accurate and higher resolution images.

The third flight of FOXSI will also be the first run by Glesener, who was a graduate student, then the project manager, for the two previous flights led by Krucker.

"This type of training and legacy projects is common in sound probe programs," Glesener said. "They are designed to grow and evolve scientific leaders and hardware!"