NASA’s FOXSI Mission Will View The Sun With X-Ray Vision

X-ray light reveals processes that heat plasma to millions of degrees Fahrenheit


Without special instrumentation, the Sun looks calm and inert. But beneath that placid façade are countless miniature explosions called nanoflares.

These small but intense eruptions are born when magnetic field lines in the Sun’s atmosphere tangle up and stretch until they break like a rubber band.

The energy they release accelerates particles to near lightspeed and according to some scientists, heats the solar atmosphere to its searing million-degree Fahrenheit temperature.

All of this happens in colors of light so extreme that the human eye can’t see them. Nanoflares aren’t visible — at least not to the naked eye.

Finding the traces of nanoflares requires X-ray vision, and scientists have been hard at work developing the best tools for the job.

The latest advance in this project is represented by NASA’s Focusing Optics X-ray Solar Imager, or FOXSI mission, soon to take its third flight from the White Sands Missile Range in White Sands, New Mexico, no earlier than Sept. 7.

FOXSI is a sounding rocket mission. Derived from the nautical term “to sound,” meaning to measure, sounding rockets make brief 15-minute journeys above Earth’s atmosphere for a peek at space before falling back to the ground.

Smaller, cheaper and faster to develop than large-scale satellite missions, sounding rockets offer a way for scientists to test their latest ideas and instruments — and achieve rapid results.

The Solar Dynamics Observatory (SDO), using 10 filters, sees connections in the solar atmosphere. This visualization experiment illustrates a mechanism for highlighting these connections.

FOXSI will travel 190 miles up, above the shield of Earth’s atmosphere, to stare directly at the Sun and search for nanoflares using its X-ray vision.

“FOXSI is the first instrument built specially to image high-energy X-rays from the Sun by directly focusing them,” said Lindsay Glesener, space physicist at the University of Minnesota in Minneapolis and principal investigator for the mission.

“Other instruments have done this for other astronomical objects, but FOXSI is so far the only instrument to optimize especially for the Sun.”

The Sun tells its story in layers of light, each of which reveals what’s happening at different temperatures. For example, the sunlight that our eyes can see is primarily from the Sun’s photosphere, which is approximately 10,000 degrees Fahrenheit.

But there’s much more going on outside the bounds of human vision. X-ray light, in particular, reveals processes that heat plasma to millions of degrees Fahrenheit, like the most violent explosions at the cores of nanoflares.

But high-quality views of X-rays from the Sun don’t come easy. Unlike visible light, X-rays are hard to focus; they are largely unaffected by the lenses and mirrors used in conventional telescopes. Previous X-ray missions had to make do without focused light.

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