Experiment to Challenge Sun’s Inferno

Unlike other instruments being built for NASA’s Solar Probe Plus, the Solar Wind Electrons, Alphas and Protons (SWEAP) experiment won’t sit comfortably behind the thick solar shield that is designed to protect the probe. Instead, SWEAP will be in front of the shield collecting data about protons, electrons and helium ions streaming away from the sun in the “pristine” solar wind.

“We wanted to put something way out in front of the shield to sample the solar wind, although that is not a very friendly environment,” said Dr. Gary Zank, one of the instrument’s creators and director of the Center for Space Plasma and Aeronomic Research (CSPAR) at UAHuntsville.

SWEAP, says Zank, is in large part one result of the unique environment at the National Space Science and Technology Center, where CSPAR sits adjacent with NASA’s Space Sciences Laboratory. That made it easy for Zank and NASA astrophysicist Jonathan Cirtain to brainstorm the idea of putting an experiment in front of Solar Probe Plus (SPP).

“Jonathan’s just down the corridor,” said Zank. “We’re talking constantly and this dovetails extremely well. They have the materials that can survive in that environment and we know the physics of this area around the sun, so we provided the theoretical expertise. We have people on campus who can work with this material, which is some kind of a ceramic, so we were able to go into a lab here to do plasma etching on the prototype.”

SWEAP will be one of five instruments on SPP, which is scheduled for launch in 2018. The size of an automobile, SPP’s exotic orbit will take it within 3.5 million miles of the sun. That is inside the orbit of Mercury and twice as close to the sun as the next nearest previous solar probe. It will approach the sun 35 times during its eight-year mission to study the sun, solar wind and space weather.

Looking like a cup no more than nine inches across, SWEAP will collect data from particles in the solar wind. Scientists hope that data will help them solve the mystery of the sun's super heated atmosphere.

“If you plot the temperature of the sun, it is really hot in the core, more than 6 million degrees Kelvin,” Zank said. “As you go out toward the surface the temperature drops in an expected way until you get to the surface, where the temperature is about 6,000 degrees K. (That is more than 10,000 degrees Fahrenheit. -ed).

“As you go up away from the sun that temperature drops until you get about 500 kilometers up and then the temperature starts to climb. At about 20,000 kilometers high something really odd happens. Over a scale of only 100 and 200 kilometers, suddenly the temperature increases from 20,000 K to more than 1 million degrees Kelvin.

“Why does it do that?” Zank asked. “Nobody knows. That’s the mystery.”

Temperatures in the sun’s corona can exceed 10 million K. That extreme heat is responsible for the solar wind. (“It’s like boiling a huge pot of water and driving out a steam that is the solar wind.”) The solar wind creates the heliosphere, a bubble in interstellar space that engulfs the solar system.

There are several competing theories about why particles in the sun’s atmosphere heat so rapidly and so hot, including one Zank was involved in developing. That theory says magnetic fields in the sun generate turbulence that dumps energy into the transition area and corona. Other theories point to small flares on the sun, x-ray flares and high-frequency waves.

“The probe will be spending a lot of time in the corona, so we’re going to be seeing all of this at its genesis,” Zank said. “We expect this will allow us to determine whether any of these proposed mechanisms is a viable explanation for what is going on there or whether we need to come up with new theories.”

Dr. Justin Kaspar at the Harvard-Smithsonian Center for Astrophysics is the principal investigator for the SWEAP instrument. Team members include: UAHuntsville, NASA's Marshall Space Flight Center, the Smithsonian Astrophysical Observatory, University of California-Berkeley, MIT and Los Alamos.

Dr. Gary Zank
256.961.7403
zank@cspar.uah.edu
OR
Ray Garner
256.824.6397
ray.garner@uah.edu