Harvard Astrophysicists Design Instruments To Sample Sun's Atmosphere

A team of Harvard astrophysicists designed a set of scientific instruments that will directly sample the sun’s atmosphere for the first time as part of NASA’s Solar Probe Plus mission to the star in 2018.

The Solar Wind Electrons Alphas and Protons Investigation received a grant of $67 million from NASA on Sept. 2, and will use the money to design and build the proposed instruments, according to a press release.

As the SPP spacecraft hurtles toward the sun, the SWEAP Investigation will sample atoms and electrons in the gases of the corona, the sun’s outermost atmosphere. The instrument acts as a “thermometer that measures the plasma we encounter in the solar atmosphere,” said SWEAP Principal Investigator Justin C. Kasper, who is also an astronomy lecturer.

Before the SPP mission became a reality, the corona had been long considered too hot for a spacecraft to penetrate. But a unique carbon-composite plate shielding the delicate instruments from direct sunlight will allow the shuttle to travel within 4 million miles of the Sun. At this distance, the Sun will appear 20 times wider and radiate 500 times brighter than it does to an observer on Earth, according to the release.

At this close proximity, the SWEAP Investigation offers astrophysicists a more accurate glimpse of the Sun’s atmosphere than has ever been possible before, according to Kasper.

He added that no previous instrument has been able to measure the movement of waves at the high frequency that SWEAP can record. SWEAP is also the first instrument of its kind designed to operate at temperatures of 1,400 to 1,600 degrees Celsius, according to Kasper.

He said that he hopes the instruments will “definitively determine the mechanism that heats the corona and accelerates the solar wind to high speeds.”

Kasper said that he had been planning the SWEAP Investigation for 10 years, and that a variation of SPP was first proposed 50 years ago, before NASA was even established. The head of that earlier committee was Professor John Simpson, Kasper’s undergraduate adviser at the University of Chicago, who encouraged Kasper to “carry the torch” to make the mission happen.

NASA first seriously considered the Solar Probe mission in 2000, but did not go forward with the project at the time because it lacked the adequate technology to design the instruments and spacecraft.

NASA renewed the project five years ago. Kasper created a team of 60 scientists from Harvard and seven other American institutions, who have since been working together to make SWEAP technologically feasible.

Astronomy Professor Abraham “Avi” Loeb said he recognizes the importance of SWEAP: “If we understand the Sun better, we will perhaps be able to get a better understanding of other astrophysical systems,” he said.

He also expects SWEAP to help scientist forecast the effects of the Sun on the earth more accurately than ever before.

As SWEAP goes into its development stage, Kasper is optimistic about the work ahead.

“I would have been happy to do this near Earth, but it’s even more fun near the Sun,” he said.