Tacking Into the Solar Wind

Artist’s concept of the Parker Solar Probe spacecraft approaching the Sun. (NASA)

Artist’s concept of the Parker Solar Probe spacecraft approaching the Sun. (NASA)

University of Chicago physicist Eugene Parker observed in 1958 that, no matter which way it was traveling around the sun, a comet’s tail always pointed away from the sun. From those observations, he inferred that there must be some kind of stream of particles flowing away from the Sun. He called that stream of particles the “solar wind.”

He was right. It’s a plasma, a soup of very high energy electrons, protons, and other particles.

It’s also incredibly hot, three hundred times hotter than the surface of the sun inside the orbit of Mercury. It varies hugely in velocity – from less than 300km/s to more than 800km/s – and density.

No one knows why. Sure, there are theories, but there’s not a lot of data.

But a new satellite named for Professor Parker, the Parker Solar Probe, may very well help astronomers and physicists get some answers.

The Parker Solar Probe was launched August 11 and is already the human-made object that is nearest the sun and the human-made object in fastest orbit around the sun. The first is its mission; the second is a consequence of orbiting as massive an object as the sun. Beginning November 9, it will start transmitting four kinds of data.

The satellite is remarkable because that close to Sol it is incredibly hot. The Parker Solar Probe had to be designed from the start to tolerate the 1,400° C (2,552° F) temperatures in the upper solar corona, the sun’s “atmosphere.” A 4.5 inch thick “shield” will be pointed at the Sun through the orbit, and the science will take place in the “shade” behind the shield. It’s so hot that the solar panels have a kind of air conditioning.

First, it will sample the composition of the solar wind, taking local measurements of the particles that make up the solar wind, including protons, electrons, smidgens of ionized helium and traces of heavier elements synthesized by the fusion process. Those instruments measure how fast the particles are moving, how hot they are, how many of them there are.

A second set of instruments will measure the solar corona’s magnetic and electric fields, which can “radically complicate” the behavior of ions floating around. If those fields are strong enough, they could create conditions that permit “nanoflares,” one theory to explain why the solar wind is so hot.

A third set of instruments will try to capture the highest energy particles. Remember energy is a combination of speed and excitation. Understanding what particles move the fastest and are the hottest may help explain why.

Lastly, there is a set of cameras that will attempt capture close-ups of solar wind plasma as it comes off the corona.

Planned orbits of the Parket Solar Probe (NASA)

Planned orbits of the Parket Solar Probe (NASA)

The Parker Solar Probe will perform a series of at least 24 elliptical orbits over about seven years, approaching within 6.2 million kilometers of the sun’s surface, well inside the corona, and then swinging out almost as far as the orbit of Venus.

It’s not all abstract science. A better understanding of what causes the solar wind might help protect satellites and allow prediction of the dangerous coronal mass ejections, the events that create spectacular aurora displays but, in extreme cases, can take out the world’s electrical distribution system.

But scientists don’t really know what they will find. Which is pretty cool. Or pretty hot, under the circumstances.