Friday, August 10, 2018

NASA is About to Launch a Sun-Skimming Solar Probe

Imagine yourself standing comfortably in front of a warm, cozy fire. Suddenly, you start to feel just a little too toasty, so you take a few steps away. But wait—now that you’re farther from the fire, it’s even hotter! Huh?

This is a rough analogy for the Sun’s corona, the rarefied halo of plasma that extends millions of miles beyond the Sun’s surface. If you were able to catch the solar eclipse in August 2017, you may have had a glimpse of the corona peeking out from behind the moon—it’s that glowing, amorphous ring of filaments. As beautiful as the corona is, it represents a massive headache for astrophysicists and solar physicists. You see, just like that whimsical fire, the corona glows far, far hotter than the furnace that is the Sun itself. While the surface of the Sun is about 10,000 degrees Fahrenheit, the corona burns at several million degrees! Based on our current understanding of physics and stellar structure, this simply doesn’t make sense. How could the outer layers of the Sun be so much hotter than the interior?

The corona shines brightly from behind the moon during a total solar eclipse.
Image Credit: Manoj Dayyala via Wikimedia Commons (CC BY-SA 3.0)
There are other mysteries surrounding the corona as well. The corona is home to intense magnetic field lines that constantly tangle and reform. It’s thought that this roiling magnetic environment accelerates solar winds to supersonic speeds, preparing them to hurtle through the Solar system, but this theory has never been verified. Furthermore, some solar particles manage to accrue enough energy in the corona to reach half the speed of light, yet the mechanisms behind this phenomenon are unclear.

What is known is the general effect of solar wind on man-made and natural systems back here on Earth. Although our own magnetic field generally does a good job deflecting the solar wind, occasionally a few “gusts” will make it into the atmosphere, creating stunning auroras. While these shows are beautiful, heavy bursts of particles called solar storms have the potential to wreak havoc on the energy grid, and back in space the high-energy particles represent a serious threat to astronauts and spacecraft. They can also affect satellites' orbits and lifetimes, causing trouble on Earth when we aren’t able to receive the signals we need. It’s clear that as we travel deeper and deeper into space, we need a much better understanding of this “space weather”.

Fortunately, we could be getting answers much sooner than you might think. NASA’s Parker Solar Probe (PSP), which is set to launch August 11, will give scientists an up-close view of the corona as it flies within 3.8 million miles of the Sun’s surface. (If that still sounds far away, consider that on any given day, we Earthlings are on the order of 93 million miles from the Sun.) The PSP will venture closer to the Sun than the planet Mercury, does and reach one-seventh the distance of earlier solar missions.

An artist's rendition of the PSP venturing close to the Sun’s surface.
Image Credit: NASA/Johns Hopkins APL/Steve Gribben
The PSP's primary goal is to trace the energy flow through the solar corona, with an eye toward solar wind acceleration. To that end, the PSP has four instruments on board—FIELDS, WISPR, SWEAP, and IS☉IS—that will allow it to make in situ measurements of the corona’s properties and image its large-scale structure. Among the properties that it will be measuring regularly are the electric and magnetic fields present, along with the velocity, density, and temperature of particles that typically make up solar wind—protons, electrons, and heavier ionized nuclei. Taking all of this information together, scientists at NASA hope that they’ll be able to piece together a picture of the physics behind the corona.

Of course, the PSP is more than a collection of instruments.* It’s headed straight for regions reaching up to 2500° F and, at its fastest, it will reach 430,000 miles per hour—giving it the record for fastest spacecraft ever! What’s more, the mission is expected to last seven years, requiring great durability despite the extreme conditions. The car-sized spacecraft boasts a 4.5-inch thick thermal shield made of carbon composite materials that will keep the interior at a balmy 85 degrees.

The launch promises to be an exciting one, requiring about 55 times the energy needed to reach Mars. If all goes as planned, it will lift off aboard a United Launch Alliance Delta IV Heavy rocket from Cape Canaveral on August 11, with a 65-minute launch window beginning at 3:33 am EDT. From Earth, it will head towards Venus, where it will execute the first of seven flybys. It is expected to orbit the Sun 24 times, with the occasional assists from Venus sending it in closer and closer to the Sun’s surface. Although the mission is scheduled for seven years, we should get the first data readouts sometime in December.

The PSP arrives at the launch pad.
Image credit: NASA/Kim Shiflett
Although much of the Sun’s structure is still something of a mystery to us, the PSP is full of possibility. As we continue to receive data over the next seven years, scientists will hopefully start to piece together a picture of why the corona is so hot and how space weather is formed, which is critical as we venture further and further into space.

You can watch the launch on NASA’s website. Don’t forget to set your alarm clock!

—Eleanor Hook

*It also holds a flash drive with the names of 1.1 million individuals who participated in NASA’s program to send their names to the Sun.

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