In the summer of 2018, we’re launching Parker Solar Probe, a spacecraft that will get closer to the Sun than any other in human history.
Parker Solar Probe will fly directly through the Sun’s atmosphere, called the corona. Getting better measurements of this region is key to understanding our Sun. For instance, the Sun releases a constant outflow of solar material, called the solar wind. We think the corona is where this solar wind is accelerated out into the solar system, and Parker Solar Probe’s measurements should help us pinpoint how that happens.
The solar wind, along with other changing conditions on the Sun and in space, can affect Earth and are collectively known as space weather. Space weather can trigger auroras, create problems with satellites, cause power outages (in extreme cases), and disrupt our communications signals. That’s because space weather interacts with Earth’s upper atmosphere, where signals like radio and GPS travel from place to place.
Parker Solar Probe is named after pioneering physicist Gene Parker. In the 1950s, Parker proposed a number of concepts about how stars — including our Sun — give off energy. He called this cascade of energy the solar wind. Parker also theorized an explanation for the superheated solar atmosphere, the corona, which is hotter than the surface of the Sun itself.
Getting the answers to our questions about the solar wind and the Sun’s energetic particles is only possible by sending a probe right into the furnace of the Sun’s corona, where the spacecraft can reach 2,500 degrees Fahrenheit. Parker Solar Probe and its four suites of instruments – studying magnetic and electric fields, energetic particles, and the solar wind – will be protected from the Sun’s enormous heat by a 4.5-inch-thick carbon-composite heat shield.
Over the course of its seven-year mission, Parker Solar Probe will make two dozen close approaches to the Sun, continuously breaking its own records and sending back unprecedented science data.
Getting close to the Sun is harder than you might think, since the inertia of a spacecraft launched from Earth will naturally carry it in repeated orbits on roughly the same path. To nudge the orbit closer to the Sun on successive trips, Parker Solar Probe will use Venus’ gravity.
This is a technique called a gravity assist, and it’s been used by Voyager, Cassini, and OSIRIS-REx, among other missions. Though most missions use gravity assists to speed up, Parker Solar Probe is using Venus’ gravity to slow down. This will let the spacecraft fall deeper into the Sun’s gravity and get closer to our star than any other spacecraft in human history.
On Aug. 21, the Moon will cast its shadow down on Earth, giving all of North America the chance to see a solar eclipse. Within the narrow, 60- to 70-mile-wide band stretching from Oregon to South Carolina called the path of totality, the Moon will completely block out the Sun’s face; elsewhere in North America, the Moon will cover only a part of the star, leaving a crescent-shaped Sun visible in the sky.
A total solar eclipse happens somewhere on Earth about once every 18 months. But because Earth’s surface is mostly ocean, most eclipses are visible over land for only a short time, if at all. The Aug. 21 total solar eclipse is different – its path stretches over land for nearly 90 minutes, giving scientists an unprecedented opportunity to make scientific measurements from the ground.
Within the path of totality, the Moon will completely obscure the Sun’s face for up to 2 minutes and 40 seconds, depending on location. This will give people within the path of totality a glimpse of the innermost reaches of the Sun’s corona, the outer region of the atmosphere that is thought to house the processes that kick-start much of the space weather that can influence Earth, as well as heating the whole corona to extraordinarily high temperatures.
In fact, scientists got their first hint at these unusually high temperatures during the total solar eclipse of 1869, when instruments detected unexpected light emission. It was later discovered that this emission happens when iron is stripped of its electrons at extremely high temperatures.
This region of the Sun’s atmosphere can’t be measured at any other time, as human-made instruments that create artificial eclipses must block out much of the Sun’s atmosphere – as well as its bright face – in order to produce clear images.
We’re funding six science investigations to study the Sun’s processes on Aug. 21. Teams will spread out across the path of totality, focusing their instruments on the Sun’s atmosphere. One team will use a pair of retro-fitted WB-57F jets to chase the Moon’s shadow across the eastern US, extending the time of totality to more than 7 minutes combined, up from the 2 minutes and 40 seconds possible on the ground.
Our scientists are also using the Aug. 21 eclipse as a natural science experiment to study how Earth’s atmosphere reacts to the sudden loss of solar radiation within the Moon’s shadow.
One region of interest is Earth’s ionosphere. Stretching from roughly 50 to 400 miles above Earth’s surface, the tenuous ionosphere is an electrified layer of the atmosphere that reacts to changes from both Earth below and space above and can interfere with communication and navigation signals.
The ionosphere is created by ionizing radiation from the Sun. When totality hits on Aug. 21, we’ll know exactly how much solar radiation is blocked, the area of land it’s blocked over and for how long. Combined with measurements of the ionosphere during the eclipse, we’ll have information on both the solar input and corresponding ionosphere response, enabling us to study the mechanisms underlying ionospheric changes better than ever before.
The eclipse is also a chance for us to study Earth’s energy system, which is in a constant dance to maintain a balance between incoming radiation from the Sun and outgoing radiation from Earth to space, called the energy budget. Like a giant cloud, the Moon during the 2017 total solar eclipse will cast a large shadow across a swath of the United States.
Our scientists already know the dimensions and light-blocking properties of the Moon, and will use ground and space instruments to learn how this large shadow affects the amount of sunlight reaching Earth’s surface, especially around the edges of the shadow. This will help develop new calculations that improve our estimates of the amount of solar energy reaching the ground, and our understanding of one of the key players in regulating Earth’s energy system — clouds.
Ten Surprises For Scientists And Skywatchers During The Total Solar Eclipse
“3.) The solar corona really did turn visibly pink in some spots. When some people looked at the corona, myself included, there were some locations around the Sun’s rim that appeared pink to the naked eye. It wasn’t your eyes playing tricks on you, although I never expected human eyes would be sensitive enough to see that color! When you ionize a hydrogen atom, which the Sun’s corona is more than hot enough to do, you create free electrons. As those electrons fall back down onto the hydrogen nuclei, they go through a series of transitions. The most powerful optical transition is a red line at precisely 656.3 nanometers. Combined with the white light of the luminous corona itself, the hydrogen line creates a pink effect where the Sun’s plasma loops near the photosphere are strongest. The pink effect was real.”
No matter how well-prepared you were for your first total solar eclipse, no amount of reading or photograph-searching could do the experience justice. There were so many things to feel, see, and be overwhelmed by that you literally needed to be there to relate to. Yet it was remarkable how many things there were that surprised scientists and skywatchers alike. The temperatures really did plummet, and they dropped by more than even the weather models predicted. There was a star and a planet visible, but not the planets we thought would arrive. The sky turned red along the horizon, which was a mystery for centuries, even after we learned why the sky is blue. And the light, the way it looked across the landscape, was a unique treat that you’ll never experience during any other time than an eclipse itself.
The total solar eclipse of 2017. A solar eclipse occurs when the moon travels between Earth and the sun, temporarily darkening our world. You can see the corona as the sun’s light peaks out from behind the moon. The middle image best shows off the ‘diamond ring’ effect.