The Spacecraft Tarot: Parker Solar Probe
The sky is always darkest before the dawn.
Without the Sun, our world would be plunged into darkness. Our plants could not photosynthesize. Time could not be marked by the rhythm of sunrises and sunsets. But with the Sun, we experience a cycle of rebirth every morning. Every day is a new day.
Parker Solar Probe is NASA’s mission to “touch the Sun.” With every tightening orbit, the spacecraft is swooping closer and closer to an understanding of our nearest star.
Long before telescopes were invented, humans have been studying the Sun. One of the earliest recording observations of the Sun includes a Babylonian stone tablet from 3,500 years ago. The stone recorded solar eclipses, events where the Moon passes perfectly in front of the Sun and blocks the sunlight.
Over the next couple millennia, solar eclipses were used to make some of the most important discoveries about the Sun’s processes. When the sunlight is blocked by the Moon, the contrast in brightness allows viewers are able to see an ever-present haze encircling the star.
On July 8, 1842, English astronomer Francis Baily proposed that this haze is actually the Sun’s atmosphere. An atmosphere is a layer of gases that envelops a celestial body. Earth’s atmosphere is composed mostly of nitrogen, oxygen, and argon. But what could the Sun’s atmosphere be made of?
On August 18, 1868, French astronomer Pierre Jules César Janssen saw a solar eclipse as an opportunity to examine the haze with a spectrometer, which allows sunlight to pass through a prism to identify the composition of the distant light source. An unknown spectral line revealed a never-before-seen chemical element: helium, which is rare on Earth but abundant on the Sun (and as it turns out, the second most abundant element in the universe, after hydrogen).
Perhaps one of the most important discoveries made during a solar eclipse was when English astronomer Sir Arthur Eddington observed starlight bending around the Sun, which proved physicist Albert Einstein’s theory of general relativity. Massive objects, like the Sun, warp the fabric of space-time around them. This distortion is felt and observed as gravity.
In November 1958, just one month after NASA officially opened its doors, Eugene Parker hypothesized that the Sun’s atmosphere expands outward in all directions, forming a solar wind that carries with it the Sun’s magnetic field.
Parker’s theory was just a theory until the Soviet Union satellite, Luna 1, became the first human-made object to escape the Earth’s gravity on its way to the Moon in 1959. Although Luna 1 ultimately missed the Moon, the probe observed a stream of charged particles, also known as plasma, originating from the Sun.
On August 27, 1962, NASA’s Mariner 2 spacecraft launched from Cape Canaveral, Florida on an 110-day journey to complete the first successful close-up observations of another planet: Venus. Along the way, Mariner 2 also observed the hot particles pouring out from the direction of the Sun at mind-blowing speeds — confirming Parker’s theory about solar wind.
Since the establishment of the existence of solar wind, scientists have launched dozens of spacecraft to study the event and its effect on Earth, astronauts, and interplanetary systems.
The solar wind influences the magnetic and radiation environments in space, causing a phenomenon known as space weather. Space weather can interfere with radio communications, space technology, and even utility grids on Earth. As our spacecraft travels farther into space, the need to understand the mechanisms that drive solar wind and space weather becomes greater.
On April 17, 1976, Helios 2, one of twin spacecraft launched to study solar wind, became the record holder for the closest flyby of the Sun. Both Helios 1 and 2 revealed that solar wind is variable to change before we experience it on Earth.
To further the discoveries made by the Helios spacecraft, Wind was launched on November 1, 1994. Still in operation today, positioned perfectly between the Earth’s and the Sun’s gravity and using almost no fuel in the process, Wind continues to observe the Sun and its powerful influence on our solar system.
One of Wind’s most important discoveries was made with a Faraday cup, which measures the speed, density, and temperature of charged particles. After millions of observations, scientists realized that solar wind can only escape the Sun’s surface if it travels faster than 161 miles per second. The faster the solar wind, the more helium it contains—suggesting that helium is somehow controlling the speed of solar wind. This revelation was an impressive one — but it also stirred more questions. How does this process work? Why does the amount of helium in the plasma determine how fast it travels through space?
In addition to these questions, another mystery still looms: the “coronal heating problem.” While the surface of the Sun maintains a temperature of about 10,000 degrees Fahrenheit, the corona — the outermost layer of the solar atmosphere that extends for millions of miles — burns at over 2 million degrees Fahrenheit. Today, scientists still don’t understand what is adding the extra heat to the atmosphere.
To solve these mysteries and many others, NASA launched Parker Solar Probe on August 12, 2018, from Cape Canaveral Air Force Station. Parker Solar Probe is the only spacecraft to be named after a living person: Eugene Parker, who had first hypothesized about the existence of solar wind sixty years ago.
Parker Solar Probe is the first spacecraft to observe the corona directly. Swooping in as close as 3.8 million miles above the Sun’s surface, Parker Solar Probe will use Venus’ gravity to fly close enough to the Sun to watch the birthplace of solar wind in action. By the time the solar wind reaches us on Earth, the charged particles have traveled 94 million miles, plenty of time to mix with other particles and dilute readings. Observing the corona up-close will reveal more to us than anything we’ve observed of the corona before.
On October 29, 2018, Parker Solar Probe broke two world records. As it approached closer to the Sun, the probe beat the previous record set by Helios 2 for the closest spacecraft to the star. Ten hours later, it also broke the record for fastest spacecraft, also set by Helios 2.
Since then, Parker Solar Probe has already expanded what we know and understand about solar wind. When solar wind reaches us on Earth, it is coming to us in straight lines, radiating directly from the direction of the Sun. But Parker Solar Probe has been able to observe the solar wind spinning with the Sun as the Sun rotates, as far away as 20 million miles away from the Sun. The strength of the rotational flow of the solar wind brings us closer to understanding how the Sun sheds energy.
In addition, Parker Solar Probe has also observed “switchbacks,” which happens when the magnetic field embedded in a blast of solar wind whips back on itself. Parker Solar Probe’s observations suggest that the switchbacks are disturbances that happen as the magnetic field travels away from the Sun, which means that it will more likely encounter more as it draws closer and closer to the star. The presence of switchbacks paints a picture of a complex, dynamic solar environment — more active that scientists previously thought.
Each star has its own influence on its environment, and there are billions of stars in every galaxy. Understanding our Sun will help us understand how stars release energy into their own unique environments.
As Parker Solar Probe swoops in closer to the Sun over the next couple of years, we will come closer to answering the questions that have puzzled scientists for hundreds of years.
Every day is a new day. Whatever we are struggling with, the promise of tomorrow’s sunrise ignites hope for new opportunities and good fortune.
