In July, humanity will send its first emissary to our star. A Delta IV Heavy rocket with an additional top stage will propel NASA's Parker solar probe away from Earth and, lashed by the gravity of Venus, it will soon become the fastest spacecraft ever flown. At its maximum speed, the spacecraft will scream through space at 430,000 mph, fast enough to travel from New York to Los Angeles in 25 seconds.
For seven years of carefully choreographed swoops, he will be closer to the sun, like a matador dancing inward towards a grizzled bull. Finally it will be installed in an elliptical orbit that, in the perihelion, is 3.9 million miles from the visible surface of the sun, more than seven times closer than any spacecraft has dared to venture. It will not touch the surface. That would be too dangerous and impossible, because the sun is a turbulent plasma furnace, a state of matter incapable of forming what could be considered a surface. Instead, the probe will fly directly to the only region of the solar system hitherto unexplored by the spacecraft: the corona. What happens here, in the atmosphere of the sun that extends millions of miles, affects this planet and any other place in our neighborhood, but its dynamics remain mysterious.
We know that the atmosphere of the sun is much hotter than its outer plasma layer, a fact that seems to defy thermodynamics. The solar wind from the corona moves outward, crossing 93 million kilometers of space to create the aurora in Earth's magnetosphere. From Earth, we can not see the corona, unless we observe during a total solar eclipse. Parker Solar Probe will take samples directly from this layer of the sun and, for the first time, we will be able to retrieve information about the kingdom that connects the Earth with our star.
**********  Comet tails were the first evidence that the sun was more than a static ball in the sky. In 1607, an appearance appeared at night: a comet that would eventually carry the name of Edmond Halley, the astronomer who predicted its 75-year orbit. The German astronomer Johannes Kepler was one of his many observers, and he wrote to Galileo Galilei asking if it was the sunlight that caused the comet's tail to stain the sky. Perhaps one day, he speculated with great vision, travelers could use this solar energy as a propulsion in trips through the stars: "Provide boats or sails adapted to the celestial breezes, and there will be some that will even challenge that emptiness".  It was not until the twentieth century that astronomers proposed that along with light, the sun emit a constant flow of particles, which pushes the tail of a comet. In the early 1950s, Eugene Parker, an astrophysicist at the University of Chicago, wanted to study why the sun's atmosphere is so hot. He read some of the documents on solar particles and began to connect the dots. Parker, now 90, says that during his research he discovered that "the crown is mostly static near the sun, there is a slight movement, but it is not flowing at a remarkable rate." But when you study this radiation much further, " he is busy blowing the tails of the comet, "he says. "That says it's a gas, a hydrodynamic flow of gas." In other words, the sun emitted not only electromagnetic radiation but gales of low density particles.
If this flow of the sun was gas, Parker could use known physics equations to better describe what is happening in the corona. Their calculations revealed that at the extremely high temperatures of the outermost layers of the corona, the gas has to be flowing away from the sun extremely fast. In fact, when they arrived on Earth, the gales would remain supersonic. Parker coined a term for the exit: the solar wind.
"It was something that most people seemed unable to swallow, they expressed deep disbelief," he recalls. "I told them, you know that the crown is static in the sun, and you know from the tails of the comet that it is moving very fast farther from the sun. You put in the temperatures that are observed [in the corona] a million degrees, and you can not avoid to be a solar wind, that's how the dynamics develop. "
In 1958, Parker published an article with what his calculations revealed: that the phenomenon is composed of a complex system of plasma flow, magnetic fields and high energy particles. He argued that it affects all planets and space throughout the solar system, and correctly predicted the twisted form, now called Parker's spiral, that would take the magnetic field of the sun when the solar wind carried it to the outer solar system. His theory was largely ignored until 1962, when Mariner 2 became the first probe to travel beyond the Earth's magnetic field. The spacecraft observed the supersonic solar wind (and the fact that our magnetosphere protects us greatly from it), and Parker was vindicated.
Parker Solar Probe, officially named last summer, is the first spacecraft that NASA has dedicated to a living person. It is a tribute to the importance of Parker's contribution to science, but also an indication of how young the field of solar research is and how far it has to go.
"I could, in my career, look to heliophysics to move from curiosity to applied science," says OC St. Cyr, solar scientist at NASA's Goddard Space Flight Center in Maryland. Parker Solar Probe will cover many gaps in the knowledge of the sun, which will help scientists understand why the star behaves the way it does. Although we generally understand what the magnetic dynamo of the sun creates, the charged gases that flow inside the sun create electric charges, which generate a powerful field. Nobody seems to know why he turns around every 11 years between a state of relative tranquility and one of fury. Nobody knows why the Sun throws ejections of coronal mbad, gigantic eruptions of energetic particles, and nobody can predict them with reliability. This means that no one can predict when the CME solar storms will hit the Earth, with the potential to fry telecommunications equipment on the ground and in space. No one yet knows exactly how or why the solar wind is generated. Nobody knows how it produces jets of violent and ephemeral material of 6,000 miles in length, called spicules. And nobody knows why the crown gets so hot.
"We do not have the power to model the sun in all its complexity," says Nicholeen Viall, a Goddard astrophysicist. It is the interconnection of various solar activities that makes it difficult to discern individual characteristics. "A spicule can launch a wave, and that triggers a magnetic reconnection event, and that heats the plasma, but this is all speculative, these are fundamental questions of plasma physics that we have to go to the sun to really respond."
The problem of coronal heating, as it is called, remains one of the most controversial problems in solar science, because it seems to flout the rules. of basic physics. The photosphere of the sun – its visible plasma surface – is about 10,000 degrees Fahrenheit, but the faint crown reaches millions of degrees. It is as if you were sitting near a bonfire, and the air in your face was a hundred times hotter than the flames themselves. The scientific literature is full of conflicting ideas about how the crown overheats: plasma waves rising from the deep interior of the sun; magnetic braids that twist and tighten, eventually break like elastic bands; "Heat pumps" or "nanoflares", which Parker proposed 30 years after his solar wind role.
"Storms in the solar wind form somewhere near where Solar Probe goes," says Parker. "You can make theoretical models of these storms, but you have to make badumptions about where the energy is introduced, and at this time we do not know the answer to that." The ship will submerge its instruments in the solar wind, a sailor could dip his fingers in the water to feel the current. Measure the direction and strength of plasma waves. Measure the speed and density of a wide range of particles, from the lowest energy solar emanations to the most energetic protons badociated with solar flares, and observe how the solar wind accelerates to supersonic. Discovering these speed differences could reveal the processes that make up the solar wind.
The probe will also measure the magnetic fields and how they change in the presence of a shock, such as that of a CME. Discovering how these clouds of charged plasma originate and flow out is one of the most important objectives of the mission. Although scientists study them from Earth and from other solar observation spacecraft, nothing compares to going there, says Nicola Fox, mission project scientist and heliophist at the Applied Physics Laboratory at Johns Hopkins University in Laurel, Maryland. . "With Parker Solar Probe, we do not just sit and take pictures," he says. "We are not just sitting in the comfortable region just outside the Earth, we dive into the sun's crown 24 times in the life of the mission."
A trip to the sun is, of course, dangerous. The probe will experience 475 times the solar radiation that the Earth has. It will not get close enough to experience the crown's highest temperatures, but it will still burn to over 2,500 degrees Fahrenheit. The probe will be protected by specially designed heat shields, cooling pumps and radiators, making it the strongest spacecraft ever launched. Juno, which has been in orbit around Jupiter since July 2016, is encased in a shell of radiation shielding, but Parker Solar Probe's 4.5-inch carbon composite sun visor is unprecedented in space exploration. The surface of the shield will be destroyed with 2.8 million watts of solar energy, and only about 20 watts will reach the instruments, and almost all will remain hidden behind the shield, and will sample the environment as it flows behind them.
Most interplanetary probes are solar powered; Solar panels are relatively inexpensive to build and launch, and the sun's energy is free and persistent. But Parker Solar Probe will have too much of a good thing. Like Juno, the elliptical orbit of the probe is a measure of protection, allowing it to take a break from the intensity as it travels. In most spacecraft, the solar panels extend permanently as wings to capture as much energy as possible, but those of the solar probe were designed with an unusual feature: articulated arms that can place the panels behind the heat shield. A computer on board continually forecasts energy needs and determines what percentage of solar panels to expose and how much to separate. To prevent overheating of the edges, water flows through the vein-type chambers inside the matrix, which is made of titanium, but resembles corrugated cardboard. The water flows in four cone-shaped radiators, which dissipate the heat in space. However, it is a perpetual system, so when it is not touching the sun, the probe also carries heaters to thwart the cold of space.
At a distance of 89 million miles, communications between the probe and the Earth will take several minutes, so many of the tasks of the probe are performed autonomously. The spacecraft is programmed with a litany of commands that you can access as your situation changes, the most important of which is to be absolutely sure that the heat shield covers what you need to cover. "The great level of independence that the spacecraft has is a great challenge," says Fox, "because you have to try each of those commands:" If this, we must do this ".
The probe uses star trackers and an inertial measurement unit to detect its position; the latter can navigate for a time by itself if the star trackers are blinded by, for example, a solar burst. Seven solar sensors mounted around the spacecraft can also issue alerts. Mary Kae Lockwood, spacecraft systems engineer at APL, says: "If the spacecraft starts to move away from the sun a little, one of the solar sensors would light up and say, 'I see the sun here, so leave me behind of the thermal protection system. "# 19659003] The scientific instruments are also packed in a cooling system that operates at room temperature, around 78 degrees Fahrenheit. But protruding like whiskers behind the heat shield are four 1/8 inch diameter antennas and a solar probe cup that will light up directly with the sun. By examining the corona so close to its source, the probe will be able to provide better data for models used to forecast space weather, and may be able to identify the causes of CME.
Understanding space weather is a crucial step for safeguard The economy of the Earth and for future missions to other planets. The material of coronal mbad ejections usually takes several hours or days to traverse the distance between the sun and the Earth. Once they reach Earth, CMEs can interfere with satellites, terrestrial communications and energy networks. They can cause radical blackouts and can throw planes and spacecraft with dangerous radiation. Serious events can be catastrophic for spacecraft and, more importantly, for any human being in orbit. In 1972, between the Apollo 16 and 17 missions, the sun unleashed a furious, high-energy proton storm, with enough energy to dig through four inches of water. A space suit would have conferred little protection. If the astronauts had been on the moon at that time, they could have been exposed to deadly radiation levels, which exceed 400 times the typical CT scan dose. Without medical treatment, approximately half of the people exposed to this level of radiation die in one or two months.
The metal used to build spacecraft, such as the Apollo capsules and the International Space Station in orbit today, blocks much of that radiation, so that astronauts can stay safe as long as they are positioned correctly in their metal shelter. Still, early warning could be a lifeline for any mission in low Earth orbit, on the moon, on Mars or on distant asteroids. However, beyond its basic relationship with the solar activity cycle, no one really understands why solar storms occur. Sunspots are carefully monitored, and spacecraft that observe the sun can warn when a CME is bubbling, but no one can predict them.
"There are processes that we do not fully understand that lead to a collection or accumulation of magnetic energy in the solar atmosphere," says Antti Pulkkinen, an astrophysicist at Goddard. "Once the accumulation of magnetic energy reaches some critical threshold, then, boom, we have significantly improved our understanding in just a couple of decades, using missions so far and models of heliophysics, but the devil is in the details …. you want to predict these things ultimately, you need to get the right details. "
Beyond giving scientists the ability to predict the dangerous activity of the sun, the mission of the Parker probe is fundamental to understanding the physics of our star . Just as the scarcity of missions anywhere except on Mars has left little raw data for planetary scientists, the lack of missions to the sun has been a challenge for heliophysicists. The ability or inability to collect new data affects the entire line of scientific research: without the incoming observations, major research programs become more difficult to maintain, and existing programs have more difficulties recruiting postdoctoral researchers and graduate students . Another upcoming mission will help probe Parker to support the field of heliophysics: the Solar Orbiter, a joint mission of NASA and the European Space Agency. After its launch next year, it will fly close to the sun to study its interior and provide close-up views of its polar regions. Goddard's St. Cyr: his participation in the Solar Orbiter and Parker probe missions is indicative of how small the field heliophysics is today: he says that both ships will provide much-needed new perspectives. Some scientists, he says, are still trying to extract new information from data from the Helios twin spacecraft, a pair of probes launched by the United States and Germany in the 1970s.
But when the Parker solar probe reaches his destiny, will change the relatively quiet field of heliophysics. "[The mission] has the potential to blow the doors of solar science," says St. Cyr. "We do not have any data like that."
When Parker, the scientist, predicted for the first time the existence of the solar wind, the Space Age was still neonatal. The first satellite built by humans, Sputnik 1, had impressed the world a few months before. It would be another five years before the first spacecraft observed the sun's launch, the first of eight small satellites called the Orbital Solar Observatory. It would be another 12 years before the sun was the main target of a space mission, the Helios twin probes. In the decades that followed, missions such as the Solar Dynamics Observatory, the Twin Earth Observatory Observatory, the Hinode spacecraft and others opened a window to the behavior of the sun, but all have been from a distance.
Up to Parker's Solar The probe reaches 3.9 million miles from the sun, the Helios spacecraft will remain the record holder for the closest approach. In 1975 and 1976, they flew within 29 and 27 million miles of the sun. The MESSENGER spacecraft, which visited Mercury, also took some solar measurements, from 28.8 million miles. Just beyond the edge of the solar system, in the neighborhoods of 13 billion miles, Voyager 1 can complete the data at the far end of the influence of the solar wind. From Earth, 93 million miles away, astronomers can measure the spectra of the sun, a way to measure its ingredients. They did this en mbade in August of 2017, when a total solar eclipse crossed the continental United States for the first time in a century. These observations help estimate the density of the crown and the speed at which the particles travel. But the biggest hole in our knowledge is what is happening in the star itself. "That's why these measurements are so innovative and revolutionary," says Fox.
For all that heliophysics hopes to learn about coronal science, the most promising data can be of the kind no one can predict. There will be information that nobody knows how to use; Whole careers will be built on the interpretation of Parker Solar Probe data and their incorporation into space weather prediction models. "There are physical phenomena in this region that we have not yet measured," says Fox. "People have different theories, but until we really do not examine them, we can not say which one is correct, or maybe they're all wrong, and there's one new that nobody has thought yet ".
Parker himself says he expects this to be the case. "Storm formation in space, I think, is going to provide a lot of information about things we know very little about, and the effects on Earth are going to be very serious," he says. "I think there will be a lot to see, but do not ask me what, because I do not know." This spring, he is happily waiting to see his namesake take off.
The launch window of the Parker Solar probe opens on July 31 and lasts 20 days. During this time, the Earth and Venus are aligned, a crucial positioning for the trajectory of the spacecraft. By September, the probe will navigate beyond the second planet. Using this gravity help, you will gain speed and a refined orbital path. Over the next few years, it will spiral around six more times around Venus, and finally it will lean towards the sun. The probe will point its protective face toward the boiling orange disc, whiskers to the wind. Defying the inscrutable heat and radiation, the spacecraft will search for material forged in the deepest heart of the star. Then he will touch it and send a message home, connecting humanity even closer to the source of everything that has ever lived, or ever will, at least in this corner of the galaxy.