There's something mysterious about the sun. Despite all logic, its atmosphere gets hotter as it moves away from the glowing surface of the sun.
The temperatures in the corona ̵
From The earth, as we see it in visible light, the appearance of the sun – calm, unchanging – deceives the life and drama of our next star. Its turbulent surface is shattered by eruptions and intense bursts of radiation that hurl the sun's material at incredible speed into every corner of the solar system. This solar activity can trigger space weather events that can interfere with radio communications, damage satellites and astronauts, and intervene in their heaviest form in the power grids.
Above the surface, the corona stretches millions of miles and seethes plasma, gases overheat so much that they separate into an electric flux of ions and free electrons. Finally, it goes outward like the solar wind, a supersonic flow of plasma that permeates the entire solar system. And so people live well in the extended atmosphere of our sun. To fully understand the corona and its secrets, one must not only understand the star that drives life on Earth, but also the space around us.
A 150-Year-Old Mystery
Most of what we know about the corona is deeply rooted in the history of total solar eclipses. Before sophisticated instruments and spacecraft, the only way to study the corona from Earth during a total eclipse was when the moon blocked the bright face of the sun and revealed the surrounding, weaker corona.
The history of the coronal warming problem begins with a green spectral line, which was observed in 1869 total darkness. Because different elements emit light at characteristic wavelengths, scientists can use spectrometers to analyze the light of the sun and determine its composition. But the green line observed in 1869 did not correspond to any known elements on earth. Scientists thought they might have discovered a new element, and they called it Coronium.
It was not until 70 years later that a Swedish physicist discovered that the element responsible for the emission is iron, overheated until it is 13 times ionized with only half of the electrons of a normal iron atom. And that's the problem: scientists calculated that such high ionization levels require coronal temperatures of around 2 million degrees Celsius – almost 200 times hotter than the surface.
For decades, this deceptively simple green line has been the Mona Lisa of sunlight science, confusing scientists who can not explain their existence. Since we identified his source, we understood that the puzzle is even more complex than it first appeared.
"I'm thinking of the coronal warming problem as an umbrella covering a few confusing issues related to it," said Justin Kasper. a space scientist at the University of Michigan in Ann Arbor. Kasper is also Principal Investigator for SWEAP, short for Solar Wind Electrons Alphas and Protons Investigation, a range of instruments onboard the Parker Solar Probe. "First, how does the corona get so hot so fast, but the second part of the problem is that it not only starts, it continues, and not only does the heating go on, it also heats different elements at different speeds." It is a fascinating indication of what happens to the warming in the sun.
Since the discovery of the hot corona, scientists and engineers have done a great deal of work to understand his behavior. They have developed powerful models and instruments and launched satellites that observe the sun around the clock. But even the most complex models and high-resolution observations can only partially explain coronal warming, and some theories contradict each other. There is also the problem of studying the corona remotely.
We may live in the expansive atmosphere of the sun, but the corona and solar plasma in the near-Earth space are dramatically different. It takes about four days for the slow solar wind to travel 93 million miles and reach the Earth or spacecraft it studies – plenty of time to mingle with other particles that travel across space and lose their distinctive features.
Studying this Homogeneous Soup Plasma for evidence of coronal warming is like trying to study the geology of a mountain by scouring sediments thousands of miles downstream in a river delta. On the way to the corona, Parker Solar Probe will scan particles that have just warmed up, eliminate the uncertainties of a 93-million-mile journey, and return the most perfect measurements of the corona ever recorded to Earth.
"All of our work over the years has reached its peak on this point: we have realized that we can never fully resolve the coronary warming problem until we find a probe Send the corona itself to take measurements, "said Nour Raouafi, Deputy Project Scientist and Solar Physicist at Parker Solar Probe at the Applied Physics Laboratory of Johns Hopkins University in Laurel, Maryland.
The Journey to the Sun is an idea older than NASA, but has taken decades to develop the technology that makes their journey possible. During this time, scientists have determined exactly what types of data – and corresponding instruments – they need to complete a picture of the corona and answer these ultimate burning questions.
Explaining the Secrets of the Corona  Parker Solar Probe will test two major theories to explain coronal warming. The outer layers of the sun are constantly cooking and rusting with mechanical energy. As massive cells of charged plasma travel through the sun – as bubbles rise through a pot of boiling water – their fluid motion creates complex magnetic fields that extend far into the corona. Somehow, the entangled fields channel this wild energy into the corona as heat – as they do what every theory tries to explain.
One theory suggests that electromagnetic waves are the root of the corona's extreme heat. Perhaps this boiling motion brings magnetic waves of a certain frequency – called Alfvén waves – from deep into the sun into the corona, which spin and charge charged particles through the air, a bit like ocean waves driving the surfers to shore and accelerating.
Another suggests that bomb explosions, so-called nanoflares, dissipate heat into the solar atmosphere via the solar surface. As with their larger counterparts, solar flares, Nanoflares, are expected by an explosive process called magnetic reconnection. Turbulent boiling on the sun twists and twists magnetic field lines and builds up tensions and stresses until they explode like an overwound rubber band breaks – particles accelerated and heated.
The two theories are not necessarily mutually exclusive. In fact, many scientists, to complicate matters, think that both could be involved in heating the corona. Sometimes, for example, the magnetic reconnection that triggers a nanoflare could also trigger Alfvén waves, which then continue to heat the plasma.
The other big question is how often do these processes occur – constantly or in different outbreaks? The answer requires a level of detail that we do not have from 93 million miles away.
"We are approaching the heating, and there are times when Parker Solar Probe rotates at the same time or the sun orbits the speed the sun is turning itself," said Eric Christian, a space scientist at NASA's Goddard Space Flight Center in Greenbelt , Maryland, and a member of the mission's scientific team. By "hovering over the same spot, we see the evolution of warming."
As soon as Parker Solar Probe arrives at the corona, as will become it help scientists to distinguish whether waves or Nanoflares drive heating? While the spacecraft carries four sets of instruments for various types of research, two will receive data in particular useful for solving the problem of coronal warming: the FIELDS and SWEAP
invisible forces surveyor, FIELDS, led by the University California, Berkeley, directly measures electric and magnetic fields to understand the shocks, waves, and magnetic reconnections that heat the solar wind.
SWEAP – led by the Harvard-Smithsonian Astrophysical Observatory in Cambridge, Massachusetts – is the complement of half the study, collecting data on the hot plasma itself. It counts the most abundant particles in the solar wind – electrons, protons and helium ions – and measures their temperature, how fast they move after heating and in which direction.
Together, the two sets of instruments paint a picture of the electromagnetic fields that are believed to be responsible for the warming, as well as the just-heated solar particles that swirl through the corona. Critical to their success are high-resolution measurements that are able to resolve interactions between waves and particles in fractions of a second.
Parker Solar Probe will appear within 3.9 million miles of the sun's surface – and that distance may seem great. the spacecraft is well positioned to detect signatures of coronal heating. "Although magnetic reconnections occur lower down near the solar surface, the spacecraft will see the plasma immediately after it occurs," said Goddard solar scientist Nicholeen Viall. "We have the chance to put our thermometer directly into the corona and watch the temperature rise, compare that to the study of plasma heated four days ago from Earth, where many 3D structures and time-critical ones are Information is washed out. "
This part of the corona is a completely unexplored area, and scientists expect everything else they've seen before. Some think the plasma there is thin and thin like cirrus clouds. Or it will seem like massive pipe cleaner-like structures emanating from the sun.
"I'm pretty sure if we get that first round of data back, we'll see the solar wind at lower altitudes near the sun prickly and impulsive," said Stuart Bale of the University of California, Berkeley, Astrophysicist and FIELDS Principal Investigator , "I would spend my money on making the data much more exciting than what we see near Earth."
The data is complicated enough – and comes from several instruments – that scientists need some time to put together an explanation for coronal warming. And because the sun's surface is not smooth and varies everywhere, Parker Solar Probe has to make several passes across the sun to tell the full story. But scientists are confident that they have the tools to answer their questions.
The basic idea is that every proposed mechanism for heating has its own unique signature. If Alfvén waves are the source of the corona's extreme heat, FIELDS will detect their activity. As heavier ions are heated at different rates, it appears that different classes of particles interact with these waves in a specific way; SWEAP will characterize their unique interactions.
When Nanoflares are responsible for this, scientists expect beams of accelerated particles to shoot in opposite directions – a telltale sign of explosive magnetic reconnection. Where magnetic reconnection occurs, they should also detect hot spots where magnetic fields change rapidly and the surrounding plasma heats up.
Discoveries Are Present
There is a zeal and excitement among the solar scientists: Parker Solar Probe's mission marks a turning point in the history of astrophysics, and they have a real chance to unlock the secrets who have messed up their field for nearly 150 years.
By combining the inner workings of the corona, scientists gain a deeper understanding of the dynamics that trigger space weather events that shape conditions in near-Earth space. But the applications of this science extend beyond the solar system. The sun opens a window to understanding other stars – especially those that also show solar-like heating – stars that could potentially boost habitable environments but are too far to ever study. And lighting the basic physics of plasmas could probably tell scientists a lot about how plasmas behave elsewhere in the universe, such as galaxy clusters or black holes.
It is also quite possible that we have not even imagined the greatest discoveries to come. It's hard to predict how solving coronary warming will change our understanding of the space around us, but fundamental discoveries like these have the ability to change science and technology forever. Parker Solar Probe's voyage introduces human curiosity into an unprecedented region of the solar system, where every observation is a potential discovery.
"I'm almost certain we'll discover new phenomena that we do not know about now, and that's very exciting for us," Raouafi said. "Parker Solar Probe will make history by helping us to understand coronal warming – as well as solar wind acceleration and solar energy particles – but I think it also has the potential to steer the direction of the future of solar physics."