Parker Solar Probe NASA and the curious case of the hot crown

Something mysterious is happening in the sun. In defiance of all logic, its atmosphere gets hotter and hotter as it extends from the flaming surface of the Sun.

Temperatures in the corona – the tenuous and outermost layer of the solar atmosphere – reach 2 million degrees Fahrenheit. only 1,000 miles below, the underlying surface simmers at a gentle temperature of 10,000 F. How the Sun handles this feat remains one of the biggest unanswered questions in astrophysics; scientists call it the problem of coronal heating. A new mission, NASA's Parker Solar Probe, which is due to be launched no earlier than August 11, 2018, will cross the crown itself, seeking clues to its behavior and offering scientists the opportunity to solve this mystery.

Earth, as we see in visible light, the appearance of the Sun – calm, immutable – denies the life and drama of our nearest star. Its turbulent surface is cradled by intense eruptions and intense bursts of radiation, which project solar materials at incredible speeds in all corners of the solar system. This solar activity can trigger space weather events that can disrupt radio communications, injure satellites and astronauts and, at worst, disrupt power grids.

Above the surface, the crown extends over millions of kilometers. plasma, the gases overheat so much that they separate into an electrical flux of ions and free electrons. Eventually, it goes on outside like the solar wind, a supersonic plasma stream impregnating the entire solar system. And so, it is that humans live well in the extended atmosphere of our Sun. Fully understand the crown and all its secrets, that is to understand not only the star that feeds life on Earth, but also the very space that surrounds us.

A 150-year-old mystery

Most of what we know about the crown is deeply rooted in the history of total solar eclipses. Before sophisticated instruments and spacecraft, the only way to study the crown of the Earth was during a total eclipse, when the Moon blocks the shining face of the Sun, revealing the weaker and surrounding crown.

The history of the coronal heating problem begins with a green spectral line observed during a 1869 total eclipse. Because different elements emit light at characteristic wavelengths, scientists can use spectrometers to analyze sunlight and identify its composition. But the green line observed in 1869 does not correspond to any known element on Earth. Scientists thought perhaps that they had discovered a new element, and they called it coronium.

It is only 70 years later that a Swedish physicist discovers that the element responsible for the emission is iron, overheated to the point that it is ionized 13 time. with only half the electrons of a normal iron atom. And that's where the problem lies: Scientists have calculated that such high levels of ionization would require coronal temperatures of about 2 million degrees Fahrenheit – nearly 200 times higher than the surface

. science, confusing scientists who can not explain its existence. Since we identified the source, we understood that the puzzle is even more complex than it first appeared.

"I'm thinking of the problem of coronal heating as an umbrella that covers two confused problems related," said Justin Kasper, a space scientist at the University of Michigan in Ann Arbor. Kasper is also principal investigator for SWEAP, abbreviation for Solar Wind Electrons Alphas and Protons Investigation, a suite of instruments on board Parker Solar Probe. "First of all, how does the corona get so hot so quickly?" But the second part of the problem is that it does not just start, it goes on, and not only does the heating continue, but different elements are heated to rhythms. different. "This is an intriguing index of what is happening with solar heating.

Since the discovery of the hot crown, scientists and engineers have worked hard to understand its behavior. and powerful instruments and launched spaceships that look at the Sun around the clock.But even the most complex models and high-resolution observations can only partially explain the coronal heating, and some theories contradict each other. there is also the problem of the remote study of the crown

We can live in the expansive atmosphere of the Sun, but the crown and the pl solar asma in the near space of the Earth differ greatly. It takes about four days for the slow solar wind to travel 93 million miles and reach Earth or the spacecraft that is studying it – plenty of time to intermingle with other particles that cross the planet. Space and lose its characteristics.

Looking for evidence of coronal warming is like trying to study the geology of a mountain, sifting through sediments in a delta thousands of miles downstream. On the way to the crown, Parker Solar Probe will take off just-heated particles, removing the uncertainties of a 93 million-mile journey and sending back to Earth the most immaculate measurements of the crown ever recorded

"All our work over the years has resulted in this point: We realized that we can never completely solve the problem of coronal heating before 39 send a probe said Nour Raouafi, deputy scientist of the Parker Solar Probe project and solar physicist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.

Traveling in the sun is an older idea than NASA itself, but it took decades to design the technology that makes its journey possible.In the meantime, scientists have determined exactly what types of data – and the corresponding instruments – they need to complete an image of the crown and answer that ultimate question

Explaining the secrets of the crown [19659003] Parker Solar Probe will test two main theories to explain the heating The outer layers of the Sun are constantly boiling and roasting with mechanical energy. As massive cells of charged plasma propagate in the Sun – in the same way that separate bubbles take place in a pot of boiling water – their fluid motion generates complex magnetic fields that extend far into the crown. In one way or another, tangled fields channel this fierce energy into the corona like heat – which each theory tries to explain.

One theory proposes that electromagnetic waves are the root of the extreme heat of the corona. Perhaps this boiling motion is launching magnetic waves of a certain frequency – called Alfvén waves – from the deep sun to the crown, which project charged particles and warm the atmosphere. , much like ocean waves push and accelerate surfers to the coast.

Another suggests bomb-like explosions, called nanoflares, across the surface of the Sun that is releasing heat into the solar atmosphere. Like their larger counterparts, solar flares, nanoflares are believed to result from an explosive process called magnetic reconnection. The turbulent boiling on the sun twists and twists the magnetic field lines, accumulating voltage and voltage until they explode explosively – like breaking a coiled elastic band – accelerating and warming up particles in their wake.

The two theories are not necessarily mutually exclusive. In fact, to complicate matters, many scientists believe that both can be involved in heating the crown. Sometimes, for example, the magnetic reconnection that triggers a nanoflare could also launch Alfvén waves, which further heat the plasma.

The other big question is: how often do these processes occur – constantly or in separate gusts? Answering this question requires a level of detail that we do not have at 93 million miles.

"We're getting closer to the heat, and there are times when Parker Solar Probe will spin at the same time, or spin around the Sun.The Sun itself is spinning faster," said Eric Christian, a scientist with Space at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and a member of the mission's science team. "It's an important part of science." Hovering in the same place, we'll see the evolution of heating. "

Discovering Evidence

Once Parker Solar Probe will arrive at the crown, how will scientists be able to distinguish whether the waves or Nanoflares drive heating? While the spacecraft carries four suites of instruments for a variety of types of research, two in particular will obtain useful data to solve the mystery of coronal heating: the FIELDS and SWEAP experiment

Surveyor of Invisible Forces, FIELDS, led by the University of California, Berkeley, directly measures the electric and magnetic fields, in order to understand the shocks, waves and magnetic reconnection events that heat the solar wind.

SWEAP – led by the Harvard-Smithsonian astrophysical observatory in Cambridge, Massachusetts – is the comp element half of the survey, 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, their speed of movement after heating and in which direction.

Together, the two suites of instruments paint an image of the electromagnetic fields believed to be responsible for heating, as well as solar particles that have just warmed up through the corona. The key to their success lies in high-resolution measurements, able to solve the interactions between waves and particles in fractions of a second.

Parker Solar Probe will melt within 3.9 million miles of the Sun's surface. the spacecraft is well positioned to detect the coronal heating signatures. "Even if the magnetic reconnection events unfold further near the surface of the Sun, the spacecraft will see the plasma just after they happen," said Nicholeen Viall, Goddard's solar scientist. "We have a chance to glue our thermometer directly into the crown and watch the temperature rise.Like that to the study of the plasma that was heated four days ago from Earth, where a lot of 3D structures and d & rsquo; # 39; temporal information is faded. "

This part of the crown is an entirely unexplored territory. they have already seen. Some think that plasma will be vaporous and tenuous, like cirrus. Or perhaps it will appear as massive structures resembling a pipe radiating from the Sun.

"I am sure that when we get this first set of data, we will see that the solar wind at low altitude near the Sun is thorny and impulsive," said Stuart Bale, University of California, Berkeley, astrophysicist and principal investigator from FIELDS. "I would put my money on the data being much more exciting than what we see near the Earth."

The data is quite complicated – and comes from several instruments – that it will take time for scientists to reconstruct an explanation of coronal heating. And because the Sun's surface is not smooth and varies throughout, Parker Solar Probe must make multiple passes over the Sun to tell the whole story. But scientists are sure to have the tools to answer their questions.

The basic idea is that each proposed heating mechanism has its own distinct signature. If the Alfvén waves are the source of the extreme heat of the crown, the FIELDS will detect their activity. Since heavier ions are heated at different speeds, it seems that different classes of particles interact with these waves in a specific way; SWEAP will characterize their unique interactions

If nanofillers are responsible, scientists expect to see accelerated particle jets set off in opposite directions – a tell-tale sign of explosive magnetic reconnection. Where magnetic reconnection occurs, they should also detect hot spots where the magnetic fields change rapidly and heat the surrounding plasma.

Discoveries Are Arising

There Is Enthusiasm and Enthusiasm Solar Probe's mission marks a decisive turning point in the history of astrophysics, and they have a real chance to unravel the mysteries that have blurred their field for nearly 150 years.

By restoring the inner workings of the crown, scientists will gain a deeper understanding of the dynamics that trigger space weather events, shaping conditions in the near-Earth space. But the applications of this science extend beyond the solar system as well. The Sun opens a window to the understanding of other stars – especially those that also have solar-like heating – stars that could potentially foster habitable environments, but are too far apart to study. And illuminating the fundamental physics of plasmas could probably teach scientists a lot about how plasmas behave elsewhere in the universe, such as in clusters of galaxies or around black holes.

It is quite possible that we have not even designed discoveries to come. It is difficult to predict how the resolution of coronal heating will change our understanding of the space around us, but fundamental discoveries like this have the ability to change science and technology forever. Parker Solar Probe's journey takes human curiosity to a region of the solar system never seen before, where every sighting is a potential discovery.

"I am almost certain that we will discover new phenomena of which we know nothing now, and it is very exciting for us," said Raouafi. "Parker Solar Probe will go down in history helping us understand coronary heating – as well as accelerating solar wind and solar energy particles – but I think it also has the potential to To orient the future of solar physics. "