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Something mysterious is happening in the sun. In defiance of all logic, its atmosphere becomes hotter, the more it stretches away from the flaming surface of the Sun.
Temperatures in the corona – the thin, ultraperipheral layer of the solar atmosphere – rise by more than 2 million degrees Fahrenheit, while the underlying surface simmers at 10,000 F. The way the sun manages this feat of the largest unanswered questions in astrophysics; scientists call it the problem of coronal heating. A new historical mission, NASA's Parker Solar Probe, which is scheduled to launch no earlier than 11 August 2018, will cross the crown itself, seeking clues to its behavior and offering scientists the opportunity to solve this mystery. The Earth, as we see in the 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 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 from the Earth was during a total eclipse, when the Moon blocks the shining face of the Sun, revealing the surrounding weaker crown
& rsquo; History of the coronal heating problem begins with green spectral line observed during a total eclipse of 1869. Because different elements emit light at characteristic wavelengths, scientists can use spectrometers to analyze the sun's light 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 here lies the problem: scientists have calculated that such high levels of ionization would require coronal temperatures around 2 million degrees Fahrenheit – nearly 200 times higher than the surface
For decades, this falsely simple green line has been the Mona Lisa of solar science, confusing scientists who can not explain its existence. Since we identified the source, we understood that the puzzle was even more complex than it was first.
"I think of the problem of coronal heating as an umbrella that covers two confusing 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, how does the corona get so hot, but the second part of the problem is that it does not start, it continues, and not only the heating continues, but the different elements are heated at different rates. This is an intriguing hint to what is happening with the heating in the sun.
Since the discovery of the hot crown, scientists and engineers have done a lot of work to understand its behavior. They have developed powerful models and 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 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 corona and the solar plasma in the near space of the Earth differ considerably. 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 sample just heated particles, removing the uncertainties of a 93-million-mile trip and sending back to Earth the most perfect measurements of the crown ever recorded.
"All our work" We realized that we will never be able to completely solve the problem of coronal heating before sending a probe to make measurements in the crown itself, "said Nour Raouafi, deputy scientist Parker Solar Probe Project and Solar Physicist at Johns Hopkins University 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 At this moment, scientists have determined exactly what types of data – and the corresponding instruments – they need to complete an image of the corona and answer that final burning question.
Explanation of the secrets of the crown
Parker Solar Probe will test two main theories to explain coronal heating. The outer layers of the Sun are constantly boiling and roasting with mechanical energy. While massive charged plasma cells move 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 and wide. the crown. In one way or another, entangled fields channel this fierce energy into the crown like heat, which each theory attempts to explain.
One theory suggests that electromagnetic waves are the root of the extreme heat of the corona. Perhaps this boiling motion launches magnetic waves of a certain frequency – called Alfvén waves – from the bottom of the Sun to the crown, which send charged particles and heat the atmosphere. Atmosphere, much like ocean waves push and accelerate surfers.
Another suggests bomb-like explosions, called nanoflares, across the surface of the Sun, which 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 voltages and voltages until they explode explosively by breaking a rolled rubber band that speeds up and warms 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 then heat up the surrounding plasma.
The other big question is: how often do these processes occur constantly or in separate bursts? Answering this question requires a level of detail that we do not have at 93 million miles.
"We are getting closer to the heat, and there are times when Parker Solar Probe will be spinning at the same time, or will be spinning around the Sun.Speed the Sun itself turns," said Eric Christian, a scientist of the Space at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and a member of the mission's science team. "This is an important part of science, hovering in the same place, we will see the evolution of heating."
Discovering Evidence
Once Parker Solar Probe arrives at the crown, how will scientists be able to tell if the waves or nanoflars are 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 electric and magnetic fields, to understand shocks, waves and magnetic reconnection events that heat the solar wind.
SWEAP-led by the Harvard-Smithsonian astrophysical observatory in Cambridge, Massachusetts-is complementary to 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. paint an image of the electromagnetic fields thought to be responsible for heating, as well as solar particles that have just heated up through the crown. 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 the opportunity to place our thermometer directly in the crown and watch the temperature rise, compare 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 washed out. "
This part of the crown is an entirely unexplored territory, and scientists are waiting at sites that look nothing like what they've seen before. Some think that plasma will be vaporous and tenuous, like cirrus. Or perhaps it will look like enormous structures in the form of pipe cleaners radiating from the Sun.
"I am sure that when we get this first set of data, we will see the solar wind at low altitude near the prickly and impulsive Sun," said Stuart Bale, University of California, Berkeley, astrophysicist and principal investigator. FIELDS. "I would put my money on the data being much more exciting than what we see near the Earth."
The data is rather complicated – and comes from several instruments – that it will take time for scientists to reconstruct an explanation of coronal warming. 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 confident 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 unleash 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 Excitement 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 present similar solar-like heating stars that could potentially foster habitable environments, but are too far to be studied. 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," Raouafi said. "Parker Solar Probe will go down in history by helping us understand coronary heating, as well as the acceleration of solar wind and solar energy particles, but I think it also has the potential to 39, steer the direction of the future of solar physics. "
Learn more:
NASA prepares to launch Parker Solar Probe, a mission to touch the sun
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