NASA’S Parker Solar Probe Touches The Sun’s Searing Upper Atmosphere





For the first time ever, a manmade object has entered the Sun’s outer atmosphere, the corona, which inexplicably is thousands of times hotter than our star’s surface (or photosphere). 

Researchers led by a team at the University of Michigan in Ann Arbor were able to predict where the Sun’s upper atmosphere began, and the probe was able to penetrate it for roughly five hours. The Parker probe was not only able to fly through the Sun’s atmosphere but was also able to sample particles and magnetic fields there, says NASA. 

“Flying so close to the Sun, Parker Solar Probe now senses conditions in the magnetically dominated layer of the solar atmosphere – the corona – that we never could before,” Nour Raouafi, the Parker project scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, said in a statement. “We can actually see the spacecraft flying through coronal structures that can be observed during a total solar eclipse.”

On April 28, 2021, during its eighth flyby of the Sun, Parker Solar Probe encountered the specific magnetic and particle conditions some 8.1 million miles above the solar surface, NASA reports. That point, known as the Alfvén critical surface, marks the end of the solar atmosphere and beginning of the solar wind, says NASA. 

The surface of the Sun is about 6000 Celsius, Justin Kasper, the first author of a paper detailing the research in the journal Physical Review Letters, and a professor of climate and space sciences at the University of Michigan in Ann Arbor, told me. Above that, the temperature rises to more than a million degrees, he says.


“That doesn't make any sense if the only source of heat is from fusion in the Sun's core, so something is able to deliver energy into the atmosphere and dissipate it, heating the corona,” said Kasper. “Some people think it is waves, some people think it is lots of tiny solar flares that we can't see individually.” 


What is known is that the solar corona produces streams of solar wind with sufficient speed to escape the gravitational influence of the Sun and expand through interplanetary space, Kasper and his co-authors note.  And near the Sun the pressure and energy density of the corona is magnetically dominated, with magnetic pressure greater than thermal pressure, the authors write.

Why does this matter?

Understanding how this solar material is heated and then crosses this boundary to become the solar wind is not only important for pure solar science but to better understand how we can protect our satellite and communication systems from solar winds and flares.  

Do other nearby stars have an outer corona that is so much hotter than their stellar surpfaces, or photospheres?

While we can't see the Alfven critical surface on other stars, all sorts of astrophysical objects are surrounded by inexplicably hot plasma: material falling into black holes, planets being born around new starts, supernova, says Kasper. 

“It's basic physics that we need to figure out in order to understand how objects in our Universe take shape and evolve,” said Kasper.


Source: https://www.forbes.com/sites/brucedorminey/2021/12/15/nasas-parker-solar-probe-touches-the-suns-searing-upper-atmosphere/?sh=6ce92be5494a


 

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