Over the years, we’ve gotten to know the solar system quite well. The inner, terrestrial planets; the outer, gas and ice giants; the Asteroid Belt that cuts through the middle of it all. But one of the solar system’s greatest mysteries remains the star at its heart.
We know that the sun is an incredible source of energy, and the provider of life on Earth but there are still plenty more questions about this fiery, explosive mass left to answer n and now we’re getting as close as possible in our pursuit of knowledge.
The Parker Solar Probe stands as one of, the most unique and interesting NASA missions in recent times. While so many space probes tend to head outwards from Earth, to explore the rest of the solar system and, indeed, the universe Parker flies in the other direction.
Toward the gravitational center of the solar system, much further in than even the innermost planet, Mercury, to our sun.
Parker launched on August 12th, 2018, and is fast approaching the halfway point of its planned seven-year mission. And, while the sun is its target for research, it’s not as though it just beelined straight for it. Rather, Parker has made (and will continue to make) use of multiple gravity assists around Venus.
This means that it cuts a tighter and tighter orbital path through the solar system, toward and away from the sun, but takes it progressively closer to the star with each repetition. As such, on October 29th, 2018, just eleven weeks after it left Earth, Parker passed closer to the sun than any other artificial object in history - beating a decades-old record set by the Helios 2 probes, back in 1976.
Since then, though, it has moved nearer and nearer, breaking new ground, until in December 2021 news broke that Parker had completed one of its most audacious mission goals by touching the sun. To understand what this means, we need to first look at how the sun is structured.
Our star might look like just a flaming ball of fire, but it’s made up of multiple layers. In the very center, there’s the core on top of that there’s the radiative zone where energy releases outwards from the core.
Over thousands of years and then there’s the convection zone, cycling that energy toward the surface. These take up most of the sun’s bulk, but then we reach the outer layers the photosphere, chromosphere, transition region, and the corona.
The photosphere is sometimes known as the solar surface, although the sun doesn’t have a solid surface like terrestrial planets do the chromosphere is a little above the photosphere, where temperatures rise the further out into it you go, and then the transition region is a thin zone marking yet another temperature increase.
Finally, the Corona encases it all, a wispy but blistering outer layer of the atmosphere, with temperatures now hitting around 2 million degrees Fahrenheit. And it’s here that the Parker Solar Probe has now reached, which is why it can claim to have touched the sun.
Parker first breached the Corona on April 28th, 2021, during its eighth solar approach, although the news wasn’t announced until December 14th, 2021. According to NASA, the probe flew “through the sun’s upper atmosphere.
The Corona and sampled particles and magnetic fields”. The Agency has also described the feat as a “Monumental Moment” and “one giant leap for solar science”. It represents such an important breakthrough because until now we’ve only ever been able to study the sun from afar, but thanks to this mission we’re starting to gather first-hand data from the star itself. And, indeed, the corona isn’t even visible to us under usual conditions, although we know it’s there.
So Parker is truly lifting a veil of mystery on that front. As far as findings go, it’s still early days. Parker only spent a few hours in the corona on this, its first visit, and there hasn’t yet been anything like a huge revelation of brand-new science to make us look at the sun differently.
But scientists do expect to gradually gather more information over the coming months. Upon announcing Parker’s latest milestone, one Thomas Zurbuchen. The associate administrator for the Science Mission Directorate at NASA HQ in Washington - said that not only would Parker “provide us with deeper insights into our Sun’s evolution” but that it would also “teach us more about the stars in the rest of the universe”.
One thing that has already been readdressed is the Alfvén critical surface. Which is the boundary between the corona and the rest of the solar system. While solar wind containing solar particles does, of course, spread throughout the system, with solar flares carrying a particular threat to Earth and the other surrounding planets, there is a kind of outer edge to the sun itself.
A final port of call before the most energetic solar particles pull away from the gravity of the star and get released as the solar wind. But Parker has reportedly found that outer edge. The Alfvén critical surface is not to be round and uniform, but jagged and staggered, instead.
This had already been predicted but that prediction is now supported by first-hand data. Another property of the sun that’s already been granted deeper analysis thanks to Parker is switchbacks. These refer to a repeating pattern in the solar wind released by the star, wherein solar waves appear to briefly double back on themselves before rushing out into space.
This results in a steady, zigzagging, ripple effect, and scientists still aren’t wholly sure why the sun releases in this way. It was Parker that first provided any direct evidence of them, during an early flyby of the sun in 2019 from which point our star, in our minds, has been imbued with a kind of pulsing rhythm.
It isn’t a random pattern, so there has to be a reason for it, but the debate continues as to what that reason is. Parker’s more recent contribution is to seemingly discover that switchbacks originate much closer to the solar surface than originally suspected.
At a much lower level of the solar atmosphere. In this case, as with so much about how the sun works, we’re only just beginning along the road to solar enlightenment. On a basic level, we’ve understood for centuries that this shining ball of light in our sky is also our life-giver.
A spectacular celestial entity that floods out energy, a tiny fraction of which manages to travel the 93 million miles between us and to reach whichever side of Earth happens to be facing it at the time.
But, while we have staged various missions in the past to get to know the sun better, the Parker Solar Probe is breaking new ground over and over again. In April 2021, when Parker first breached the Corona, it was still some 8.1 million miles away from the solar surface itself.
It has since passed even closer than that, to within six million miles. But, over the coming years, as the probe continues to orbit the sun, that distance is predicted to be cut again to just 3.8 million miles by the time its closest approach and its mission end in 2022.
It’s one reason why this mission has been variously described as one of the most exciting space projects in modern times because although records have already fallen and a wealth of new data has already been captured, it still has years left to run.
By the end of Parker’s unique journey through space, we will have learned even more about the solar system and the star at its center. While most other space missions look outwards with wonder at the rest of the universe, with Parker NASA has bucked the trend to get a grip on what’s ultimately one of the most important locations in all the cosmos from our point of view.
We know that the sun won’t be there forever and that in around one billion years it’ll most likely become too hot for life on Earth to withstand, on its way toward expanding into a red giant in about five billion years.
But, between now and then, there’s ample opportunity to remove the mystery of our solar centerpiece and to improve our knowledge of stellar science in general. The Parker Solar Probe is leading the way, on the frontline of this new frontier. And that’s how a NASA probe has managed to touch the sun.