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The Parker Solar Probe: Firing Sensors into the Sun

Recently on Megaprojects, we did a video on the quite extraordinary journey still taking place as Voyager 1 hurtles through interstellar space 22.8 billion km (14.2 billion miles) from our sun – and counting. But today, we’re moving in the opposite direction. While Voyager 1 continues to set new distance records from Earth for a man-made object, the Parker Solar Probe has now become the closest object to the sun that we’ve ever sent – and it’s far from finished yet. 

Nearly three years into a planned seven-year mission, NASA’s Parker Solar Probe is already providing us with a clearer understanding of the sun than ever and in the coming years, it’s hoped that information beamed back from this adventurous little probe can help us to solve some of the fundamental mysteries about our star.   

Just like Voyager 1, there is no way we’ll ever be seeing the Parker Solar Probe again as this is very much a scientific kamikaze mission – you don’t get that close to the sun and live to tell the tale. This may be a doomed flight, but it’s one that will first venture into the cauldron that is the sun’s corona – just to see what it’s like.      

The Sun

Sun layers

Before we start talking about the probe itself, let’s just begin with the gigantic ball of hot fury that lies at the centre of our solar system. Our understanding of this star has grown exponentially over the years but much of it remains a mystery – which is exactly why the Parker Solar Probe is currently hurtling towards it. 

To call the sun large would be like calling Hitler a man with issues. The colossal sphere of burning plasma accounts for an astonishing 99.8% of the total mass in our solar system. Conversely – and to make us Earthlings feel insignificant – if you added up all the planets and moons in our neighbourhood, they would form just 0.2% of the total mass throughout the solar system. The sun is gigantic – 330,000 times the mass of Earth – but is still small(ish) in comparison to other stars. The largest star that we know of would reach Saturn if it was placed inside our system where our sun is. 

It is a middle-aged sun, give or take 4.59 billion years, mostly formed of hydrogen and helium, but with a little oxygen, carbon, neon and iron thrown in for good measure. It’s ferociously hot and as you might expect, with a surface temperature of 5,505 °C (9,941 F) and a core temperature of a difficult to comprehend 15 million°C (27 million F).

A lot is going on in and around the sun and we only have a vague idea of much of it. The star is formed of various layers, starting with the Core and followed by the Radiative Zone and Convection Zone. It doesn’t have a surface per se, but its visible layer is known as the Photosphere – which is probably as close to your stereotypical idea of hell as you’re ever going to get. This is followed by the Chromosphere and Transition Zone, before ending with Corona – a peculiar outer layer that somehow manages to be 500 times hotter than the Photosphere down near the surface. The corona is so significant it can even be seen by the human eye. When you look at the sun during a solar eclipse, the glowing orb that appears around it is the sun’s corona.    

The sun is constantly producing raging energy and fuses about 600 million tons of hydrogen into helium every second, meaning 4 million tons of matter is converted into energy each second. This energy rises up from the core but can take up to 170,000 years to do so. So next time you’re sitting with your face in the sun sipping a cocktail, remember that that light just took 8 minutes and 20 seconds to reach you from the Sun – but also a period to rise through the sun that takes us all the way back to the very early days of modern humans.  

You might also have heard rumours that the sun will one day consume the Earth, which I’m afraid to say is entirely accurate, but with the sun heating up by 10% every billion years, in just one billion years, the heat on earth will be so high that liquid water won’t exist on the surface anymore – leaving the Earth a barren hell whole where very little, if anything, survives. These conditions will gradually worsen as the sun expands and in roughly 7.6 billion years, the sun will engulf our earth and that, as they say, will be the end of that. 

Exploring the Sun

But before we reach the downfall of the human race and the cataclysmic end to our planet, there’s plenty still to explore regarding this menacing sphere at the centre of our solar system. It’s easy to rest on our laurels knowing that solar annihilation is so far away, but in truth, the sun can knock us out whenever it wants. 

A solar flare is a sudden increase of brightness from a patch of the sun’s surface often accompanied by a coronal mass ejection, which is a significant release of plasma and accompanying magnetic field from the solar corona that shoots out from the star. These events cause the beautiful auroras here on Earth, but don’t get complacent, they could also be deadly. We’ve only begun to notice these in the last 150 years and thankfully they’re normally small enough to not affect us at all, but a major solar flare could well knock out communication and even electrical grids on earth. 

We spend our time worrying about asteroids and meteors, but we’re essentially living next to a massive unstable nuclear reactor with little knowledge of how it all works. Apart from the apocalyptical, there’s plenty of other questions to answer. Why is the Sun’s atmosphere hundreds of times hotter than its surface? How is the solar wind accelerated? And what are the sources of the high energy solar particles?    

Solar Probe Concepts

There have been concepts surrounding probes to the sun that go back to the early stages of the Space Race. A report published in 1958 by the Fields and Particles Group of the National Academy of Sciences’ Space Science Board first suggested the idea of sending an object towards the sun to study the particles and magnetic fields in its vicinity. 

The following decades saw numerous similar ideas emerge but without anything concrete and it wasn’t until the 1990s that the first plans for solar probes really began to emerge. In a strange quirk, the first solar probe was to first travel away from the sun not towards it. After reaching Jupiter, it would have then used a gravitational slingshot to swing around the planet, before dropping into a direct course for the sun. Space can be a confusing place at the best of times. 

But as mathematically sound as this epic roundabout journey was, it was also hugely expensive and time-consuming. The entire project was scrapped after George W Bush became president and it wasn’t until the early 2010s that a new slimmed-down mission appeared that came with a new flight path that would see it use multiple Venus gravity assists for a more direct flight path. 

The Parker Solar Probe   

Parker Solar Probe
Parker Solar Probe

Considering that this little probe is venturing not only into the unknown but also into the kind of temperature that puts a scorching summer day on earth in perspective, it needed to be made of stern stuff. With that in mind, the heat shield is probably the most important place to start. The heat shield – or Thermal Protection System (TPS) to use its official name – is an 11.4 cm (4.5 in) thick hexagonal that is 2.3 metres (7 ft 7 in) in diameter and made of reinforced carbon-carbon composite, capable of withstanding temperatures 1,370 °C (2,500 °F). If that number sounds a little low to you considering the sun’s corona experiences temperatures well over a million degrees, it’s because the area has a very low density meaning that there are very few particles capable of actually transferring the heat. As NASA describes it, it’s the difference between putting your hand in an oven vs putting it in a pan of boiling water.   

The TPS weighs just 73 kg (160lbs) and is only mounted on the sun-facing side of the probe, with all the important instruments hurled behind it. If the shield was to malfunction – or simply fall off – it would only be a matter of seconds before the entire probe began to fail. Amazingly, the interior of the probe will remain at a comfortable room temperature even when inside the sun’s corona.  

The probe itself is 3 meters (9.8 feet) tall and around 1 meter ( 3.3 feet) in diameter, with two solar arrays – each 1.12 meters (3.7 feet) long by 0.69 meters ( 2.26 feet) wide. These arrays are essentially the solar panels for the probe and can produce roughly 388 watts of power, depending on configuration – which is just about enough to power a kitchen blender. But even solar panels need some sun protection and these arrays come with their own water-cooled solar array thermal management system. This involves water flowing through tiny channels embedded in the solar arrays to absorb heat, which then flows into four radiators to release that heat into space. 

The Parker Probe comes with a white reflective alumina surface layer designed to minimise absorption and comes with three antennas; a High-Gain Antenna (HGA), a Two Fan-beam Antenna and a Two Low-Gain Antenna (LGA). 

It has a wide variety of instruments onboard which all essentially come down to five separate investigations. 

  1. Electromagnetic Fields Investigation will take direct measurements of electric and magnetic fields, radio waves, Poynting flux, absolute plasma density, and electron temperature
  2. Integrated Science Investigation of the Sun will measure energetic electrons, protons and heavy ions and uses two Energetic Particle Instruments to study higher and lower energy particles
  3. Wide-field Imager for Solar Probe will capture images of the corona and inner heliosphere through optical telescopes 
  4. Solar Wind Electrons Alphas and Protons will count the electrons, protons and helium ions, and measure their properties such as velocity, density, and temperature.
  5. Heliospheric Origins with Solar Probe Plus will be used for theory and modeling investigation to maximize the scientific return from the mission. 

Mission

The Parker Solar Probe blasted off from Cape Canaveral on 12th August 2018 on the back of a Delta IV Heavy rocket to begin its journey towards the Sun – or rather towards Venus for the time being. The fearsome power of the sun is such that you can’t just plough straight towards it, so instead the Parker Probe is going to use seven flybys of Venus, over the course of seven years, to gradually decrease its orbital perihelion, which is fancy science talk for the closest point to the sun during an elliptical orbit. 

The Parker Probe is set to complete 24 perihelions over the next four and half years as it slowly shortens its distance to the sun. To give you an idea of these distances, the first three perihelions, which occurred between the 6th November 2018 and 1st September 2019, were around 21 million km (13 million miles) from the sun, while the final five, scheduled between 24th December 2024 and 12th December 2025, will be just 6.1 million km (3.8 million miles) from the sun. 

In these final stages of the mission, the spacecraft will be travelling at roughly 430,000 miles per hour. If that speed means absolutely nothing to you, it’s quick enough to get from Washington, D.C., to Tokyo in under a minute. 

The mission is using the flybys of Venus to slow the probe down and it completed its fourth flyby in March 2021, with its next scheduled for 16th October 2021. During its third pass over our closest planetary neighbour back in July 2020 the probe detected a low-frequency radio signal coming from Venus. Before you get too excited it has nothing to do with living beings, but rather ionospheres, which are electrically charged layers of gas or plasma located in the upper atmosphere of planets that emit radio waves. 

Early Findings

With the Parker Solar Probe now comfortably the closest object we’ve ever gotten to the Sun, early findings are already emerging.

One of the earliest discoveries was actually about an absence rather than a new find. The probe found that space dust, which we’ve always assumed floats throughout the solar system, is vaporized once it comes within 3.5 million miles of the sun.

Something else we’ve taken as a given is that magnetic field lines flow evenly out from the sun, but the Parker Probe recorded these lines performing a whip-like motion in which they turn 180 degrees and then back again in a fraction of second. To add a little bit of mystery, these strange switch back magnetic field lines seemed to come in glumps rather than in continuous motions. 

Solar wind was always a major focus of the probe and humans have long debated whether it moves in a sustained motion or comes in spurts, a little like the wind on our own planet. It now seems clear that solar wind behaves erratically and doesn’t follow any clear pattern, with some shooting out into space, while others fall back down into the sun. Scientists have also long pondered at which point in space does the Sun’s Corona – the outermost part of its atmosphere which is always rotating – become the solar winds which travel straight and come towards Earth. While we’re still only scratching the surface, it now seems this transition point is much further away from the sun than what was first thought. 

The Parker Probe has also witnessed several small scale particiale events, when plasma bursts randomly from the sun – imagine all of the volcanoes on Earth going off together and you might have the right kind of mental image. We’ve witnessed these events before, but because of our distance from the sun, we’ve only ever seen the largest. It’s now clear that these small scale events are occurring all of the time, but we’re just too far away to either see or experience them. 

To Boldly Go

Over the next four and half years, the Parker Solar Probe will creep ever closer to the sun as it becomes the first object to beam back information from within the corona itself. It’s probably fair to say that we have absolutely no idea what we’re going to find, which makes the entire adventure so intoxicating. 

Compared to the mesmerizing images recently beamed back from the surface of Mars, which really captured the human imagination, the information sent from the Parker Solar Probe will be much more complex. An object the size of the sun is difficult enough to picture in an abstract way without adding solar winds, solar flares, magnetic fields and energetic particles. But the work of this probe looks set to improve our understanding of this giant ball of gas further than we ever have. 

Let’s not forget that everything on Earth is dependent on our sun and it’s probably within our best interests to learn as much about it as we possibly can. Might we one day be able to use solar winds to skip through the Solar System? Or perhaps even to harness its power for use on Earth? Neither of these questions will be answered anytime soon, but as the Parker Solar Probe inches nearer to the sun, we might just be getting that little bit closer.  

Parker Solar Probe: The Mission (jhuapl.edu)

NASA’s Parker Solar Probe has gone faster than any spacecraft ever | New Scientist

The Parker Solar Probe will have company on its next pass by the sun | Science News

5 New Discoveries from NASA’s Parker Solar Probe – YouTube

NASA’s Parker Solar Probe Measures Radio Signal in Venus’ Upper Atmosphere | Smart News | Smithsonian Magazine

The sun keeps getting stranger, dive-bombing solar probe shows (nationalgeographic.com)

]Parker Solar Probe (jhuapl.edu)

parkersolarprobe_presskit_august2018_final.pdf (nasa.gov)

SolarProbe_FS_WEB.pdf (jhuapl.edu)

Parker Solar Probe – Wikipedia

Credits

featured image source: https://solarsystem.nasa.gov/

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