“THIS COMING DECADE WILL BE THE GOLDEN AGE OF SOLAR AND HELIOPHYSICS RESEARCH”
All About Space catches up with the project scientist for NASA’s incredible Parker Solar Probe mission, Dr Nour Raouafi – a spacecraft continuously breaking records and surpassing all expectations as it orbits the Sun
How’s the Parker Solar Probe doing? Are there any updates that we should be aware of?
The Parker Solar Probe is doing great. We are going through our fifth encounter and recently we were the closest we’ve ever been to the Sun. After a period of five days where we could not communicate with the spacecraft, it sent us a signal that it’s healthy and it’s doing what it’s supposed to do. In terms of science, it’s just amazing. Whenever the spacecraft gets closer to the Sun, we are learning new things that we’ve never seen before.
What is the major mystery surrounding the Sun and its corona that astronomers are desperately trying to solve, and are hoping the Parker Solar Probe will help shed light on?
There are a few phenomena that were discovered decades ago, but we are still struggling to understand. I think the one that is most puzzling is what we call the ‘coronal heating problem’.
The corona, which is the outermost layer of the solar atmosphere, is 300-times hotter than the solar surface. And we know that all the energy is coming from inside the Sun, so in a way it’s counter-intuitive that the source is cooler than the environment around it. But the Parker Solar Probe is giving us clues and hints as to what might be causing excess heating there.
Another phenomenon, which is very closely related to coronal heating as well, is what we call the acceleration of solar wind. The solar wind is a flow of charged particles – electrons, protons, ionised helium and heavy elements – that are constantly flowing away from the Sun to the rest of the Solar System. The issue with the solar wind is that low down [within the solar atmosphere] these particles are flowing at very slow speeds, but they get accelerated to hundreds of kilometres per second in a very short distance. We don’t know exactly what is the physical mechanism that gives them the energy to accelerate to these high speeds.
The third phenomenon, and we are impacted by it every day, is big explosions on the Sun. Whenever there is a flare or a coronal mass ejection (CME) erupting on the Sun, there is a population of particles that get accelerated to almost the speed of light. We call them solar energetic particles.
The Parker Solar Probe was built specifically to be able to shield its instruments in a really dangerous environment. How has its heat shield been constructed so that it can withstand such dangerous temperatures and radiation while remaining relatively lightweight?
The heat shield is basically made of carbon foam. Most of it is a vacuum. It’s like a sponge made out of carbon that is sandwiched between two sheets, which are also compressed carbon. The other thing that is specific to the Parker Solar Probe is a plasma spray that is white and is on top of the heat shield. The goal here is to reflect as much light from the Sun as possible.
When we are closest to the Sun in 2024, that side of the heat shield will be more than 2,500 degrees
Fahrenheit [1,371 degrees Celsius]. 4.5 inches (11.5 centimetres) inward, which is the other side of the heat shield, will be at almost 700 degrees Fahrenheit [371 degrees Celsius], so there we have already lost a lot of heat. And from that backside of the heat shield to the bus, where the instruments are mounted, it is at room temperature.
What impacts can space weather and solar wind have to us on Earth?
Let me start by saying, we are now starting to think about sending women and men to the Moon, and maybe to Mars in the near future. If we are going to do that, we need to protect these people out there. We cannot just launch them out there. If we don’t protect them sufficiently, these solar energetic particles will not be good for them and also for the space equipment. It will have a different impact on our environment here on Earth and also the other planets as well.
Just as a simple example: we rely a lot on GPS, which is functional because we have spacecraft orbiting Earth. And if there is a big explosion on the Sun and it burns some of these satellites out, some of us will be in trouble because GPS will not be working anymore.
Another example is if we have a huge CME or flare that will cause a humongous geomagnetic storm here on Earth – that can cause a shutdown of power grids. That will be devastating for the economy and for the societal fabric. That’s actually why space weather is a big topic now for research and for all of us here.
It’s been two years now since the Parker Solar Probe was launched. Do you have any favourite moments or a favourite result that has come from the mission so far?
A lot of them. One of my favourite moments – I may not have enjoyed it when it happened, but now with hindsight I enjoyed it a lot – was the launch of the mission. I mean, we have been waiting for the Parker Solar Probe for 60 years, and on 12 August 2018 we put it on top of the most powerful rocket in existence, and all you hope for is that everything goes smoothly. I was so stressed when I was watching it, and it all went really well.
But after that, what we have discovered is something amazing. The spacecraft we designed at APL is functioning way better than we had thought it would. What we are getting back from this machine is amazing. Let me give you an example in terms of science data: we are bringing three to four times the volumes we thought we would do pre-launch. We also thought pre-launch that we were only going to operate instruments when we were close to the Sun and after launch. We are now basically operating the instruments almost all of the time.
The planned mission duration is currently seven years. Do you think it could possibly reach ten years or more?
If by the end of the seven years, if everything is going well, it’s a no-brainer that we will request an extension of the mission. During these seven years we will have basically covered half of the solar cycle. We launched at the minimum, and by 2025 we will be at the maximum of the solar cycle. What I want to see from the Parker Solar Probe is to basically complete a whole cycle, going from the maximum to the other minimum, which is an extension of the mission by five to six years. I would love to see that.
Could this information be used for stars beyond our Solar System as well?
That’s a very good remark. By understanding how the Sun works, we can actually project all we gain from what we learned about the Sun to other stellar systems. Other stellar systems are so far away that we cannot study them in detail as we are currently doing with the Sun. What we learn from the Parker Solar Probe, by explaining all these big phenomena we talked about at the beginning, we can basically take that and project it onto other stellar systems – and why would you want to do that?
It’s because we are so curious about whether there are other planets out there and whether there is habitability around other stars. The interaction between the stars and the planets is so crucial for life and for habitability. By understanding how the Sun behaves and how it interacts with us here on Earth and other planets, it will help us tremendously in understanding other stellar systems. In a way the Parker Solar Probe is our ambassador to other stellar systems as well, as it will help us understand other stellar systems.
In December 2019 news came out around the Parker Solar Probe regarding the release of the first year of scientific results. Could you explain some of the main news stories that came out after this first year?
That was really an ideal time for the Parker team, but also for everybody. For humanity. Flying a spacecraft around this star is something very challenging. In terms of science, it was amazing. But before going into this, let me say this. You will have to wait a little bit, probably a few months, and you will be seeing another wave of big discoveries from the Parker Solar Probe. We just got the new data from orbit four, which is the closest perihelion to the Sun, and we are seeing new things that we have not seen before.
Going back to what we released in December and later on in February in a special issue in the Astrophysical Journal, there are a key number of discoveries that are breakthrough discoveries. One of them is what we call the ‘dust-free zone’.
When you look at the heliosphere, there is dust almost everywhere. The dust comes from asteroids and comets that grind up in the Solar System, but the closer the dust particles get to the Sun, the smaller they get. At a certain point they will evaporate. The result of that is you create a zone around the Sun where there is no dust. This was hypothesised in 1929, and since then people have looked for it over and over again, but nobody has seen it. The Parker Solar Probe is giving the first hints that this dust-free zone exists.
The objectives of the mission are obviously to explain the heating and the acceleration of the plasma in the coronal heating and acceleration of the solar wind. In other terms, what we are looking for are energy sources that we cannot see from Earth, and the Parker Solar Probe is giving us one possible smoking gun.
When the Parker Solar Probe got closer to the Sun, it saw kinks in the magnetic field. Magnetic fields essentially make an S-shape. They bend all the way back to the Sun and outward again in a matter of a few tens of seconds to several minutes. The reason why this is so important is that you cannot do that to a magnetic field easily. Creating this structure and maintaining it means that there is a big source of energy creating that. That’s exactly what we are looking for.
Surely with this mission, the fact that it’s achieving so many milestones and performing so well, that’s going to inform what kind of mission you could do next, and what sort of boundaries you could push.
You are touching on a very sensitive nerve there. Go back in history to the 1960s. There was a committee that proposed three key missions that NASA had to implement. One of the missions was a probe that orbits the poles of the Sun, which has already been implemented. This was the Ulysses mission. Now that mission is over. The second one is a probe that will orbit the Sun within the orbit of Mercury. That is the Parker Solar Probe. We did it after 60 years. It has been challenging, but we did it.
The third one is a probe that will fly out of the Solar System, very, very far away. We are working on that, but why have we started working on that? It’s because we realised the success of the Parker Solar Probe.
Now the community is so bold. Realising that a challenging mission like the Parker Solar Probe can be so successful, we are able to do it for other missions as well. The outer solar probe is certainly one of them. It’s an extremely challenging mission, but we started working on it at APL and hopefully one day it will see the light.
There is another idea out there, which is having a solar polar mission, which is an amazing mission. This is a mission that will fly above the poles of the Sun for an extended period of time, and that’s also not easy at all. Getting a spacecraft out of the ecliptic is extremely hard, but again, realising the success of the Parker Solar Probe is pushing the community to be bold and start thinking about these big challenges.
The European Space Agency (ESA) recently launched the Solar Orbiter spacecraft in collaboration with NASA. Are there any plans to coordinate on observations with the Parker Solar Probe and the Solar Orbiter?
These two solar missions can complement each other in many ways. I can tell you that working together will provide the scientists – and also everybody else – with way more than the sum of the two missions.
I’m almost sure that with these two missions, and also if you add DKIST, the Daniel K. Inouye Solar Telescope, which is a large solar telescope in Hawaii, this coming decade will be the golden age of solar and heliophysics research.
I don’t think we have ever witnessed the amount of enthusiasm around the Parker Solar Probe,
Solar Orbiter and DKIST as we are seeing now, and honestly we have never been able to achieve this much in such a short amount of time. Having a mission that is approaching the Sun like never before, having another mission that is flying above the ecliptic to see the poles for the first time and also having the largest solar telescope on the ground… it’s amazing.