In search of ever-higher velocities leaving the Solar System, we need to keep in mind the options offered by the solar wind. This stream of charged plasma particles flowing outward from the Sun carves out the protective bubble of the heliosphere, and in doing so can generate ‘winds’ of more than 500 kilometers per second. Not bad if we’re thinking in terms of harnessing the effect, perhaps by a magnetic sail that can create the field needed to interact with the wind, or an electric sail whose myriad tethers, held taut by rotation, create an electric field that repels protons and produces thrust.
But like the winds that drove the great age of sail on Earth, the solar version is treacherous, as likely to becalm the ship as to cause its sails to billow. It’s a gusty, turbulent medium, one where those velocities of 500 kilometers and more per second can as likely fall well below that figure. Exactly how it produces squalls in the form of coronal mass ejections or calmer flows is a topic under active study, which is where missions like Solar Orbiter come into play. Studying the solar surface to pin down the origin of the wind and the mechanism that drives it is at the heart of the mission.
Launched in 2020, Solar Orbiter carries a panoply of instruments, ten in all, for the analysis, including an Electron Analyzer System (EAS), a Proton-Alpha Sensor (PAS) for measuring the speed of the wind, and a Heavy Ion Sensor (HIS) designed to measure the heavy ion flow. Critical to the analysis of this paper is the Spectral Imaging of the Coronal Environment (SPICE) instrument, as we’ll see below. Steph Yardley (Northumbria University) is lead author of the paper on this work, which has just appeared on Nature Astronomy:
“The variability of solar wind streams measured in situ at a spacecraft close to the Sun provide us with a lot of information on their sources, and although past studies have traced the origins of the solar wind, this was done much closer to Earth, by which time this variability is lost. Because Solar Orbiter travels so close to the Sun, we can capture the complex nature of the solar wind to get a much clearer picture of its origins and how this complexity is driven by the changes in different source regions.”
What the work is analyzing is a theory that the process of magnetic field lines breaking and reconnecting is critical to producing the slower solar wind. Different areas of the Sun’s corona are implicated in the origin of both the fast and slow winds, with the ‘open corona’ being those regions where magnetic field lines extend from the Sun into space, tethered to it at one end only and creating the pathway for solar material to flow out in the form of the fast solar wind. Closed coronal regions, on the other hand, are those where the magnetic field lines connect to the surface at both ends, forming loops.
As you would imagine, the process is wildly turbulent and marked by the frequent breakage of these closed magnetic loops and their subsequent reconnection. The researchers have probed the theory that the slow solar wind originates in the closed corona during these periods of breakage and reconnection by studying the composition of solar wind streams, for the heavy ions emitted vary depending on their origins in either the closed or open corona. Solar Orbiter’s Heavy Ion Sensor (HIS) is able to take the needed measurements to relate the effects of this activity on the surrounding plasma.
The image below is from the Solar Dynamics Observatory spacecraft rather than Solar Orbiter, reminding us of the different views we are gaining by our various missions to our star. The comparison of key datasets tells the story.
Image: This is part of Figure 1 from the paper. The caption reads: SDO/AIA [Solar Dynamics Observatory data using its Atmospheric Imaging Assembly] 193 Å image showing the source region from the perspective of an Earth observer. Open magnetic field lines that are constructed from the coronal potential field model are overplotted, coloured by their associated expansion factor F. The large equatorial CH [Coronal Hole] and AR [Active Region] complex are labeled in white. The FOVs [fields of view] of SO EUI/HRI and PHI/HRT [references to instruments aboard Solar Orbiter] are shown in cyan and pink, respectively. The back-projected trajectory of SO [Solar Orbiter] from 1 March 2022 until 9 March 2022 is shown by the olive dotted line (from right to left).
So because we have Solar Orbiter, we can now combine observations of the Sun from various sources including other space missions, like the Solar Dynamics Observatory, with the measurements of the solar wind actually flowing past the spacecraft. Susan Lepri (University of Michigan) is deputy principal investigator on the HIS system:
“Each region of the Sun can have a unique combination of heavy ions, which determines the chemical composition of a stream of solar wind. Because the chemical composition of the solar wind remains constant as it travels out into the solar system, we can use these ions as a fingerprint to determine the origin of a specific stream of the solar wind in the lower part of the Sun’s atmosphere.”
The results have been productive. The analysis gives us a precise breakdown of just what Solar Orbiter has encountered during the period studied. This is a thorny quotation but it includes a key finding. From the paper:
Combining the SO [Solar Orbiter] trajectory, coronal field model, magnetic connectivity tool, the SPICE composition analysis of the AR [Active Region] complex, and the in situ plasma and magnetic field parameters, we suggest that SO was immersed in three fast wind streams… originating from the three linked sections of the large equatorial CH [Coronal Hole]… These were followed by two slower streams associated with the negative polarities of the AR complex… The decrease of the solar wind speed can be explained by the expansion of the open magnetic field associated with the CH-AR complex, as the connectivity of SO transitioned across these regions. Credit: Yardley et al.
The findings described here are significant. We learn from this work just how complex the solar wind flow is, in this case involving three fast streams and two slower ones, all involving changes in magnetic field connectivity. Matching the composition of the solar wind streams to different areas on the corona gives us new insights into the turbulent mix found where the open and closed corona meet. The slow solar wind’s ‘breakout’ from closed magnetic field lines is demonstrated. The phenomenon of magnetic reconnection proves critical to the wind’s variability.
Demonstrating these linkages means that we can now use the findings to probe further into the origins of the solar wind. But this is a variability that is in no way predictable, making the prospect of riding the solar wind via electric or magnetic sail a daunting one. We’ll continue to learn more, though, as we bring in data from missions like the Parker Solar Probe. It will be fascinating to see one day how we use the solar wind to test out possible spacecraft designs in search of a faster route to the outer Solar System.
Addendum: In an earlier draft, I mistakenly criticized the authors for not initially clarifying some of the acronyms in this paper. I’ve removed that comment because a later reading showed I was mistaken about the two examples I cited.
The paper is Yardley et al., “Multi-source connectivity as the driver of solar wind variability in the heliosphere,” Nature Astronomy 28 May 2024 (full text).
I appreciate your grumpiness about abbreviations. It is one of my pets peeves about scientific papers.
Even when they are defined, there are often so many of them that they are hard to follow.
Thanks! I did have to add an addendum, though, when I realized that the two examples I cited had been defined. I just didn’t see them. But I still think acronyms are way overused!
I find “search” in the Acrobat PDF reader is a good way to find the first instance of an acronym and hopefully what it stands for. This is especially useful when skimming a paper and coming upon an acronym for the first time somewhere in the content.
I did all that but didn’t allow for a leading ( in the sentence. In other words, I was searching forAR to avoid getting every hit on ‘ar’ in the middle of other words. So (AR) didn’t pop up. My fault.
Include me in the peeved with the overuse of acronyms and abbreviations camp (since we’ve started down that rabbit hole).
If the reader has to, for example, go back and term search and/or use an acronym or abbreviation “cheat sheet” or guide so that they can follow the discussion, that cuts against effective writing.
Particularly with our shortened attention spans in the Information Clutter Age, it’s best to engage the reader and keep them engaged. Rather than them having to disengage from the flow of the discussion to try and chase down minutiae.
Lawyers are the worst (in this as in many things of course).
They’ll take a case with a plethora of involved entities and reduce them all down to abbreviations.
So, for example, the quite easy to follow “Liberty Mutual” becomes LMIC or LMG (for “Liberty Mutual Group”).
And then their briefs become just alphabet soup.
You sorta’ can figure out what (allegedly) was being done, but to figure out by whom to whom, you have to go back and decipher which of the twenty odd entities in the suit correspond to those particular abbreviations.
In each paragraph that you read.
When they could have just used easily and immediately understood shorthand names, like “Liberty Mutual,” which rolls off the pen (or keyboard) just as easily as it rolls off the tongue during oral argument or other speech.
Which is a pretty good indication of good effective writing.
It flows.
Anyway, that may not be the case for this post . . . but, yeah, the over-reliance on acronyms and abbreviations gets to me, too.
Never good, as a writer, to have the reader asking, like Kevin Kline’s Otto in A Fish Called Wanda, “what was the middle part?”
It’s wonderful to see that my thoughts on overuse of acronyms are so widely shared! And what a good memory A Fish Called Wanda is. Thanks for giving me a chuckle.
This tangential thread sent me down a rabbit hole. Like many in this word-processing age, I use abbreviations to save on typing and typing errors, and then do a global “find and replace”. It does require not using abbreviations like “AR” that would really mess up the text and have to be reversed out. In this case, I would use something like “XARX” to ensure uniqueness.
While abbreviations have been around for a long time, (and writing is itself an abbreviation of speech) I have to wonder if the use of abbreviations before the word-processing age almost forced the form that we use today – the long form with the abbreviation in parentheses and then the abbreviation afterwards. My memory is fading after nearly 40 years, but I think British English reversed the abbreviation order – abbreviation first, then long form in parentheses.
To note George’s comment about flow, HTML has an abbr tag that allows a mouse hover to display the unabbreviated version. This seems like a good compromise. [The acronym tag was deprecated.]
@Paul – can this be done in WordPress?
Wikipedia has nice pages on abbreviations and acronyms to peruse over a morning coffee.
I have no idea if this can be implemented in WordPress, but it sounds like a useful idea.
500 Km/s sounds like a lot but is only around 0.2% c – plus it’s a sketchy source. That does not cut the mustard for interstellar usage. Inside the solar system we can do a lot better with lasers and sails, I am pretty sure.
The nice thing about the SW is that the components are ionised and therefore can be accelerated with a suitable electric field. Needs a bit of infrastructure though to get the best out of it.
It would be interesting to design such devices to compare to other means of propellantless systems. I can imagine a solar-powered collector to concentrate the protons in the solar wind (SW) and then an accelerator that creates a faster, concentrated beam (with injected electrons to maintain beam neutrality to reduce divergence?) directed at the mag/electric sail craft. If the velocity could be increased 10x from the average 400km/s SW, and the beam density 10x the SW in deep space, this suggests a potential 10-100x performance increase for the various proposed sail designs [magsail, electric sail, plasma magnet].
If we had a propulsion system with a magnetic field that was stronger than our Sun, we could not only accelerate particles faster, but we carry our own particles and accelerate them making solar sails superfluous. It’s the temperature of the nuclear fusion in the core of the Sun that give the particles enough energy to escape the gravity of the Sun and the charged particles are carried away by the Sun’s magnetic field. Due to the inverse square law where gravity attenuates with the square of the distance, for it is the Sun’s gravitational field that has to be overcome by the kinetic energy of temperature of the heated plasma by the fusion in the core of the Sun. https://www.jpl.nasa.gov/nmp/st5/SCIENCE/solarwind.html
Magnetic fields can’t accelerate charged particles only change their direction unless the magnetic field is moving.
Magnetic fields accelerate charged particles if they are perpendicular to the direction of the field. Solar flares accelerate electrons in a helical motion which creates a radio frequencies at 245 mhz. The Sun’s magnetic field accelerates the solar wind. Magnetic fields accelerate protons in the LHC. The VASIMR propulsion engine accelerates heated argon gas with magnetic fields. We both stand corrected though since the Sun’s solar wind acceleration is caused by the energy release from the re-connection of open and closed magnetic fields.
From the paper online:
“New study identifies mechanism driving the sun’s fast wind
Release of magnetic energy near the sun’s surface enables the solar wind to reach gravity-defying speeds” Science Daily.
Geoffrey, in all cases the magnetic fields are moving. A stationary magnetic field can only change charge particles direction and lose energy via radiation. In the SW case the magnetic field is rotating with the sun, any reconnections are movements as well, energy is sapped from the sun’s rotation i.e. it slows down over time.
Yes. The Sun’s magnetic field does accelerate the solar wind, but the heat from the Sun gives the particles the kinetic energy to escape from the Sun’s gravity. Source: AI chat GPT. The magnetic field carries the particles away from the Sun. Yes, magnetic reconnection accelerates particles. Of course the Sun has both stationary and moving magnetic fields. Solar flares are magnetic fields that accelerate charged particles, electrons and protons. It is interesting that the moving magnetic field also create electric fields “according to Faraday’s Law of Induction.” which can directly accelerate charged particles, but with a magnetic field the particle has to be moving at right angles to the field. Of course the kinetic energy is from the heat of the Sun’s interior. With the reconnection, the solar flares release energy from the kinetic energy of motion, the accelerated particles. Charged particles emit EMR. X rays show they are very hot. They also emit radio waves at 245 mhz. Ibid and Culhane and Stanford 1979.
The magnetic fields of solar flares are stationary but move over time. Their cause is the differential rotation of the Sun which twists the poloidial magnetic field lines which twist like ropes. They tie up or bunch up like a loop and go through the surface or photosphere. Where the loop meets it are the sun spots and faculae which connect the magnetic field loop in solar flares. Charged particles and protons and electrons are accelerated in these loops called solar flares.
These of course are all related to the Sun’s eleven year solar cycle which is caused by the Alpha Omega dynamo. The alpha effect is the stretching of poloidal magnetic field into a toroidal magnetic. The Beta effect is the reverse. The magnetic dynamo caused by the Sun’s convection and the differential rotation. The non uniform speed of rotation and shearing effect twisting the poloidal magnetic field. AI Chat GPT.
Perhaps a large magnetic funnel for the solar wind and then a series of electric accelerators to increase the velocity of those particles and as you say neutralise them with the electron injection. The hard work of ionisation has been done by the sun.
If we had a magnetic field with the SW gathering power of the moon we would have about 40 grams of hydrogen/helium per second at around 400km/s. If you took all the energy falling on the area it would be around 1.2 exp 16 J. If took all that energy and pumped it into the 40 grams of material it would traveling near the speed of light !
Likely we will need to train an AI navigator to plot the magnetic courses driven by the solar wind that can predict the strong ‘re-connection’ events that can drive a magsail on the desired heading.
Of course field lines are never not connected, re-connection is just a term that describes a rapid localised change in field direction. What a kick!
Makes me wonder whether we could tap the re-connection event itself to drive an unmanned probe at high acceleration?
Solar horse latitudes
Sunlight, sunlight everywhere, and how the Starwisp fields did shrink…
-publiusr
If we go towards the polar regions the SW is around 750 km/s
A Ulysses type mission?
Staging a Starwisp off a lightsail that tacks a bit?