Solar Orbiter and Parker Solar Probe jointly take a step forward in understanding coronal heating

(Solar Orbiter nugget #20 by Daniele Telloni1, Marco Romoli2, Marco Velli3, Gary P. Zank4,5, Laxman Adhikari4, Cooper Downs6, Aleksandr Burtovoi7, Roberto Susino1, Daniele Spadaro8, Lingling Zhao4, Alessandro Liberatore9, Chen Shi3, Yara De Leo10,11, Stuart D. Bale12,13, Justin C. Kasper14,15, and the Metis team​)

 

Introduction

The Sun is the source of energy that sustains life on Earth. Energy is produced within the Sun’s core by thermonuclear fusion reactions, which cause electromagnetic radiation (light and heat) to be generated. Eventually, this electromagnetic radiation reaches the Sun’s visible surface (called the photosphere) before escaping through the outermost layers of the Sun’s atmosphere (namely the chromosphere, the transition region and finally the corona) into the solar system and beyond. If it is traveling in the correct direction, light reaches the Earth in as little as 8 minutes after it escapes from the photosphere.

The photosphere exists at a temperature of around 6000 degrees. In the 1940s, following correct interpretation of solar spectra it was discovered that the temperature of the corona is instead about 150 times hotter, reaching one million degrees (coronal temperatures can even be an order of magnitude higher during high-energy events such as flares). If the only energy transport processes occurring in the solar atmosphere were thermal in nature, this temperature imbalance would violate the second law of thermodynamics, which states that heat cannot flow from the photosphere to the corona, away from the energy source at the Sun’s core, to raise coronal temperatures above 6000 degrees. Clearly, there must be other physical mechanisms that heat the corona to such high temperatures. But what are they? In this consists of the long-standing problem of coronal heating.

In 1958, Eugene Parker [1] showed mathematically that such a hot corona could not be in hydrostatic equilibrium and was the first to theoretically predict the existence of the solar wind, namely a continuous flow of magnetized plasma expanding from the corona into interplanetary space. In 1962, Marcia Neugebauer [2], based on data from the Mariner 2 spacecraft, provided the first direct measurements of the solar wind and its properties. More than 60 years later, and despite the tremendous progress made from both observational and numerical/modeling perspectives, the mechanisms that heat the coronal plasma and accelerate the solar wind are still heavily debated. It is now well established that the source of energy that powers the solar wind is provided by the magnetic field and that, most likely (but direct evidence is not yet forthcoming!), it is the dissipation of turbulence that transfers the required energy from the magnetic field to the plasma [3,4,5]. However, until now, the rate of coronal heating by turbulence had not yet been directly measured.

 

Solar Orbiter - Parker Solar Probe synergies

The NASA Parker Solar Probe [6] and ESA/NASA Solar Orbiter [7] missions were launched in 2018 and 2020, respectively, with the goal of, amongst other things, unlocking the mystery related to the so-called “coronal heating problem” and the acceleration of plasma flows. Despite both satellites individually leading to discoveries that are revolutionizing our understanding of the Sun and its environment, it is when they operate in synergy that the most important breakthroughs can be achieved [8,9,10,11,12]. On June 1, 2022, Parker Solar Probe and Solar Orbiter were in a very special orbital configuration (a spacecraft quadrature) that allowed the first empirical measurement of the rate of energy deposition by turbulence in the corona. During its twelfth perihelion passage, Parker Solar Probe was in fact in a very peculiar position, skimming, but not entering, the field of view of the Italian coronagraph Metis aboard Solar Orbiter. 

 

 

 

 

 

 

Movie 1. An animation displaying the spacecraft trajectories and the Metis field of view during the quadrature.

The Metis team realized the potential importance of having Parker Solar Probe in the field of view of Metis. At that point, the Solar Orbiter operations team planned and executed an unprecedented (and not without risk) spacecraft maneuver: they actually rolled the spacecraft 45 degrees from its axis pointing toward the center of the Sun and then moved this pointing to the edge of the Sun to allow Parker Solar Probe to enter the portion of the plane of the sky remotely imaged by Metis. The different spacecraft maneuvers along with the position of Parker Solar Probe in the Metis field of view are sketched in Figure 1. This allowed the first-ever simultaneous measurement of the large-scale configuration of the corona and its microphysical/kinetic properties, ultimately enabling the first empirical estimate in the solar corona of the heating rate due to turbulent fluctuations.

Figure 1.  Schematic Solar Orbiter maneuvers required to have Parker Solar Probe within the Metis field of view.

 

Estimate of the coronal heating rate

Figure 2 shows the coordinated Solar Orbiter/Metis and Parker Solar Probe observations of the same plasma element. Relying on the basic equations of magnetohydrodynamics and on the joint Solar Orbiter/Metis and Parker Solar Probeobservations, the rate of energy deposition in the corona has then been estimated. It was found that the average turbulent heating rate per unit volume is about 5.5×10-12 J m-3 s-1, while the coronal energy loss is 33% of the total energy flux of the solar wind. What has emerged from the study published on The Astrophysical Journal Letters [13], is that the energy deposited to the coronal flow is sufficient to explain its observed residual acceleration and to maintain the plasma in a non-adiabatic state. Indeed, a collisionless plasma with no additional heating is expected to cool with distance according to a definite scaling law [14]. Since the temperature decreases less rapidly than expected [15], this implies that plasma heating (via turbulence dissipation) occurs both in the extended corona and interplanetary space.

Figure 2.  Left: White-light corona imaged by Metis on 2022 June 1 at 22:40 UT with Parker Solar Probe marked in its plane of the sky as a blue dot; the Parker Solar Probe direction is indicated by a white dashed line. Right: Parker Solar Probe magnetic field and plasma time series (from top to bottom: wind bulk and Alfvén speed, magnetic field intensity and angle with the radial, and proton density and temperature) during the quadrature with Solar Orbiter.

 

What’s next?

In addition to being a very important result that will help refine turbulence-based modeling of coronal heating and subsequent solar wind acceleration, this is also a virtuous example of synergy between Solar Orbiter and Parker Solar Probe, showing how coordination of the two missions can lead to groundbreaking achievements. New and even more promising orbital configurations that will occur in the coming years are under consideration by the Solar Orbiter and Parker Solar Probe teams, which are already coordinating to exploit them and thus obtain further exciting results.

 

This study has been published in Daniele Telloni, et al. 2023, ApJL, 955, L4 https://doi.org/10.3847/2041-8213/ace112

 

Acknowledgements

Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. D.T. was partially supported by the Italian Space Agency (ASI) under contract 2018-30-HH.0. G.P.Z., L.A., and L.-L.Z. acknowledge the partial support of a NASA Parker Solar Probe contract SV4- 84017, an NSF EPSCoR RII-Track-1 Cooperative Agreement OIA-2148653, and a NASA IMAP grant through SUB000313/ 80GSFC19C0027. S.B. and J.K. acknowledge support from NASA contract NNN06AA01C. The Metis program is supported by ASI under contracts to the National Institute for Astrophysics and industrial partners. Metis was built with hardware contributions from Germany (Bundesministerium für Wirtschaft und Energie through theDeutsches Zentrum für Luft- und Raumfahrt e.V.), the Czech Republic (PRODEX), and ESA. The Metis team thanks the former PI, Ester Antonucci, for leading the development of Metis until the final delivery to ESA. D.T. also wishes to thank her for the helpful comments on the paper. The Metis data analyzed in this paper are available from the PI on request. Parker Solar Probe data were downloaded from NASA’s Space Physics Data Facility (https://spdf.gsfc.nasa.gov).

 

Affiliations

1 National Institute for Astrophysics, Astrophysical Observatory of Torino, Via Osservatorio 20, I-10025 Pino Torinese, Italy; daniele.telloni@inaf.it

2 University of Florence, Department of Physics and Astronomy, Via Giovanni Sansone 1, I-50019 Sesto Fiorentino, Italy

3 Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095, USA

4 Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL 35805, USA

5 Department of Space Science, University of Alabama in Huntsville, Huntsville, AL 35805, USA

6 Predictive Science Inc., San Diego, CA 92121, USA

7 National Institute for Astrophysics, Astrophysical Observatory of Arcetri, Largo Enrico Fermi 5, I-50125 Firenze, Italy

8 National Institute for Astrophysics, Astrophysical Observatory of Catania, Via Santa Sofia 78, I-95123 Catania, Italy

9 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA

10 Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany

11 University of Catania, Department of Physics and Astronomy, Via Santa Sofia 64, I-95123 Catania, Italy

12 Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA

13 Physics Department, University of California, Berkeley, CA 94720, USA

14 BWX Technologies, Inc., Washington, DC 20002, USA

15 Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA

 

References

[1] Parker, E. N. 1958, ApJ, 128, 664 https://doi.org/10.1086/146579

[2] Neugebauer, M., & Snyder, C. W. 1962, Sci, 138, 1095 https://doi.org/10.1126/science.138.3545.1095.b

[3] Matthaeus, W. H., Zank, G. P., Oughton, S., Mullan, D. J., & Dmitruk, P. 1999, ApJL, 523, L93 https://doi.org/10.1086/312259

[4] Zank, G. P., Adhikari, L., Hunana, P., et al. 2017, ApJ, 835, 147 https://doi.org/10.3847/1538-4357/835/2/147

[5] Zank, G. P., Adhikari, L., Hunana, P., et al. 2018, ApJ, 854, 32 https://doi.org/10.3847/1538-4357/aaa763

[6] Fox, N. J., Velli, M. C., Bale, S. D., et al. 2016, SSRv, 204, 7 https://doi.org/10.1007/s11214-015-0211-6

[7] Müller, D., Cyr, O. C., St., Zouganelis, I., et al. 2020, A&A, 642, A1 https://doi.org/10.1051/0004-6361/202038467

[8] Telloni, D., Sorriso-Valvo, L., Woodham, L. D., et al. 2021, ApJL, 912, L21 https://doi.org/10.3847/2041-8213/abf7d1

[9] Telloni, D., Andretta, V., Antonucci, E., et al. 2021, ApJL, 920, L14 https://doi.org/10.3847/2041-8213/ac282f

[10] Telloni, D., Zank, G. P., Sorriso-Valvo, L., et al. 2022, ApJ, 935, 112 https://doi.org/10.3847/1538-4357/ac8103

[11] Telloni, D., Zank, G. P., Adhikari, L., et al. 2023, ApJ, 944, 227 https://doi.org/10.3847/1538-4357/acb693

[12] Telloni, D., Romoli, M., Velli, M., et al. 2023, ApJ, 954, 108 https://doi.org/10.3847/1538-4357/aceb64

[13] Telloni, D., Romoli, M., Velli, M., et al. 2023, ApJL, 955, L4 https://doi.org/10.3847/2041-8213/ace112

[14] Chew, G. F., Goldberger, M. L., & Low, F. E. 1956, RSPSA, 236, 112 https://doi.org/10.1098/rspa.1956.0116

[15] Zhao, L.-L., Zank, G. P., & Adhikari, L. 2019, ApJ, 879, 32 https://doi.org/10.3847/1538-4357/ab2381

Nuggets archive

2024

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29/05/2024: SoloHI's viewpoint advantage: Tracking the first major geo-effective coronal mass ejection of the current solar cycle

22/05/2024: Real time space weather prediction with Solar Orbiter

15/05/2024: Hard X ray and microwave pulsations: a signature of the flare energy release process

01/02/2024: Relativistic electrons accelerated by an interplanetary shock wave

18/01/2024: Deformations in the velocity distribution functions of protons and alpha particles observed by Solar Orbiter in the inner heliosphere

11/01/2024: Modelling Two Consecutive Energetic Storm Particle Events observed by Solar Orbiter

 

2023

14/12/2023: Understanding STIX hard X-ray source motions using field extrapolations

07/12/2023: Multi-Spacecraft Observations of the 2022 March 25 CME and EUV Wave: An Analysis of their Propagation and Interrelation

16/11/2023: EUI data reveal a "steady" mode of coronal heating

09/11/2023: A new solution to the ambiguity problem

02/11/2023: Solar Orbiter and Parker Solar Probe jointly take a step forward in understanding coronal heating

25/10/2023: Observations of mini coronal dimmings caused by small-scale eruptions in the quiet Sun

18/10/2023: Fleeting small-scale surface magnetic fields build the quiet-Sun corona

11/10/2023: Unusually long path length for a nearly scatter free solar particle event observed by Solar Orbiter at 0.43 au

27/09/2023: Solar Orbiter reveals non-field-aligned solar wind proton beams and its role in wave growth activities

20/09/2023: Polarisation of decayless kink oscillations of solar coronal loops

23/08/2023: A sharp EUI and SPICE look into the EUV variability and fine-scale structure associated with coronal rain

02/08/2023: Solar Flare Hard Xrays from the anchor points of an eruptive filament

28/06/2023: 3He-rich solar energetic particle events observed close to the Sun on Solar Orbiter

14/06/2023: Observational Evidence of S-web Source of Slow Solar Wind

31/05/2023: An interesting interplanetary shock

24/05/2023: High-resolution imaging of coronal mass ejections from SoloHI

17/05/2023: Direct assessment of far-side helioseismology using SO/PHI magnetograms

10/05/2023: Measuring the nascent solar wind outflow velocities via the doppler dimming technique

26/04/2023: Imaging and spectroscopic observations of EUV brightenings using SPICE and EUI on board Solar Orbiter

19/04/2023: Hot X-ray onset observations in solar flares with Solar Orbiter/STIX

12/04/2023: Multi-scale structure and composition of ICME prominence material from the Solar Wind Analyser suite

22/03/2023: Langmuir waves associated with magnetic holes in the solar wind

15/03/2023: Radial dependence of the peak intensity of solar energetic electron events in the inner heliosphere

08/03/2023: New insights about EUV brightenings in the quiet sun corona from the Extreme Ultraviolet Imager